homeostasis

Question 1

Explain how insulin reduces the blood glucose concentration.

Answer 1

• (More) insulin binds to receptors on cell surface membrane of target cells
• (Stimulates) uptake of glucose by channel/transport proteins
• Activates enzymes which convert glucose to glycogen;

Question 2

Explain the action of Glucagon

Answer 2

• Attaches to receptors on target cells and activates/stimulates enzymes;
• Glycogen to glucose / glycogenolysis;
• Gluconeogenesis;

Question 3

Explain the effect of sweating or panting on temperature control.

Answer 3

• Evaporation (of water from lining of mouth or skin);
• Heat transferred from blood;

Question 4

Describe the secondary messenger model

Answer 4

• Adenylate cyclase activated
  cAMP produced / second messenger produced;
• Activates protein kinase
• (So) glycogenolysis/ gluconeogenesis occurs / glycogenesis inhibited;

OR
adrenaline and glucagon bind to protein receptors on the surface of the target cell membrane

hormone receptor complex changes its tertiary structure

actives adenylate cyclase results in conversion of atp into cyclic amp
second messenger causes a series of chemical changes

camp is the second messenger and actives protein kinase enzymes which help conversion of glycogen to glucose

Question 5

Describe how blood glucose levels can be increased using hormones

Answer 5

• Release of glucagon;
• Leads to formation of glucose in liver (cells);
• From non-carbohydrates/amino acids/fatty acids;

Question 6

Describe how ultrafiltration occurs in a glomerulus.

Answer 6

• High blood/hydrostatic pressure;
• Two named small substances pass out eg water, glucose, ions, urea;
• (Through small) gaps/pores/fenestrations in (capillary) endothelium;
• (And) through (capillary) basement membrane;

Question 7

explain why a thicker medulla leads to more concentrated urine.

Answer 7

• Thicker medulla means a longer loop of Henle;
• (The longer the loop of Henle means) increase in sodium ion concentration (in medulla) so sodium ion gradient maintained for longer (in medulla);
• (Therefore) water potential gradient maintained (for longer), so more water (re)absorbed (from loop and collecting duct) by osmosis;

Question 8

Describe the action of ADH in the kidney

Answer 8

• Permeability of membrane/cells (to water) is increased;
• More water absorbed from/leaves distal tubule/collecting duct;
• Smaller volume of urine;
• Urine becomes more concentrated;

Question 9

describe how glucagon increases blood glucose levels

Answer 9

glucagon binds to receptors on the cell surface membrane of target cells

activates enzymes involved in the hydrolysis of glycogen to glucose (glycogenolysis)

activates enzymes involved in the conversion of glycerol and amino acids into glucose (gluconeogenesis)

Question 10

how Is urea removed from the blood

Answer 10

hydrostatic pressure

causes ultrafiltration

bowman caspsule

through basement membrane

enabled by small size of urea molecule

Question 11

describe how ultrafiltration produces glomerular filtrate

Answer 11

higher than normal blood pressure

pass through basement membrane

protein too large to go through

presence of pores

presence of podocytes

Question 12

reabsorbtion of water - loop of henle

Answer 12

the conc of Na+ in the PCT is decreased as the Na+ are actively transported out of the PCT cells into the blood into the capillaries

allowing Na+ to move back into the cells in the lining of the PCT via diffusion by a co transporter such as glucose

useful molecules to be reabsorbed back into the blood