BIOL 2420 Lecture Notes - Lecture 3: Renal Function, Renal Corpuscle, Basal Lamina
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26 Apr 2018
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Unit 7 – Lecture 3
Filtration
- filtration of plasma into the kidney tubule is the first step in urine formation
- nonspecific process
- creates a filtrate
o composition is like plasma minus the plasma proteins
- normal conditions
o blood cells remain in the capillary
o filtrate is composed of water and dissolved solutes
- filtration of all plasma would leave a sludge-like lood, hih does’t happe
o only 1/5th of the plasma that flows through the kidneys filters into the nephrons
o 4/5th of plasma remaining plus the plasma proteins and blood cells flow into the
peritubular capillaries
o percentage of total plasma volume that filters into the tubule is called filtration fraction
The Renal Corpuscle Contains Filtration Barriers
- filtration takes place in the renal corpuscle
o osists of the gloerular apillaries surrouded y Boa’s apsule
- substances leaving plasma must pass through three filtration barriers before entering the tubule
lumen
o glomerular capillary endothelium
o basal lamina (basement membrane)
o epithelium of Boa’s apsule
- first barrier
o capillary endothelium
o glomerular capillaries are fenestrated capillaries
▪ large pores that allow most components of the plasma to filter through the
endothelium
▪ pores are small enough to prevent blood cells from leaving the capillary
▪ negatively charged proteins on the pore surfaces also help repel negatively
charged plasma proteins
- second barrier
o basal lamina
▪ acellular layer of extracellular matrix separating the capillary endothelium from
the epitheliu of Boa’s apsule
▪ consists of negatively charged glycoproteins, collagen, other proteins
▪ acts as a coarse sieve, excluding most plasma proteins from the fluid that filters
through it
- third barrier
o epitheliu of Boa’s apsule
▪ the portion of the capsule epithelium that surrounds each glomerular capillary
consists of specialized cells – podocytes
• podocytes have long cytoplasmic extensions – foot processes
o foot processes
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