Chapter 19: Chemical Coordination and Integration (Human Physiology)

(a) Exocrine gland: a gland with a duct that carries its secretion to a surface or cavity, e.g. salivary, sweat, gastric glands. (b) Endocrine gland: a ductless gland that releases its secretion (hormones) directly into the blood, e.g. thyroid, pituitary, adrenal. (c) Hormone: a non-nutrient chemical that acts as an intercellular messenger and is produced in trace amounts (classically, secreted by an endocrine gland into the blood and carried to a distant target organ).

See the figure on page 2: hypothalamus and pituitary at the base of the brain, pineal on the dorsal forebrain, thyroid and parathyroids in the neck around the trachea, thymus behind the sternum, adrenals above the kidneys, pancreas below the stomach, ovaries in the female abdomen and testes in the male scrotal sac.

(a) Hypothalamus: releasing hormones (e.g. GnRH, TRH, CRH) and inhibiting hormones (e.g. somatostatin); also makes oxytocin and ADH. (b) Pituitary: GH, PRL, TSH, ACTH, LH, FSH (pars distalis); MSH (pars intermedia); oxytocin and vasopressin released by pars nervosa. (c) Thyroid: T₄ (thyroxine), T₃, thyrocalcitonin. (d) Parathyroid: PTH. (e) Adrenal: adrenaline, noradrenaline (medulla); glucocorticoids (cortisol), mineralocorticoids (aldosterone), small androgens (cortex). (f) Pancreas: glucagon (α), insulin (β). (g) Testis: androgens (testosterone). (h) Ovary: estrogen, progesterone. (i) Thymus: thymosins. (j) Atrium: atrial natriuretic factor (ANF). (k) Kidney: erythropoietin. (l) G-I tract: gastrin, secretin, cholecystokinin, gastric inhibitory peptide.

(a) Pituitary (anterior). (b) Thyroid. (c) Adrenal cortex. (d) Gonads (testis, ovary). (e) Melanocytes of the skin.

(a) PTH: raises blood Ca²⁺ by bone resorption, renal Ca²⁺ reabsorption and Ca²⁺ absorption from food; hypercalcemic; with TCT keeps calcium balance. (b) Thyroid hormones: regulate BMR; support RBC formation; control carbohydrate, protein, fat metabolism; water and electrolyte balance; needed for normal growth and brain development (lack causes cretinism). (c) Thymosins: differentiation of T-lymphocytes (cell-mediated immunity) and antibody production (humoral immunity). (d) Androgens: development and function of male accessory organs, secondary sex characters (muscles, facial hair, low voice, aggressiveness), spermatogenesis, libido, anabolic effects. (e) Estrogens: growth of female accessory organs, follicle development, secondary sex characters (high voice), mammary gland development, female sexual behaviour. (f) Insulin: increases glucose uptake by hepatocytes and adipocytes and glycogenesis, lowering blood glucose; glucagon: glycogenolysis and gluconeogenesis in liver, raising blood glucose; together they keep glucose homeostasis.

(a) Hyperglycemic: glucagon (also adrenaline, cortisol); hypoglycemic: insulin. (b) PTH. (c) LH and FSH. (d) Progesterone. (e) ANF. (f) Androgen: testosterone; estrogen: estradiol.

(a) Insulin (deficiency or resistance). (b) Thyroid hormones (T₃, T₄) due to iodine deficiency. (c) Thyroid hormones during foetal development and infancy (maternal hypothyroidism).

FSH is a protein (glycoprotein) hormone from the anterior pituitary. It cannot enter its target cells (follicle cells of the ovary; Sertoli cells of the testis), so it binds specific membrane-bound receptors, forming a hormone-receptor complex. This generates a second messenger (cyclic AMP), which triggers biochemical changes in the cell. Result: in females, growth and development of ovarian follicles (and estrogen secretion); in males, with androgens, spermatogenesis.

(a)–(ii); (b)–(iv); (c)–(i); (d)–(iii).