CLINICAL

BIOCHEMISTRY

GLOSSARY TERMS

Short Notes for Medical and Paramedical Students

 

SECTION XII – HORMONAL BIOCHEMISTRY

A Quick Reference Guide for Undergraduate Medical Students, Postgraduate Medical Students, and Paramedical Students.

BY

 

DR.C.GANESAN M.D

PROFESSOR OF MEDICINE

 

 

 

 

 

 

 

 

CLINICAL

BIOCHEMISTRY

GLOSSARY TERMS

SECTION XII – HORMONAL BIOCHEMISTRY

Chapter 117: Introduction to Hormones

1.  Hormone
A hormone is a chemical messenger produced by specialized endocrine glands and released into the bloodstream. It travels to distant target cells and organs where it regulates specific biological activities. Hormones control growth, metabolism, reproduction, and homeostasis. They act in very small concentrations but produce significant physiological effects. Proper hormonal balance is essential for normal body function and health.

2.  Endocrine Gland
An endocrine gland is a ductless gland that secretes hormones directly into the blood circulation. These glands include the pituitary, thyroid, adrenal, and pancreas. The hormones released travel throughout the body to influence target organs. Endocrine glands help coordinate growth, metabolism, reproduction, and stress responses. Their secretions are precisely regulated through feedback mechanisms.

3.  Endocrine System
The endocrine system is a network of glands that produce and secrete hormones to regulate body functions. It works closely with the nervous system to maintain internal balance and adaptation. Major components include the hypothalamus, pituitary, thyroid, parathyroid, adrenal glands, pancreas, and gonads. The system controls growth, metabolism, fluid balance, and reproduction. Hormonal communication ensures coordinated functioning of different organs.

4.  Target Cell
A target cell is a cell that possesses specific receptors for a particular hormone. When the hormone binds to its receptor, it triggers a biological response within the cell. Different target cells respond differently to the same hormone depending on receptor type and intracellular pathways. Hormonal effects may include changes in metabolism, gene expression, or cell activity. Without the appropriate receptor, a cell cannot respond to that hormone.

5.  Target Organ
A target organ is an organ that responds to the action of a specific hormone because it contains appropriate receptors. Hormones travel through the bloodstream and exert their effects only on these responsive organs. Examples include the liver responding to insulin and the uterus responding to estrogen. Target organs carry out physiological changes directed by hormonal signals. Their proper response is essential for maintaining normal body functions and homeostasis.

Chapter 117: Introduction to Hormones

6.  Receptor
A receptor is a specialized protein that recognizes and binds a specific hormone. It may be located on the cell membrane or inside the cell. Hormone-receptor binding initiates cellular responses through signaling pathways. Receptors determine the specificity of hormone action. Proper receptor function is essential for normal hormonal regulation.

7.  Hormonal Signaling
Hormonal signaling is the process by which hormones communicate information between cells and organs. Hormones travel through the bloodstream to reach target tissues. Binding to receptors triggers physiological responses. This communication regulates growth, metabolism, reproduction, and homeostasis. Hormonal signaling ensures coordinated body function.

8.  Chemical Messenger
A chemical messenger is a substance that carries signals from one cell to another. Hormones, neurotransmitters, and cytokines are examples of chemical messengers. They regulate various physiological processes. Chemical messengers bind to specific receptors on target cells. Their actions help maintain normal body activities.

9.  Endocrine Secretion
Endocrine secretion refers to the release of hormones directly into the bloodstream by endocrine glands. These hormones travel to distant target organs. The process allows widespread communication within the body. Endocrine secretion regulates metabolism, growth, and reproduction. It is controlled by feedback mechanisms.

10.               Exocrine Gland
An exocrine gland secretes its products through ducts onto epithelial surfaces or into body cavities. Examples include salivary glands and sweat glands. Their secretions are not released into the bloodstream. Exocrine products perform local functions such as digestion and lubrication. They differ structurally and functionally from endocrine glands.

11.               Paracrine Signaling
Paracrine signaling occurs when a cell releases chemical messengers that act on nearby cells. The signaling molecules diffuse through the local tissue environment. This form of communication does not involve the bloodstream. Paracrine regulation is important in inflammation and tissue repair. It enables rapid local cellular responses.

12.               Autocrine Signaling
Autocrine signaling occurs when a cell secretes a substance that acts on itself. The released messenger binds to receptors on the same cell. This mechanism regulates cell growth, differentiation, and function. It is common in immune and cancer cells. Autocrine signaling provides self-regulation of cellular activity.

13.               Neuroendocrine System
The neuroendocrine system integrates nervous and endocrine functions to regulate body activities. It consists mainly of the hypothalamus and pituitary gland. Neural signals influence hormone secretion. This system coordinates stress responses, growth, and reproduction. It helps maintain physiological homeostasis.

14.               Neurohormone
A neurohormone is a hormone produced and released by specialized neurons. It enters the bloodstream and acts on distant target organs. Oxytocin and vasopressin are examples of neurohormones. They bridge communication between the nervous and endocrine systems. Neurohormones regulate many essential body functions.

15.               Second Messenger
A second messenger is an intracellular signaling molecule generated after hormone-receptor interaction. It transmits signals within the cell to produce a response. Examples include cAMP and calcium ions. Second messengers amplify hormonal effects. They play a key role in signal transduction pathways.

16.               Cyclic AMP (cAMP)
Cyclic AMP is a common intracellular second messenger derived from ATP. It is produced by the enzyme adenylate cyclase. cAMP activates protein kinase A and other signaling pathways. It mediates the effects of many hormones. This molecule amplifies cellular responses to hormonal stimulation.

17.               Cyclic GMP (cGMP)
Cyclic GMP is an intracellular second messenger synthesized from GTP. It mediates the effects of nitric oxide and certain hormones. cGMP activates protein kinase G and regulates cellular functions. It plays an important role in smooth muscle relaxation. It is also involved in visual signal transduction.

18.               Signal Transduction
Signal transduction is the process by which a hormonal signal is converted into a cellular response. It begins when a hormone binds to its receptor. Intracellular signaling pathways then become activated. These pathways regulate gene expression and enzyme activity. Signal transduction ensures effective communication within cells.

19.               Hormone Synthesis
Hormone synthesis is the biochemical process through which hormones are produced. Different endocrine glands synthesize different classes of hormones. Protein, peptide, steroid, and amine hormones have unique synthetic pathways. Hormone production is tightly regulated. Proper synthesis is essential for normal endocrine function.

20.               Hormone Release
Hormone release is the secretion of synthesized hormones from endocrine cells into circulation. This process occurs in response to specific physiological stimuli. Neural, hormonal, or chemical signals may trigger release. Hormone secretion is often pulsatile. Controlled release maintains hormonal balance.

21.               Hormone Transport
Hormone transport refers to the movement of hormones through the bloodstream to target tissues. Water-soluble hormones circulate freely in plasma. Lipid-soluble hormones are transported bound to carrier proteins. Transport determines hormone availability and duration of action. Efficient transport is necessary for hormonal communication.

22.               Hormone Metabolism
Hormone metabolism involves biochemical modifications of hormones within tissues. These changes may activate or inactivate hormonal activity. The liver is a major site of hormone metabolism. Metabolism helps regulate hormone concentration in the body. It contributes to endocrine homeostasis.

23.               Hormone Degradation
Hormone degradation is the breakdown of hormones into inactive metabolites. It occurs mainly in the liver, kidneys, and target tissues. Degradation terminates hormonal action. This process prevents excessive hormonal effects. Efficient degradation helps maintain normal endocrine function.

24.               Feedback Mechanism
A feedback mechanism is a regulatory process that controls hormone secretion. Hormone levels influence further hormone production and release. Feedback loops help maintain physiological stability. Most endocrine systems operate through feedback regulation. This mechanism is fundamental to homeostasis.

25.               Negative Feedback
Negative feedback is the most common endocrine regulatory mechanism. Increased hormone levels inhibit further hormone secretion. This prevents excessive hormonal activity. Negative feedback maintains stable internal conditions. It is essential for hormonal homeostasis.

26.               Positive Feedback
Positive feedback occurs when a hormone stimulates further hormone release. This amplifies the original physiological response. Examples include oxytocin release during childbirth. Positive feedback is usually temporary and self-limiting. It helps achieve rapid physiological outcomes.

27.               Hormonal Homeostasis
Hormonal homeostasis is the maintenance of stable hormone levels within the body. It is achieved through coordinated endocrine regulation. Feedback mechanisms play a major role in this process. Homeostasis supports normal growth, metabolism, and reproduction. Disturbances may result in endocrine disorders.

28.               Tropic Hormone
A tropic hormone is a hormone that stimulates another endocrine gland to secrete hormones. Examples include TSH, ACTH, and FSH. These hormones regulate endocrine gland activity. They are primarily produced by the anterior pituitary. Tropic hormones coordinate hormonal hierarchies.

29.               Non-Tropic Hormone
A non-tropic hormone acts directly on target tissues rather than another endocrine gland. Examples include insulin and growth hormone. These hormones produce direct physiological effects. Their actions regulate metabolism, growth, and tissue function. Non-tropic hormones are essential for daily body activities.

30.               Hormone Half-Life
Hormone half-life is the time required for the concentration of a hormone in blood to decrease by half. It varies among different hormones. Protein-bound hormones generally have longer half-lives. Half-life influences the duration of hormonal action. It is important in endocrine physiology and therapeutics.

Chapter 118: Hypothalamic Hormones

1.  Hypothalamus
The hypothalamus is a small but vital region of the brain that links the nervous and endocrine systems. It produces releasing and inhibiting hormones that regulate pituitary function. It also controls body temperature, hunger, thirst, and circadian rhythm. The hypothalamus maintains internal homeostasis through neuroendocrine regulation. It serves as the master regulator of endocrine activity.

2.  Releasing Hormone
A releasing hormone is a hypothalamic hormone that stimulates the anterior pituitary to secrete specific hormones. These hormones travel through the hypophyseal portal system. Examples include TRH, CRH, and GnRH. Releasing hormones coordinate endocrine gland activity. They play a key role in hormonal regulation.

