module 5

• Homeostasis is the maintenance of a constant internal environment via physiological control systems
• Control systems involved in homeostasis

  • Maintaining body temperature
  • Maintaining blood pH
  • Maintaining blood glucose concentration
  • Maintaining blood water potential
• Negative feedback loop

  A deviation from set limits is detected and mechanisms are put in place to bring conditions back within set limits
• Positive feedback

  A deviation from set limits triggers a response to increase the deviation from that set limit even further
• Positive feedback example

  • During childbirth, the baby's head pressing on the cervix causes release of oxytocin, which leads to more uterine contractions and more oxytocin release
• Ectotherms

  • Cannot regulate their internal temperature, instead control it through changing their behaviour
  • Most animals are ectotherms (e.g. fish, amphibians, reptiles, invertebrates)
• Endotherms

  • Regulate their internal body temperature using the nervous system and a range of mechanisms (e.g. sweating, vasodilation/vasoconstriction, shivering)
• Ectotherms living in aquatic environments don't have to regulate body temperature much because water has a high specific heat capacity
• Ectotherms living on land have a bigger challenge regulating temperature because air temperature can fluctuate
• Metabolic reactions continuously produce waste products that can become toxic if not removed
• Excretion

  The removal of waste products
• Key waste products

  • Carbon dioxide
  • Nitrogenous waste (e.g. urea)
• Mammals produce urea as nitrogenous waste, fish produce ammonia, and birds produce uric acid
• Liver

  • Involved in formation of urea from ammonia
  • Stores glucose as glycogen
  • Detoxifies unwanted chemicals
• Liver cells (hepatocytes) have many mitochondria, large nuclei, and prominent Golgi apparatus to enable a high metabolic rate
• Blood flow through the liver

  1. Enters through hepatic portal vein and hepatic artery

  2. Mixes in sinusoids surrounding hepatocytes

  3. Drains out through hepatic vein
• Kupffer cells

  • Macrophage-like cells in liver sinusoids that help destroy pathogens
• Functions of hepatocytes

  • Produce bile
  • Absorb excess glucose and convert to glycogen
  • Break down and detoxify unwanted chemicals
• Urea cycle (ornithine cycle)

  1. Excess amino acids are deaminated in liver

  2. Ammonia is converted to less toxic urea

  3. Urea is transported in blood to kidneys for excretion
• Kidney structure

  • Cortex, medulla, and pelvis
  • Renal artery supplies blood to be filtered
  • Renal vein takes filtered blood away
• Filtration in nephron

  1. Blood enters glomerulus with high pressure

  2. Water and small molecules are forced out through basement membrane and podocytes

  3. Filtrate enters proximal convoluted tubule
• Glomerular filtrate

  Fluid forced out of glomerular capillaries, containing water, small molecules, but not large proteins or blood cells
• Reabsorption in proximal convoluted tubule

  1. Sodium ions are actively transported out, creating a concentration gradient

  2. Glucose and small amino acids are co-transported with sodium down the gradient back into the blood
• Loop of Henle

  1. Sodium ions are actively transported out of ascending limb

  2. Creates osmotic gradient for water reabsorption in descending limb
• Filtration and reabsorption in the kidney

  1. Filtrate enters the loop of Henle

  2. Filtrate passes into the descending limb

  3. Filtrate enters the ascending limb

  4. Sodium ions actively transported out of ascending limb

  5. Filtrate enters the distal convoluted tubule

  6. Water diffuses out of distal convoluted tubule and collecting duct
• Glucose

  Not a waste product, needed for respiration, can be stored as glycogen
• Loop of Henle

  Plays a key role in maintaining a sodium ion gradient and therefore water being reabsorbed
• Descending limb of loop of Henle

  • Connected to the proximal convoluted tubule, tube goes down first
• Ascending limb of loop of Henle

  • Mitochondria in cell walls provide energy to actively transport sodium ions out
• Sodium ion accumulation in medulla

  Lowers water potential, causing water to diffuse out of descending limb by osmosis
• Dilute filtrate entering distal convoluted tubule

  Due to sodium ions being actively transported out of loop of Henle
• Osmoreceptors


  Receptors in the hypothalamus that detect changes in water potential
• Regulation of water potential by the brain

  1. Osmoreceptors detect low water potential

  2. Hypothalamus produces more ADH

  3. ADH binds to receptors in distal convoluted tubule and collecting duct

  4. More aquaporins inserted, increasing water reabsorption

  5. Urine becomes more concentrated and less volume
• Regulation of water potential by the brain

  1. Osmoreceptors detect high water potential

  2. Hypothalamus produces less ADH

  3. Less ADH binds to receptors

  4. Fewer aquaporins inserted, less water reabsorption

  5. Urine becomes more dilute and greater volume
• Urine


  Composed of substances filtered out of the blood, can be used for diagnostic testing
• Substances tested for in urine

  • Diabetes
  • Pregnancy
  • Anabolic steroids
  • Other drugs
• Pregnancy test


  Uses monoclonal antibodies to detect human growth hormone
• Pregnancy test procedure


  1. Urine sample absorbed

  2. Monoclonal antibodies with dye move up test strip

  3. Antibodies bind to human growth hormone

  4. Coloured line indicates positive result
• Kidney failure can be caused by infection, high blood pressure, genetic conditions, or physical damage
• Glomerular filtration rate (GFR)

  Measure of kidney function, indicated by blood creatinine levels