Homeostasis

• Homeostasis


  The regulation of the internal conditions of a cell or organism to maintain optimum conditions for function in response to internal and external changes
• Enzymes and cells require very stable conditions in order to work
• The body has systems in place to keep the internal conditions optimum for the cells to function
• Internal conditions maintained by homeostasis

  • Blood glucose concentration
  • Body temperature
  • Water levels
• How the hormone ADH is used to control the water level in the blood

  1. Blood becomes too concentrated

  2. Pituitary gland releases ADH

  3. ADH causes kidneys to reabsorb more water

  4. Blood water level returns to normal

  5. Pituitary gland stops releasing ADH
• How the blood becomes too dilute

  1. Person drinks large amount of water

  2. Concentration of water in blood rises

  3. Pituitary gland stops releasing ADH

  4. Kidneys reabsorb less water

  5. Concentration of water in blood returns to normal
• Kidney dialysis


  Process to adjust levels of water, ions and urea when kidneys fail
• How kidney dialysis works

  1. Patient's blood passes over a semipermeable membrane

  2. Urea, ions and water pass through but not larger molecules

  3. Dialysis fluid contains normal concentrations of water and ions but no urea

  4. Urea diffuses from blood into dialysis fluid

  5. Water and ions diffuse from blood into dialysis fluid
• Kidney dialysis


  • Patients have to visit hospital several times a week
  • Patients have to eat controlled diet
• Kidney transplant


  Diseased kidney replaced with healthy kidney from donor
• Donated kidney


  May be rejected by patient's immune system
• Advantages of kidney dialysis

  • No shortage of dialysis machines
• Disadvantages of kidney dialysis

  • Inconvenient for patients
  • Patients require controlled diet
  • Expensive and requires long-term treatment
• Advantages of kidney transplant

  • Patients can lead normal life
• Disadvantages of kidney transplant

  • Shortage of donors
  • Patients have to take anti-rejection drugs for life
• Ways water can leave the human body

  1. Lungs (exhaling)

  2. Skin (sweating)

  3. Kidneys (urination)
• Sweating


  • Part of the body's temperature control system
  • Body cannot control how much water, ions, or urea is lost
• Homeostasis


  The body's system to maintain water balance
• How kidneys maintain blood concentration

  1. Blood passes through capillaries

  2. Small molecules filtered out (urea, ions, water, glucose)

  3. Glucose, some ions, some water reabsorbed

  4. Urea, excess ions, excess water released as urine
• Concentration of glucose in blood does not change as it is all reabsorbed
• Concentration of ions in blood decreases as kidneys filter them out but reabsorb some
• Concentration of urea in blood falls to virtually zero as it is all filtered out and not reabsorbed
• Deamination


  Process where liver breaks down excess amino acids and produces ammonia
• How body deals with excess amino acids

  1. Liver breaks down excess amino acids

  2. Produces ammonia

  3. Ammonia converted to urea

  4. Urea excreted by kidneys
• Thermoregulatory center


  Part of the brain that monitors and controls body temperature
• Thermoregulatory center


  • Contains receptors sensitive to the temperature of the blood
  • Receives electrical impulses from temperature receptors in the skin
• Body temperature gets too high


  Sweat glands secrete sweat onto the skin surface, which evaporates and cools the body
• Body temperature gets too high


  Blood vessels in the skin dilate (vasodilation), allowing more blood flow and heat transfer out of the body
• Body temperature drops too low

  Blood vessels in the skin constrict (vasoconstriction), reducing blood flow and heat loss
• Body temperature drops too low


  Skeletal muscles contract (shivering) to generate heat through increased respiration
• Body temperature drops too low


  Sweating stops to prevent further heat loss
• The thermoregulatory center detects changes in body temperature from the normal value and triggers responses to restore it
• Control of body temperature is an example of homeostasis