Physiology of the Renal System II:Glomerular Filtration Flashcards
What are the key components of the kidney?
Cortex
Medulla
Ureter
Renal artery
Renal vein
What is the nephron?
The functional unit of the kidney.
Where is the glomerulus of the nephron located?
In the cortex of the kidney
What is special about the blood flow to the kidney?
1.1L/min goes to the two kidneys.
This is about 20% going to the kidney where about of this is 50% is plasma (625ml/min per kidney)
What is the schematic of the glomerulus?
Tuft of capillaries surrounded by the bowman’s space
What is the process of glomerular ultrafiltration?
Filtration in the kidney occurs in the glomerulus, where a ‘semipermeable membrane’ separates the cells and plasma in the capillaries from the ‘filtrate’ which forms in the Bowman’s space.
What forces drive flow of plasma during glomerular filtration?
Hydrostatic pressure: higher hydrostatic pressure (55 mmHg) in the capillaries drives fluid out
Osmotic/oncotic: higher osmotic pressure in the capillaries (particularly due to plasma proteins) impedes the flow.
• The osmotic force increase along the length of the capillaries, but equilibrium is not normally achieved (in people).
How is hydrostatic pressure controlled locally in the glomerular capillary?
constrict the afferent arteriole (decreases filtrate leakage due to drop in hydrostatic pressure)
Contract the efferent arteriole (increases filtrate leakage due to increase hydrostatic pressure.
Why is the total osmotic pressure of plasma high?
the molecular weight of proteins is large and therefore the moles of protein is small, so the oncotic pressure is low (less than the hydrostatic pressure)
Why does the osmotic pressure increase from afferent to efferent arteriole?
As you move along the capillary, water is lost so the concentration of proteins increases and thus the osmotic pressure increases but will not exceed the glomerular hydrostatic pressure
What are the barriers to diffusion separating the blood from the bowman’s capsule lumen?
Endothelial cells of glomerular capillaries
Glomerular basement membrane
Epithelial cells of Bowman’s capsule
How are the endothelial cells specialised?
Have small holes (60nm) between them which are too small for cells to get through but enables small ions to pass through.
Have a negative charge (glycocalyx) which creates a charge barrier that is effective for proteins. Allows for preferential movement of positively charged ions
What is the purpose of podocytes
Podocytes cooperate with mesangial cells to support the structure and function of the glomerulus
What is filtration fraction?
The proportion of the plasma flow that is filtered by the glomerulus (about 20%)
How is the filtration fraction calculated?
Filtration faction = GFR / RPF
GFR - glomerular filtration rate
RPF - renal plasma flow
