PRELIMS

Human Endocrine System and Hormones

Endocrine glands are ductless glands that secrete hormones directly into the blood plasma.

I. Pituitary Gland: The Master Gland

Situated in the Sphenoid bone (Sella-tunica) of the fore brain; weighs ~0.6g. Controlled by the Hypothalamus.

• STH: Full Name: Somatotropic. Major Functions: Growth of bones. Excess: Gigantism. Lack: Dwarfism.
• TSH: Full Name: Thyroid Stimulating. Major Functions: Stimulates thyroid secretion.
• ACTH: Full Name: Adrenocorticotropic. Major Functions: Controls adrenal cortex secretion.
• GTH: Full Name: Gonadotropic Hormone. Major Functions: Controls gonads (FSH - Follicle Stimulating Hormone: Sperm/Oestrogen production, LH - Luteinizing Hormone: Testosterone/ovulation).
• LTH: Full Name: Lactogenic. Major Functions: Stimulates milk secretion.
• ADH: Full Name: Antidiuretic. Major Functions: Restricts urine volume; maintains water balance.

II. Thyroid Gland: Metabolic Hub

Situated below the larynx in the throat. Secretes Thyroxine (Iodine-rich).

• Functions: Accelerates cellular respiration; necessary for bone and hair growth.
• Deficiency Disorders:
  • Cretinism: Mental/physical retardation in children.
  • Myxedema: Reduction in metabolism (youth).
  • Goitre: Abnormal enlargement due to Iodine deficiency.
• Excess Disorder: Exophthalmic Goitre (bulging eyes).

III. Adrenal Gland: Stress Response

Consists of the Cortex (outer) and Medulla (inner).

1. Cortex: Essential for life. Secretes Glucocorticoids (metabolism) and Mineralocorticoids (ions). Deficiency leads to Addison's Disease.
2. Medulla: Secretes Epinephrine (Adrenaline) and Nor-epinephrine.
   • Fight, Flight, Fright Hormone: Prepares the body for emergencies.

IV. Parathyroid and Gonads

• Parathyroid: Controls blood calcium using Parathormone (increases calcium) and Calcitonin (decreases calcium).
• Ovary (Female):
  • Estrogen: Oviduct growth.
  • Progesterone: Uterus lining thickening.
  • Relaxin: Widens cervix during childbirth.
• Testes (Male): Testosterone for secondary sexual characters.

V. Pancreas: Mixed Gland

The pancreas is a heterocrine gland — both endocrine and exocrine. Endocrine function is via the Islets of Langerhans.

• Beta (β) cells: Secrete Insulin — lowers blood glucose (promotes glucose uptake/glycogen storage). Deficiency causes Diabetes Mellitus (hyperglycemia).
• Alpha (α) cells: Secrete Glucagon — raises blood glucose (breaks down glycogen).
• Insulin was discovered by Banting and Best (1921).

VI. Pineal and Thymus Glands

• Pineal Gland: Located in the brain; secretes Melatonin, which regulates the sleep-wake cycle (circadian rhythm).
• Thymus Gland: Located near the heart; secretes Thymosin, essential for the maturation of T-lymphocytes (immune function). Most active in childhood; shrinks with age.

UPSC Relevance

The Endocrine system is a core area for medical Science & Technology and global health issues.

• Hormonal Balance: Differentiating between the roles of Insulin (Pancreas) and Thyroxine (Thyroid) for metabolic regulation.
• Iodine Health: The historical and public health significance of Goitre and universal salt iodization.
• Emergency Physiology: The role of Adrenaline (Medulla) as the primary emergency response chemical.
• Confused Pair — Diabetes Mellitus vs Insipidus: Diabetes Mellitus = Insulin deficiency/resistance (Pancreas), high blood sugar. Diabetes Insipidus = ADH deficiency (Pituitary), excessive dilute urination — sugar levels are normal.
• Confused Pair — Gigantism vs Acromegaly: Both from excess STH/GH; Gigantism occurs in childhood (before bone plates fuse, causing excess height); Acromegaly occurs in adulthood (causes enlarged hands, feet, jaw — not height).