Exocrine and endocrine

• Endocrine system


  Needed to regulate the body functions continuously as the nerve forces do not
• Hormones

  Not-nutrient chemical messengers produced in trace amounts by ductless glands called endocrine glands
• Hormones

  Act as intracellular messengers in addition to endocrine glands
• Organs that produce hormones

  • Hypothalamus
  • Pituitary gland
  • Thyroid gland
  • Parathyroid glands
  • Adrenal glands
  • Pancreas
  • Thymus
  • Pineal gland
  • Gonads
  • Heart
  • Kidney
  • Gastrointestinal Tract
• Hypothalamus

  1. Neuro secretory cells produce hormones

  2. Hormones regulate synthesis and secretion of pituitary gland hormones

  3. Hypothalamic neurons pass through axons and reach anterior pituitary through hypophysial portal drop
• Pituitary gland

  • Also called master gland, the regulating unit of hormonal system
  • Formed of pars dorsalis and pars intermedia (adenohypophysis) and pars nervosa (neurohypophysis)
  • Safely harboured in sella turcica
• Hormones secreted by anterior pituitary

  • Growth hormone
  • Gonadotropic hormones
  • Prolactin
  • ACTH (adrenocorticotropic hormone)
  • Thyroid stimulating hormone
  • Lipotropin
• Posterior pituitary

  • Releases hormones (ADH, oxytocin) secreted by hypothalamus in the time of need
  • Under direct neural regulation of hypothalamus
• Thyroid gland

  • Largest endocrine gland, made up of two lobes connected by isthmus
  • Composed of follicles and stromal tissues made up of cuboidal epithelium
• Hormones synthesised by thyroid gland

  • Thyroxine (T4)
  • Triiodothyronine (T3)
  • Calcitonin
• Thyrocalcitonin (TC)

  Antagonistic to parathormone (PTH), plays a role in calcium metabolism, proteinaceous, non-iodised hormone secreted by thyroid gland
• Parathyroid glands

  • Developed from epithelial buds, consist of chief cells and oxyphil cells
  • Hormone secreted is parathormone (PTH) or Collip's hormone
• Parathormone (PTH)

  Hypercalcemic, promotes bone demineralisation and increases absorption from gut
• Components of adrenal gland

  • Adrenal cortex
  • Adrenal medulla
• Adrenal cortex


  Responsible for secretion of steroid hormones called corticoids (mineralcorticoids, glucocorticoids, sexcorticoids)
• Adrenal medulla

  • Produces adrenaline and epinephrine (catecholamines)
  • Responsible for the fight and fright during stressful condition, lipolytic, proteolytic, promote glycogenolysis
• Pancreas


  Heterocrine gland, endocrine part consists of islets of Langerhans with alpha, beta, and delta cells that secrete glucagon, insulin, and somatostatin respectively
• Thymus

  • Endocrine gland that mainly secretes thymosin hormone, involved in proliferation and maturation of T-lymphocytes, also promotes antibody production
  • Degeneration in elderly leads to weaker immune system
• Pineal gland

  Small rounded, reddish-brown gland that secretes melatonin (targets melanophore cells of skin) and adrenoglomerulotropin (stimulates adrenal cortex to secrete aldosterone)
• Sex hormones secreted by gonads

  • Androgens (testosterone) secreted by testes in males
  • Oestrogen, progesterone, relaxin, human chorionic gonadotropin secreted by ovaries in females
• Other organs that secrete hormones

  • Heart (atrial natriuretic factor)
  • Kidney (erythropoietin)
  • Gastrointestinal Tract (enterogastrone, cholecystokinin)
• Mechanism of hormone action

  • Peptide/water-soluble hormones bind to surface receptors, form hormone-receptor complex that acts on cAMP
  • Steroid/water-insoluble hormones cross cell membrane, bind to cytoplasmic receptors, hormone-receptor complex enters nucleus and changes gene expression
• Hormones maintain homeostasis by integrated action and feedback control