biology a level
How does filtering and reabsorption occurs?
*Stage 1 (ultrafiltration)
Occurs due to high hydrostatic pressure. Water and small molecules are forced out of the glomerulus capillaires into the renal capsule
*Stage 2( Selective reabsorption)
Occurs in the proximal convoluted tubule reabsorbs ions water and nutrients and removes toxins and adjusts filtate PH
*Stage 3+4(The loop of henle) maintains sodium ion gradient so water can be reabsorbed by blood
*Stage 5+6 Water moves out of the distal convoluted tubule and collecting duct to return back to blood. The collecting duct then carries remaining liquid (urine) to the ureter
Deeply describe ultrafiltration
Blood eneters through the afferent arteriole and this splits it lots of smaller capillaries which make up the glomerulus.This causes a hugh hydrostatic pressure of the blood. Water and small molecules are forced out of capillaries. Large Proteins and blood cells are too big to fit through the gaps in the capillary endothelium so remain in blood. This blood leaves via efferent ateriole
selective reabsorption
Occurs in the proximal convoluted tubule.Here 85% of the glomerulus filtrate is reabsorbed back into the blood leavinf urea and excess minerals behind
what are the two structures in selective reabsorption that help effiency
Microvilli provide a large surface area for reabsorptiom
Lots of mitochondria to provide energy for active transport
Selective reabsorption in detail
The concentration of sodium ions in the PCT cell is decreased as the sooduhm ions are actively transported of the cells into the PCT cells into the blood in the capillaries
Due too the conc gradient sodium ions diffuse down the gradient from the lumen pf the PCT into the cells lining the PCT. This is an exampls of contransport as thr proteins which transport sodium ions also carry glucose
glucose can then diffuse frim the PCT epithilial cell into the bloodstream and therefore glucose is reabsorbed
In the loop of henle what is the ascending limb
wall are impermeable to water has much thicker walls and sodium ions are actively transported out
in the loop of henle what is descending limb
walla are permeable to water walls are much thinner
How to maintain a sodium ion gradient by the loop pf henle
1 Mitochondria in the walls of the cells provide energy to actively transport sodium ions out of the ascending limb of the loop of the henle
2 The accumulation of sodium ions outidde of the nephron in the medulla lowers the water potential
3Therefore the water diffuses out by osmosis into the interstital space and then the blood capillaries
4 At the base of the ascending limb some of the sodium ions will move out by diffusion
Reabsorption of water at the DCT and collecting duct
Due to all the sodim ions being actively transported out of the loop of henle when the filtrate reached the DCT it is very dilute
The filtrate moves into the DCT and collecting duct. This section of the medulla is very concentrated
Thereforee even more water diffuses out of the DCT and CD
What remains is transported to form urine
what is the nephron made up of ?
Renal Capsule
Proximal Convoluted tubule
loop of henle
Distal convoluted tubule
collecting ducts
what are nephrons surrounded by?
capillaries
Where is the glomerular filtrate created ?
renal capsule
What is absrobed into the blood by the proximal convoluted tubule
glucose and wated
Where does the reabsorption of water occur ?
Distal convoluted tubules and collecting duct