3.  Inhibiting Hormone
An inhibiting hormone is a hypothalamic hormone that suppresses pituitary hormone secretion. Examples include somatostatin and dopamine. These hormones prevent excessive endocrine activity. They help maintain hormonal balance. Inhibiting hormones are essential components of feedback regulation.

4.  Hypothalamic-Pituitary Axis
The hypothalamic-pituitary axis is the functional connection between the hypothalamus and pituitary gland. Hormones from the hypothalamus regulate pituitary hormone secretion. This axis controls growth, metabolism, reproduction, and stress responses. It serves as the central endocrine control system. Proper functioning is necessary for hormonal homeostasis.

5.  Thyrotropin-Releasing Hormone (TRH)
TRH is a hypothalamic hormone that stimulates the release of thyroid-stimulating hormone from the anterior pituitary. It also promotes prolactin secretion. TRH plays a major role in regulating thyroid function. Its secretion is influenced by circulating thyroid hormone levels. It is an important component of the hypothalamic-pituitary-thyroid axis.

6.  Corticotropin-Releasing Hormone (CRH)
CRH is a hypothalamic hormone that stimulates the release of ACTH from the anterior pituitary. ACTH subsequently promotes cortisol secretion from the adrenal cortex. CRH is released during stress and physiological challenges. It helps coordinate the body's stress response. CRH is a key regulator of the hypothalamic-pituitary-adrenal axis.

7.  Gonadotropin-Releasing Hormone (GnRH)
GnRH is a hypothalamic hormone that stimulates the secretion of FSH and LH from the anterior pituitary. It regulates reproductive function in both sexes. GnRH is released in a pulsatile manner. Proper pulsatile secretion is essential for fertility. It controls gonadal hormone production and gametogenesis.

8.  Growth Hormone-Releasing Hormone (GHRH)
GHRH is a hypothalamic hormone that stimulates growth hormone secretion from the anterior pituitary. It promotes growth and metabolism through GH and IGF-1. GHRH secretion is influenced by sleep, nutrition, and exercise. It acts opposite to somatostatin. Together they regulate growth hormone release.

9.  Somatostatin
Somatostatin is a hypothalamic inhibitory hormone that suppresses growth hormone secretion. It also inhibits TSH release and various gastrointestinal hormones. Somatostatin helps regulate endocrine and digestive functions. It acts as a universal inhibitory regulator. Its effects maintain hormonal balance.

10.               Growth Hormone-Inhibiting Hormone (GHIH)
Growth Hormone-Inhibiting Hormone is another name for somatostatin. It inhibits growth hormone secretion from somatotroph cells of the anterior pituitary. This regulation prevents excessive growth hormone production. GHIH works in coordination with GHRH. Together they control normal growth processes.

11.               Dopamine
Dopamine is a neurotransmitter that also functions as a hypothalamic hormone. It inhibits prolactin secretion from the anterior pituitary. Because of this action, dopamine is known as prolactin-inhibiting hormone. It participates in neuroendocrine regulation and brain function. Dopamine deficiency may result in hyperprolactinemia.

12.               Prolactin-Inhibiting Hormone (PIH)
PIH is another name for hypothalamic dopamine. It continuously suppresses prolactin secretion from lactotroph cells. This inhibition prevents unnecessary milk production. Reduced dopamine activity increases prolactin release. PIH is essential for normal reproductive physiology.

13.               Prolactin-Releasing Hormone (PRH)
PRH refers to hypothalamic factors that stimulate prolactin secretion. TRH and other neuropeptides may contribute to this effect. PRH activity becomes important during pregnancy and lactation. It supports milk production after childbirth. Its effects oppose those of dopamine.

14.               Oxytocin
Oxytocin is a neurohormone synthesized in the hypothalamus and released from the posterior pituitary. It stimulates uterine contractions during labor. Oxytocin also promotes milk ejection during breastfeeding. It contributes to maternal bonding and social behavior. Oxytocin operates through positive feedback mechanisms.

15.               Vasopressin
Vasopressin is a hypothalamic neurohormone released from the posterior pituitary. It regulates water balance by increasing renal water reabsorption. Vasopressin also causes vasoconstriction at higher concentrations. It helps maintain blood pressure and plasma osmolarity. Deficiency results in diabetes insipidus.

16.               Antidiuretic Hormone (ADH)
ADH is another name for vasopressin. It acts on kidney collecting ducts to conserve water. ADH secretion increases during dehydration and high plasma osmolarity. It reduces urine volume and maintains fluid balance. ADH is essential for water homeostasis.

17.               Supraoptic Nucleus
The supraoptic nucleus is a hypothalamic nucleus that primarily synthesizes ADH. Its neurons project to the posterior pituitary. ADH produced here is stored and released into circulation. The nucleus responds to osmotic changes in body fluids. It plays a crucial role in water balance.

18.               Paraventricular Nucleus
The paraventricular nucleus is a hypothalamic nucleus that mainly produces oxytocin. It also contributes to ADH synthesis. Neurons from this nucleus project to the posterior pituitary. The nucleus regulates reproduction, stress responses, and fluid balance. It is a major neuroendocrine control center.

19.               Hypophyseal Portal System
The hypophyseal portal system is a specialized vascular network connecting the hypothalamus and anterior pituitary. It transports releasing and inhibiting hormones directly to pituitary cells. This arrangement allows rapid hormonal communication. It minimizes dilution of hypothalamic hormones. The system is essential for anterior pituitary regulation.

20.               Median Eminence
The median eminence is a region at the base of the hypothalamus. It serves as the site where hypothalamic hormones enter the portal circulation. This structure connects neural and endocrine functions. It facilitates hormone transport to the anterior pituitary. The median eminence is vital for neuroendocrine communication.

21.               Neurosecretory Cell
A neurosecretory cell is a specialized neuron that synthesizes and releases hormones. These cells convert neural signals into endocrine responses. They are abundant in the hypothalamus. Neurosecretory cells regulate pituitary hormone secretion. They form the basis of neuroendocrine integration.

22.               Neuroendocrine Regulation
Neuroendocrine regulation is the coordination of endocrine activity by the nervous system. The hypothalamus plays a central role in this process. Neural stimuli influence hormone secretion and endocrine responses. This regulation maintains physiological homeostasis. It integrates environmental and internal signals.

23.               Magnocellular Neuron
Magnocellular neurons are large hypothalamic neurons located mainly in the supraoptic and paraventricular nuclei. They synthesize oxytocin and vasopressin. Their axons extend to the posterior pituitary. Hormones are released directly into the bloodstream. These neurons are crucial for fluid balance and reproduction.

24.               Parvocellular Neuron
Parvocellular neurons are smaller hypothalamic neurons that produce releasing and inhibiting hormones. Their secretions enter the hypophyseal portal circulation. These neurons regulate anterior pituitary function. They control growth, metabolism, and reproductive hormones. Parvocellular neurons are essential for endocrine regulation.

25.               Neurohypophysis
The neurohypophysis is the posterior lobe of the pituitary gland. It stores and releases oxytocin and ADH synthesized in the hypothalamus. It contains axons of hypothalamic neurons. Unlike the anterior pituitary, it does not synthesize hormones. Its main role is hormone storage and release.

26.               Adenohypophysis
The adenohypophysis is the anterior lobe of the pituitary gland. It synthesizes and secretes several trophic hormones. Its activity is regulated by hypothalamic hormones delivered through the portal system. The adenohypophysis controls multiple endocrine glands. It is often called the master endocrine gland.

27.               Osmoreceptor
An osmoreceptor is a specialized sensory receptor that detects changes in plasma osmolarity. These receptors are located in the hypothalamus. Increased osmolarity stimulates thirst and ADH release. Osmoreceptors help regulate body water balance. They are essential for fluid homeostasis.

28.               Thirst Center
The thirst center is a hypothalamic region responsible for generating the sensation of thirst. It responds to increased plasma osmolarity and reduced blood volume. Activation encourages water intake. This mechanism helps maintain fluid balance. The thirst center works closely with osmoreceptors and ADH.

29.               Circadian Rhythm
Circadian rhythm is the approximately 24-hour biological cycle that regulates physiological functions. It influences hormone secretion, sleep, body temperature, and metabolism. The hypothalamic suprachiasmatic nucleus acts as the biological clock. Light exposure synchronizes circadian rhythms. Proper circadian function supports overall health.

30.               Hypothalamic Dysfunction
Hypothalamic dysfunction refers to impaired hypothalamic regulation of endocrine and autonomic functions. Causes include tumors, trauma, infections, and genetic disorders. Symptoms may involve hormonal imbalance, obesity, sleep disturbances, and reproductive problems. The condition affects multiple body systems. Early diagnosis improves management and outcomes.

Chapter 119: Pituitary Hormones

1.  Pituitary Gland
The pituitary gland is a small endocrine gland located in the sella turcica at the base of the brain. It is often called the master gland because it regulates many other endocrine glands. The pituitary consists of anterior and posterior lobes. It secretes hormones that control growth, metabolism, reproduction, and water balance. Its activity is regulated by the hypothalamus.

2.  Hypophysis
Hypophysis is another name for the pituitary gland. It serves as the central organ of the endocrine system. The gland is divided into adenohypophysis and neurohypophysis. It coordinates hormonal activity throughout the body. Proper hypophyseal function is essential for homeostasis.

3.  Anterior Pituitary
The anterior pituitary, or adenohypophysis, is the glandular portion of the pituitary gland. It synthesizes and secretes hormones such as GH, TSH, ACTH, FSH, LH, and prolactin. Its activity is regulated by hypothalamic releasing and inhibiting hormones. These hormones enter through the hypophyseal portal system. The anterior pituitary controls several endocrine glands.

4.  Posterior Pituitary
The posterior pituitary, or neurohypophysis, is the neural portion of the pituitary gland. It stores and releases oxytocin and ADH synthesized in the hypothalamus. The hormones travel through hypothalamic nerve fibers to reach the posterior lobe. It functions mainly as a storage and release site. The posterior pituitary regulates water balance and reproduction.

5.  Adenohypophysis
The adenohypophysis is the anterior lobe of the pituitary gland composed of glandular tissue. It produces several trophic and non-trophic hormones. Hormone secretion is controlled by hypothalamic factors. It regulates growth, metabolism, and reproductive function. The adenohypophysis is essential for endocrine coordination.

