Excretion
1- describe the mechanisms involved in reabsorption in the proximal convulted tubule and
describe how the epithelial cells of the pct are adapted to carry out their functions (9)
1. Glucagon binds to receptor on cell membrane by transduction
2. the change in receptor activates
3. the G-protein activates
4. adenyl cyclase (membrane)
5. active adenyl cyclase
6. ATP → cAMP - 2nd messenger
7. inactive kinase A enzyme → (cAMP) active kinase
8. inactive phosphorylation → active PO4 kinase
9. inactive glycogen → active glycogen phosphorylate enzyme
10. glycogen→ glucose
Cell signalling:
1. ligand-receptor binding
2. phosphorylation and signal transduction
3. signal amplification
Renal Threshold:
(blood glucose above threshold)
1. not all glucose are reabsorbed in PCT → glucose present in urine (test strip)
2. glucose + oxygen → glucose oxidase → gluconic acid + hydrogen peroxide
3. hydrogen peroxide + chromogen (colourless) → peroxidase → oxidised chromogen
(coloured) + water + oxygen
Test Strips test for:
glucose
pH
ketones
proteins
but it does not measure the concentration of glucose (just its presence)
Biosensor
1. glucose enters active site of enzyme to produce → gluconic acid and H2O2
2. which is oxidised at an electrode → e- flow is proportional to glucose molecule
3. biosenor amplifies the current
4. read by digital reading/meter
, Excretion
removal of metabolic waste products, e.g. urea
deamination- liver
o amino group (NH2) is removed from amino acid together with a hydrogen
o it combines with the hydrogen to make ammonia
Structure of Kidney
Renal artery → afferent arteriole
Glomerulus (ultrafiltration)
Lumen of Bowman’s capsule (ultrafiltration)
Proximal Convuluted Tubule (selective reabsorption)
Descending limb of loop of henle. (selective reabsorption)
ascending limb of loop of henle (selective reabsorption)
distal convoluted tubule. (selective reabsorption)
collecting duct (selective reabsorption)
Osmoregulation
Mode of action of ADH
o ADH binds to receptor on CD
o activation of a 2nd messenger cAMP
o activates protein kinase
o protein kinase cause vesicles within the cells to move and fuse with cell
membrane
Walls of PCT and CD become more permeable to H2O
o Pituitary gland to secrete ADH
o ADH binding also increases transcription of gene coding for aquaporin protein
o osmoreceptors also stimulate thrist centre in the brain
Normal H2O potential→ increase in H2O potential (detected by the osmoreceptors in the
hypothalamus)
o drinking too much water
o by not enough salt as they were used up in metabolism or excreted or not being
replaced in diet
o pituitary gland releases less ADH
o Walls of CD become less permeable to H2O
o No stimulus from ADH
o Aquaporins are moved out of cell membrane of CD back into the cytoplasm as
vesicles
1- describe the mechanisms involved in reabsorption in the proximal convulted tubule and
describe how the epithelial cells of the pct are adapted to carry out their functions (9)
1. Glucagon binds to receptor on cell membrane by transduction
2. the change in receptor activates
3. the G-protein activates
4. adenyl cyclase (membrane)
5. active adenyl cyclase
6. ATP → cAMP - 2nd messenger
7. inactive kinase A enzyme → (cAMP) active kinase
8. inactive phosphorylation → active PO4 kinase
9. inactive glycogen → active glycogen phosphorylate enzyme
10. glycogen→ glucose
Cell signalling:
1. ligand-receptor binding
2. phosphorylation and signal transduction
3. signal amplification
Renal Threshold:
(blood glucose above threshold)
1. not all glucose are reabsorbed in PCT → glucose present in urine (test strip)
2. glucose + oxygen → glucose oxidase → gluconic acid + hydrogen peroxide
3. hydrogen peroxide + chromogen (colourless) → peroxidase → oxidised chromogen
(coloured) + water + oxygen
Test Strips test for:
glucose
pH
ketones
proteins
but it does not measure the concentration of glucose (just its presence)
Biosensor
1. glucose enters active site of enzyme to produce → gluconic acid and H2O2
2. which is oxidised at an electrode → e- flow is proportional to glucose molecule
3. biosenor amplifies the current
4. read by digital reading/meter
, Excretion
removal of metabolic waste products, e.g. urea
deamination- liver
o amino group (NH2) is removed from amino acid together with a hydrogen
o it combines with the hydrogen to make ammonia
Structure of Kidney
Renal artery → afferent arteriole
Glomerulus (ultrafiltration)
Lumen of Bowman’s capsule (ultrafiltration)
Proximal Convuluted Tubule (selective reabsorption)
Descending limb of loop of henle. (selective reabsorption)
ascending limb of loop of henle (selective reabsorption)
distal convoluted tubule. (selective reabsorption)
collecting duct (selective reabsorption)
Osmoregulation
Mode of action of ADH
o ADH binds to receptor on CD
o activation of a 2nd messenger cAMP
o activates protein kinase
o protein kinase cause vesicles within the cells to move and fuse with cell
membrane
Walls of PCT and CD become more permeable to H2O
o Pituitary gland to secrete ADH
o ADH binding also increases transcription of gene coding for aquaporin protein
o osmoreceptors also stimulate thrist centre in the brain
Normal H2O potential→ increase in H2O potential (detected by the osmoreceptors in the
hypothalamus)
o drinking too much water
o by not enough salt as they were used up in metabolism or excreted or not being
replaced in diet
o pituitary gland releases less ADH
o Walls of CD become less permeable to H2O
o No stimulus from ADH
o Aquaporins are moved out of cell membrane of CD back into the cytoplasm as
vesicles
