Glomerular Filtration Flashcards
Definition of ‘filtration’
Bulk flow of solvent through a filter, carrying with it those solutes which are small enough to pass through the filter
What are the 3 layers separating the blood from the lumen of Bowman’s capsule?
Endothelial cell lining of the glomerular capillaries
Glomerular basement membrane
Visceral epithelial cells of Bowman’s capsule
What forms the dense, negatively-charged meshwork on the endothelial cell surface?
Glycocalyx
What is the glycocalyx composed of?
Siagloglycoproteins, heparan sulfate
What does the basement membrane consist of?
Glycoproteins - mainly type IV collagen, laminin and fibronectin - all negatively charged
What are podocytes?
Epithelial cells of Bowman’s capsule
What are trabeculae of podocytes?
Projections from the cell body
What are the small processes from the trabeculae of podocytes called?
Pedicles
What are the two forces that drive the bulk flow into the Bowman’s capsule?
Hydrostatic and Osmotic/oncotic
What is the function of the capillary endothelium?
Acts as a barrier to blood cells and platelets
Glycocalyx reduces the penetration of plasma proteins into the filter
What is the function of the basement membrane?
Allows passage of molecules depending on their molecular size, shape and charge
Is a major filtration barrier for proteins
Main site of restriction of water flow
What is the function of visceral epithelial layer of Bowman’s capsule?
maintains the basement membrane and ma phagocytose macromolecules (as do mesangial cells)
Has a role in permselectivity
Where are mesangial cells located?
In the central part of the glomerular tuft
What type of cell are mesangial cells?
Macrophages
What do mesangial cells do?
Actively phagocytic - prevent the accumulation in the basement membrane of macromolecules which have escaped from the capillaries
Also a structural role in holding the delicate glomerular structure in position
Capable of contraction so modify surface area of glomerular capillaries available for filtration
What are the mesangial cells outside the glomerular area (close to the macula densa) called?
Extraglomerular mesangial cells
Definition of filtration fraction
Proportion of the plasma flow that is filtered by the glomerulus
What is the normal filtration fraction?
0.2 (20%)
What is the main determinant of whether a substance will be filtered or will be retained in the capillaries?
Molecular size
Which molecules will be filtered faster, anions or cations?
Cations
What is the molecular weight cut-off for the filter?
70,000
What is the normal glomerular filtration rate (GFR)?
About 180L/day or 125mL/min
What is the filtration rate of each nephron?
30-50nL/min
What is the sequence of blood vessels in the kidneys?
Arteries, afferent arterioles, glomerular capillaries, efferent arterioles, peritubular capillaries, venules, veins