6.  Neurohypophysis
The neurohypophysis is the posterior lobe of the pituitary gland. It consists mainly of nerve fibers and supporting cells. It stores and releases oxytocin and vasopressin. These hormones are synthesized in the hypothalamus. The neurohypophysis plays a major role in fluid balance and childbirth.

7.  Growth Hormone (GH)
Growth hormone is a protein hormone secreted by somatotroph cells of the anterior pituitary. It stimulates growth of bones, muscles, and tissues. GH promotes protein synthesis and fat metabolism. Many of its effects are mediated through IGF-1. It is essential for normal growth and development.

8.  Somatotropin
Somatotropin is another name for growth hormone. It promotes linear growth during childhood and adolescence. The hormone increases protein synthesis and cell proliferation. Somatotropin also influences carbohydrate and lipid metabolism. Its secretion is regulated by GHRH and somatostatin.

9.  Prolactin (PRL)
Prolactin is a hormone secreted by lactotroph cells of the anterior pituitary. Its primary function is to stimulate milk production after childbirth. Prolactin also influences reproductive and immune functions. Dopamine inhibits its secretion under normal conditions. Elevated prolactin levels may cause infertility and galactorrhea.

10.               Thyroid-Stimulating Hormone (TSH)
TSH is a tropic hormone secreted by thyrotroph cells of the anterior pituitary. It stimulates the thyroid gland to synthesize and release T3 and T4. TSH secretion is controlled by TRH and thyroid hormone feedback. It regulates metabolic activity throughout the body. TSH is essential for normal thyroid function.

11.               Adrenocorticotropic Hormone (ACTH)
ACTH is a pituitary hormone secreted by corticotroph cells. It stimulates the adrenal cortex to produce cortisol. ACTH release is regulated by CRH from the hypothalamus. It plays a major role in stress adaptation. Excess ACTH may lead to hypercortisolism.

12.               Follicle-Stimulating Hormone (FSH)
FSH is a gonadotropin secreted by gonadotroph cells of the anterior pituitary. In females, it stimulates ovarian follicle development. In males, it promotes spermatogenesis within the testes. FSH secretion is regulated by GnRH. It is essential for reproductive function.

13.               Luteinizing Hormone (LH)
LH is a gonadotropin produced by gonadotroph cells of the anterior pituitary. In females, it triggers ovulation and corpus luteum formation. In males, it stimulates testosterone production by Leydig cells. LH secretion is regulated by GnRH. It is critical for fertility and reproductive health.

14.               Melanocyte-Stimulating Hormone (MSH)
MSH is a hormone that stimulates melanin production by melanocytes. It is derived from the precursor molecule POMC. Increased MSH activity may cause skin pigmentation. It also influences appetite and energy balance. MSH has a limited physiological role in humans.

15.               Somatomedin
Somatomedins are growth-promoting peptides produced mainly by the liver in response to GH stimulation. They mediate many effects of growth hormone. Somatomedins stimulate cell growth and tissue development. IGF-1 is the most important somatomedin. They are essential for normal body growth.

16.               Insulin-Like Growth Factor-1 (IGF-1)
IGF-1 is a peptide hormone produced primarily in the liver under the influence of GH. It promotes bone and tissue growth. IGF-1 mediates many anabolic effects of growth hormone. Its concentration reflects GH activity. It is important in growth assessment and endocrine evaluation.

17.               Gigantism
Gigantism is a disorder caused by excessive GH secretion before closure of the epiphyseal growth plates. It results in abnormal linear growth and extreme height. The condition is usually caused by a pituitary adenoma. Affected individuals have enlarged bones and soft tissues. Early treatment can reduce complications.

18.               Acromegaly
Acromegaly results from excessive GH secretion after epiphyseal closure. It causes enlargement of hands, feet, jaw, and facial bones. Most cases are due to a GH-secreting pituitary adenoma. Patients may develop hypertension and diabetes mellitus. Early diagnosis improves outcomes.

19.               Pituitary Dwarfism
Pituitary dwarfism is caused by growth hormone deficiency during childhood. Affected individuals have proportionate short stature. Intelligence is usually normal. Early GH replacement therapy promotes growth. The condition highlights the importance of GH in development.

20.               Hyperpituitarism
Hyperpituitarism refers to excessive secretion of one or more pituitary hormones. It is commonly caused by pituitary adenomas. Clinical manifestations depend on the hormone involved. Examples include acromegaly and Cushing disease. Treatment may involve surgery, medication, or radiotherapy.

21.               Hypopituitarism
Hypopituitarism is the deficiency of one or more pituitary hormones. Causes include tumors, trauma, infarction, and infections. Symptoms vary according to the affected hormones. Growth failure, infertility, and adrenal insufficiency may occur. Hormone replacement therapy is often required.

22.               Empty Sella Syndrome
Empty sella syndrome is a condition in which the sella turcica appears partially or completely filled with cerebrospinal fluid. The pituitary gland becomes compressed. Many patients remain asymptomatic. Some may develop hormonal abnormalities. Diagnosis is usually made by imaging studies.

23.               Pituitary Adenoma
Pituitary adenoma is a benign tumor arising from pituitary cells. It may secrete excess hormones or cause hormone deficiency through compression. Common types include prolactinomas and GH-secreting adenomas. Symptoms depend on tumor size and hormone activity. Treatment includes surgery and medical therapy.

24.               Diabetes Insipidus
Diabetes insipidus is a disorder characterized by excessive thirst and passage of large volumes of dilute urine. It results from ADH deficiency or renal resistance to ADH. Central diabetes insipidus involves inadequate ADH production. Patients are at risk of dehydration. Treatment depends on the underlying cause.

25.               SIADH
SIADH stands for Syndrome of Inappropriate Antidiuretic Hormone Secretion. Excessive ADH release causes water retention and dilutional hyponatremia. Patients may develop headache, confusion, and seizures. Various diseases and medications can cause SIADH. Treatment focuses on correcting fluid imbalance.

26.               Lactotroph
Lactotrophs are specialized cells of the anterior pituitary that secrete prolactin. They increase in number during pregnancy. Their activity is normally inhibited by dopamine. Excessive lactotroph activity may lead to hyperprolactinemia. They play a central role in lactation.

27.               Somatotroph
Somatotrophs are anterior pituitary cells that produce growth hormone. They constitute a major proportion of pituitary cells. Their secretion is stimulated by GHRH and inhibited by somatostatin. Somatotroph dysfunction can result in growth disorders. They are essential for normal development.

28.               Corticotroph
Corticotrophs are anterior pituitary cells that secrete ACTH. ACTH stimulates cortisol production by the adrenal cortex. Corticotroph activity is regulated by CRH and cortisol feedback. Excess activity may cause Cushing disease. These cells are important in stress regulation.

29.               Gonadotroph
Gonadotrophs are pituitary cells that secrete FSH and LH. They regulate ovarian and testicular function. Their activity is controlled by pulsatile GnRH secretion. Gonadotroph hormones are essential for fertility and reproduction. Dysfunction may result in hypogonadism and infertility.

30.               Thyrotroph
Thyrotrophs are specialized anterior pituitary cells that produce TSH. They respond to hypothalamic TRH stimulation. TSH regulates thyroid hormone synthesis and release. Thyrotroph activity is controlled by negative feedback from T3 and T4. They are essential for maintaining normal metabolic function.

Chapter 120: Thyroid Hormones

1.  Thyroid Gland
The thyroid gland is a butterfly-shaped endocrine gland located in the anterior neck below the larynx. It produces the hormones thyroxine (T4) and triiodothyronine (T3). These hormones regulate metabolism, growth, and development. The gland also secretes calcitonin, which influences calcium metabolism. Proper thyroid function is essential for overall health.

2.  Thyroxine (T4)
Thyroxine is the principal hormone secreted by the thyroid gland. It contains four iodine atoms and serves mainly as a prohormone. In peripheral tissues, T4 is converted to the more active T3. Thyroxine regulates metabolic rate and energy production. It is essential for normal growth and development.

3.  Triiodothyronine (T3)
Triiodothyronine is the biologically active thyroid hormone containing three iodine atoms. Most T3 is formed by peripheral conversion of T4. It increases cellular metabolism and oxygen consumption. T3 influences growth, thermogenesis, and cardiovascular function. It is more potent than T4.

4.  Thyroglobulin
Thyroglobulin is a large glycoprotein synthesized by thyroid follicular cells. It serves as the storage form and precursor of thyroid hormones. Iodination of tyrosine residues occurs within thyroglobulin. T3 and T4 are formed from these iodinated residues. It is stored in the follicular colloid.

5.  Thyroid Follicle
The thyroid follicle is the structural and functional unit of the thyroid gland. It consists of follicular cells surrounding a central colloid-filled cavity. The colloid contains thyroglobulin. Follicles are responsible for thyroid hormone synthesis and storage. They form the bulk of thyroid tissue.

6.  Follicular Cell
Follicular cells are epithelial cells lining the thyroid follicles. They synthesize thyroglobulin and produce T3 and T4. These cells actively concentrate iodide from the bloodstream. Their activity is stimulated by TSH. Follicular cells are essential for thyroid hormone production.

7.  Parafollicular Cell
Parafollicular cells, also called C cells, are specialized thyroid cells located between follicles. They secrete calcitonin. Calcitonin helps reduce blood calcium levels by inhibiting bone resorption. These cells are distinct from follicular cells. They contribute to calcium homeostasis.

8.  Calcitonin
Calcitonin is a peptide hormone secreted by thyroid parafollicular cells. It lowers blood calcium levels by inhibiting osteoclast activity. Calcitonin opposes some actions of parathyroid hormone. Its role in adults is relatively minor. It contributes to calcium balance and bone health.

9.  Iodine
Iodine is an essential trace element required for thyroid hormone synthesis. It is obtained mainly through dietary intake. The thyroid gland concentrates iodine from the bloodstream. Deficiency can lead to goiter and hypothyroidism. Adequate iodine intake is necessary for normal thyroid function.

10.               Iodide Trapping
Iodide trapping is the active transport of iodide ions into thyroid follicular cells. This process is mediated by the sodium-iodide symporter. It is the first step in thyroid hormone synthesis. TSH stimulates iodide trapping. Efficient iodide uptake is essential for hormone production.

