selective reabsorption Flashcards
where does selective reabsorption take place
the proximal convoluted tubule
what is the purpose of selective reabsorption
the re-absorption of all glucose and amino acids, most of the water and ions from the filtrate back into the blood
what direction does the filtrate move when being reabsorbed
from the lumen of the PCT, through the cuboidal cells and into the capillaries
how are the PCT’s cuboidal cells adapted for selective reabsorption
1) micro villi which increases the surface area for materials
2) close association with the capillaries decreasing the diffusion pathway
3) tight junctions between cells- multiprotein complexes surround the cell attaching it tightly to the adjacent one as well as preventing molecules diffusing between cells or back into glomerular filtrate
4) many mitochondria allowing increased ATP synthesis for active transport
state how glucose is transported from the glomerular filtrate into the capillaries
co-transport with sodium ions via facilitated diffusion
outline process of the co-transportation of glucose
1) sodium-potassium pumps actively transport sodium ions out of the cell and potassium ions into the cell
2) this creates a higher concentration of Na+ ions in the filtrate than in the cell so Na+ moves into the cell via facilitated diffusion
3) the protein only allows the entry of a Na+ ion if coupled with a glucose
4) Na+ and glucose diffuse through the membrane into the cell
5) glucose diffuses through the cell where a channel protein allows it to pass into the blood, down the conc gradient via facilitated diffusion
outline how most the water is reabsorbed into the blood during selective reabsorption
water molecules move freely from the filtrate into the blood via osmosis as when glucose and amino acid concentrations decrease water potential increases
- 90% of the water is reabsorbed
outline how urea is absorbed into the blood
50% is reabsorbed into the blood by diffusion as there are higher concs in the filtrate that the blood
