Write short notes on the functions of the following hormones: (a) Parathyroid hormones (PTH) (b) Thyroid hormones (c) Thymosin

(a) Parathyroid Hormone (PTH):

• Parathyroid hormone (PTH) is produced by the parathyroid glands, which are small endocrine glands located behind the thyroid gland in the neck.
• Functions:
  1. Calcium Homeostasis: PTH plays a crucial role in regulating calcium levels in the blood by acting on bones, kidneys, and the intestines.
  2. Bone Resorption: PTH stimulates osteoclast activity in bones, leading to the breakdown of bone tissue and the release of calcium ions into the bloodstream.
  3. Renal Calcium Reabsorption: PTH enhances the reabsorption of calcium in the kidneys, reducing urinary calcium excretion and increasing blood calcium levels.
  4. Calcium Absorption: PTH indirectly promotes the absorption of calcium from the intestines by stimulating the production of active vitamin D, which enhances intestinal calcium absorption.
  5. Phosphate Regulation: PTH decreases phosphate reabsorption in the kidneys, leading to increased phosphate excretion in urine and decreased serum phosphate levels.

(b) Thyroid Hormones:

• Thyroid hormones include thyroxine (T4) and triiodothyronine (T3), which are produced by the thyroid gland located in the neck.
• Functions:
  1. Metabolic Regulation: Thyroid hormones play a key role in regulating metabolism by influencing the rate of cellular energy production and consumption.
  2. Heat Production: Thyroid hormones increase basal metabolic rate and heat production in the body, helping to maintain body temperature.
  3. Protein Synthesis: Thyroid hormones stimulate protein synthesis in various tissues, contributing to growth, development, and tissue repair.
  4. Regulation of Heart Rate and Contractility: Thyroid hormones influence heart rate and contractility, affecting cardiac function and cardiovascular health.
  5. Neurological Function: Thyroid hormones are essential for normal neurological function, including cognition, mood regulation, and reflexes.
  6. Development: Thyroid hormones play a critical role in fetal development, particularly in the development of the central nervous system and skeletal growth.

(c) Thymosin:

• Thymosin is a group of hormones produced by the thymus gland, which is located in the chest region behind the sternum.
• Functions:
  1. Immune System Regulation: Thymosin plays a vital role in the development and maturation of T lymphocytes (T cells), which are crucial components of the adaptive immune system.
  2. T Cell Differentiation: Thymosin promotes the differentiation of T cells into various subtypes, including helper T cells, cytotoxic T cells, and regulatory T cells, each with distinct functions in immune responses.
  3. Immune Response: Thymosin enhances the function of T cells, helping to coordinate and regulate immune responses against pathogens, foreign substances, and cancer cells.
  4. Tolerance: Thymosin contributes to the establishment of immune tolerance, preventing autoimmune reactions and maintaining immune homeostasis.
  5. Aging and Immunity: Thymosin levels decline with age, which is associated with decreased immune function and increased susceptibility to infections and autoimmune diseases.