Urine formation is a result of three processes:
1) Glomerular Filtration
2) Tubular Reabsorption
3) Tubular secretion
Urine= Filtration – Absorption + Secretion
Glomerular Filtration:
Glomerular filtration is the filtration of protein free plasma from glomerular capillaries into bowman’s capsule.
This is the first step in urine formation.
Glomerular Filtration Rate:
The volume of glomerular filtrate formed per minute.
This is nearly 125 ml/min.
Glomerular Filtration Membrane:
It has three layers:
1) Capillary endothelial layer
2) Basement membrane
3) Podocyte layer
Determinants of Glomerular Filtration Rate:
1) Filtration Coefficient
2) Net filtration pressure
Regulation of Glomerular Filtration Rate:
There are three primary regulators:
1) Autoregulation
2) Neural control
3) Hormonal and autocoid control
Regulation of Urine Output:
There are two lines of defence:
1) Tubuloglomerular Feedback
2) Glomerulotubular Feedback
How does the severe constriction of efferent arteriole causes decrease in glomerular filtration rate…??
Severe efferent arteriolar constriction reduces blood flow and hence increases filtration fraction. increased filtration fraction concentrates plasma proteins and raises glomerular capillary colloid osmotic pressure which then reduces GFR.