Physiology Revision - The Renal system Flashcards
What is the role of renin and where does it come from?
- Secreted from the juxtaglomerular cells, renin converts angiotensinogen to angiotensin 1, which is then further converted to Angiotensin 2
Angiotensin 2 then acts on the adrenal gland/cortex to produce aldosterone which increases H2O and Na+ reabsorption/retention
Angiotensin 2 also cause afferent arteriole vasoconstriction therefore reducing GFR
What triggers the release of renin from the juxtaglomerular cells?
A decrease in plasma volume which in turn:
- Decreases arterial pressure
- Increases activity of renal sympathetic nerves
- Decreases GRF which causes decreased flow to the macula densa cells; thus decreased NaCl sensed
What is Artrial Natrieutic Peptide?
- Synthesized in atrial myocytes, ANP is released in response to stretching of the atria (increased circulating blood volume)
- Increase in ANP causes an increase in Na+ secretion (increased GFR)
-Decreased distal nephron Na+ reabsorption - Inhibition of renin release
What is the formula for Renal Clearance?
RC = (U)(V)/(P)
What are the starling forces that govern the net filtration pressure in the glomerular capillaries?
- Hydrostatic pressure in the glomerular capillaries favors filtration
- Osmotic forces due to the protein in the plasma opposes filtration
- Fluid pressure in Bowman’s capsule opposes filtration
What is tubular reabsorption and secretion?
Tubular reabsorption - Peritubular capillaries reabsorb filtrate through both active and passive transport
Tubular secretion - H+, K+, and organic anions move from the peritubular capillaries to the tubular lumen
Where does the majority of tubular reabsorption occur?
In the proximal tubule and the loop of henle
What is the difference btw GRF and Renal Clearance?
GFR is the amount of blood filtered by the glomeruli each minute and renal clearance is the amount of substance filtered by the glomeruli each minute, divided by its plasma C
What is filtration fraction and what is a typical value?
The filtration fraction is the proportion of the plasma that enters the kidneys that is subsequently filtered at the glomerulus and passes into the renal tubules
Typical value is 0.16-0.20 meaning about 20% of blood that enters the kidneys is filtered
What is local osmolarity?
The local water solute concentration.
- If water osmolarity is high ADH secretion will be increased by the posterior pituitary gland
What is the basic renal process for how water is reabsorbed?
Water reabsorption is by osmosis and is dependent on Na+ reabsorption (but not exclusively)
Water movement is also governed by the presence of aquaporin channels. Their presence varies across the tubular segments but highly expressed in the proximal tubule. They are absent in the collecting duct unless ADH is active
How is Na+ reabsorbed in the proximal tubule and the collecting duct?
Luminal membrane :
Proximal tubule - co-transport/counter-transport of organic molecules
Cortical collecting ducts - Via Na+ channels
Basolateral membrane:
Proximal tubule and cortical collecting duct -Via Na+/K+ ATPase pump
What do aquaporins do?
ADH/vasopressin causes a cascade of events within the collecting duct causing an increased number of AQP2 channels in the tubular/luminal membrane. Water then diffuses through these channels into the CD cells and through AQP3/4 channels into the interstitial fluid
What causes ADH secretion by the posterior pituitary?
Baroreceptors sense changes in plasma volume
Osmoreceptors sense changes in body fluid osmolarity
What happens when the plasma volume increases? What mechanism maintains homeostasis?
Atrial myocytes are activated in response to stretching of the atria with increased plasma volume. Atrial Natriuretic Peptide is released and causes increased Na+ excretion through increasing GFR (due to afferent dilation and efferent constriction) and decreased Na+ reabsorption
