Renal Physiology Flashcards
What is the main waste product excreted by the kidneys?
nitrogen, mostly from ammonia in dietary proteins
excreted as urea
Generally how is ammonia transported to the kidneys for excretion?
The liver converts ammonia to urea to be transported to the kidneys (80 percent)
Any ammonia not converted transported to kidneys in a bound form, either as glutamine or glutamic acid (20 percent)
How is glutamine made in the liver?
By adding NH3 to glutamate via glutamine synthase
how is ammonia from muscle transported to the kidneys?
incorporated into alanine to be transported to the liver where it is converted to glutamate
What is the standard osmolality of the body?
285 mosmoles
What are Starling’s forces in terms of renal?
Hydrostatic pressure which is the pressure generated by blood pressure (is greater than oncotic pressure at the arterial end of a capillary hence fluid leaves)
Oncotic pressure generated by the osmotic forces caused by the plasma proteins drawing fluid into the capillary (greater than hydrostatic pressure at the venous end of the capillary so causes net inward movement)
What is the value for oncotic pressure in normal vessels?
25mmHg
What are the order of vessels through the kidney from renal artery to vein?
Renal artery Segmenral arteries Interlobar arteries arcuate arteries cortical radial arteries afferent arterioles glomerular capillaries efferent arterioles peritubular capillaries venules and veins
What are the 3 main layers of the glomerular membrane?
Fenestrated capillary membrane
Basement membrane
Visceral epithelium of bowmans capsule (made of podocytes)
What prevents proteins entering the ultrafiltrate in bowmans capsule?
Negatively charged basement membrane repels the like charged plasma proteins
what is the overall equation for GFR?
GFR= filtation constant (hydrostatic pressure inward [Pcap] x oncotic pressure inward [nbc]) - (hydrostatic pressure outward [Pbc] x oncotic pressure outward [ncap])
p.s. filtaration constant = surface area x permeability
What is the equation for filtration fraction?
GFR/RPF
GFR glomerular filtaration rate
RPF renal plasma flow
what is a normal value for filtation fraction?
20 percent, around 120ml/min
How does sodium concentration change along the proximal tubule?
It remains the same as blood plasma at 140mM as it is freely filtered.
It enters the tubule and is the reabsorbed but in equal amounts to water so the concentration doesnt change
What is the inital pottasium concentration and how does it change throughout the proximal tubule?
Initally 4mM the same as in the plasma and there is no change in concentration throughout proximal tubule
how is na+ reabsobed in the proximal tubule?
the Na+/K+ ATPAse pump on the basolateral membrane generates an electrochemical gradient.
this causes na+ to move in from the lumen down its electrochemical gradient, in exchange for H+