Homeostasis

• What is homeostasis


  Internal environment is maintained within set limits around an optimum
• Why is it important that core temperature remains stable

  ~Maintain stable rate of enzyme controlled reactions and prevent damage to membranes

  ~Temperature too low = enzyme and substrate molecules have insufficient kinetic energy

  ~Temperature too high = enzymes denature
• Why is it important that blood pH remains stable

  ~Maintain stable rate of enzyme controlled reactions

  ~Acidic pH = H+ interact with H-bonds and ionic bonds in tertiary structure of enzymes so shape of active site changes so no ES complexes form
• Why is it important that blood glucose concentration remains stable

  ~Maintain constant blood water potential = prevent osmotic lysis/crenation of cells

  ~Maintain constant concentration of respiratory substrate = organism maintains constant level of activity regardless of environmental conditions
• Define negative and positive feedback

  Negative feedback = self regulatory mechanisms return internal environment to optimum when there is a fluctuation

  Positive feedback = A fluctuation triggers changes that result in an even greater deviation from the normal level
• Suggest why separate negative feedback mechanisms control fluctuations in different directions

  Provides more control, especially in case of overcorrection, which would lead to a deviation in the opposite direction from the original one
• Suggest why coordinators analyse inputs from several receptors before sending an impulse to effectors

  ~Receptors may send conflicting information

  ~Optimum response may require multiple types of effector
• Why is there a time lag between hormone production and response by an effector

  ~Produce hormone

  ~Transport hormone in the blood

  ~Cause required change to the target protein
• Name the factors that affect blood glucose concentration

  ~Amount of carbohydrate digested from diet

  ~Rate of glycogenolysis

  ~Rate of gluconeogenesis
• Define glycogenesis, glycogenolysis and gluconeogenesis

  Glycogenesis = liver converts glucose into the storage polymer glycogen

  Glycogenolysis = liver hydrolyses glycogen into glucose which can diffuse into blood

  Gluconeogenesis = liver converts glycerol and amino acids into glucose
• Outline the role of glucagon when blood glucose concentration decreases

  ~a cells in islets of Langerhans in pancreas detect decrease and secrete glucagon into bloodstream

  ~Glucagon binds to surface receptors on liver cells and activates enzymes for glycogenolysis and gluconeogenesis

  ~Glucose diffuses from liver into bloodstream
• Outline the role of adrenaline when blood glucose concentration decreases

  ~Adrenal glands produce adrenaline. It binds to surface receptors on liver cells and activates enzymes for glycogenolysis

  ~Glucose diffuses from liver into bloodstream
• Outline what happens when blood glucose concentration increases

  ~b cells in islets of Langerhans in pancreas detect increase and secrete insulin into bloodstream

  ~Insulin binds to surface receptors on target cells

  ~Increase cellular glucose uptake

  ~Activate enzymes for glycogenesis

  ~Stimulate adipose tissue to synthesise fat
• Describe how insulin leads to a decrease in blood glucose concentration

  ~Increase permeability of cells to glucose

  ~Increases glucose concentration gradient

  ~Triggers inhibition of enzymes for glycogenolysis
• How does insulin increase permeability of cells to glucose

  ~Increases number of glucose carrier proteins

  ~Triggers conformational change which opens glucose carrier proteins
• How does insulin increase the glucose concentration gradient

  ~Activates enzymes for glycogenesis in liver and muscles

  ~Stimulates fat synthesis in adipose tissue
• Use the secondary messenger model to explain how glucagon and adrenaline work

  ~Hormone receptor complex forms

  ~Conformational change to receptor activates G-protein

  ~Activates adenylate cyclase, which converts ATP to cyclic AMP (cAMP)

  ~cAMP activates protein kinase A pathway

  ~Results in glycogenolysis
• Explain the causes of Type 1 diabetes and how it can be controlled

  ~Body cannot produce insulin

  ~Treat by injecting insulin
• Explain the causes of Type 2 diabetes and how it can be controlled

  ~Glycoprotein receptors are damaged or become less responsive to insulin

  ~Strong positive correlation with poor diet/obesity

  ~Treat by controlling diet and exercise regime
• Name some signs and symptoms of diabetes

  ~High blood glucose concentration

  ~Glucose in urine

  ~Polyuria

  ~Polyphagia

  ~Polydipsia

  ~Blurred vision

  ~Sudden weight loss

  ~Blurred vision
• Suggest how a student could produce a desired concentration of glucose solution from a stock solution

  Volume of stock solution = required concentration x final volume needed/concentration of stock solution

  Volume of distilled water = final volume needed - volume of stock solution
• Outline how colorimetry could be used to identify the glucose concentration in a sample


  ~Benedict's test on solutions of known glucose concentration. Use colorimeter to record absorbance

  ~Plot calibration curve with absorbance on y axis and glucose concentration on x axis

  ~Benedict's test on unknown sample. Use calibration curve to read glucose concentration at its absorbance value
• Define osmoregulation

  Control of blood water potential via homeostatic mechanisms
• Describe the gross structure of a mammalian kidney

  Fibrous capsule = protects kidney

  Cortex = outer region consists of Bowman's capsules, convoluted tubules, blood vessels

  Medulla = inner region consists of collecting ducts, loops of Henle, blood vessels

  Renal pelvis = cavity collects urine into ureter

  Ureter = tube carries urine to bladder

  Renal artery = supplies kidney with oxygenated blood

  Renal vein = returns deoxygenated blood from kidney to heart
• Describe the structure of a nephron

  Bowman's capsule at start of nephron = cup-shaped, surrounds glomerulus, inner layer of podocytes

  Proximal convoluted tubule = series of loops surrounded by capillaries, walls made of epithelial cells with microvilli

  Loop of Henle = hairpin loop extends from cortex into medulla

  Distal convoluted tubule = similar to PCT but fewer capillaries

  Collecting duct = DCT from several nephrons empty into collecting duct, which leads into pelvis of kidney
• Describe the blood vessels associated with a nephron

  ~Wide afferent arteriole from renal artery enters renal capsule and forms glomerulus = branched knot of capillaries which combine to form narrow efferent arteriole

  ~Efferent arteriole branches to form capillary network that surrounds tubules
• Explain how glomerular filtrate is formed

  ~Ultrafiltration in Bowman's capsule

  ~High hydrostatic pressure in glomerulus forces small molecules out of capillary fenestrations against osmotic gradient

  ~Basement membrane acts as filter. Blood cells and large molecules
• How are cells of the Bowman's capsule adapted for ultrafiltration

  ~Fenestrations between epithelial cells of capillaries

  ~Fluid can pass between and under folded membrane of podocytes
• State what happens during selective reabsorption and where is occurs

  ~Useful molecules from glomerular filtrate

  ~Occurs in proximal convoluted tubule
• How are cells in the proximal convoluted tubule adapted for selective reabsorption

  Microvilli = large surface area for co-transporter proteins

  Many mitochondria = ATP for active transport of glucose into intercellular spaces

  Folded basal membrane = large surface area
• What happens in the loop of Henle

  ~Active transport of Na+ and Cl- out of ascending limb

  ~Water potential of interstitial fluid decreases

  ~Osmosis of water out of descending limb

  ~Water potential of filtrate decreases going down descending limb = lowest in medullary region, highest at top of ascending limb
• Explain the role of the distal convoluted tubule

  ~Reabsorption of water via osmosis and of ions via active transport

  ~Permeability of walls is determined by action of hormones
• Explain the role of the collecting duct

  Reabsorption of water from filtrate into interstitial fluid via osmosis through aquaporins