1Describe how ultrafiltration produces glomerular filtrate (5 marks)
Blood pressure/hydrostatic pressure
Small molecules
Pass through basement membrane
Proteins too large to go through
Pires in capillaries / presence of podocytes
2Explain how a lack of insulin affects reabsorption of glucose in the kidneys of a person who does not secrete insulin (6 marks)
High glucose conc in blood
High conc in tubule / filtrate
Reabsorbed by FD/AT
Requires proteins
These proteins are saturated
Not all glucose Reabsorbed / some lost in urine
3Desert animals have long loops of Henle and secrete large amounts of ADH. Explain how these 2 features are adaptations to living in desert conditions (8 marks)
More water reabsorbed
By osmosis
From collecting duct
Due to longer loop of Henle
Loop of Henle:
Na+/Cl- absorbed from filtrate in ascending limb
Gradient established in medulla
ADH:
Acts on collecting duct
Inserts aqauporins in plasma membrane
4Explain how adrenaline binding to receptors on plasma membrane of liver cells causes blood glucose conc to increase (3 marks)
Activates adenylate cyclase
Converts ATP to cAMP
Activates enzymes in glycogenolysis
5Explain how cells of proximal tubule are adapted to reabsorb glucose (3 marks)
Lots of microvilli so high SA
Lots of mitochondria so lots of ATP produced for AT
Carrier proteins for AT / Channel proteins for FD
6Explain the role of negative feedback in the control of plasma glucose conc (3 marks)
Deviation of value from norm initiates corrective mechanisms
Fluctuations in plasma glucose conc detected by hypothalamus
Increase / decrease uptake of glucose by cells due to increase / decrease in membrane permeability
7How does maintaining constant body temp allow metabolic reactions in cells to proceed with maximum efficiency (5 marks)
Optimum temp for enzymes
Temp too high changes 3° structure / AS shape so substrate can't bind
Reaction slows
Too little KE of molecules
Reduced collisions / ESC formed
8Explain how people with type 2 diabetes who have cells which don't respond to insulin have a reduced ability to regulate blood glucose conc. (5 marks)
Fewer receptors on membrane
Fewer glucose transport proteins
Less glucose can enter cells
Less glucose converted to glycogen
Blood glucose conc. not lowered when it is high
9Explain why the refractory period makes it impossible for info about differences in intensity to reach the brain when intensity is too high (2 marks)
Refractory period makes nerve impulses discrete
When max frequency is reached all intensities seem the same
10Stimulation of osmoreceptors can lead to secretion of the hormone ADH. Describe and explain how the secretion of ADH affects urine produced by the kidneys. (4 marks)
1. Permeability of membrane / cells (to water) is increased;
2. More water absorbed from / leaves distal tubule / collecting duct;
3. Smaller volume of urine;
4. Urine becomes more concentrated.
11Describe how urea is removed from the blood. (4 marks)
Hydrostatic pressure / description of pressure / description of how pressure generated;
Causes ultrafiltration (Allow description of ultrafiltration) at Bowman’s capsule / glomeruli / renal capsule;
Through basement membrane;
Enabled by small size urea molecule;
12Explain how urea is concentrated in the filtrate. (4 marks)
Reabsorption of water / by osmosis;
At the PCT / descending LoH;
At the DCT / CD;
Active transport of ions / glucose creates gradient (in context);
13Describe the role of the hormone glucagon in the control of blood sugar concentration. (6 marks)
Binds to (specific) receptor;
On muscle / liver cell;
Activation of enzymes (in liver);
Hydrolysis of glycogen;
(Facilitated) diffusion of glucose out of (liver cells) cells;
Increases blood glucose levels;
14Explain how insulin lowers the concentration of blood glucose. (6 marks)
Binds to receptor on target/liver/muscle cell;
Reject reference to insulin as an enzyme
Causes more transport/carrier proteins to become active/ move to (plasma) membrane;
Glucose (diffuses) into cells (and lowers blood glucose);
(Enzymes in cells) convert glucose to glycogen;
Stimulates fatty acids/lipid/fat formation (from glucose);
Raises rate of respiration (in cells), using more glucose;
15Explain how the loop of Henle maintains the gradient of ions which allows water to be reabsorbed from filtrate in the collecting duct. (6 marks)
(epithelial cell) of tubule cells carry out active transport;
transport chloride / sodium ions out (of filtrate);
against concentration gradient;
into surrounding tissue / tissue fluid;
creates / maintains water potential gradient for water reabsorption;
countercurrent multiplier;
16Explain how ADH is involved in the control of the volume of urine produced. (5 marks)
if water potential of blood falls, detected by receptors in hypothalamus;
leads to ADH released from pituitary gland;
ADH makes cells of collecting duct / distal convoluted tubule permeable to water;
(accept DCT)
water leaves filtrate by osmosis;
smaller volume of urine produced;