kidney function Flashcards
what is left in the capillary following ultrafiltration and what happens to the water potential of the blood
-blood cells and proteins
-proteins mean there is a low water potential which will help in the reabsorption of water later on
where does selective reabsorption occur
in the proximal convoluted tubule
explain the process of selective reabsorption
- Active transport of sodium ions out of the PCT cells lining the tubule into the bloodstream via the sodium potassium pump
- concentration of sodium ions in the cell cytoplasm decreases-creating a concentration gradient
- Sodium ions diffuse into the PCT cells from the lumen of the tubule via co-transport protein- carrying glucose or amino acid
- water potential of PCT cells decreases so water moves into the cell from the lumen by osmosis
- glucose and amino acids diffuse into the blood stream (reabsorption) whilst the sodium ions diffuse via transport protein
how are the cells lining the proximal convoluted tubule specialised to achieve reabsorption
-microvilli= increase surface area for reabsorption
-co-transport proteins on membrane in contact with proximal tubule lumen
-mitochondria= provide ATP for active transport
-folding of membrane in contact with tissue fluid and blood capillaries
-sodium-potassium pumps
what must the kidney balance
-need to excrete and need to conserve water so produce small volume of highly concentrated urine
what kind of mechanism occurs in the loop of henle and what is the function of it in the loop of henle
counter current multiplier mechanism
-lowers the water potential in the medulla by increasing concentration of sodium chloride in the tissue fluid in the medulla = causes vigorous osmotic flow of water out of the collecting duct= results in urine that is hypertonic compared to blood
explain the loop of henle and the reabsorption of water
- ascending limb (ascends back out to the cortex pumps out sodium and chloride ions= increases conc of ions in tissue fluid surrounding tubule (salty medulla)
2.water moved out of descending limb by osmosis due to low water potential in the tissue fluid of medulla, water enters surrounding capillaries and tubule fluid becomes more concentrated
3.mineral ions leave ascending limb at the bottom due to diffusion because the tubule fluid from the descending limb is so concentrated and at the top active transport moves sodium and chloride ions out - as the ascending limb is permeable to water and actively pumps out sodium and chloride ions the fluid at the top of the ascending limb is dilute
- the ion movements ensure the water potential is higher in the ascending limb, it decreases the water potential of the tissue fluid in medulla, wp lowest at the bottoom of the loop of henle
what is the difference between in the descending and ascending limb
-descending limbs walls are permeable to water ascending is impermeable
which mammals will have longer loops of Henle, those living in watery or very dry environments
dry environments= longer loop conserves more water
describe the changes in the relative concentrations of certain substances as fluid passes along the nephron
1.glucose concentration decreases in PCT = actively transported out of tubule
2.sodium ions increase at start and decrease in loop of henle = the ions enter descending limb and leave leave ascending limb
3.urea concentration increases as water is removed from the tubule
4.sodium and potassium ion conc increases in collecting duct as water is absorbed from the tubule increasing relative conc
compare the components within plasma of glomerulus, glomerulus filtrate and urine
proteins= high in plasma, little/none in filtrate (any present are hormones) and urine
amino acids= same concentration in filtrate and plasma, none in urine
glucose = same in filtrate and plasma, none in urine
urea = very little in plasma and filtrate, high in urine due to absorption of water
mineral ions= higher, same in filtrate and plasma, little lower in urine
