Glomerular filtrations Flashcards
Glomerulus structure
capillary knot that is supplied by the afferent arteriole, a division of the renal artery and drained by the efferent arteriole
enveloped in the Bowman’s capsule
brief blood vessels after glomerulus
efferent arteriole takes blood to peritubular capillaries of the vasa recta, finally ending in the renal vein
peritubular capillaries lie alongside the renal tubule
vasa recta form hair pin capillary loops
who described the microscopic structure of the glomerulus?
Bowman
Who proposed the theory of capillary ultrafiltration?
Ludwig, influenced Starling’s laws depicting the movement of fluids
filtrate versus blood key difference
Filtrate has no proteins
hydrostatic pressure in the glomerulus
45mmHg
stages of moving from glomerulus into the bowman’s capsule
- move through the fenestrated endothelial cell wall of the capillaries, preventing only the movement of cells
- endothelium cell wall
- between the pedicels of podocytes
component of endothelial cell wall + function
negatively charged glycosaminoglycans, preventing the movement of positive molecules
structure of podocytes
extensions of the podocytes called pedicels, which interdigitate to form slit pores
nephrins present in the pedicels interdigitate to form the pores - negatively charged
nephrotic syndrome definition
damage to basement membrane occurs resulting in proteinuria
what does the filtration rate depend on?
net filtration pressure= pressure out - pressure in
what forms the pressure out of the capillary?
hydrostatic pressure in capillary and oncotic pressure of filtrate in bowman’s capsule
what forms the pressure into the capillary?
hydrostatic pressure in the bowman’s capsule and oncotic pressure in the capillary
different expressions for the different values
PGC- hydrostatic pressure in capillary
PBS- hydrostatic pressure in Bowman’s capsule
PiGC- oncotic pressure of glomerular capillary plasma
PiBS- oncotic pressure of bowman capsule filtrate
what value should PiBS be?
0 as there should not be any proteins in the filtrate
what value should be low+why?
PBS- hydrostatic pressure in Bowman’s capsule, as the space acts like a sink, with the filtrate moving into the proximal tubule
rate of formation filtrate
GFR- Kf x PUF
Kf= the filtration coefficient, which is permeability x surface area
PUF- is the net filtration pressure
how is the driving force sustained?
greater afferent arteriole and smaller efferent arteriole, so there is a high hydrostatic pressure in the capillary
what changes along the length of the glomerulus capillary?
net filtration pressure diminishes, as less water in the capillaries
oncotic pressure rises, more fluid moves out and the concentration of proteins remaining in the blood rises
what can lead to an increase in pressure in the bowman’s capsule?
kidney stones in the ureter, urine can’t pass, back log of fluid, fills bowman’s capsule
how can the GFR be modified?
sympathetic nervous system leads to the vasodilation or contraction of either the efferent or afferent arteriole
what other cells surround the glomerulus? + function
mesangial cells which are contractile cells that can contract to change the surface area of the capillary wall and thus alter GFR
what is the glomerulus pressure range?
80-180 mmHg
2 main autoregulatory mechanisms of GFR
myogenic Bayliss mechanism and tubuloglomeruluar feedback
myogenic Bayliss mechanism explained
- increased pressure, arteriole smooth muscle stretched
- activates stretch mediated ion channels, leading to depolarisation
- induces voltage gated calcium channels, leading to contraction of afferent to reduce volume in kidney
explain tubuloglomerular feedback
macula densa in the juxtaglomerular apparatus detects distal flow rate in the renal tubule
if flow rate is increased, signal is released to constrict the afferent arteriole
clearance definition
the volume of plasma from which substance X is completely removed in a minute by the kidneys. the minimum volume of plasma which could have contained the filtered substance
GFR in humans
125 ml per minute
filtration fraction definition
ratio of glomerular filtration rate to renal plasma flow
represents the proportion of the fluid reaching the kidneys that passes into the renal tubules
normal filtration fraction
20%
renal plasma flow definition
the amount of plasma flowing into the kidneys
renal plasma flow figure
600ml/min
what can be used to approximate the glomerular filtration?
creatine or inulin
why does creatine approximate the GFR?
endogenous chemical that is excreted only by filtration
produced by breakdown of creatine phosphate
only secreted by the peritubular capillaries in small amounts
what is inulin?
group of naturally occurring plant polysaccharides
why does inulin approximate the GFR?
Inulin is not reabsorbed nor secreted by the kidneys
so rate of excretion is directly proportional to the rate of filtration of water and solutes
