Mammalian Physiology

• Endocrine hormones


  Have to be transported by blood to target cell
• Exocrine glands


  Salivary, sweat - transport by ducts
• Hormones


  • Produced in small quantities
  • Slow response (as it takes time for them to flow through the bloodstream to reach the target cells)
  • Have long term affect
• Hormones can be made from

  • Proteins - water soluble
  • Steroids - lipid soluble
• Protein based hormones


  • Cannot pass through membrane
  • Bind to a membrane receptor
  • Trigger a response inside cell
• Steroids


  • Can pass through
  • Trigger a response directly in the nucleus
• Parts of the endocrine system

  • Hypothalamus
  • Pituitary Gland
  • Thyroid
  • Pancreas
  • Liver
  • Adrenal gland
• Hypothalamus


  The main function is homeostasis: maintaining the body's balance, managing blood pressure and gut distension, controlling circadian rhythms, regulating temperature and water balance, detecting harmful substances and causing vomiting, regulating behaviours like eating and reproduction
• Temperature regulation


  1. Skin temp down (Cold): Hair follicles, muscles, blood vessels constrict

  2. Body temp up (Hot): Blood vessels dilate, sweat glands increase output
• Kidney & Water Regulation

  1. Water excretion from kidneys regulated by antidiuretic hormone (ADH)

  2. High osmolarity: Osmoreceptors trigger pituitary to release more ADH

  3. ADH increases water permeability in kidney tubules, more water reabsorbed, less excreted

  4. Low osmolarity: ADH release reduced, less water reabsorbed, more excreted
• Pituitary Gland


  • Posterior lobe controlled by nerve fibers from hypothalamic neurons, releases ADH and oxytocin
  • Anterior lobe influenced by substances transported from hypothalamus via blood vessels, releases growth hormone, thyroid-stimulating hormone, adrenocorticotropic hormone, gonadotropic hormones
• Hypothalamus


  Controls almost all secretions of the pituitary, the "master gland"
• Posterior pituitary


  Controlled by nerve fibres from hypothalamus
• Anterior pituitary


  Controlled by hormones released from hypothalamus
• Releasing hormones


  Hormones released by hypothalamus that signal anterior pituitary to produce and release certain hormones
• Inhibiting hormones


  Hormones released by hypothalamus that signal anterior pituitary to stop or reduce production and release of specific hormones
• Thyroid hormones


  • Thyroxin (T4)
  • Calcitonin
• Conversion of T4 to T3

  1. T4 converted to T3 in target cells

  2. T3 is the active hormone fully active in bloodstream
• Effects of T3


  • Increase in metabolic rate
  • Increase in rate and strength of heartbeat
• Pancreas cell types


  • Alpha cells (A cells) - secrete glucagon
  • Beta cells (B cells) - secrete insulin
  • Delta cells (D cells) - secrete somatostatin
• Glucagon


  Catabolic hormone, promotes breakdown of glucose, fatty acids, amino acids from stores into bloodstream, increases blood glucose levels
• Insulin


  Anabolic hormone, promotes storage of glucose, fatty acids, amino acids in cells and tissues, decreases blood glucose levels
• High blood glucose


  Triggers insulin production in beta cells
• Somatostatin


  Inhibits release of insulin and glucagon, regulates digestion and absorption
• Islets of Langerhans


  • Innervated by parasympathetic and sympathetic neurons
  • Nervous signals modulate secretion of insulin and glucagon
• Insulin and glucagon are important in regulation of carbohydrate, protein and lipid metabolism
• Sympathetic nervous system


  Enhances glucagon secretion, inhibits insulin secretion
• Parasympathetic nervous system


  Enhances insulin secretion, inhibits glucagon secretion
• Liver functions


  • Converts T4 to T3
  • Creates Glucose Tolerance Factor (GTF)
  • Target organ for insulin - glucose storage
  • Produces and packages cholesterol
  • Cholesterol precursor for steroid hormones
  • Breaks down hormones for disposal or recycling
• Adrenal gland hormones


  • Mineralocorticoids (aldosterone)
  • Gonadocorticoids (male and female sex hormones)
  • Adrenaline and noradrenaline
• Adrenal cortex


  Produces steroid hormones including mineralocorticoids and gonadocorticoids
• Adrenal medulla


  Secretes adrenaline and noradrenaline in response to sympathetic nerve stimulation, the "fight or flight" hormones
• Prolonged stress


  Leads to prolonged secretion of adrenaline and noradrenaline, causing circulatory stress