BIOL 2420 Lecture Notes - Lecture 3: Renal Function, Renal Corpuscle, Basal Lamina

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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, hih 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 osists of the gloerular apillaries surrouded y Boa’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 Boa’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 Boa’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 Boa’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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