tubular reabsorption

Question 1

what are the 5 barriers that a substance must cross in order to be reabsorbed

Answer 1

1. luminal membrane (apical)
2. cytosol of epithelial cell
3. basolateral membrane
4. interstitial fluid
5. capillary wall

Question 2

explain the mechanism of the Na+/K+ ATPase pump

Answer 2

situated on the basolateral membrane of epithelial cells
3 Na+ is pumped out of the cell into lateral space
2K+ is pumped into the cell from the lateral space
Na+ diffuses down the concentration gradient across the interstitial fluid and into peritubular capillary
K+ diffuses out of cell and back into interstitial fluid to be recycled

Question 3

how is glucose reabsorbed

Answer 3

1. the Na+/K+ pump generates a concentration gradient
2. Na+ concentration is lower in the cell than in the tubule
3. SGLT secondary active SYMPORTER couples favourable movement of Na+ down concentration gradient with glucose transport against its concentration gradient
4. glucose diffuses down its concentration gradient from the cell to interstitial fluid through the GLUT facilitated diffusion carrier
5. Na+ pumped out by ATPase pump

Question 4

where does glucose and Na+ reabsorption take place

Answer 4

proximal convoluted tubule

Question 5

what happens in the descending loop of Henle

Answer 5

water is readily reabsorbed because the medulla is salty

Question 6

what happens in the ascending loop of Henle

Answer 6

reabsorption of ions via active transport

Question 7

what happens in the distal convoluted tubule

Answer 7

pH regulation and hormone mediated Na+ reabsorption

Question 8

what is the purpose of the RAAS system and what does it stand for

Answer 8

to increase blood pressure

renin-angiotensin-aldosterone-system

Question 9

what lowers BP

Answer 9

natriuretic peptides

Question 10

what does renin do

Answer 10

converts angiotensiongen into angiotensin 1

Question 11

what is renin released by and what 3 triggers cause release

Answer 11

1. the JG cells sense low blood pressure
2. sympathetic nerve cells fire next to the JG cells
3. maccula densa cells sense low salt so send prostaglandin to JG cells

Question 12

where is angiotensin 1 converted into angiotensin 2

Answer 12

the lungs

Question 13

what does angiotensin 2 do

Answer 13

1. vasoconstrictor of the efferent arteriole which increases BP
2. stimulates aldosterone release
3. stimulates thirst, increased water intake increases blood volume and raises BP

Question 14

where is aldosterone released from

Answer 14

adrenal cortex

Question 15

what does aldosterone do and where does it work

Answer 15

it is a hormone that drives the Na+/K+ pump to work harder which increases Na+ reabsorption in distal/collecting tubules
this causes water to follow via osmosis which increases BP

Question 16

how does aldosterone work

Answer 16

1. it inserts K+ leakage channels into the luminal membrane (apical)
2. this drives K+ into the tubule lumen so the pump works harder to replace the K+
3. inserts Na+ channels into luminal membrane which drives Na+ into the epithelial cells
4. Pump works even harder to pump Na+ out of cell and into interstitial fluid
5. gain of Na+ in the flood , water drawn in, increased BP

Question 17

what triggers aldosterone release

Answer 17

angiotensin 2 / increased K+ in blood

Question 18

what is ADH (anti diuretic hormone)

Answer 18

a small peptide hormone released by the hypothalamus to increase BP

Question 19

how does ADH work

Answer 19

1. acts of smooth muscle cells of blood vessels to cause vasoconstriction
2. inserts aquaporin channels from vesicles into luminal membrane to allow water reabsorption

Question 20

what are the 2 types of natriuretic peptide and where are they secreted

Answer 20

atrial natriuretic peptide ANP and brain natriuretic peptide BNP
ANP-atria
BNP-ventricles

Question 21

what are natriuretic peptides released in response to

Answer 21

high BP and high blood volume, detected by stretching of the heart wall

Question 22

4 things natriuretic peptides do to lower BP

Answer 22

1. increases sodium excretion
2. vasodilates afferent arteriole and increases permeability of glomerulus (Kf) which causes an increase in GFR, increase of GFR prevents renin release
3. reduces RAAS activity by inhibiting sympathetic activity
4. inhibits ADH

Question 23

which hormones act in the distal/collecting tubules

Answer 23

ADH (vasopressin) and aldosterone