Detailed Notes -3 -Chapter-19-Chemical Coordination And Integration

19.2.9 Testis

1. Anatomy and Location:

   • Testis is a pair of primary male reproductive organs located in the scrotal sac outside the abdomen.

2. Dual Function:

   • Testis serves both as a primary sex organ involved in sperm production and as an endocrine gland producing hormones.

3. Composition:

   • Testis is composed of seminiferous tubules and stromal or interstitial tissue.

4. Hormones Secreted:

   • Leydig cells or interstitial cells, present in the intertubular spaces of the testis, produce a group of hormones called androgens, mainly testosterone.

5. Functions of Androgens (Testosterone):

   • Regulation of Male Accessory Sex Organs: Androgens regulate the development, maturation, and functions of male accessory sex organs such as the epididymis, vas deferens, seminal vesicles, prostate gland, and urethra.
   • Secondary Sexual Characteristics: Androgens stimulate the growth of facial and axillary hair, deepening of the voice (low pitch), and aggressiveness.
   • Stimulation of Spermatogenesis: Androgens play a major stimulatory role in the process of spermatogenesis, which is the formation of spermatozoa (sperm).
   • Influence on Sexual Behavior: Androgens act on the central nervous system and influence male sexual behavior, including libido (sexual desire).
   • Anabolic Effects: Androgens produce anabolic effects on protein and carbohydrate metabolism, promoting muscle growth and energy production.

19.2.10 Ovary

1. Anatomy and Location:

   • Females have a pair of ovaries located in the abdomen.

2. Primary Function:

   • Ovary is the primary female reproductive organ responsible for producing ova (eggs) during each menstrual cycle.

3. Hormones Secreted:

   • Ovary produces two groups of steroid hormones: estrogen and progesterone.

4. Composition:

   • Ovary is composed of ovarian follicles and stromal tissues.

5. Functions of Estrogen:

   • Stimulation of Growth and Activities: Estrogen stimulates the growth and activities of female secondary sex organs.
   • Development of Ovarian Follicles: Estrogen plays a role in the development of growing ovarian follicles.
   • Appearance of Female Secondary Sex Characters: Estrogen contributes to the appearance of female secondary sex characteristics, such as high pitch of voice.
   • Mammary Gland Development: Estrogen is involved in mammary gland development.
   • Regulation of Female Sexual Behavior: Estrogen also regulates female sexual behavior.

6. Functions of Progesterone:

   • Support of Pregnancy: Progesterone supports pregnancy by maintaining the endometrial lining of the uterus.
   • Mammary Gland Function: Progesterone acts on the mammary glands, stimulating the formation of alveoli (milk-secreting sac-like structures) and milk secretion.

19.3 HORMONES OF HEART, KIDNEY AND GASTROINTESTINAL TRACT

1. Atrial Natriuretic Factor (ANF):

   • Source: Atrial wall of the heart.
   • Function: Decreases blood pressure by causing dilation of blood vessels.
   • Mechanism: Secreted in response to increased blood pressure, ANF promotes vasodilation, leading to a reduction in blood pressure.

2. Erythropoietin:

   • Source: Juxtaglomerular cells of the kidney.
   • Function: Stimulates erythropoiesis, the formation of red blood cells (RBCs).
   • Mechanism: Erythropoietin is released in response to low oxygen levels in the blood, stimulating the production of RBCs to increase oxygen-carrying capacity.

3. Peptide Hormones of the Gastrointestinal Tract:

   • Gastrin:
     • Source: Endocrine cells in the gastrointestinal tract.
     • Function: Stimulates secretion of hydrochloric acid and pepsinogen from gastric glands.
   • Secretin:
     • Source: Endocrine cells in the gastrointestinal tract.
     • Function: Stimulates secretion of water and bicarbonate ions from the exocrine pancreas.
   • Cholecystokinin (CCK):
     • Source: Endocrine cells in the gastrointestinal tract.
     • Function: Stimulates secretion of pancreatic enzymes and bile juice from the pancreas and gall bladder, respectively.
   • Gastric Inhibitory Peptide (GIP):
     • Source: Endocrine cells in the gastrointestinal tract.
     • Function: Inhibits gastric secretion and motility, regulating gastrointestinal activity.

4. Growth Factors:

   • Secreted by various non-endocrine tissues.
   • Function: Essential for normal tissue growth, repair, and regeneration.
   • Mechanism: These factors promote cell proliferation, differentiation, and survival, contributing to tissue development and maintenance.

19.4 MECHANISM OF HORMONE ACTION

1. Hormone-Receptor Interaction:

   • Hormones exert their effects by binding to specific proteins called hormone receptors, which are located in target tissues.
   • Hormone receptors can be membrane-bound receptors (on the cell membrane) or intracellular receptors (mostly nuclear receptors).
   • Binding of a hormone to its receptor forms a hormone-receptor complex, which initiates downstream signaling cascades.

2. Specificity of Receptors:

   • Each receptor is specific to a particular hormone, ensuring precise targeting and response.

3. Biochemical Changes in Target Tissue:

   • Formation of the hormone-receptor complex leads to biochemical changes in the target tissue.
   • These changes regulate target tissue metabolism and physiological functions.

4. Classification of Hormones:

   • Hormones can be classified into different groups based on their chemical nature:
     • Peptide, polypeptide, and protein hormones (e.g., insulin, glucagon, pituitary hormones, hypothalamic hormones).
     • Steroids (e.g., cortisol, testosterone, estradiol, progesterone).
     • Iodothyronines (thyroid hormones).
     • Amino-acid derivatives (e.g., epinephrine).

5. Mechanisms of Action:

   • Hormones interacting with membrane-bound receptors typically do not enter the target cell.
   • Instead, they generate second messengers (e.g., cyclic AMP, IP3, Ca++) that regulate cellular metabolism.
   • Hormones interacting with intracellular receptors (e.g., steroid hormones, iodothyronines) often regulate gene expression or chromosome function by interacting with the genome.

6. Physiological and Developmental Effects:

   • Cumulative biochemical actions resulting from hormone-receptor interactions lead to physiological and developmental effects.
   • These effects are essential for maintaining homeostasis, regulating metabolism, and orchestrating development and growth.