Function of the nephron Flashcards
What is filtered in the renal corpuscle?
Everything except for proteins
What occurs in the proximal tubule
Reabsorption of all of the glucose, and 2/3of all other solutes
What occurs in the loop of henle
Further reabsorption of remaining solutes and reabsorption of water
What force governs the movement of water and solutes between the plasma and ISF in the capillary tuft
Starlings forces- hydrostatic pressure and oncotic pressure
What percentage of plasma volume is filtered through glomerular capillaries
20%
What is the typical GFR
125mL per minute
What is the primary regulatory mechanism for controlling GFR
Changing the hydrostatic pressure through vasodilation or vasoconstriction of the afferent/efferent arterioles.
Describe the effect of the renin angiotensin system on GFR
Macula Densa cells detect a decrease in NaCl which is a proxy for flow. Stimulate the JG cells to release renin which stimulates the RAAS whereby the penultimate step is the production of angiotensin II which causes moderate constriction of the efferent arteriole increasing back pressure and thus increasing GFR.
Describe the effects of aldosterone
Aldosterone is released from the adrenal cortex in response to high circulating levels of Angiotensin II, also high potassium levels. It acts on the distal tubule to up regulate ENaC channels which increase reabsorption of Na+ and secretion of K+. This increases water retention and thus increases blood volume.
What effect does atrial and brain natriuretic peptide hormone have on GFR and what is it’s release stimulated by?
Dilates the afferent arteriole increasing GFR also increases Na+ loss in the distal convoluted tubule.
Released when heart muscle stretched- increased volume
Describe the tubuloglomerular feedback mechanism
Macular Densa cells in the distal tubule monitor NaCl levels. If they are high the MD cells release paracrine signals that cause the afferent arteriole to constrict. This reduces GFR
What are the consequences of too high or too low GFR
Too high- wash out of the salt gradient.
Too low- kidney hypoxia.
What are the transport mechanisms in the proximal tubule
Primary active transport. Na+ gradient established via Na+ K+ ATPase pumps. Solutes reabsorbed via Na+ coupled transporters. Water follows Na+ via leaky paracellular pathways
Describe how HCO3- is reabsorbed
In the lumen of the tubule HCO3- combines with a H+ to form carbonic acid. Then carbonic anhydrase (secreted by tubule cell) converts it to H2O and CO2 which freely diffuses into the cell where CA again converts it back into carbonic acid which dissociates in HCO3- and h+ The HCO3- can freely move across the basal membrane via a channel.
Describe another mechanism for HCO3- production by the proximal tubule cells
The metabolise glutamine (aa) into ammonium ion and bicarbonate.
