Resabsorption and Secretion

Question 1

what is different between Pgc and Ppc

Answer 1

Pgc is greater than Ppc, because filtration at glomerulus but reabsorption at peritubular

Question 2

other than hydrostatic forces what other force is in favour of reabsorbtion into the peritubular capillaries

Answer 2

oncotic pressure (20% of plasma is in bowman’s capsule meaning higher protein conc in capillary)

Question 3

true/false many substances are reabsorbed by carrier mediated transport systems

Answer 3

true - glucose, amino acids, acis, sulphate and phosphate ions all require carriers

Question 4

what is Tm

Answer 4

the maximum transport capacity (the rate at full saturation)

Question 5

what happens when Tm is exceeded

Answer 5

the excess is excreted into urine

Question 6

what is the renal threshold

Answer 6

the plasma concentration of a substance at which full saturation and hence Tm occurs

Question 7

what is the renal threshold for glucose

Answer 7

10mmoles/L

Question 8

what happens to the glucose at a conc of 15mmoles/L

Answer 8

all 15mmoles/L will be filtered, 10mmoles/L will be reabsorbed and 5mmoles/L will be excreted

Question 9

true/false there is a threshold for glucose filtration

Answer 9

false - glucose is freely filtered from glomerulus

Question 10

at what concentration will the kidneys begin excreting glucose

Answer 10

10mmoles/L

Question 11

true/false Tm for amino acids is low and they are often excreted

Answer 11

false - Tm for amino acids is set so high that excretion does not occur

Question 12

how do kidney tightly regulate a substances concentration

Answer 12

by having a Tm whereby normal plasma concentration causes saturation

Question 13

where does most Na+ reabsorption occur

Answer 13

proximal tubule (about 65-75%)

Question 14

how is Na+ reabrobed

Answer 14

by active transport driven by Na+ pumps

Question 15

where are Na+ pumps

Answer 15

basolateral cell surfaces where there is a high density of mitochondria (ATP supply)

Question 16

process of Na+ moving into interstitial fluid

Answer 16

high conc in tubule and low conc in tubule cell –> Na+ moves in by gradient –> moved out by Na+ K+ ATPase pump

Question 17

true/false Na+ is not usually membrane permeable but proximal tubule has higher permeability

Answer 17

true - it is achieved by large surface area of microvilli and large number of Na+ ion channels

Question 18

what facilitates negative ions like Cl- reabsorption

Answer 18

the electrical gradient created by Na+

Question 19

what facilitates water’s reabsorption

Answer 19

the osmotic force created by all the ions moving across

Question 20

how much urea is reabsorbed

Answer 20

only about 50%, onyl moderately permeable

Question 21

true/false the active transport of Na+ is important for inducing lots of other resorption

Answer 21

true - any impairment to it’s active transport results in a disruption of renal function

Question 22

effect of high [Na+] on glucose transport

Answer 22

stimulates it

Question 23

glucose transport and connection to Na+

Answer 23

Na+ uses SGLT transporter to get into cell and pulls glucose with it (like in gut) –> out cell by GLUT2 –>Na+ out by Na+K+ATPase

Question 24

sites of secretion along tubule

Answer 24

proximal, distal and collecting duct

Question 25

true/false carrier-mediated secretory mechanisms are not very specific so they can be used to transport a variety of substances

Answer 25

true - helps so that even if the body doesn’t know the substance and have specific mechanisms for it, it can still be secreted

Question 26

what drugs can the organic acid mechanism secrete

Answer 26

penicillin, aspirin and PAH

Question 27

what drugs can the organic base mechanism secrete

Answer 27

morphine and atropine

Question 28

cholin and creatinine are organic acids/bases

Answer 28

bases

Question 29

5.5mmoles/L is hyper/hypokalaemia

Answer 29

hyperkalaemia

Question 30

consequence of hyperkalaemia on cell signals

Answer 30

resting membrane potential decreased –> ventricular fibrillation

Question 31

consequence of hypokalaemia on cell signals

Answer 31

resting membrane increases –> cardiac arrhythmias

Question 32

what hormone is triggered by high K+

Answer 32

aldosterone

Question 33

what K+ reducing effect does aldosterone have

Answer 33

stimulates an increase in renal tubule K+ secretion

Question 34

effect of aldosterone on Na+

Answer 34

promotes reabsorption in distal tubule