Homeostasis

Question 1

Negative feedback

Answer 1

System where a change away from normal/optimal conditions causes a response to reverse the change and bring conditions back closer to normal

Question 2

Where are glucagon and insulin produced?

Answer 2

Pancreas, islets of Langerhans
- a cells, glucagon
- b cells, insulin

Question 3

Insulin action

Answer 3

caused by high blood glucose levels

attaches to receptors on liver cell surface mem. + changes 3* structure of channel proteins so more glucose absorbed by f. diffusion, more protein carriers incorporated into cell membranes

enzymes involved in glycogenesis are activated

Question 4

Glucagon action

Answer 4

caused by low blood glucose levels on

-attaches to receptors on liver cell surface mem.
- activates enzymes that hydrolyse glycogen -> glucose (2nd messenger model)
- also activates enzymes involved in conversion of amino acids + glycerol into glucose (gluconeogenesis)

Question 5

What is the second messenger model?

Answer 5

Used by glucagon + adrenaline

• hormone binds to receptor on target cell surface
• changes protein shape activating adenyl cyclase which converts ATP -> cAMP
• cAMP acts as 2nd messenger, bonds to protein kinase, activating it
• p. kinase catalyses conversion of glycogen -> glucose

Question 6

What causes type 1 diabetes and how is it treated?

Answer 6

unable to produce enough insulin (B cells affected), develops fast

injections of insulin + biosensors to monitor blood glucose conc. to ensure right dosage

Question 7

What causes type 2 diabetes and how is it treated?

Answer 7

glycoprotein receptors on cells lose responsiveness to insulin, or inadequate insulin supply from pancreas
slower development

control of diet (intake of carbs), exercise, drugs + insulin injections can be used

Question 8

How is the glomerular filtrate formed?

Answer 8

Ultrafiltration

• diameter of afferent > efferent creating high hydrostatic pressure
• H2O, glucose + ions forced out of capillary to form filtrate (blood cells + proteins too large
• podocytes w/ spaces + endothelium of capillaries has spaces to minimise resistance

Question 9

What happens to the filtrate in the proximal convoluted tubule?

Answer 9

85% reabsorbed (inc all glucose and amino acids)

adapted w. microvilli, infoldings, many mitochondria

Question 10

How is water reabsorbed in the loop of Henle?

Answer 10

• Na+ ions actively transported out of asc. limb
• H2O passes out of des. limb by osmosis, some Na+ diffuses in
• H2O moves into blood capillaries by osmosis from collecting duct w/ varying permeability

increasing ion conc. down the loop, counter current multiplier set up
conc. of urine directly linked to length of loop

Question 11

What detects changes to water potential in the blood?

Answer 11

Osmoreceptors in hypothalamus

if low water pot. then cells shrink as water moves out by osmosis, release ADH which passes to pos. pituitary then to blood

Question 12

How is water potential in the blood controlled by ADH?

Answer 12

• ADH binds to receptors on mem. of cells lining collecting duct
• activates series of enzyme controlled reactions
• vesicles containing aquaporins fuse to membrane
• water moves down potential gradient