Module 5

• Homeostasis


  The maintenance of a constant internal environment via physiological control systems
• Control systems involved in homeostasis

  • Keeping the body at the same temperature
  • Maintaining the same blood pH
  • Maintaining the same blood glucose concentration
  • Maintaining the same blood water potential
• Negative feedback loop


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


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


  • Cannot regulate their internal temperature, instead control it through changing their behavior
  • 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, fur/feather movement)
• Thermoregulation in endotherms


  1. Peripheral receptors in skin detect temperature change

  2. Impulse sent to brain's hypothalamus

  3. Hypothalamus coordinates response via glands or muscles (e.g. sweat glands, blood vessels, skeletal muscles)
• Excretion


  The removal of waste products from metabolic reactions that can become toxic if not removed
• Key waste products excreted

  • Carbon dioxide
  • Nitrogenous waste (e.g. urea)
• Nitrogenous waste


  Excess amino acids are broken down in the liver, producing ammonia, which is then converted to urea for excretion by the kidneys
• Mammals produce urea as nitrogenous waste, fish produce ammonia, and birds produce uric acid
• Liver


  • Large organ that receives oxygenated blood via the hepatic artery and deoxygenated blood via the hepatic portal vein
  • Contains hepatocytes with many mitochondria, large nuclei, and prominent Golgi apparatus for high metabolic rate
  • Involved in glycogen storage, detoxification, and urea production
• Urea production in the liver

  1. Excess amino acids are deaminated, producing ammonia

  2. Ammonia is converted to urea

  3. Urea is transported in the blood to the kidneys for excretion
• Lobule


  The functional unit of the liver, where blood from the hepatic portal vein and hepatic artery mix and flow through sinusoids surrounded by hepatocytes
• Hepatocytes


  • Liver cells that produce bile, absorb excess glucose, and break down toxins and unwanted chemicals
• Canaliculus


  Spaces between hepatocytes where bile is secreted and drained into the bile duct
• Kupffer cells


  Macrophage-like cells in the liver sinusoids that help destroy pathogens
• Kidney


  Organ responsible for the excretion of urea and osmoregulation (control of blood water potential)
• Blood filtration in the kidney

  1. Blood enters through the renal artery

  2. Filtration occurs in the glomerulus of the nephron

  3. Filtrate passes through the proximal convoluted tubule, loop of Henle, and distal convoluted tubule

  4. Useful substances are reabsorbed back into the blood

  5. Remaining fluid forms urine that is excreted
• Glomerular filtration


  High blood pressure in the glomerular capillaries forces water and small molecules out of the blood and into the Bowman's capsule
• Reabsorption in proximal convoluted tubule

  Glucose and small amino acids are reabsorbed back into the blood via sodium-glucose cotransport
• Sodium gradient maintenance in loop of Henle

  1. Sodium ions are actively transported out of the ascending limb

  2. This creates a water potential gradient that allows water reabsorption from the descending limb and distal convoluted tubule
• The remaining fluid in the collecting duct forms urine, containing water, dissolved salts, urea, and other substances
• Reabsorption


  Process where substances are reabsorbed from the filtrate back into the blood
• Glucose


  Not a waste product, needed for respiration, can be stored as glycogen in the liver
• Filtrate entering the loop of Henle

  1. Enters the descending limb

  2. Enters the ascending limb

  3. Sodium ions actively transported out of the ascending limb

  4. Water diffuses out of the descending limb by osmosis

  5. Filtrate enters the distal convoluted tubule
• Loop of Henle


  • Maintains a sodium ion gradient
  • Facilitates water reabsorption
• Sodium ion accumulation in the medulla

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


  More water diffuses out due to the concentrated medulla
• Osmoreceptors


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

  1. Hypothalamus detects water potential

  2. Hypothalamus produces more/less ADH

  3. ADH binds to receptors in the kidney

  4. Aquaporins embedded in cell membranes

  5. More/less water reabsorbed
• Urine can be used to diagnose various conditions
• Monoclonal antibodies


  Single type of antibody that can be isolated and cloned
• Pregnancy test


  1. Urine sample absorbed

  2. Monoclonal antibodies bind to human growth hormone

  3. Colored dye indicates positive result
• Anabolic steroids and other drugs can also be detected in urine
• Kidney failure


  • Causes include infection, high blood pressure, genetic conditions, physical damage
  • Affects filtration, large molecules can pass through
  • Leads to buildup of urea and electrolyte imbalance
• Glomerular filtration rate (GFR)


  Measure of kidney function, indicated by blood creatinine levels
• Dialysis


  1. Hemodialysis - blood filtered externally

  2. Peritoneal dialysis - uses peritoneum as natural filter
• Kidney transplant


  • Best long-term treatment, but risk of rejection and need for immunosuppressants
• Neuron


  Nerve cell with cell body, dendrites, and axon