2.12 - Filtration Flashcards
What is the name of the blood volume that flows through the arteriole?
Renal plasma flow
What is filtration fraction?
The proportion of filtered renal plasma flow
What 3 elements make up the filter in the glomerulus?
Endothelial fenestrations between cells
Matrix of basal memebrane - collagen and proteins
Bowman’s epithelial cells (podocyte) - fine filter. Much smaller than the fenestrae so has more control over what is filtered
Describe the qualities of molecules that are filterable
Molecular weight <69,000 (similar albumin)
Positively charged peptides more easily filterable than negative ones
Describe the concept of renal reserve
When one kidney is lost, within a few days there is functional compensation via hypertrophy in the remaining glomeruli
What keeps the glomerulus clean?
Molecules that get trapped in the glomerulus are believed to be eliminated by glomerular podocytes (via pinocytosis) and phagocytic mesangial macrophages
What is the formula for effective filtration pressure? And describe each of the constituents
Peff = Pcap - πcolosm - Pinterst
Pcapis the filtration force produced by the left ventricle (about three times higher than other capillary beds)
πcolosm (colloid osmotic pressure) is caused by proteins/macromolecules in the plasma (not filtered but osmotically active)
Pinterst is a property of bowman’s capsule and is the resistance to filtration imposed by the capsule
What is the effective filtration pressure in mmHg?
~20mmHg
Does effective filtration pressure remain constant over the length of the capillary?
No.
Capillary pressure and interstitial pressure remain constant whereas colloid osmotic pressure rises as water without colloids is filtered away. This decrease effective filtration pressure.
Describe the autoregulation of renal perfusion
autoregulation ensures capillary pressure remains around 60mmHg irrespective of MAP (over a range of 80-180torr) in the renal artery
This ensures constancy of plasma flow –> filtration rate –> filtration fraction –> excretion
Describe the vascular component of renal autoregulation
A myogenic response in the smooth muscle of the arterioles. When blood pressure increases this stretches the wall, opening TRPC channels. When these channels open calcium comes in, resulting in contration of the SMC –> decreased flow through kidney
Describe the glomerulo-vascular arm of renal autoregulation
Detection of increased [NaCl] leads to vasoconstriction of the afferent arteriole.
Although a lot of NaCl is taken back up in the loop, a lot of NaCl still reaches the distal tubule (where it meets the afferent/efferent arteriole), where the concentration is recognised and sensed by the macula densa cells in the juxtaglomerular apparatus. A variety of compounds is believed to be released, such as adenosine, ATP, lipids etc. resulting in constriction of the afferent arteriole
Describe how glomerular filtration rate can be indepently of renal blood flow. Draw the four scenarios
The afferent or efferent artioles can be either constricted or dilated.
What are the vascular modulators of renal blood flow that act via constriction?
Sympathetic nerves (via alpha1)
AngII
Endothelin
Adenosine (paradoxical in the kdieny, it typically dilates)
What are the vascular modulators of renal blood flow that act via dilation?
Prostaglandings (PGI2, PGE2)
NO from endothelia
Bradykinin
Dopamine
AngII (via AT2 receptor)
Jonathan Miles, 50y old, has been acutely administered a vasodilator drug that causes a 50% decrease in renal efferent arteriolar resistance with no change in afferent arteriolar resistance or arterial pressure. As compared to normal, which of the following rows best describes the expected changes:
B
