Homeostasis

Homeostasis

1. Process of maintaining a constant internal environment within the body

2. Enables body to function efficiently, despite changes that might occur in internal or external environment

3. Negative Feedback mechanism

   • Step one: An imbalance is detected
   • Step two: A control centre is stimulated
   • Step three: Control centre responds
   • Step four: Message sent to target organ/s
   • Step five: The target organ responds
   • Step six: It opposes/reverses the imbalance
   • Step seven: Balance is restored

4. Regulation of glucose levels in internal environment

   • When glucose levels in blood increases above normal
     • Step one: Glucose levels in blood increase above normal levels
     • Step two: Beta cells in pancreas are stimulated
     • Step three: to secrete insulin in the blood
     • Step four: Insulin travels in the blood to the liver
     • Step five: where it stimulates the conversion of excess glucose to glycogen which is then stored. Body cells take up more glucose
     • Step six: The glucose level in the blood decreases
     • Step seven: and returns to normal
   • When glucose levels in the blood decreases below normal
     • Step one: Glucose levels in the blood decrease below normal
     • Step two: Alpha cells in pancreas are stimulated
     • Step three: to secrete glucagon into the blood
     • Step four: Glucagon travels in the blood to the liver
     • Step five: where it stimulates the conversion of stored glucagon to glucose
     • Step six: The glucose levels in the blood now increases
     • Step seven: and returns to normal

5. Regulation of carbon dioxide levels in internal environment

   • When CO2 levels in blood increase above normal levels
     • Step one: Co2 levels in blood increase above normal levels
     • Step two: Drop in blood pH. Low pH detected by chemoreceptor cells in the cartiod artery in the neck are stimulated
     • Step three: To send impulses to the Medulla Oblongata in the brain
     • Step four: Medulla Oblongata stimulates the breathing muscles (intercostal muscles and diaphragm) and heart
     • Step five: Breathing muscles contract more actively - increasing the rate and depth of breathing. The heart beats faster. Increased rate of removal of CO2 from the body
     • Step six: Increased rate of removal of CO2 from the body and exhaled from the lungs
     • Step seven: The CO2 level in the blood and blood pH returns to normal

6. Regulation of water balance in the internal environment (osmoregulation)

   • When blood has less water than normal
     • Step one: Blood has less water than normal (too salty)
     • Step two: Monitored by osmoreceptors in hypothalamus, hypothalamus is stimulated
     • Step three: and sends impulses to the pituitary gland to secrete more ADH
     • Step four: ADH travels in the blood to the kidneys
     • Step five: ADH increases the permeability of the collecting ducts and the distal convoluted tubles of the kidneys
     • Step six: More water is re-absorbed into blood vessels
     • Step seven: Small volume of hypertonic urine and the water level in the blood returns to normal
   • When blood has more water than normal
     • Step one: Blood has more water than normal (too watery)
     • Step two: Monitored by osmoreceptors in hypothalamus, hypothalamus is stimulated
     • Step three: and sends impulses to the pituitary gland to stop secreting ADH/secrete less
     • Step four: No ADH/less ADH travels in blood to kidneys
     • Step five: The collecting ducts and the distal convoluted tubules of the kidney become less permeable to water
     • Step six: Less water is re-absorbed into blood vessels
     • Step seven: Large volume of dilute urine and the water level in the blood returns to normal

7. Regulation of salt balance in the internal environment

   • When the salt level in the blood decreases
     • Step one: The salt level in the blood decreases
     • Step two: Receptor cells in the afferent and efferent arterioles of the kidney detect the low salt level
     • Step three: The adrenal gland is stimulated
     • Step four: into secreting more aldosterone
     • Step five: Aldosterone increases the re-absorption of sodium ions from the renal tubules in the kidney into the surrounding blood vessels
     • Step six: The salt level in the blood increases
     • Step seven: and returns to normal
   • When the salt level in the blood increases
     • Step one: The salt level in the blood increases
     • Step two: Receptor cells in the afferent and efferent arterioles of the kidney detect the high salt level
     • Step three: The adrenal gland is stimulated
     • Step four: to stop secreting aldosterone/secrete less aldosterone
     • Step five: This decreases the re-absorption of sodium ions from the renal tubules in the kidney into the surrounding blood vessels
     • Step six: The salt level in the blood decreases
     • Step seven: and returns to normal

8. All cells in multi-cellular organism surrounded by liquid called tissue fluid

9. Tissue fluid makes up internal environment of body

10. Optimal internal environment has to be maintained for body enzymes to function properly

11. Factors to keep constant in the internal environment

    • Carbon dioxide concentration
    • Glucose concentration
    • Water and mineral salt concentration
    • Urea concentration
    • Oxygen concentration
    • pH
    • Temperature

12. Negative Feedback System has 3 parts

    • Receptor detects move away from normal concentration and alerts appropriate control centre
    • Control centre processes information and initiates a response
    • Effector corrects imbalance and brings conditions back to normal

13. Temperature Regulation

    • Temperature must be constant
    • Optimal body temperature in humans between 36.6 and 37
    • All cells, antibodies, enzymes, most hormones made of protein. Protein sensitive to temperature
    • If temperature too high, proteins will denure, be unable to function
    • If temperature too low, proteins become inactive. Human body work hard to keep temperature constant
    • Temperature too high
      • Blood warmer than hypothalamic set point
      • Activates heat-loss centre in hypothalamus. Hypothalamus stimulates pituitary gland to release more ADH keeping more water in blood
      • Skin blood vessels dilate: capillaries flushed with warm blood, head radiates from skin surface, more blood reaches sweat glands
      • Sweat glands activated: secrete perspiration, vaporized by body heat, helping to cool body
      • Body temperature decreases: blood temperature declines, hypothalamus heat-loss centre shuts off
      • Need more water in blood to make more sweat to cool down
      • More concentrated urine (less water)
    • Temperature too low
      • Blood cooler than hypothalamic set point
      • Activates heat-promoting centre in hypothalamus. Hypothalamus stimulates pituitary gland to release less ADH having less water in blood
      • Less water is needed in blood as less sweat needed to be produced
      • Vasoconstriction : Skin blood vessels constrict: blood diverted from skin capillaries and withdrawn to deeper tissues; minimizes heat loss from skin surface. Less blood reaches sweat glands
      • No sweat evaporates, no cooling of skin, blood in surface vessels
      • Produce less concentrated urine
      • Skeletal muscles activated when more heat must be generated; shivering begins

14. The conditions within cells depend on the conditions within the internal environment