Homeostasis

• The secretion of osteocalcin (in an inactive form) by osteoblasts is controlled by positive feedback. Use information from the diagram to explain why this is positive feedback?

  1. Osteocalcin causes more release of insulin
  2. More insulin causes more release of inactive osteocalcin

  
• The acidic pH conditions created by osteoclasts cause the inactive form of the protein osteocalcin to change into the active form of osteocalcin. Suggest how?

  1. Change in pH breaks ionic/hydrogen bonds
  2. Change in tertiary structure
• Binding of insulin leads to an increase in the rate of respiration in cells such as osteoblasts. Explain how?

  1. Insulin leads to more carrier proteins for glucose
  2. More glucose (for respiration) enters cell
• Neonatal diabetes is a disease that affects newly born children. The disease is caused by a change in the amino acid sequence of insulin. This change prevents insulin binding to its receptor. Explain why this change prevents insulin binding to its receptor?

  1. Changes tertiary structure
  2. Insulin no longer complementary to receptor
• Using your knowledge of the kidney, explain why glucose is found in the urine of a person with untreated diabetes?

  1. High concentration of glucose in blood/filtrate
  2. Not all the glucose is reabsorbed at the proximal convoluted tube
  3. Carrier proteins are in use
• Describe the role of glucagon in gluconeogenesis. Do not include in your answer details on the second messenger model of glucagon action?

  1. Attaches to receptors on target cells and activates enzymes
  2. Glycerol/amino acids/fatty acids into glucose
• Metformin is a drug commonly used to treat type II diabetes. Metformin’s ability to lower the blood glucose concentration involves a number of mechanisms including: • increasing a cell’s sensitivity to insulin • inhibiting adenylate cyclase. Explain how increasing a cell’s sensitivity to insulin will lower the blood glucose concentration?

  1. More insulin binds to receptors
  2. Stimulates uptake of glucose by channel proteins
• Explain how inhibiting adenylate cyclase may help to lower the blood glucose concentration?

  1. Less ATP is converted to cyclic AMP
  2. Less kinase is activated
  3. Less glycogen is converted to glucose OR less glycogenolysis
• Give two reasons why pancreas transplants are not used for the treatment of type II diabetes?

  1. Usually people with type II diabetes produce insulin
  2. Controlled by diet/exercise
• Give two ways in which people with type 1 diabetes control their blood glucose concentration?

  1. Insulin injections
  2. Control diet/sugar intake
• Diabetes can damage the nervous system. The response of the rats with diabetes is different from the response of the healthy rats. Use your knowledge of the control of heart rate by the nervous system to suggest an explanation for these results?

  1. Damage to autonomic nervous system in diabetic rats
  2. Baroreceptors in carotid body don't work as well
  3. Damage to medulla
  4. When pressure drops, damage to sympathetic system so doesn't speed up enough
  5. When pressure rises, damage to parasympathetic system so doesn't slow down enough

  
• Alport syndrome (AS) is an inherited disorder that affects kidney glomeruli of both men and women. Affected individuals have proteinuria (high quantities of protein in their urine). Suggest how AS could cause proteinuria?

  1. Damages basement membrane
  2. Proteins can pass into the glomerular filtrate
• Describe how ultrafiltration occurs in a glomerulus?

  1. High hydrostatic pressure
  2. Water and glucose pass out
  3. Through small pores/fenestration in capillary endothelium
• Furosemide is sometimes used to treat high blood pressure. Suggest how furosemide would cause a decrease in blood pressure?

  1. Lower volume of blood
• Furosemide inhibits the absorption of sodium and chloride ions from the filtrate produced in the nephrons. Explain how furosemide causes an increase in the volume of urine produced?

  1. Water potential of filtrate decreased
  2. Less water reabsorbed by osmosis from filtrate
  3. Collecting duct is where osmosis occurs
• Osmoreceptors are specialised cells that respond to changes in the water potential of the blood. Give the location of osmoreceptors in the body of a mammal?

  1. Hypothalamus
• When a person is dehydrated, the cell volume of an osmoreceptor decreases. Explain why?

  1. Water potential of cell will decrease
  2. Water moves from osmoreceptor into blood by osmosis
• Stimulation of osmoreceptors can lead to secretion of the hormone ADH. Describe and explain how the secretion of ADH affects urine produced by the kidneys?

  1. Permeability of cells to water is increased
  2. More water absorbed from collecting duct
  3. Smaller volume of urine
  4. Urine becomes more concentrated
• Creatinine is a breakdown product of creatine found in muscle tissues. Apart from age and gender, give two factors that could affect the concentration of creatinine in the blood?

  1. Muscle/body mass
  2. Exercise
• Name the 2 parts of a nephron where osmoreceptors are located?

  1. Distal convoluted tube
  2. Collecting duct
• Describe and explain how three features of the cells in the proximal convoluted tube allow the rapid reabsorption of glucose into the blood?

  1. Microvilli give large surface area
  2. Many mitochondria provide ATP for active transport of glucose
  3. Many carrier proteins for active transport of glucose
• A decrease in blood pressure stimulates the release of ADH. Give the location of the receptors that detect a decrease in blood pressure and explain how the release of ADH will affect blood pressure?

  1. Location - Carotid artery
  2. Release of ADH increases absorption of water, and decreases volume of water
  3. Increases the volume of blood