Revision notes on ultrafiltration, selective reabsorption and reabsorption of water. Kidney function notes. A level biology OCR A revision notes. Notes on module 5: Communication, homeostasis and energy. Summary/ information you need to memorize for a level biology OCR A exams.
Ultrafiltration, Selective Reabsorption, Reabsorption of Water:
Ultrafiltration:
o The basement membrane acts as a filter.
o Water, glucose, mineral ions & other small molecules are
forced out of the capillary into the glomerular filtrate.
o The diameter of the afferent (coming in) arteriole is
greater than the diameter of the efferent (exiting)
arteriole, so there is a build up of hydrostatic pressure in
the glomerulus (network of capillaries) that forces fluid
into the renal capsule.
o The filtrate passes through the basement membrane and
then through the fenestrations in the podocytes.
o 125cm3 of blood is filtered each minute – this is the
glomerular filtrate rate (GFR).
o However lots of useful substances need to be reabsorbed
from the filtrate, this is done in the proximal convoluted
tubule (PCT).
Selective reabsorption:
o In the PCT nearly 65% of the filtrate is reabsorbed back
into the blood,
o Cells of the PCT:
Cuboidal epithelial cells.
They have microvilli to create a large surface area.
They have lots of mitochondria to provide ATP.
The blood capillaries lie very close to the cells.
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