11.               Thyroid Peroxidase
Thyroid peroxidase is an enzyme present in thyroid follicular cells. It catalyzes the oxidation of iodide and iodination of tyrosine residues. It also promotes coupling reactions that form T3 and T4. The enzyme is crucial for thyroid hormone synthesis. Autoantibodies against it are common in autoimmune thyroid disease.

12.               Organification
Organification is the process by which iodine binds to tyrosine residues in thyroglobulin. This reaction is catalyzed by thyroid peroxidase. Organification produces MIT and DIT. It is a critical step in thyroid hormone synthesis. Defects can impair hormone production.

13.               Coupling Reaction
The coupling reaction refers to the joining of iodinated tyrosine residues within thyroglobulin. MIT and DIT combine to form T3, while two DIT molecules form T4. This process occurs in the thyroid follicle. Thyroid peroxidase catalyzes the reaction. It is essential for thyroid hormone formation.

14.               Monoiodotyrosine (MIT)
MIT is an iodinated tyrosine molecule containing one iodine atom. It is formed during organification within thyroglobulin. MIT serves as a precursor in thyroid hormone synthesis. Coupling of MIT with DIT forms T3. It is an intermediate in hormone production.

15.               Diiodotyrosine (DIT)
DIT is an iodinated tyrosine molecule containing two iodine atoms. It is produced during organification of thyroglobulin. Coupling of two DIT molecules forms T4. DIT also combines with MIT to produce T3. It is an important precursor of thyroid hormones.

16.               Thyroid-Binding Globulin (TBG)
Thyroid-binding globulin is the major plasma protein responsible for transporting thyroid hormones. Most circulating T3 and T4 are bound to TBG. Protein binding prolongs hormone half-life. Only free hormones are biologically active. TBG helps maintain stable thyroid hormone levels.

17.               Euthyroid State
The euthyroid state refers to normal thyroid function with appropriate levels of T3, T4, and TSH. Metabolic processes occur at a normal rate. Individuals are free from symptoms of thyroid dysfunction. Hormonal feedback mechanisms remain balanced. Euthyroidism represents normal endocrine homeostasis.

18.               Hypothyroidism
Hypothyroidism is a condition characterized by deficient thyroid hormone production. Symptoms include fatigue, weight gain, cold intolerance, and constipation. Causes include autoimmune disease and iodine deficiency. Metabolic activity becomes reduced. Treatment usually involves thyroid hormone replacement.

19.               Hyperthyroidism
Hyperthyroidism is a disorder caused by excessive thyroid hormone production. Symptoms include weight loss, heat intolerance, palpitations, and nervousness. Graves disease is a common cause. Metabolic processes become accelerated. Treatment may involve medication, radioactive iodine, or surgery.

20.               Goiter
Goiter is an abnormal enlargement of the thyroid gland. It may occur in euthyroid, hypothyroid, or hyperthyroid states. Common causes include iodine deficiency and autoimmune disease. The enlargement may be diffuse or nodular. Large goiters can cause compressive symptoms.

21.               Graves Disease
Graves disease is an autoimmune disorder causing hyperthyroidism. Autoantibodies stimulate TSH receptors on thyroid cells. This results in excessive thyroid hormone production. Patients may develop exophthalmos and diffuse goiter. It is the most common cause of hyperthyroidism.

22.               Hashimoto Thyroiditis
Hashimoto thyroiditis is an autoimmune disease causing chronic thyroid inflammation. Autoimmune destruction of thyroid tissue leads to hypothyroidism. Anti-thyroid peroxidase antibodies are commonly present. The thyroid gland may initially enlarge. It is a leading cause of hypothyroidism worldwide.

23.               Myxedema
Myxedema is severe hypothyroidism occurring in adults. It is characterized by non-pitting edema due to mucopolysaccharide accumulation in tissues. Symptoms include lethargy, cold intolerance, and weight gain. Untreated cases may progress to myxedema coma. Prompt treatment is essential.

24.               Cretinism
Cretinism is congenital hypothyroidism occurring during infancy or childhood. It causes severe growth retardation and intellectual disability if untreated. Iodine deficiency and thyroid developmental defects are common causes. Early diagnosis is crucial. Thyroid hormone replacement prevents complications.

25.               Thyrotoxicosis
Thyrotoxicosis refers to the clinical state resulting from excessive circulating thyroid hormones. Hyperthyroidism is a common cause of thyrotoxicosis. Symptoms include tachycardia, weight loss, and increased sweating. Metabolic activity becomes markedly elevated. Appropriate treatment reduces complications.

26.               Basal Metabolic Rate (BMR)
Basal metabolic rate is the amount of energy expended by the body at rest. Thyroid hormones significantly influence BMR. Increased thyroid hormone levels raise energy expenditure. Reduced hormone levels lower metabolic activity. BMR reflects the metabolic effects of thyroid function.

27.               Radioactive Iodine Uptake
Radioactive iodine uptake is a diagnostic test used to assess thyroid function. The thyroid gland absorbs radioactive iodine similarly to normal iodine. Uptake measurements help differentiate causes of thyroid disease. Increased uptake is seen in Graves disease. The test is valuable in endocrine evaluation.

28.               TSH Receptor
The TSH receptor is a membrane receptor located on thyroid follicular cells. Binding of TSH stimulates thyroid hormone synthesis and secretion. It activates intracellular signaling pathways. Autoantibodies against this receptor cause Graves disease. The receptor is central to thyroid regulation.

29.               Thyroid Function Test
Thyroid function tests are laboratory investigations used to evaluate thyroid status. Common tests include TSH, free T4, and free T3 measurements. These tests help diagnose hypo- and hyperthyroidism. They also monitor treatment effectiveness. Thyroid function testing is a cornerstone of endocrine assessment.

30.               Wolff-Chaikoff Effect
The Wolff-Chaikoff effect is a temporary reduction in thyroid hormone synthesis caused by excess iodine exposure. It protects the body from producing excessive thyroid hormones. The effect usually lasts for a short period. Normal thyroid function eventually resumes through an escape mechanism. This phenomenon has clinical significance in thyroid disease management.

Chapter 121: Parathyroid Hormones

1.  Parathyroid Gland
The parathyroid glands are four small endocrine glands located on the posterior surface of the thyroid gland. They secrete parathyroid hormone (PTH), which regulates calcium and phosphate metabolism. These glands play a crucial role in maintaining mineral balance. Their activity is influenced by blood calcium levels. Normal parathyroid function is essential for neuromuscular and skeletal health.

2.  Parathyroid Hormone (PTH)
Parathyroid hormone is the principal hormone secreted by the parathyroid glands. It increases blood calcium levels by acting on bone, kidneys, and intestines. PTH stimulates bone resorption and renal calcium reabsorption. It also promotes calcitriol formation in the kidneys. PTH is the major regulator of calcium homeostasis.

3.  Chief Cell
Chief cells are the predominant cells of the parathyroid glands. They synthesize and secrete parathyroid hormone. Their activity is regulated by blood calcium concentration. A fall in serum calcium stimulates PTH release. Chief cells are essential for calcium regulation.

4.  Oxyphil Cell
Oxyphil cells are larger parathyroid cells with abundant eosinophilic cytoplasm. Their exact physiological function remains uncertain. They appear in greater numbers with age. Oxyphil cells may represent inactive or modified chief cells. They are a normal histological component of the parathyroid gland.

5.  Calcium Homeostasis
Calcium homeostasis is the maintenance of stable calcium levels in body fluids. It is regulated primarily by PTH, calcitriol, and calcitonin. Proper calcium balance is necessary for muscle contraction and nerve conduction. Bones serve as the major calcium reservoir. Disruption leads to significant clinical disorders.

6.  Phosphate Homeostasis
Phosphate homeostasis refers to the regulation of phosphate concentration in the body. PTH decreases phosphate reabsorption by the kidneys. Calcitriol enhances intestinal phosphate absorption. Balanced phosphate levels are important for energy metabolism and bone health. Homeostasis prevents abnormal mineral deposition.

7.  Hyperparathyroidism
Hyperparathyroidism is a disorder characterized by excessive PTH secretion. It leads to hypercalcemia and increased bone resorption. Causes include parathyroid adenoma, hyperplasia, or chronic kidney disease. Patients may develop bone pain and kidney stones. Treatment depends on the underlying cause.

8.  Hypoparathyroidism
Hypoparathyroidism is a condition caused by deficient PTH secretion. It results in hypocalcemia and increased neuromuscular excitability. Common causes include surgical removal or autoimmune destruction of parathyroid glands. Patients may develop tetany and muscle spasms. Calcium and vitamin D supplementation are often required.

9.  Secondary Hyperparathyroidism
Secondary hyperparathyroidism occurs when chronic hypocalcemia stimulates excessive PTH secretion. Chronic kidney disease is the most common cause. The parathyroid glands enlarge due to persistent stimulation. Elevated PTH attempts to restore calcium balance. Treatment focuses on correcting the underlying disorder.

10.               Tertiary Hyperparathyroidism
Tertiary hyperparathyroidism develops when prolonged secondary hyperparathyroidism becomes autonomous. The enlarged glands continue secreting excessive PTH despite correction of hypocalcemia. Hypercalcemia commonly occurs. This condition is often seen in long-standing renal disease. Surgical intervention may be necessary.

11.               Bone Resorption
Bone resorption is the breakdown of bone tissue with release of minerals into the bloodstream. PTH indirectly stimulates osteoclast activity. This process increases serum calcium levels. Bone remodeling requires a balance between resorption and formation. Excessive resorption weakens skeletal structure.

12.               Osteoblast
Osteoblasts are bone-forming cells responsible for synthesizing bone matrix. They produce collagen and other structural proteins. Osteoblasts contribute to bone growth and repair. PTH influences their activity indirectly. They play a key role in skeletal maintenance.

13.               Osteoclast
Osteoclasts are large multinucleated cells responsible for bone resorption. They dissolve mineralized bone and release calcium into circulation. Their activity is indirectly stimulated by PTH. Osteoclasts are essential for bone remodeling. Excessive activity may lead to osteoporosis.

