Glomerular filtration Flashcards
What is a nephron?
A functional unit of the kidney which regulates the concentration of water and solutes through filtration, reabsorption and secretion.
What is a nephron composed of?
The glomerulus surrounded by Bowman’s capsule and its tubular system to the renal pelvis.
What is the RPF received by a kidney?
600ml.min of the 1.1L.min of blood passing through
How much plasma is filtered by both kidneys in total?
120ml.min
180L.day
How does the plasma become filtrate in the nephron and what forces are contributing?
The filtrate forms within Bowman’s space, separated from plasma by the endothelial cells of the capillaries and their BM. Ions move between the plasma and filtrate at equilibrium so only oncotic has an effect but as hydrostatic pressure is higher in the capillaries than oncotic, fluid moves into Bowman’s space.
What is the osmolarity of the filtrate as it enters the tubule?
285osm.L as equal to plasma
Which two forces drive filtration?
Hydrostatic - Higher in capillaries so fluid moves out
Oncotic - Higher in capillaries as the proteins are impermeable. As more filtrate moves out along the length of the capillaries the flow of filtrate reduces as the oncotic force increases.
How can the volume of filtrate entering be altered?
Increasing glomerular hydrostatic pressure will increase the filtrate. This can be achieved by dilating afferent capillary or constricting efferent.
Where does the efferent capillary travel and what forces play a role?
Leaves the glomerulus to enter the portal vein and form a second capillary bed that surrounds the loop of Henle. As the capillary has a low hydrostatic but a high oncotic pressure it can recieve the reabsorbed products from the tubules.
Define net perfusion pressure.
Glomerulus hydrostatic pressure - (Bowman’s space hydrostatic pressure + colloid)
Define net hydrostatic pressure.
Glom. hydrostatic - Bowman’s space hydrostatic
What forms the diffusion barrier of the glomerulus?
Endothelial cells
BM (collagen = -ve charge)
Podocytes
What are podocytes?
Cells of the Bowman’s capsule that have small processes that surround a capillary loop to produce filtration slits. They have a -ve charge on glycocalyx to prevent entry of proteins.
Which molecules can pass through the filtration barrier and which cannot?
Cationic (+) and neutral molecules pass through and are at EQUILIBRIUM to the plasma. All small molecules will filter e.g. Na, K, Cl, Hco3, glucose, urea
Anions (-) do not pass due to the -vely charged membrane e.g. albumin
What is the glomerular filtration rate?
The amount of blood passing through the glomeruli for filtartion per minute. = 120ml.min (total of both)
