Control of Plasma Volume Flashcards
Explain how you would change plasma volume. (3)
Because you cannot add or remove water because this would change the osmolarity of the ECF, you have to change the [Na+]e and water will follow.
Describe where Na+ is absorbed in the kidney. (3)
Most (2/3) of Na+ is reabsorbed in the PCT, then another 1/4 in the in the aLoH. After this is a ‘region of choice’, so if more volume is needed, more reabsorption occurs.
Describe how the possible changes in excretion of sodium occur. (3)
Changes in the osmotic and hydrostatic pressure alter PCT reabsorption. PCT reabsorption stimulated by RAAS, DCT principle cells stimulated by aldosterone.
Explain how the kidney reacts to an increased renal artery blood pressure. (5)
Downregulation of the Na+/K+ ATPase and the Na+/H+ anti porter causes a reduction in Na+ reasborption and a reduction in H2O resorption in PCT. This causes pressure natiuresis (increased sodium excretion) and pressure diuresis (increased water excretion). This means the initial rise in BP is lessened.
Explain the difference between transcellular and paracellular reabsorption in the kidney. (2)
Paracellular moves a substance from the lumen to the capillary through the tight junctions that exist between the tubule cell.
Transcellular moves a substance from the lumen through the capillary by transporting it through the apical and then basolateral membranes of the cell.
Describe the distribution of aquaporin channels throughout the nephron. (4)
PCT and dLoH - AQP1 always present.
aLoH - no channels
CD - AQP2 on apical (dependant on ADH) and AQP3/4 on basolateral (always present).
Explain the driving forces behind reabsorption of the filtrate into the peri-tubular capillary. (4)
The high osmotic gradient in the interstitium from the action of ion channels encourages water to move from the lumen to the interstitium. This increases the hydrostatic pressure within the interstitium, forcing fluid into the Capillary. The oncotic pressure created by proteins within the capillary also helps to draw water in.
Explain the changes in the osmolarity of the filtrate within the nephron as it moves round the Loop of Henle. (6)
In the cortex, filtrate is isosmotic with plasma. As it moves down the descending limb, water moves out due to the increasing concentration of the medulla, meaning at the bottom of the loop, the filtrate and the interstitium are concentrated. At the bottom of the ascending limb, solutes begin to move out (passive diffusion) due to the high concentration gradient. At the top of the ascending limb, solutes are actively pumped out, and because this bit is impermeable to water, water cannot move back in. This means the filtrate returns to being isosmotic.
Describe the two different cell types in the collecting duct. (4)
Principle cells - similar to the DCT, with ENaC and ROMK on the apical membrane, and a Na+/K+ ATPase on the basolateral membrane.
Intercollated cells - active reabsorption of chlorine. Type A secrete H+ ions, Type B secrete HCO3- ions.