14.               Calcitriol
Calcitriol is the active form of vitamin D produced in the kidneys. It increases intestinal absorption of calcium and phosphate. Calcitriol works together with PTH to maintain calcium homeostasis. It also supports bone mineralization. Deficiency may contribute to bone disease.

15.               Vitamin D
Vitamin D is a fat-soluble vitamin important for calcium and phosphate metabolism. It is obtained from sunlight exposure and dietary sources. The vitamin undergoes activation in the liver and kidneys. Active vitamin D promotes calcium absorption from the intestine. Adequate levels are essential for bone health.

16.               Calcium-Sensing Receptor (CaSR)
The calcium-sensing receptor is a membrane receptor present on parathyroid chief cells. It detects changes in blood calcium concentration. High calcium levels suppress PTH secretion through this receptor. CaSR plays a crucial role in calcium regulation. Mutations may cause calcium metabolism disorders.

17.               Renal Calcium Reabsorption
Renal calcium reabsorption is the process by which calcium is reclaimed from the filtrate in the kidneys. PTH enhances calcium reabsorption, especially in the distal tubules. This reduces urinary calcium loss. The mechanism helps maintain normal serum calcium levels. It is essential for mineral homeostasis.

18.               Phosphaturia
Phosphaturia refers to increased phosphate excretion in the urine. PTH decreases renal phosphate reabsorption, leading to phosphaturia. This action helps prevent excessive phosphate accumulation. It contributes to calcium-phosphate balance. Increased phosphaturia is a characteristic effect of PTH.

19.               Hypercalcemia
Hypercalcemia is an abnormally elevated level of calcium in the blood. It commonly results from hyperparathyroidism or malignancy. Symptoms include weakness, constipation, and kidney stones. Severe cases may cause cardiac arrhythmias. Early recognition is important for effective treatment.

20.               Hypocalcemia
Hypocalcemia is a reduced concentration of calcium in the bloodstream. Causes include hypoparathyroidism and vitamin D deficiency. Patients may develop muscle cramps and tetany. Severe hypocalcemia can cause seizures and cardiac abnormalities. Prompt correction is often required.

21.               Tetany
Tetany is a condition characterized by involuntary muscle spasms due to increased neuromuscular excitability. It commonly occurs in hypocalcemia. Symptoms include carpopedal spasm and facial muscle twitching. Tetany indicates significant calcium deficiency. Treatment involves calcium replacement.

22.               Chvostek Sign
Chvostek sign is a clinical sign of hypocalcemia. Tapping the facial nerve causes contraction of facial muscles. The sign indicates increased neuromuscular irritability. It is commonly observed in hypoparathyroidism. Chvostek sign aids clinical diagnosis.

23.               Trousseau Sign
Trousseau sign is another indicator of hypocalcemia. Inflation of a blood pressure cuff induces carpal muscle spasm. The sign reflects latent tetany. It is more specific than Chvostek sign. Trousseau sign is useful in evaluating calcium deficiency.

24.               Osteitis Fibrosa Cystica
Osteitis fibrosa cystica is a skeletal disorder caused by severe hyperparathyroidism. Excessive bone resorption results in bone weakness and deformity. Fibrous tissue replaces normal bone. Patients may develop fractures and bone pain. The condition reflects advanced PTH excess.

25.               Renal Osteodystrophy
Renal osteodystrophy is a bone disorder associated with chronic kidney disease. It results from abnormalities in calcium, phosphate, and vitamin D metabolism. Secondary hyperparathyroidism commonly contributes to its development. Patients may experience bone pain and fractures. Management focuses on correcting mineral imbalance.

26.               Nephrolithiasis
Nephrolithiasis refers to the formation of kidney stones. Hypercalcemia and hypercalciuria increase the risk of stone formation. Primary hyperparathyroidism is a common endocrine cause. Stones may cause pain, obstruction, and infection. Prevention involves controlling underlying metabolic abnormalities.

27.               Bone Mineralization
Bone mineralization is the deposition of calcium and phosphate into the bone matrix. This process gives bone its strength and rigidity. Vitamin D and adequate calcium levels are essential for normal mineralization. Defective mineralization leads to skeletal disorders. Healthy mineralization supports skeletal integrity.

28.               PTH Receptor
The PTH receptor is a cell surface receptor found in bone and kidney tissues. Binding of PTH activates intracellular signaling pathways. These pathways regulate calcium and phosphate metabolism. The receptor mediates the physiological effects of PTH. Proper receptor function is essential for mineral balance.

29.               Calcium Balance
Calcium balance refers to the equilibrium between calcium intake, absorption, storage, and excretion. Hormones such as PTH, calcitriol, and calcitonin regulate this balance. Proper calcium balance is necessary for normal cellular function. Disturbances can affect bones, nerves, and muscles. Maintaining balance is essential for health.

30.               Mineral Metabolism
Mineral metabolism encompasses the absorption, distribution, utilization, and excretion of minerals in the body. Calcium and phosphate are the principal minerals regulated by parathyroid hormones. Hormonal control ensures optimal skeletal and cellular function. Disruptions may cause metabolic bone disease. Proper mineral metabolism is fundamental to overall physiological health.

Chapter 122: Adrenal Hormones

1.  Adrenal Gland
The adrenal glands are paired endocrine organs located above the kidneys. Each gland consists of an outer cortex and an inner medulla. They produce hormones essential for metabolism, stress adaptation, and electrolyte balance. Adrenal hormones influence cardiovascular and immune functions. Proper adrenal function is vital for survival.

2.  Suprarenal Gland
Suprarenal gland is another name for the adrenal gland because it lies superior to the kidneys. These glands synthesize steroid hormones and catecholamines. They play a central role in stress responses and metabolic regulation. The cortex and medulla have distinct embryological origins. Together they maintain physiological stability.

3.  Adrenal Cortex
The adrenal cortex is the outer portion of the adrenal gland. It produces mineralocorticoids, glucocorticoids, and adrenal androgens. The cortex is divided into three distinct zones. Its hormones regulate electrolyte balance, metabolism, and sexual development. ACTH influences much of its activity.

4.  Adrenal Medulla
The adrenal medulla is the inner region of the adrenal gland. It consists of modified sympathetic neurons called chromaffin cells. The medulla secretes epinephrine and norepinephrine. These hormones mediate the body's fight-or-flight response. The adrenal medulla links the nervous and endocrine systems.

5.  Zona Glomerulosa
The zona glomerulosa is the outermost layer of the adrenal cortex. It synthesizes and secretes aldosterone. Aldosterone regulates sodium and potassium balance. Its secretion is mainly controlled by the renin-angiotensin-aldosterone system. This zone is essential for fluid and electrolyte homeostasis.

6.  Zona Fasciculata
The zona fasciculata is the middle and largest layer of the adrenal cortex. It produces glucocorticoids, primarily cortisol. ACTH stimulates hormone secretion from this zone. Cortisol regulates metabolism and stress adaptation. The zona fasciculata is vital for maintaining energy balance.

7.  Zona Reticularis
The zona reticularis is the innermost cortical layer of the adrenal gland. It produces adrenal androgens such as DHEA. These hormones contribute to secondary sexual characteristics. ACTH influences their secretion. The zona reticularis supports reproductive and metabolic functions.

8.  Cortisol
Cortisol is the principal glucocorticoid hormone produced by the adrenal cortex. It regulates carbohydrate, protein, and fat metabolism. Cortisol increases blood glucose levels during stress. It also has anti-inflammatory and immunosuppressive effects. Proper cortisol secretion is essential for survival.

9.  Aldosterone
Aldosterone is the major mineralocorticoid hormone secreted by the zona glomerulosa. It promotes sodium and water reabsorption in the kidneys. Simultaneously, it increases potassium excretion. Aldosterone helps maintain blood pressure and fluid volume. Its secretion is regulated mainly by RAAS.

10.               Adrenal Androgens
Adrenal androgens are weak sex hormones produced by the adrenal cortex. They include DHEA and androstenedione. These hormones contribute to pubertal development and libido. Their effects are more significant in females than males. Excess production may cause virilization.

11.               Dehydroepiandrosterone (DHEA)
DHEA is the most abundant adrenal androgen secreted by the zona reticularis. It serves as a precursor for testosterone and estrogen synthesis. DHEA contributes to secondary sexual characteristics. Its production increases during puberty. Levels decline gradually with aging.

12.               Catecholamines
Catecholamines are hormones produced by the adrenal medulla. The major catecholamines are epinephrine and norepinephrine. They prepare the body for immediate physical activity. Catecholamines increase heart rate, blood pressure, and glucose availability. They are essential components of the stress response.

13.               Epinephrine
Epinephrine, also known as adrenaline, is a catecholamine secreted by the adrenal medulla. It increases cardiac output and blood glucose levels. Epinephrine promotes bronchodilation and enhances blood flow to muscles. It is released during stress and emergencies. The hormone supports rapid physiological adaptation.

14.               Norepinephrine
Norepinephrine is a catecholamine that functions as both a hormone and neurotransmitter. It causes vasoconstriction and increases blood pressure. Norepinephrine contributes to alertness and attention. It is released during sympathetic nervous system activation. The hormone is essential for cardiovascular regulation.

15.               Mineralocorticoid
Mineralocorticoids are steroid hormones that regulate electrolyte and water balance. Aldosterone is the principal mineralocorticoid in humans. These hormones act mainly on the kidneys. They maintain blood volume and blood pressure. Mineralocorticoids are crucial for fluid homeostasis.

16.               Glucocorticoid
Glucocorticoids are steroid hormones involved in metabolism and stress adaptation. Cortisol is the primary glucocorticoid produced by humans. These hormones increase glucose availability and suppress inflammation. They influence nearly every organ system. Glucocorticoids are essential for normal physiological function.

17.               Steroid Hormone
Steroid hormones are lipid-soluble hormones synthesized from cholesterol. They diffuse across cell membranes and bind intracellular receptors. Examples include cortisol, aldosterone, estrogen, and testosterone. Steroid hormones regulate gene expression. Their effects are generally slower but longer-lasting than peptide hormones.

