Exocrine glands include salivary and digestive glands. Endocrine glands include pituitary, thyroid, adrenal and others. Hormones travel to target tissues and regulate metabolism, growth, development and physiological activities.
(a) Exocrine glands have ducts and pour secretions onto body surfaces or into cavities. (b) Endocrine glands are ductless glands that release hormones into blood. (c) Hormones are non-nutrient chemicals produced in trace amounts that act as intercellular messengers.
The posterior pituitary stores and releases oxytocin and vasopressin made by hypothalamus. Adrenal medulla secretes adrenaline and noradrenaline, while adrenal cortex secretes cortisol, aldosterone and small amounts of androgenic steroids. The endocrine pancreas has alpha cells secreting glucagon and beta cells secreting insulin.
Hypothalamus: releasing and inhibiting hormones. Pituitary: GH, PRL, TSH, ACTH, LH, FSH, MSH, oxytocin and vasopressin release. Thyroid: T3, T4, TCT. Parathyroid: PTH. Adrenal: catecholamines, glucocorticoids, mineralocorticoids and small androgens. Pancreas: insulin and glucagon. Testis: androgens. Ovary: estrogens and progesterone. Thymus: thymosins. Atrium: ANF. Kidney: erythropoietin. G-I tract: gastrin, secretin, CCK and GIP.
Hypothalamic releasing/inhibiting hormones regulate pituitary hormones. TSH acts on thyroid, ACTH on adrenal cortex, LH/FSH on gonads, and MSH on melanocytes to regulate pigmentation.
(a) Pituitary gland. (b) Thyroid gland. (c) Adrenal cortex. (d) Gonads: testes and ovaries. (e) Melanocytes.
(a) PTH increases blood Ca2+ by bone resorption, renal Ca2+ reabsorption and intestinal absorption. (b) Thyroid hormones regulate BMR, metabolism of carbohydrates/proteins/fats, RBC formation and water-electrolyte balance. (c) Thymosins help T-lymphocyte differentiation and antibody production. (d) Androgens regulate male accessory sex organs, secondary characters, spermatogenesis and libido. (e) Estrogens regulate female accessory organs, secondary sex characters, ovarian follicle development and mammary gland development. (f) Insulin lowers blood glucose by uptake/utilisation and glycogenesis; glucagon raises blood glucose by glycogenolysis and gluconeogenesis.
These hormones regulate calcium balance, metabolism, immunity, male and female reproductive traits, and blood glucose homeostasis.
Glucagon increases blood glucose, while insulin decreases it. PTH increases blood calcium. LH and FSH stimulate gonadal activity. Progesterone supports pregnancy. ANF causes vasodilation and lowers blood pressure. Testosterone is a major androgen and estradiol is a major estrogen.
(a) Glucagon and insulin respectively. (b) Parathyroid hormone. (c) LH and FSH. (d) Progesterone. (e) Atrial natriuretic factor. (f) Testosterone and estradiol/estrogen.
Diabetes mellitus is associated with prolonged hyperglycemia due to insulin deficiency/resistance. Goitre commonly results from iodine deficiency causing reduced thyroid hormone synthesis and thyroid enlargement. Cretinism results from hypothyroidism during pregnancy/early development, affecting growth and neural maturation.
(a) Insulin deficiency or ineffective insulin action. (b) Thyroid hormone deficiency due to iodine deficiency. (c) Thyroid hormone deficiency during development.
FSH is a protein/glycoprotein hormone, so it does not enter target cells. It binds membrane-bound receptors, forming a hormone-receptor complex that generates second messengers such as cyclic AMP. These regulate cellular metabolism and gene activity needed for ovarian follicle growth in females and spermatogenesis support in males.
FSH acts by binding to specific membrane receptors on gonadal target cells and triggering intracellular second-messenger responses.
T4 is thyroxine from thyroid. PTH is parathyroid hormone. GnRH is secreted by hypothalamus. LH is secreted by anterior pituitary.
(a)-(ii), (b)-(iv), (c)-(i), (d)-(iii).