shorter endocrine

Hormone

Chemical messenger; released by endocrine cells → travels in blood → regulates body functions

Target cell

Has matching receptors for a specific hormone → responds to it

Endocrine vs exocrine gland

Endocrine: ductless, hormones → blood. Exocrine: has ducts, non-hormone secretions (sweat, salivary)

Water-soluble vs lipid-soluble hormones

Water-soluble: amino acid-based (amines, peptides, proteins); can't cross membrane; surface receptor; uses second messenger. Lipid-soluble: steroids from cholesterol; cross membrane; intracellular receptor

Cyclic AMP (cAMP)

Second messenger; made from ATP by adenylate cyclase; activates protein kinases

3 stimuli for hormone release

Humoral: blood ions/nutrients (low Ca2+ → PTH). Neural: nerves (sympathetic → adrenal medulla → epinephrine). Hormonal: another hormone (TSH → thyroid)

Negative feedback

Response reduces/reverses the stimulus → maintains homeostasis

Infundibulum and hypophyseal portal system

Infundibulum: stalk from hypothalamus to pituitary. Portal system: blood vessels carrying releasing/inhibiting hormones hypothalamus → anterior pituitary

Posterior pituitary

Neural lobe (axon terminals of hypothalamic neurons); STORES and RELEASES ADH + oxytocin; makes no hormones itself

ADH (antidiuretic hormone)

Made in hypothalamus, released by posterior pituitary; kidney reabsorbs more water → less urine

Diabetes insipidus

Low ADH (or kidneys insensitive to it) → large volumes of dilute urine + excessive thirst

Oxytocin

Made in hypothalamus, released by posterior pituitary; uterine contractions in childbirth (positive feedback) + milk ejection

Tropic hormones

Anterior pituitary hormones that stimulate other glands: TSH, ACTH, FSH, LH

TSH and ACTH

TSH (after hypothalamic TRH) → thyroid → T3 + T4. ACTH (after CRH) → adrenal cortex → cortisol

FSH and LH (gonadotropins)

FSH: egg development + estrogen (ovary); sperm production (testes). LH: ovulation + ovarian sex hormones (female); testosterone (male)

Prolactin (PRL)

Non-tropic anterior pituitary hormone; milk production after childbirth

Growth hormone (GH) and IGF-1

GH (anterior pituitary): bone + muscle growth, protein synthesis, fat breakdown, raises blood glucose. IGF-1: released by liver in response to GH; promotes tissue/bone growth

Gigantism vs acromegaly

Both = excess GH. Gigantism: in children, before growth plates close → very tall. Acromegaly: in adults, after plates close → hands/feet/face bones thicken, no height gain

Endocrine axis

Hypothalamus → anterior pituitary → target gland; controlled by negative feedback

Thyroid structure

Isthmus: bridge connecting the 2 lobes. Follicles: sacs filled with colloid = site of hormone synthesis/storage. Follicular cells: trap iodide, make T3/T4. Thyroglobulin: protein scaffold for T3/T4. Parafollicular (C) cells: make calcitonin

T4 vs T3

T4 (thyroxine): main thyroid secretion; 4 iodines. T3: more active; 3 iodines; mostly made in tissues by removing 1 iodine from T4

Hypothyroidism, hyperthyroidism, goiter

Hypo: low thyroid hormone → slow metabolism, fatigue, weight gain, cold intolerance. Hyper: excess → fast metabolism, rapid heart rate, weight loss, heat intolerance. Goiter: swollen thyroid (neck); can occur with low, normal, or high hormone

Parathyroid glands and PTH

4 small glands on back of thyroid. Low blood Ca2+ → PTH → raises Ca2+ (bone resorption, kidney reabsorbs Ca2+, activates vitamin D for gut absorption)

Calcitonin

From thyroid C cells; HIGH blood Ca2+ → lowers Ca2+ (inhibits bone resorption); minor role in adults

Adrenal cortex

Outer region; makes steroids: mineralocorticoids (aldosterone), glucocorticoids (cortisol), adrenal androgens

Aldosterone

Main mineralocorticoid; kidneys: more Na+ reabsorbed, K+ secreted → raises blood volume + BP

Cortisol

Main glucocorticoid; stress: mobilizes energy, liver gluconeogenesis, suppresses inflammation + immune response

RAAS (and angiotensin II)

Low BP/flow → kidney releases renin → angiotensin I → (ACE) angiotensin II → vasoconstriction + aldosterone release → restores blood volume + BP

Cushing syndrome vs Addison disease

Cushing: too much cortisol → high glucose, muscle wasting, purple stretch marks, hypertension, fat on face/trunk/upper back. Addison: too little cortisol + aldosterone (adrenal cortex damage) → weakness, weight loss, dehydration, low BP, hyperpigmentation

Adrenal medulla and catecholamines

Inner adrenal; stimulated directly by sympathetic nerves; releases epinephrine + norepinephrine → fight-or-flight

Pancreas: acinar cells vs islets

Acinar cells: exocrine, digestive enzymes → ducts → small intestine. Islets: endocrine; alpha cells → glucagon, beta cells → insulin

Insulin vs glucagon (blood-glucose homeostasis)

High glucose → beta cells → insulin → cells take up glucose, glycogen synthesis. Low glucose → alpha cells → glucagon → liver breaks down glycogen, releases glucose. Antagonistic pair

Type 1 vs type 2 diabetes mellitus

Type 1: autoimmune destruction of beta cells → severe insulin deficiency → needs insulin. Type 2: insulin resistance in tissues + relatively low insulin secretion

3 P's of diabetes

Polyuria: lots of urine (glucose in filtrate pulls water out by osmosis). Polydipsia: excessive thirst (dehydration). Polyphagia: excessive hunger (cells can't use glucose)

Other hormones: melatonin, ANP, EPO, leptin

Melatonin: pineal gland; released in darkness; sleep-wake cycle. ANP: heart (when stretched); kidneys excrete Na+ and water → lowers BP. EPO: kidneys (hypoxia) → bone marrow makes more RBCs. Leptin: fat tissue; signals energy stores → suppresses appetite