HOMEOSTASIS

Question 1

Explain how insulin reduces the blood glucose concentration.

Answer 1

· (More) insulin binds to receptors;

· (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 how a change in blood pH or blood pressure can cause a change in heart rate.

Answer 4

· (Carbon dioxide) detected by chemoreceptors / (pressure) detected by baroreceptors;

· Medulla/cardiac centre involved;

· More impulses to SAN/along sympathetic nerve;

· (Decrease) pH detected by chemoreceptors in carotid artery /aorta;

· Sends (more) impulses to medulla (oblongata);

· More Nerve impulses sent by sympathetic nervous system to SAN;

Question 5

Less CO2 in the blood leads to a reduction in heart rate.

Describe how.

Answer 5

· (less CO2 in blood) Detected by chemoreceptors;

· (Chemoreceptors) located in aorta / carotid artery;

· Fewer impulses to cardiac centre / medulla (oblongata);

· (More) impulses along parasympathetic nerve OR less impulses along sympathetic nerve;

· (To) SAN;

Question 6

Describe the secondary messenger model

Answer 6

· Adenylate cyclase activated / cAMP produced / second messenger produced;

· Activates enzyme(s) (in cell);

· (So) glycogenolysis/ gluconeogenesis occurs / glycogenesis inhibited;

Question 7

Describe the role of glycogen formation and its role in lowering blood glucose levels.

Answer 7

· Glucose concentration in cell/liver falls;

· Below that in blood (plasma)/ higher in blood;

· Creates/maintains glucose concentration/diffusion gradient;

· Glucose enters cell/leaves blood by facilitated diffusion/via carrier(protein)/channel (protein);

Question 8

Describe how blood glucose levels can be increased using hormones

Answer 8

· Release of glucagon;

· Leads to formation of glucose in liver (cells);

· From non-carbohydrates/amino acids/fatty acids;

Question 9

Describe how ultrafiltration occurs in a glomerulus.

Answer 9

· 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 10

Explain why a thicker medulla leads to more concentrated urine.

Answer 10

· 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 11

Describe the action of ADH in the kidney

Answer 11

· 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;