why is selective reabsorption called that
only certain substances are reabsorbed
where does the selective reabsorption of glucose occur
in the proximal convoluted tubule
describe the lining of the proximal convoluted tubule
composed of a single layer of adapted epithelial cells
what are the adaptations of the epithelial cells of the proximal convoluted tubule
microvilli
co-transporter proteins
high number of mitochondria
tightly packed cells
what substances are reabsorbed at the loop of henle and collecting duct
water and salts
how microvilli aid reabsorption
many microvilli increase the surface area of the luminal membrane
how co-transporter proteins aid reabsorption
many co-transporters on the luminal membrane each transport a specific solute across the membrane
how mitochondria aid reabsorption
many mitochondria provide energy for sodium-potassium pump proteins in the basal membranes of the cells
how closely packed cells aid reabsorption
means that no fluid can pass between the cells and forced to pass through cells
STEP 1 (occurrence): stalker much
blood capillaries are located vey close to the outer surface of the proximal convoluted tubule
what are the components of the blood in the capillaries near the proximal convoluted tubule
very little plasma
lost much of water, inorganic ions, and other small solutes
STEP 2 (occurrence); inches away
the basal membranes of the PCT epithelial cells are the sections of the CSM that are closest to the blood capillaries
STEP 3 (occurrence); the pumps
Sodium-potassium pumps in the basal membranes move sodium ions out of the epithelial cells and into the blood where they are carried away
STEP 4( occurrence); effect of the pumps
lowers the concentration of sodium ions inside the epithelial cells causing sodium ions in the filtrate to diffuse down their concentration gradient through the luminal membranes of the same cells
STEP 5 ; luminal helpers
sodium ions do not diffuse freely through the luminal membranes so must pass through co-transporter proteins in the membrane
how does a co-transporter work
transports a sodium ion and another solute from the filtrate
STEP 6; safe passage through
once inside the epithelial cells these solutes diffuse down their concentration gradients passing through transport proteins in the basal membranes into the blood
what molecules should NOT be present in the urine
glucose, amino acids, vitamins, inorganic ions
how water reabsorption occurs
due to the movement of solutes into the blood from the filtrate increases the water potential of the filtrate and decreases that of the blood creating water potential gradient causing water to move into the blood by osmosis
why is a significant amount of urea absorbed back into the blood
the concentration of urea is high in the filtrate than that of the blood which causes urea diffuse from the filtrate into the blood
true or false
co-transporter proteins use energy
false, passive process
location of co-transporter proteins in the epithelial cell
luminal membrane and basal membrane
location of sodium/potassium pumps in the epithelial cell
basal membrane
where is water reabsorbed
in the proximal convoluted tubule, loop of henle, collecting duct
where are salts reabsorbed and by what process
in the loop of henle by diffusion
reabsorption of salts causes
reabsorption of water
true or false
water reabsorption in the collecting duct is variable
true , depends on how much water the body needs
what is indirect/secondary transport in the reabsorption process
sodium ions moving passively down the gradient the the co transporter protein provides energy to reabsorb the solutes