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+
what are the inital and final hco3- concentrations in the proximal tubule and explain this
initally 25mM then falls to 5mM this is due to the hco3- being reabsorbed through conversion to co2 and h2o by carbonic anhydrase. More hco3- is reabsobed or converted to h2o and co2 than water is reabsobed, this results in less hco3- remaining in the tubule so the concentration falls
What is the difference between chronic and acute kidney disease?
Acute kidney disease occurs over a matter of hours or days and is usually reversible.
Chronic kidney disease occurs over longer periods of time and is often irreversible.
What are the two main tests for acute kidney injury and how do they tend to change over time?
Serum createnine will increase with worsening injury as the damaged kidney is unable to remove it
Urine production decreases with worsening injury
Why are people who have had acute kidney injury more likely to develop chronic kidney disease?
The kidneys are damaged and the scarring means that chronic kidney disease is more likely
What are the three general causes of acute kidney injury?
Pre-renal - perfusion failure
Renal - intrinsic disease of the kidney
Post-renal - obstruction of the urinary system
In terms of renal, what is the auto-regulatory range?
The range of blood pressures within which the kidney is able to keep the flow constant through autoregulation.
Above and below these pressures the flow increases and decreases.
In brief how does the renin-angiotensin system work?
Renin is released from the juxtaglomerular apparatus in response to low blood pressure or low sodium levels
This causes angiotensionogen to be cleaved to angiotensin 1
This in converted to angiotensin 2 in the endothelial cells of the lungs by ACE (angiotensin converting enzyme)
Angiotensin 2 stimulates vasoconstriction, thirst and release of aldosterone from the adrenal cortex
Aldosterone acts to increase sodium reabsorption and increase pottasium excretion.
How does urine move down the ureters?
By peristalsis aswell as gravity, causes urine to propogate down ureter. Due to atypical smooth muscle cells.
What is the most common cause of ureter obstruction?
kidney stones
What does the wall of the urinary bladder consist of?
inside -urothelium-corrugated so unfolds when bladder fills -lamina propria -detrusor smooth muscle -serosa outside
What are the junction type between the urothelial cells in the bladder wall?
Tight junctions to reduce permeability of the wall.
What are the urine facing specialised cells in the bladder wall?
Umbrella cells
What is contained in the lamina propria of the bladder wall?
blood vessels, lymphatics, nerves (detect mechanical and chemical stimuli) and interstitial cells
What are the roles of the interstitual cells in the wall of the bladder?
Unknown but thought to mediate signalling between the urothelium and detrusor smooth muscle
What is the structure of the detrusor smooth muscles in the bladder wall and why?
It is in a basket weave pattern in order to resist forces in all directions.
What is the innervation of the detrusor muscles of the bladder wall?
Autonomically innervated
Sympathetic nerves release NAd into beta 3 adrenoceptors to cause relaxation.
Parasympathetic nerves release Ach which acts on M3 muscarinic receptors to cause contraction.
What is the storage reflex and voiding reflex in the bladder?
The storage reflex causes relaxation of the detrusor muscles and contraction of the internal urethral sphincter.
For the voiding reflex there is stimulation of the detrusor muscles and relaxation of the internal urethral sphincter.
what are the hydrostatic pressures within the capillarys at the arterial and venous ends?
32mmhg at the arterial end
12mmhg at the venous end
what is the oncotic pressure in the capillaries
25mmhg
what is the typical value for balanced water intake and output in the body daily?
2,400ml
what are the most important ions in the body fluids intracellularly and extracellularly?
sodium extracellularly
potassium intracellularly
why do losses of K+ from the body have only a small effect on plasma k+ concentration?
k+ can move out of the cells to maintain equilibrium between intracellular and extracellular fluid
what is a simple method for measuring body fluid compartments?
add a substance that uniformally distributes throughout the body compartment. then use colourimetry to measure the concentration of the substance, this will allow you to calculate the volume by dividing the amount of substance over the concentration.
what is the volume of distribution equation?
volume of distribution = (quantity administered)-(quantity metabolised or lost)/concentration
how is plasma volume typically measured?
need a substance that doesnt cross the capillaries so typically use labelled plasma proteins. then can calculate volume by measuring concentration of the protein after a known amount has been injected
which substance is used to measure extracellular fluid volume?
thiosulphate is typically used as it can readily cross between plasma, interstitial fluid and transcellular fluid (joint capsules etc) but doesnt enter cells
