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Endocrine System Anatomy & Physiology

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  • Difference between nervous and endocrine systems
    Nervous system uses nerve impulses for fast, brief, specific responses. Endocrine system uses hormones for slower, longer-lasting, broader effects.
  • Types of glands in the endocrine system
    Exocrine glands have ducts; endocrine glands are ductless and secrete hormones into interstitial fluid and blood.
  • Examples of endocrine glands
    Pituitary, thyroid, parathyroid, adrenal, pineal glands; thymus, pancreas, ovaries, and testes are not exclusively endocrine.
  • Hormone receptor regulation
    Down-regulation: decrease in receptors to reduce hormone sensitivity. Up-regulation: increase in receptors to enhance hormone sensitivity.
  • Types of hormones by action range
    Circulating hormones travel through blood; local hormones act nearby as paracrines or on the same cell as autocrines.
  • Chemical classes of hormones
    Lipid-soluble: steroids, thyroid hormones, nitric oxide; Water-soluble: amines, peptides, proteins, glycoproteins.
  • Mechanism of lipid-soluble hormone action
    Diffuse through plasma membrane, bind intracellular receptors, hormone-receptor complex enters nucleus to regulate gene transcription.
  • Mechanism of water-soluble hormone action
    Bind plasma membrane receptors, activate G-protein, adenylate cyclase converts ATP to cAMP, cAMP activates protein kinases triggering cell responses.
  • Factors affecting target cell responsiveness
    Hormone concentration, receptor abundance, and influence of other hormones (permissive, synergistic, antagonistic effects).
  • Permissive, synergistic, and antagonistic hormone effects
    Permissive: one hormone enhances another (e.g., cortisol and glucagon). Synergistic: combined effect greater (e.g., ADH and aldosterone). Antagonistic: opposing effects (e.g., PTH and calcitonin).
  • Role of hypothalamus in endocrine system
    Links nervous and endocrine systems; produces releasing and inhibiting hormones controlling anterior pituitary; produces hormones stored in posterior pituitary.
  • Anterior pituitary hormones and functions
    hGH promotes growth; TSH stimulates thyroid; FSH and LH regulate gonads; PRL promotes milk; ACTH stimulates adrenal cortex; MSH role unclear.
  • Posterior pituitary hormones
    Stores and releases hypothalamic hormones: Oxytocin (uterine contraction, milk ejection) and ADH (water retention, blood pressure).
  • Thyroid gland structure and hormones
    Located below larynx; follicles produce T3 and T4 increasing metabolism; parafollicular cells produce calcitonin lowering blood calcium.
  • Parathyroid glands and hormone function
    Four small glands on thyroid; secrete PTH which increases blood calcium by stimulating osteoclasts and reducing phosphate.
  • Adrenal gland regions and hormones
    Cortex zones: glomerulosa (mineralocorticoids like aldosterone), fasciculata (glucocorticoids like cortisol), reticularis (androgens). Medulla secretes epinephrine and norepinephrine.
  • Pancreatic islets cell types and hormones
    Alpha cells secrete glucagon (raises blood sugar), beta cells secrete insulin (lowers blood sugar), delta cells secrete somatostatin (inhibits insulin and glucagon).
  • Functions of ovaries and testes in endocrine system
    Ovaries produce estrogens, progesterone, inhibin, relaxin; testes produce testosterone and inhibin, regulating reproduction and secondary sex characteristics.
  • Pineal gland and melatonin
    Located in brain; secretes melatonin which regulates biological clock and promotes sleepiness, with higher secretion in darkness.
  • Other endocrine tissues and hormones
    Thymus produces thymosin for T cell maturation; placenta produces estrogens and progesterone; heart produces ANP; GI tract enteroendocrine cells aid digestion.