1. Chapter at a glance
- Neural coordination is fast but short-lived; hormones provide continuous chemical coordination and integration as intercellular messengers produced in trace amounts.
- Endocrine glands are ductless; their secretions (hormones) regulate metabolism, growth, development and physiological functions jointly with the neural system.
- Hypothalamus produces releasing and inhibiting hormones that control anterior pituitary via portal circulation and directly regulates posterior pituitary.
- Pituitary (adenohypophysis + neurohypophysis) secretes six hormones from pars distalis, MSH from pars intermedia, and stores oxytocin and ADH.
- Thyroid secretes T3, T4 and TCT; parathyroid secretes PTH; both regulate basal metabolic rate, carbohydrate/protein/fat metabolism and Ca2+ homeostasis.
- Adrenal cortex secretes glucocorticoids (cortisol) and mineralocorticoids (aldosterone); medulla secretes catecholamines (adrenaline, noradrenaline) as emergency hormones.
- Pancreas (Islets of Langerhans) secretes insulin (hypoglycemic) and glucagon (hyperglycemic) to maintain blood glucose homeostasis.
- Gonads, pineal (melatonin), thymus (thymosins), heart (ANF), kidney (erythropoietin) and GI tract (gastrin, secretin, CCK, GIP) also secrete hormones regulating specific functions.
2. Definitions and laws
Hormones are non-nutrient chemicals which act as intercellular messengers and are produced in trace amounts.
3. Important diagrams and activities
- Figure 19.1 Location of endocrine glands: shows positions of hypothalamus, pituitary, pineal, thyroid, parathyroid, thymus, adrenal, pancreas, testis and ovary.
- Figure 19.2 Diagrammatic representation of pituitary and its relationship with hypothalamus: illustrates hypothalamic nuclei, portal circulation to anterior pituitary and direct neural control of posterior pituitary.
- Figure 19.3 Diagrammatic view of the position of Thyroid and Parathyroid: ventral and dorsal views showing lobes, isthmus and parathyroid glands on thyroid.
- Figure 19.4 Diagrammatic representation of adrenal gland: shows kidney, adrenal cortex and adrenal medulla.
- Figure 19.5 Diagrammatic representation of the mechanism of hormone action: (a) membrane-bound receptor with second messenger for protein hormones; (b) intracellular receptor regulating gene expression for steroid/thyroid hormones.
4. Common misconceptions and exam pitfalls
- Confusing anterior pituitary (pars distalis) hormones with posterior pituitary (stores oxytocin/ADH synthesised in hypothalamus).
- Mixing up insulin (lowers blood glucose via glycogenesis) and glucagon (raises blood glucose via glycogenolysis/gluconeogenesis).
- Assuming all thyroid effects are due to T3/T4 only; forgetting TCT lowers blood Ca2+ while PTH raises it.
- Overlooking that pars intermedia is almost merged with pars distalis in humans and secretes only MSH.
- Stating adrenal medulla hormones as steroids instead of catecholamines (amino-acid derivatives).
5. Formula sheet
No mathematical formulas or equations are present in the chapter.