An overview of the endocrine system, its functions, and the role of hormones in regulating various physiological processes in the body.
Introduction to Endocrinology
The study of hormones, their glands, and the physiological processes they regulate.
| Aspect | Description |
|---|---|
| Definition | Branch of physiology and medicine that deals with the endocrine system – the network of glands that secrete hormones into the bloodstream. |
| Goal | Understand how hormones control growth, metabolism, reproduction, stress response, and homeostasis, and how disorders arise when this system malfunctions. |
| Key Disciplines | - Basic science (cellular & molecular biology) - Clinical medicine (diagnosis & treatment of endocrine diseases) - Pharmacology (hormone analogs, antagonists, and modulators) |
| Concept | Explanation | Example |
|---|---|---|
| Hormone | Chemical messenger produced by endocrine cells; travels through blood to target cells. | Insulin, cortisol, estrogen |
| Receptor | Protein (membrane‑bound or intracellular) that binds a specific hormone, triggering a cellular response. | Insulin receptor (tyrosine‑kinase) |
| Signal Transduction | Cascade of intracellular events (often phosphorylation) that convert hormone binding into a functional outcome. | cAMP pathway activated by glucagon |
| Feedback Regulation | Mechanisms (negative or positive) that maintain hormone levels within a narrow range. | Negative feedback: high thyroid hormone → ↓ TSH |
| Target Specificity | Hormones affect only cells that express the appropriate receptor. | Testosterone acts on muscle cells expressing androgen receptors |
| Gland | Location | Principal Hormones | Primary Functions |
|---|---|---|---|
| Hypothalamus | Base of brain | CRH, TRH, GnRH, ADH, oxytocin (via posterior pituitary) | Regulates pituitary, autonomic functions, water balance |
| Pituitary (Anterior) | Sella turcica | GH, ACTH, TSH, LH, FSH, PRL | Growth, adrenal stimulation, thyroid regulation, reproduction, lactation |
| Pituitary (Posterior) | Sella turcica | ADH, Oxytocin | Water reabsorption, uterine contraction, milk ejection |
| Thyroid | Neck (C5‑T1) | T₃ (triiodothyronine), T₄ (thyroxine), calcitonin | Metabolic rate, calcium homeostasis |
| Parathyroid | Posterior thyroid | PTH (parathyroid hormone) | ↑ serum Ca²⁺, ↓ phosphate |
| Adrenal Cortex | Upper kidney | Cortisol, aldosterone, androgens | Stress response, sodium/potassium balance, sexual development |
| Adrenal Medulla | Inner adrenal | Epinephrine, norepinephrine | “Fight‑or‑flight” sympathetic response |
| Pancreas (Islets) | Abdomen | Insulin, glucagon, somatostatin | Blood‑glucose regulation |
| Gonads | Testes / Ovaries | Testosterone, estrogen, progesterone | Sexual development, reproduction, secondary sex traits |
| Pineal | Brain (epithalamus) | Melatonin | Circadian rhythm, seasonal reproduction |
| Kidney (Juxtaglomerular cells) | Renal cortex | Renin (enzyme → angiotensin II) | Blood |