Glomerular Filtration Flashcards
How much percent of the CO does the kidneys recieve?
20-25%
Because the RBC arent filtered through the bowmans capsule, where does it pass ?
Passes via the efferent arterioles into the peritubular capillaries and then to the renal vein
What is the glomerular filtration dependent on?
The balance between the hydrostatic forces favoring filtration and the oncotic pressure forces favoring reabsorption
What is the purpose of the glomeruli membrane having pores?
To prevent RBC passing through but allowing all contents of plasma to
Is the glomerular capillary pressure high or low and why is this?
Pressure is high due to the afferent arteriole being wide and short (offers little resistance)
The efferent arterioles is also long and narrow creating high post capillary resistance
If you have high resistance, does the hydrostatic pressure increase or decrease upstream?
Pressure upstream is increased
Why is it important that the capillaries in the glomerulus have a high hydrostatic pressure?
Because high hydrostatic pressure favours filtration
What affects the glomerular capillary pressure and thus glomerular filtration rate?
Sympathetic VC nerves = afferent and efferent constriction, highly sensitive afferent arterioles
Circulating catecholamines = primarily afferent constriction
Angiotensin II = constriction of efferent and at low conc and constriction of both at high conc
How are we able to maintain adequate glomerular filtration rate even with decreased blood supply to the kidneys?
Constriction of the efferent arterioles will increase the pressure down stream
Increased hydrostatic pressure = increased GF
Regarding autoregulation, if there is a rise in MAP how would the glomerular arterioles respond?
Rise in MAP would cause constriction of afferent arterioles reducing blood flow to the glomerulus
How can blood pressure be maintained in the kidney for glomerular filtration in the case of a haemorrhage?
Decreased blood flow to the kidney would cause the efferent arterioles to constrict
This would increase pressure downstream (glomerulus) = maintained hydrostatic pressure for GFR
What is the main function of the peritubular and glomerular capillaries?
glomerular = filtration Periventricular = Reabsorption
What volume of blood is filtered per day by the kidneys?
180 litres
Is the pressure within periventricular capillaries high or low and why?
Pressure is low because hydrostatic pressure is low overcoming the high resistance along the length of efferent capillaries
Is the oncotic pressure high or low in periventricular capillaries and why?
High oncotic pressure to to the reduced plasma volume
This high oncotic pressure favours reabsorption
