Endocrinology
Endocrinology is the branch of medicine and biology concerned with the structure, function, and disorders of the endocrine glands and hormones. It explores the intricate communication network that regulates metabolism, growth, reproduction, mood, and overall homeostasis.
Hormones & Mechanisms
Hormones are chemical messengers secreted directly into the bloodstream, acting on distant target organs via specific receptors. Regulation involves finely tuned feedback systems:
- Peptide hormones – Hydrophilic, bind to cell-surface receptors (e.g., insulin, GH).
- Steroid hormones – Lipophilic, pass through membranes to bind intracellular receptors (e.g., cortisol, testosterone).
- Amino acid derivatives – Derived from tyrosine or tryptophan (e.g., thyroid hormones, adrenaline).
Signal transduction may involve G-protein coupled receptors, tyrosine kinase pathways, or nuclear receptor-mediated transcription.
Major Endocrine Glands & Hormones
| Gland | Primary Hormones | Main Actions |
|---|---|---|
| Hypothalamus | CRH, TRH, GnRH, GHRH, somatostatin | Controls pituitary release of tropic hormones |
| Pituitary (Anterior) | ACTH, TSH, GH, PRL, LH, FSH | Regulates adrenal, thyroid, growth, reproduction, lactation |
| Pituitary (Posterior) | ADH, oxytocin | Water balance, uterine contractions, milk ejection |
| Thyroid | T3, T4, calcitonin | Regulates metabolism, calcium balance |
| Parathyroid | PTH | Increases blood calcium |
| Adrenal Cortex | Cortisol, aldosterone, androgens | Stress response, metabolism, electrolyte balance |
| Adrenal Medulla | Adrenaline, noradrenaline | Fight-or-flight response |
| Pancreas | Insulin, glucagon, somatostatin | Regulates blood glucose |
| Gonads | Testosterone, estrogen, progesterone | Sexual development, reproduction |
| Pineal Gland | Melatonin | Regulates circadian rhythms |
Feedback Loops
Endocrine systems maintain balance via feedback regulation:
- HPA Axis – Cortisol regulation via ACTH & CRH.
- HPT Axis – Thyroid hormones via TSH & TRH.
- HPG Axis – Reproductive hormones via LH/FSH & GnRH.
Positive feedback occurs in rare cases like LH surge for ovulation and oxytocin during labor.
Common Endocrine Disorders
- Diabetes Mellitus (Type 1, Type 2)
- Hypothyroidism & Hyperthyroidism
- Cushing’s Syndrome & Addison’s Disease
- Acromegaly & Growth Hormone Deficiency
- Polycystic Ovary Syndrome (PCOS)
- Hyperparathyroidism & Hypoparathyroidism
Diagnostics in Endocrinology
- Blood hormone assays
- Dynamic testing (e.g., glucose tolerance test, dexamethasone suppression)
- Imaging: Ultrasound, MRI, CT for gland evaluation
- Genetic testing for inherited endocrine disorders
Therapeutic Approaches
- Hormone replacement therapy (insulin, levothyroxine)
- Pharmacologic modulation (antithyroid drugs, dopamine agonists, steroids)
- Minimally invasive & surgical interventions (thyroidectomy, adrenalectomy)
- Lifestyle and dietary changes (for metabolic/endocrine syndromes)