18.               Addison Disease
Addison disease is a disorder caused by chronic adrenal insufficiency. It results in deficient production of cortisol and often aldosterone. Symptoms include fatigue, weight loss, and hypotension. Hyperpigmentation may occur due to increased ACTH levels. Lifelong hormone replacement therapy is usually required.

19.               Cushing Syndrome
Cushing syndrome is a condition caused by prolonged exposure to excess glucocorticoids. Patients develop central obesity, moon face, and muscle weakness. Hypertension and diabetes are common complications. Causes include adrenal tumors and excessive corticosteroid therapy. Early treatment improves prognosis.

20.               Conn Syndrome
Conn syndrome, or primary hyperaldosteronism, results from excessive aldosterone secretion. It causes hypertension and hypokalemia. Adrenal adenoma is a common cause. Increased sodium retention contributes to elevated blood pressure. Treatment may involve surgery or aldosterone antagonists.

21.               Adrenal Insufficiency
Adrenal insufficiency refers to inadequate production of adrenal hormones. It may be primary, secondary, or tertiary in origin. Symptoms include fatigue, weakness, and hypotension. Severe deficiency can be life-threatening. Hormone replacement is the cornerstone of treatment.

22.               Congenital Adrenal Hyperplasia
Congenital adrenal hyperplasia is a group of inherited disorders affecting adrenal steroid synthesis. Enzyme deficiencies impair cortisol production. Increased ACTH stimulation causes adrenal enlargement. Excess androgen production is common. Early diagnosis improves outcomes and prevents complications.

23.               Pheochromocytoma
Pheochromocytoma is a catecholamine-secreting tumor arising from chromaffin cells. It causes episodic hypertension, headache, sweating, and palpitations. Excess catecholamine release produces characteristic symptoms. Diagnosis involves biochemical testing and imaging studies. Surgical removal is the preferred treatment.

24.               Stress Response
The stress response is the body's coordinated reaction to physical or emotional challenges. It involves activation of the hypothalamic-pituitary-adrenal axis and sympathetic nervous system. Cortisol and catecholamines play central roles. These hormones increase energy availability and cardiovascular performance. The response helps the body adapt to stress.

25.               ACTH
Adrenocorticotropic hormone is produced by the anterior pituitary gland. It stimulates cortisol production by the adrenal cortex. ACTH secretion is regulated by CRH and cortisol feedback. Excess ACTH may lead to hypercortisolism. It is a key component of the stress response pathway.

26.               Renin-Angiotensin-Aldosterone System (RAAS)
RAAS is a hormonal system that regulates blood pressure and fluid balance. Renin initiates a cascade that produces angiotensin II. Angiotensin II stimulates aldosterone secretion from the adrenal cortex. This promotes sodium retention and water conservation. RAAS is essential for cardiovascular homeostasis.

27.               Chromaffin Cell
Chromaffin cells are specialized neuroendocrine cells found in the adrenal medulla. They synthesize and secrete catecholamines. These cells originate from neural crest tissue. Chromaffin cells respond to sympathetic nervous stimulation. They are essential for the fight-or-flight response.

28.               Corticosteroid
Corticosteroids are steroid hormones produced by the adrenal cortex. They include glucocorticoids and mineralocorticoids. These hormones regulate metabolism, immunity, and electrolyte balance. Synthetic corticosteroids are widely used in medicine. Their actions mimic natural adrenal hormones.

29.               Adrenocortical Hormone
Adrenocortical hormones are hormones produced by the adrenal cortex. They include aldosterone, cortisol, and adrenal androgens. These hormones regulate metabolism, electrolyte balance, and reproductive functions. Their secretion is controlled by ACTH and RAAS. They are essential for maintaining homeostasis.

30.               Adrenal Crisis
Adrenal crisis is an acute, life-threatening condition caused by severe adrenal hormone deficiency. It may occur in untreated adrenal insufficiency or during severe stress. Symptoms include shock, hypotension, dehydration, and altered consciousness. Immediate corticosteroid replacement is required. Early recognition can be lifesaving.

Chapter 123: Pancreatic Hormones

1.  Pancreas
The pancreas is a mixed gland that performs both exocrine and endocrine functions. Its endocrine portion consists of the Islets of Langerhans. The pancreas produces hormones that regulate blood glucose levels. It plays a central role in carbohydrate, fat, and protein metabolism. Proper pancreatic function is essential for metabolic homeostasis.

2.  Islets of Langerhans
The Islets of Langerhans are clusters of endocrine cells scattered throughout the pancreas. They contain alpha, beta, delta, and PP cells. These cells secrete hormones directly into the bloodstream. The islets regulate glucose metabolism and energy balance. They are the functional endocrine units of the pancreas.

3.  Alpha Cell
Alpha cells are endocrine cells located within the pancreatic islets. They secrete glucagon in response to low blood glucose levels. Glucagon raises blood sugar by stimulating glycogen breakdown and gluconeogenesis. Alpha cells help prevent hypoglycemia. Their action complements that of insulin.

4.  Beta Cell
Beta cells are the most abundant endocrine cells in the pancreatic islets. They produce and secrete insulin in response to elevated blood glucose levels. Insulin promotes glucose uptake and storage. Beta cells are essential for maintaining glucose homeostasis. Their destruction causes Type 1 diabetes mellitus.

5.  Delta Cell
Delta cells are endocrine cells that secrete somatostatin. Somatostatin inhibits the release of insulin, glucagon, and gastrointestinal hormones. It helps regulate nutrient absorption and metabolism. Delta cells act as local modulators within the pancreatic islets. Their activity contributes to endocrine balance.

6.  PP Cell
PP cells, also called F cells, secrete pancreatic polypeptide. This hormone influences pancreatic exocrine secretion and gastrointestinal motility. PP cells are found mainly in the head of the pancreas. Their exact physiological role is not fully understood. They contribute to digestive regulation.

7.  Insulin
Insulin is a peptide hormone produced by pancreatic beta cells. It lowers blood glucose by promoting cellular glucose uptake. Insulin stimulates glycogen synthesis, protein synthesis, and fat storage. It is the major anabolic hormone of the body. Deficiency or resistance leads to diabetes mellitus.

8.  Glucagon
Glucagon is a peptide hormone secreted by alpha cells of the pancreas. It increases blood glucose levels during fasting. Glucagon stimulates glycogenolysis and gluconeogenesis in the liver. It acts as the physiological antagonist of insulin. Together, insulin and glucagon maintain glucose balance.

9.  Somatostatin
Somatostatin is a peptide hormone secreted by pancreatic delta cells and the hypothalamus. It inhibits the secretion of insulin, glucagon, and growth hormone. Somatostatin slows gastrointestinal activity and nutrient absorption. It acts as a universal inhibitory regulator. Its effects help maintain metabolic stability.

10.               Pancreatic Polypeptide
Pancreatic polypeptide is a hormone secreted by PP cells of the pancreas. It influences digestive processes and pancreatic secretion. The hormone also affects appetite and gastrointestinal motility. Its secretion increases after meals. Pancreatic polypeptide contributes to digestive regulation.

11.               Insulin Receptor
The insulin receptor is a transmembrane receptor located on target cells. Binding of insulin activates intracellular signaling pathways. These pathways promote glucose uptake and metabolic effects. The receptor possesses intrinsic tyrosine kinase activity. Proper receptor function is essential for insulin action.

12.               Glucose Homeostasis
Glucose homeostasis refers to the maintenance of stable blood glucose levels. Insulin and glucagon are the principal hormones involved. The liver, muscles, and adipose tissue play important roles. Homeostasis ensures a continuous energy supply to cells. Disturbances result in metabolic disorders.

13.               Glycogenesis
Glycogenesis is the process of glycogen synthesis from glucose. It occurs mainly in the liver and skeletal muscles. Insulin stimulates glycogenesis after meals. This process stores excess glucose for future energy needs. Glycogenesis helps maintain normal blood glucose levels.

14.               Glycogenolysis
Glycogenolysis is the breakdown of glycogen into glucose. It occurs primarily in the liver and muscles. Glucagon and epinephrine stimulate this process. Glycogenolysis provides a rapid source of glucose during fasting. It helps maintain energy availability.

15.               Gluconeogenesis
Gluconeogenesis is the synthesis of glucose from non-carbohydrate precursors. The liver is the primary site of this process. Amino acids, lactate, and glycerol serve as substrates. Glucagon and cortisol stimulate gluconeogenesis. It helps maintain blood glucose during prolonged fasting.

16.               Lipogenesis
Lipogenesis is the process of converting excess glucose into fatty acids and triglycerides. It occurs mainly in the liver and adipose tissue. Insulin strongly promotes lipogenesis. The process stores surplus energy as fat. Lipogenesis contributes to long-term energy reserves.

17.               Lipolysis
Lipolysis is the breakdown of stored triglycerides into fatty acids and glycerol. It occurs primarily in adipose tissue. Glucagon and catecholamines stimulate lipolysis. The released fatty acids provide energy during fasting. Lipolysis supports metabolic adaptation to energy demands.

18.               Ketogenesis
Ketogenesis is the production of ketone bodies from fatty acids in the liver. It occurs during prolonged fasting or insulin deficiency. Ketone bodies serve as alternative energy sources. Excessive ketogenesis may lead to ketoacidosis. The process helps preserve glucose for critical tissues.

19.               Hyperglycemia
Hyperglycemia is an abnormally elevated blood glucose level. It commonly occurs in diabetes mellitus. Symptoms include excessive thirst, frequent urination, and fatigue. Persistent hyperglycemia damages blood vessels and organs. Effective glucose control reduces complications.

20.               Hypoglycemia
Hypoglycemia is a condition characterized by abnormally low blood glucose levels. Symptoms include sweating, tremors, confusion, and weakness. Severe hypoglycemia may cause seizures or coma. It often results from excessive insulin administration. Prompt glucose replacement is essential.

21.               Diabetes Mellitus
Diabetes mellitus is a metabolic disorder characterized by chronic hyperglycemia. It results from insulin deficiency, insulin resistance, or both. Long-term complications affect the eyes, kidneys, nerves, and blood vessels. Diabetes is a major global health problem. Effective management reduces morbidity and mortality.

