Kidneys Flashcards
(46 cards)
What are the adaptations of the PTC to carry filtrate away from the Bowmans Capsule?
- Close association with Capillaries (capillaries around the PCT reabsorb all glucose, AA, some urea, most water and Na+/Cl-
- cubodial epithelial cells in its walls. Microvilli facing lumen increase SA.
- PCT is the longest and widest part of the nephron, it has a large SA because it is long and there are millions of nephrons in the kidney
- many mitochondria to provide ATP for active transport
- tight junctions (protein complexes attaching cells to their neighbours) between cells of the PCT and epithelium. They prevent molecules diffusing between adjacent cells or back into the glomerular filtrate.
How are all relevant components reabsorbed from the PCT into blood?
- salts- some passive reabsorption but mainly AT
- Water= passively by osmosis. As ions are absorbed the WP of the blood decreases
- 50% of urea and small proteins by diffusion (as water is lost from the filtrate there is a high concentration there)
- glucose and AA are reabsorbed by co-transport by Na+ ions (see page 127 for specifics on this)
Where is the PCT?
Bowmans capsule to the loop of henle
What does the blood in the capillaries surrounding the PCT reabsorb?
all glucose and amino acids, some urea, most of the water and some of the sodium and chloride ions.
What is the problem with relying on co-transport for glucose reabsorption? When may this occur?
Problem: if glucose concentration is high there may be too few transport molecules in the membrane of the PCT to absorb it all so it will be lost in urine.
This may happen if:
- the pancreas secretes too little insulin
- the response of liver cells to insulin is reduced because insulin receptors in surface membranes are damaged
What are the components of filtrate in the bowmans capsule?
Water, glucose, salts, urea, amino acids
What are the layers of the bowmans space (space separating glomerulus and bowmans capsule)?
- endothlium cells of the capillary walls
- basement membrane (extracellular layer of proteins and collagen), it is the selective barrier
- Wall of bowmans capsule is made of squamos epithelial cells called podocytes, each has pedicels (like arms) that wrap around a capillary pulling the podocyte closer to the basement membrane.
What are the vasa recta?
capillaries surrounding the loop of henle
Where are the afferent and efferent arterioles?
- Afferent- into the Bowmans capsule
- efferent- out of the bowmans capsule
Is the ascending limb of the loop of henle permeable to water?
No
Is the descending limb permeable to water?
Yes
What happens in the ascending limb?
sodium and chloride ions are actively transported out of the filtrate into tissue fluid in the medulla.
Filtrate becomes progressively more dilute as it looses ions
A longer loops of Henle means more ions are transported into medulla, therefore lower wp
What happens in the descending limb?
water diffuses out into the tissue fluid (which has a low wp) then into the vasa recta (capillaries surrounding the loop of Henle)
Sodium and chloride ions diffuse into the descending limb
As filtrate flows down the descending limb it contains less water and more ions so the filtrate is most concentrated at the hairpin
Order of travel through the kindney
Glomerulus, Bowmans capsule, PCT, descending limb, ascending limb, distal convoluted tubule, collecting duct
What is the counter current multiplier?
two limbs of the loop of henle flow in opposite directions (counter current) and the concentration of salts is increased (multiplied)
What is the advantage of the collecting duct running back down into the medulla?
It passes back through the region of low water potential, therefore water diffuses back out of the colllecting duct by osmosis. The longer the loop of Henle, the lower the water potential in the medulla and the more water leaves the collecting duct by osmosis. The water is then reabsorbed into the vasa recta.
Where is ADH released from?
Hypothalamus uses osmoreceptors to monitor the solute potential of the blood. This a coordinator as it signals to the PITUITARY GLAND (effector) to release ADH
(hypothalamus is the coordinator and the recptor)
How does ADH get into the blood stream?
reduced wp is detected by osmoreceptors in the hypothalamus.
Secretory granules carry ADH along axons from the hypothalamus to the posterior lobe of the pituitary gland where ADH is secreted into the blood stream
What are aquaporins and where are they found?
they are intrinsic membrane proteins through which water moves. Particularly found within the walls of the distal convoluted tubule and the collecting duct
What is the ADH mechanism?
- ADH binds to membrane receptors (in the walls of DCT and collecting duct)
- Adenyl cyclase catalyses the production of cyclic AMP, the second messenger
- Cytoplasmic vesicles containing aquaporins move to fuse with the cell membrane
- aquaporins are incoporated into the cell membrane
- water molecules move down the wp gradient
- when intracellular AMP levels fall the aquaporins are removed from the cell membrane they accumulate again in vesicles
Explain how the loop of Henle maintains the gradient of ions which allows water to be reabsorbed from the filtrate in the collecting duct?
Na+ ions pumped out of the ascending limb
water passes out of descending limb (into high concentration in tissue fluid)
some sodium ions re-enter descending limb (by diffusion)
high concentration at the base of loop (of ions)
some ions diffuse out near the base increasing concentration outside the loop
What are the common causes of Kidney failure?
- Type two diabetes- high glucose conc in plasma results in glomeruli loosing protein into filtrate
- High blood pressure - damages capillaries of the glomerulus preventing ultrafiltration
- Autoimmune disease- body makes antibodies against its own tissues
- infection
- crushing injuries e.g RTA
If both Kidneys are damaged, regulation of solute concentration and volume of bodily fluids is required? How might you do this?
- reduce intake of protein to reduce urea formation
- reduce intake of calcium and potassium ions
- Drugs to reduce blood pressure. e.g. calcium channel blockers dilate blood vessles, Beta blockers reduce effect of adrenaline (adrenaline makes your heart beat faster), Angiotensin-converting enzyme (ACE) inhibitors reduce the effect of angiotensin (the hormone that constricts blood vessles)
Why might you need to reduce intake of potassium and calcium ions if your kidneys are damaged?
Concentration of both is usually maintained by absorption in SI and selective reabsorption at nephron.
- High potassium concentration in the blood leads to arrhythmias (treated with a combination of glucose and insulin)
- High calcium in the blood is correlated with increased risk of heart disease, kidney stones and osteoporosis. Treated with Bisphosphonates (causes calcium to accumulate in bone therefore less circulates in blood)
