Physiology - Glomerular Filtration and Renal Blood Flow Flashcards
Is the diameter of afferent or efferent arteriole larger?
Afferent is larger
Describe the pathway of plasma from glomerulus into bowman’s capsule?
Through endothelial lining
Through basement membrane/basal lamina
Through podocytes
Of the following 4 forces that act on glomerular arteries in Bowman’s capsule name which ones oppose/favour filtration:
- glomerular capillary BP
- Capillary oncotic pressure
- Bowman’s capsule hydrostatic pressure
- Bowman’s capsule oncotic pressure
Glomerular capillary BP - favour
Bowman’s capsule hydrostatic pressure = oppose
Capillary oncotic pressure = oppose
Bowman’s capsule oncotic pressure = favour
When ever hear oncotic pressure think plasma proteins (plasma proteins have a osmotic effect - draw H2O towards them)
(Bowman’s capsule oncotic pressure should be zero as there should be no plasma proteins in the glomerular fluid under normal physiological conditions)
Define GFR
Rate at which protein-free plasma is filtered from glomeruli into Bowman’s capsule PER UNIT TIME
(per unit time as a rate)
How can GFR be calculated if looking directly at the glomerulus
As a result what is the main determinant of GFR?
GFR = Kf x net filtration pressure
Kf = filtration coefficient = how ‘holey’ the glomerular membrane is
Main determinant = Glomerular capillary BP as has the biggest impact on net filtration pressure
If afferent arteriole is constricted what effect does this have on GFR?
GFR decreases
Afferent arteriole decreases volume of blood flowing into glomerulus -> decreases NFP
What are the two parts of the autoregulation of GFR?
Describe how they work
Myogenic
(if vascular smooth muscle is stretched it contracts the arteriole)
Tubuloglomerular feedback
- if GFR rises, increase NaCl flow
- Causes macula densa to release chemical sensors which cause arteriole to contract -> decreases blood flow to glomerulus -> decrease GFR
How do you calculate the clearance of a substance?
Clearance of substance X = rate of excretion of X/plasma conc. of X
Inulin is the gold standard way of measuring GFR, however it needs to infused into the subject to be measured. Therefore, what other substance do we use to measure GFR?
Creatinine
What is used to measure renal plasma flow?
How does it work?
Para-amino hippuric acid
Majority filters through into tubule at glomerulus
Not reabsorbed
Completely secreted from peritubular capillaries/vasa recta into tubule
What is filtration fraction and how is it calculated?
Fraction of plasma flowing through the glomeruli that is filtered into the tubules
FF = GFR/renal plasma flow
(=~20% in the average healthy adult)
