tubular reabsorption Flashcards
what are the 5 barriers that a substance must cross in order to be reabsorbed
- luminal membrane (apical)
- cytosol of epithelial cell
- basolateral membrane
- interstitial fluid
- capillary wall
explain the mechanism of the Na+/K+ ATPase pump
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
how is glucose reabsorbed
- the Na+/K+ pump generates a concentration gradient
- Na+ concentration is lower in the cell than in the tubule
- SGLT secondary active SYMPORTER couples favourable movement of Na+ down concentration gradient with glucose transport against its concentration gradient
- glucose diffuses down its concentration gradient from the cell to interstitial fluid through the GLUT facilitated diffusion carrier
- Na+ pumped out by ATPase pump
where does glucose and Na+ reabsorption take place
proximal convoluted tubule
what happens in the descending loop of Henle
water is readily reabsorbed because the medulla is salty
what happens in the ascending loop of Henle
reabsorption of ions via active transport
what happens in the distal convoluted tubule
pH regulation and hormone mediated Na+ reabsorption
what is the purpose of the RAAS system and what does it stand for
to increase blood pressure
renin-angiotensin-aldosterone-system
what lowers BP
natriuretic peptides
what does renin do
converts angiotensiongen into angiotensin 1
what is renin released by and what 3 triggers cause release
- the JG cells sense low blood pressure
- sympathetic nerve cells fire next to the JG cells
- maccula densa cells sense low salt so send prostaglandin to JG cells
where is angiotensin 1 converted into angiotensin 2
the lungs
what does angiotensin 2 do
- vasoconstrictor of the efferent arteriole which increases BP
- stimulates aldosterone release
- stimulates thirst, increased water intake increases blood volume and raises BP
where is aldosterone released from
adrenal cortex
what does aldosterone do and where does it work
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
how does aldosterone work
- it inserts K+ leakage channels into the luminal membrane (apical)
- this drives K+ into the tubule lumen so the pump works harder to replace the K+
- inserts Na+ channels into luminal membrane which drives Na+ into the epithelial cells
- Pump works even harder to pump Na+ out of cell and into interstitial fluid
- gain of Na+ in the flood , water drawn in, increased BP
what triggers aldosterone release
angiotensin 2 / increased K+ in blood
what is ADH (anti diuretic hormone)
a small peptide hormone released by the hypothalamus to increase BP
how does ADH work
- acts of smooth muscle cells of blood vessels to cause vasoconstriction
- inserts aquaporin channels from vesicles into luminal membrane to allow water reabsorption
what are the 2 types of natriuretic peptide and where are they secreted
atrial natriuretic peptide ANP and brain natriuretic peptide BNP
ANP-atria
BNP-ventricles
what are natriuretic peptides released in response to
high BP and high blood volume, detected by stretching of the heart wall
4 things natriuretic peptides do to lower BP
- increases sodium excretion
- vasodilates afferent arteriole and increases permeability of glomerulus (Kf) which causes an increase in GFR, increase of GFR prevents renin release
- reduces RAAS activity by inhibiting sympathetic activity
- inhibits ADH
which hormones act in the distal/collecting tubules
ADH (vasopressin) and aldosterone