22.               Type 1 Diabetes Mellitus
Type 1 diabetes mellitus is an autoimmune disease causing destruction of pancreatic beta cells. It results in absolute insulin deficiency. Patients require lifelong insulin therapy. The condition commonly begins during childhood or adolescence. Early diagnosis prevents life-threatening complications.

23.               Type 2 Diabetes Mellitus
Type 2 diabetes mellitus is characterized by insulin resistance and relative insulin deficiency. It is strongly associated with obesity and sedentary lifestyle. Blood glucose levels rise gradually over time. Management includes lifestyle modification and medication. It is the most common form of diabetes.

24.               Insulin Resistance
Insulin resistance is a condition in which target tissues respond poorly to insulin. Higher insulin levels are required to maintain normal glucose levels. It is a key feature of Type 2 diabetes mellitus. Obesity is a major contributing factor. Insulin resistance increases cardiovascular risk.

25.               C-Peptide
C-peptide is a peptide released during the conversion of proinsulin to insulin. It is secreted in equal amounts with endogenous insulin. Measurement of C-peptide helps assess beta-cell function. It distinguishes endogenous from exogenous insulin sources. C-peptide is useful in diabetes evaluation.

26.               Proinsulin
Proinsulin is the precursor molecule from which insulin is formed. It is synthesized within pancreatic beta cells. Enzymatic cleavage produces insulin and C-peptide. Proinsulin has limited biological activity. It is an essential intermediate in insulin biosynthesis.

27.               GLUT4
GLUT4 is an insulin-responsive glucose transporter found in muscle and adipose tissue. Insulin stimulates its movement to the cell membrane. GLUT4 facilitates glucose uptake into cells. This process lowers blood glucose concentration. Impaired GLUT4 function contributes to insulin resistance.

28.               Incretins
Incretins are gastrointestinal hormones released after food intake. Major incretins include GLP-1 and GIP. They enhance insulin secretion in a glucose-dependent manner. Incretins also reduce glucagon release and slow gastric emptying. They play an important role in glucose regulation.

29.               HbA1c
HbA1c, or glycated hemoglobin, reflects average blood glucose levels over the previous two to three months. It is formed by the nonenzymatic attachment of glucose to hemoglobin. HbA1c is used to diagnose and monitor diabetes mellitus. Higher values indicate poorer glycemic control. It is an important clinical marker.

30.               Metabolic Syndrome
Metabolic syndrome is a cluster of metabolic abnormalities including obesity, hypertension, hyperglycemia, and dyslipidemia. It is strongly associated with insulin resistance. Individuals with metabolic syndrome have an increased risk of cardiovascular disease. Lifestyle modification is a key component of management. Early intervention improves long-term outcomes.

Chapter 124: Reproductive Hormones

1.  Gonad
A gonad is a primary reproductive organ responsible for producing gametes and sex hormones. The testes are the male gonads, while the ovaries are the female gonads. Gonads are regulated by pituitary gonadotropins. They play essential roles in reproduction and sexual development. Proper gonadal function is necessary for fertility.

2.  Gonadal Hormones
Gonadal hormones are hormones produced by the testes and ovaries. These include estrogens, progesterone, and androgens. They regulate reproductive functions and secondary sexual characteristics. Their secretion is controlled by FSH and LH. Gonadal hormones are vital for normal sexual maturation.

3.  Estrogen
Estrogen is the principal female sex hormone produced mainly by the ovaries. It regulates female reproductive development and menstrual cycles. Estrogen promotes growth of reproductive organs and secondary sexual characteristics. It also influences bone and cardiovascular health. The hormone plays a central role in female physiology.

4.  Estradiol
Estradiol is the most potent and abundant estrogen during the reproductive years. It is produced primarily by ovarian follicles. Estradiol regulates the menstrual cycle and reproductive function. It supports bone growth and maintenance. It is the major estrogen in premenopausal women.

5.  Estrone
Estrone is a naturally occurring estrogen found predominantly after menopause. It is produced mainly in adipose tissue through androgen conversion. Estrone is less potent than estradiol. It contributes to estrogenic activity in postmenopausal women. It plays a role in maintaining hormonal balance.

6.  Estriol
Estriol is a weak estrogen produced in significant amounts during pregnancy. It is synthesized by the placenta using fetal precursors. Estriol levels increase progressively throughout gestation. Measurement of estriol may help assess fetal well-being. It is an important pregnancy-related hormone.

7.  Progesterone
Progesterone is a steroid hormone produced by the corpus luteum and placenta. It prepares the uterus for implantation of a fertilized ovum. Progesterone helps maintain pregnancy and inhibits uterine contractions. It also influences breast development. The hormone is essential for successful reproduction.

8.  Testosterone
Testosterone is the principal male sex hormone produced mainly by Leydig cells of the testes. It promotes male reproductive development and secondary sexual characteristics. Testosterone supports spermatogenesis and muscle growth. It also influences libido and bone density. The hormone is essential for male reproductive health.

9.  Dihydrotestosterone (DHT)
DHT is a potent androgen formed from testosterone by the enzyme 5-alpha reductase. It is responsible for development of external male genitalia. DHT also influences prostate growth and male-pattern hair distribution. It is more biologically active than testosterone. Excess DHT contributes to certain androgen-related disorders.

10.               Androgen
Androgens are male sex hormones that promote masculine characteristics. Testosterone and DHT are the principal androgens. These hormones regulate reproductive organ development and sexual function. They also influence muscle mass and bone growth. Androgens are present in both males and females.

11.               Gonadotropin
Gonadotropins are pituitary hormones that regulate gonadal function. The two major gonadotropins are FSH and LH. They stimulate gamete production and sex hormone secretion. Gonadotropins are controlled by GnRH from the hypothalamus. They are essential for fertility and reproduction.

12.               Follicle-Stimulating Hormone (FSH)
FSH is a gonadotropin secreted by the anterior pituitary gland. In females, it stimulates ovarian follicle growth and estrogen production. In males, it promotes spermatogenesis. FSH secretion is regulated by GnRH and inhibin. It is vital for reproductive function.

13.               Luteinizing Hormone (LH)
LH is a pituitary gonadotropin involved in reproductive regulation. In females, it triggers ovulation and corpus luteum formation. In males, LH stimulates testosterone production by Leydig cells. Its secretion is regulated by GnRH. LH is essential for normal reproductive physiology.

14.               Gonadotropin-Releasing Hormone (GnRH)
GnRH is a hypothalamic hormone that stimulates FSH and LH release from the anterior pituitary. It is secreted in a pulsatile manner. Proper pulsatile release is necessary for normal reproductive function. GnRH controls gonadal hormone production. It forms the basis of the hypothalamic-pituitary-gonadal axis.

15.               Human Chorionic Gonadotropin (hCG)
hCG is a hormone produced by the placenta during pregnancy. It maintains the corpus luteum and progesterone production in early pregnancy. hCG is detected in pregnancy tests. Its levels rise rapidly during the first trimester. The hormone is essential for pregnancy maintenance.

16.               Human Placental Lactogen (hPL)
Human placental lactogen is a hormone produced by the placenta during pregnancy. It modifies maternal metabolism to support fetal growth. hPL promotes lipolysis and reduces maternal glucose utilization. This increases nutrient availability for the fetus. It plays an important role in pregnancy physiology.

17.               Inhibin
Inhibin is a hormone produced by the ovaries and testes. It selectively inhibits FSH secretion from the anterior pituitary. Inhibin helps regulate reproductive hormone balance. It participates in feedback control of the reproductive system. Its action supports normal gamete production.

18.               Activin
Activin is a hormone that stimulates FSH secretion from the anterior pituitary. It acts opposite to inhibin. Activin promotes follicular development and reproductive function. It is produced by various tissues including gonads. The hormone contributes to endocrine regulation.

19.               Relaxin
Relaxin is a hormone produced by the corpus luteum and placenta during pregnancy. It relaxes pelvic ligaments and softens the cervix. These effects facilitate childbirth. Relaxin also influences uterine and vascular function. It plays an important role in reproductive adaptation.

20.               Puberty
Puberty is the developmental period during which sexual maturity is achieved. Increased GnRH secretion activates the reproductive endocrine system. Secondary sexual characteristics develop during this stage. Puberty enables reproductive capability. Hormonal changes drive physical and psychological development.

21.               Menstrual Cycle
The menstrual cycle is a monthly sequence of hormonal and reproductive changes in females. It prepares the uterus for possible pregnancy. Estrogen and progesterone regulate the cycle. The cycle includes follicular, ovulatory, and luteal phases. Normal cycling reflects healthy reproductive function.

22.               Ovulation
Ovulation is the release of a mature ovum from the ovarian follicle. It is triggered by the mid-cycle LH surge. Ovulation usually occurs around the middle of the menstrual cycle. The released ovum enters the fallopian tube. It is a critical event in female fertility.

23.               Corpus Luteum
The corpus luteum is a temporary endocrine structure formed after ovulation. It secretes progesterone and smaller amounts of estrogen. These hormones prepare the uterus for implantation. If pregnancy does not occur, the corpus luteum degenerates. It plays a vital role in the menstrual cycle.

24.               Spermatogenesis
Spermatogenesis is the process of sperm production within the seminiferous tubules of the testes. It is stimulated by FSH and testosterone. The process involves cell division and maturation. Continuous sperm production supports male fertility. Normal spermatogenesis is essential for reproduction.

25.               Oogenesis
Oogenesis is the process of ovum formation in the ovaries. It begins before birth and continues until menopause. Oocytes undergo maturation during each menstrual cycle. Hormonal regulation controls this process. Oogenesis is essential for female fertility.

26.               Fertilization
Fertilization is the union of a sperm and an ovum to form a zygote. It usually occurs in the fallopian tube. Fertilization restores the diploid chromosome number. The resulting zygote begins embryonic development. This process marks the beginning of a new individual.

27.               Pregnancy
Pregnancy is the physiological state in which a developing embryo or fetus grows within the uterus. Hormones such as hCG, progesterone, and estrogen support gestation. Pregnancy involves significant maternal adaptations. It normally lasts about forty weeks. Successful pregnancy results in childbirth.

28.               Menopause
Menopause is the permanent cessation of menstruation due to loss of ovarian follicular activity. It typically occurs between 45 and 55 years of age. Estrogen production declines significantly. Symptoms may include hot flashes and mood changes. Menopause marks the end of reproductive capacity.

29.               Hypogonadism
Hypogonadism is a condition characterized by reduced gonadal function. It results in decreased production of sex hormones and impaired fertility. Causes may be primary gonadal failure or pituitary disorders. Symptoms vary according to age and sex. Hormone replacement therapy may be required.

30.               Reproductive Endocrinology
Reproductive endocrinology is the branch of endocrinology that studies hormones involved in reproduction. It focuses on the hypothalamic-pituitary-gonadal axis. The field includes fertility, menstrual disorders, and hormonal regulation of pregnancy. Understanding reproductive endocrinology aids diagnosis and treatment of reproductive diseases. It is fundamental to reproductive medicine.

Chapter 125: Prostaglandins and Eicosanoids

1.  Eicosanoid
Eicosanoids are biologically active lipid mediators derived from arachidonic acid. They include prostaglandins, thromboxanes, leukotrienes, and lipoxins. Eicosanoids regulate inflammation, immunity, and vascular function. They act locally near their site of synthesis. These compounds are important mediators of physiological and pathological processes.

2.  Prostaglandin
Prostaglandins are lipid compounds synthesized from arachidonic acid through the cyclooxygenase pathway. They regulate inflammation, pain, fever, and smooth muscle activity. Different prostaglandins exert different biological effects. They act mainly as local hormones. Prostaglandins are important mediators in many body systems.

3.  Prostacyclin (PGI₂)
Prostacyclin is a prostaglandin produced mainly by vascular endothelial cells. It causes vasodilation and inhibits platelet aggregation. Prostacyclin helps maintain normal blood flow. Its actions oppose those of thromboxane A₂. It plays a protective role in the cardiovascular system.

4.  Thromboxane A₂
Thromboxane A₂ is an eicosanoid produced primarily by platelets. It promotes platelet aggregation and vasoconstriction. These actions support blood clot formation. Thromboxane A₂ acts opposite to prostacyclin. The balance between the two regulates hemostasis.

5.Leukotriene
Leukotrienes are inflammatory mediators produced through the lipoxygenase pathway. They increase vascular permeability and attract inflammatory cells. Leukotrienes also cause bronchoconstriction. They play a major role in asthma and allergic reactions. These compounds are important mediators of inflammation.

6.  Lipoxin
Lipoxins are anti-inflammatory eicosanoids derived from arachidonic acid through the lipoxygenase pathway. They help terminate inflammatory responses and promote tissue healing. Lipoxins inhibit neutrophil migration and activation. They contribute to the resolution phase of inflammation. These mediators protect tissues from excessive inflammatory damage.

7.  Arachidonic Acid
Arachidonic acid is a polyunsaturated fatty acid present in cell membrane phospholipids. It serves as the precursor for eicosanoid synthesis. Cellular injury or stimulation releases arachidonic acid from membranes. It is metabolized by cyclooxygenase and lipoxygenase enzymes. Arachidonic acid is central to inflammatory mediator production.

8.  Cyclooxygenase (COX)
Cyclooxygenase is an enzyme that converts arachidonic acid into prostaglandins and thromboxanes. It exists in two major forms, COX-1 and COX-2. COX enzymes play key roles in inflammation and physiological regulation. Many anti-inflammatory drugs target these enzymes. Their activity influences pain, fever, and vascular function.

9.  COX-1
COX-1 is a constitutive form of cyclooxygenase present in many tissues. It produces prostaglandins involved in normal physiological functions. These functions include gastric mucosal protection and platelet aggregation. COX-1 activity helps maintain tissue homeostasis. Inhibition may lead to gastrointestinal side effects.

10.               COX-2
COX-2 is an inducible form of cyclooxygenase expressed during inflammation. It produces prostaglandins responsible for pain, fever, and inflammatory responses. Cytokines and tissue injury stimulate COX-2 expression. Selective COX-2 inhibitors reduce inflammation with fewer gastric effects. COX-2 is a major therapeutic target.

11.               Lipoxygenase (LOX)
Lipoxygenase is an enzyme that converts arachidonic acid into leukotrienes and lipoxins. It plays an important role in inflammatory and allergic reactions. LOX products influence immune cell function. Increased activity contributes to asthma and hypersensitivity disorders. Lipoxygenase is essential in eicosanoid metabolism.

12.               Phospholipase A₂
Phospholipase A₂ is an enzyme that releases arachidonic acid from membrane phospholipids. It represents the first step in eicosanoid synthesis. Various inflammatory stimuli activate this enzyme. Corticosteroids inhibit phospholipase A₂ activity. The enzyme is crucial for inflammatory mediator production.

13.               Cell Membrane Phospholipid
Cell membrane phospholipids are structural components of cellular membranes. They serve as reservoirs for arachidonic acid. Enzymatic cleavage releases arachidonic acid during cellular activation. These phospholipids participate in signal transduction and membrane integrity. They are the starting point of eicosanoid synthesis.

14.               Inflammation
Inflammation is a protective response to tissue injury, infection, or harmful stimuli. It involves vascular, cellular, and biochemical changes. Eicosanoids contribute significantly to inflammatory processes. The response helps eliminate harmful agents and initiate healing. Excessive inflammation may cause tissue damage.

15.               Pain Mediator
Pain mediators are substances that stimulate or sensitize pain receptors. Prostaglandins are among the most important pain mediators. They increase the sensitivity of nerve endings to painful stimuli. This enhances the perception of pain. Inhibiting prostaglandin synthesis reduces pain symptoms.

16.               Fever Mediator
Fever mediators are substances that elevate body temperature during infection or inflammation. Prostaglandin E₂ is a major fever-producing mediator. It acts on the hypothalamic thermoregulatory center. Fever enhances immune defense mechanisms. Antipyretic drugs reduce fever by inhibiting prostaglandin production.

17.               Vasodilation
Vasodilation is the widening of blood vessels due to relaxation of vascular smooth muscle. Certain prostaglandins and prostacyclin promote vasodilation. This increases blood flow to tissues. Vasodilation contributes to redness and warmth during inflammation. It supports nutrient and immune cell delivery.

18.               Vasoconstriction
Vasoconstriction is the narrowing of blood vessels caused by smooth muscle contraction. Thromboxane A₂ and some leukotrienes induce vasoconstriction. This process increases vascular resistance and blood pressure. Vasoconstriction also helps limit blood loss after injury. It plays an important role in circulatory regulation.

19.               Platelet Aggregation
Platelet aggregation is the clumping together of platelets during blood clot formation. Thromboxane A₂ strongly promotes this process. Aggregation helps prevent excessive bleeding following vascular injury. Prostacyclin inhibits platelet aggregation to maintain blood flow. A balance between these mediators is essential for hemostasis.

20.               Bronchoconstriction
Bronchoconstriction is the narrowing of airways due to contraction of bronchial smooth muscle. Leukotrienes are potent bronchoconstrictors. Excessive bronchoconstriction occurs in asthma and allergic reactions. It reduces airflow and causes breathing difficulty. Targeting leukotrienes helps relieve respiratory symptoms.

21.               Bronchodilation
Bronchodilation is the widening of airways due to relaxation of bronchial smooth muscle. Certain prostaglandins can promote bronchodilation. This process improves airflow to the lungs. Bronchodilation is beneficial in respiratory disorders. It helps maintain effective gas exchange.

22.               NSAIDs
Nonsteroidal anti-inflammatory drugs (NSAIDs) are medications that inhibit cyclooxygenase enzymes. They reduce prostaglandin synthesis and thereby decrease pain, fever, and inflammation. Common NSAIDs include aspirin and ibuprofen. These drugs are widely used in clinical practice. Their adverse effects may include gastric irritation and bleeding.

23.               Aspirin
Aspirin is an NSAID that irreversibly inhibits cyclooxygenase enzymes. It reduces inflammation, pain, and fever. Aspirin also inhibits platelet aggregation by decreasing thromboxane A₂ production. Low-dose aspirin is commonly used for cardiovascular protection. It is one of the most widely used medications worldwide.

24.               Prostaglandin Synthesis
Prostaglandin synthesis begins with the release of arachidonic acid from membrane phospholipids. Cyclooxygenase enzymes convert arachidonic acid into prostaglandin intermediates. These intermediates are further transformed into specific prostaglandins. The process occurs in many tissues. Prostaglandin synthesis is important in inflammation and physiological regulation.

25.               Eicosanoid Pathway
The eicosanoid pathway refers to the biochemical pathways that generate prostaglandins, thromboxanes, leukotrienes, and lipoxins. It begins with arachidonic acid release from membranes. Cyclooxygenase and lipoxygenase enzymes mediate the pathway. The products regulate inflammation and vascular function. This pathway is a major target of anti-inflammatory therapy.

26.               Cytokine
Cytokines are signaling proteins released by immune and other cells. They regulate inflammation, immunity, and cell communication. Cytokines can stimulate eicosanoid production during inflammatory responses. Examples include interleukins and tumor necrosis factor. They are essential mediators of immune regulation.

27.               Inflammatory Mediator
An inflammatory mediator is a substance that initiates or amplifies inflammation. Examples include prostaglandins, leukotrienes, histamine, and cytokines. These mediators regulate vascular permeability and immune cell recruitment. They coordinate the inflammatory response. Excessive mediator activity can contribute to disease.

28.               Resolution of Inflammation
Resolution of inflammation is the active process through which inflammatory responses are terminated. Lipoxins and other specialized mediators promote this phase. Resolution restores normal tissue structure and function. It prevents chronic inflammation and tissue injury. Effective resolution is essential for healing.

29.               Thromboxane
Thromboxanes are eicosanoids derived from arachidonic acid through the cyclooxygenase pathway. They promote platelet aggregation and vasoconstriction. Thromboxane A₂ is the most important member of this group. These compounds contribute to blood clot formation. Balanced thromboxane activity is necessary for normal hemostasis.

30.                     Autacoid
An autacoid is a locally acting biological mediator produced within tissues. Examples include prostaglandins, histamine, serotonin, and leukotrienes. Autacoids exert their effects near the site of synthesis. They regulate inflammation, vascular tone, and smooth muscle activity. Autacoids play important roles in local physiological regulation.

 

END OF SECTION XII