* L05-Renal Tubular function 1 Flashcards
How does Na+ concentration change along the proximal tubule?
It remains constant as any sodium that leaves the tubule is in proportion to the amount of water leaving so it remains the same concentration
How much water is reabsorbed by the end of the tubule?
70%
How is sodium reabsorbed in the proximal tubule?
It moves down its electrochemical gradient into the epithelial cells on the apical membrane and then the ATPase pump is used to move the sodium across the basolateral membrane.
This drives the movement of other substances.
How is water reabsorbed in the proximal tubule?
It is driven by the sodium movement and the movement of other ions. It either moves paracellularly (Through tight junctions and lateral intracellular spaces) or transcellularly through the aquaporin 1 channels.
What are the two types of nephrons and the proportions in which they exist?
Cortical (85%) - Short loops of henle with glomeruli in the outer two-thirds of the cortex
Juxtamedullary (15%) - long loops of henle that extend into the medulla with glomeruli in the inner third of the cortex.
How does the concentration of inulin change along the proximal tubule?
It increases as it is not absorbed. This means as water leaves the tubule the concentration of insulin will increase.
How does the concentration of urea change along the proximal tubule?
It increases as it is weakly absorbed. This means that as water leaves the tubule the urea concentration increases.
How does the concentration of chlorine change along the tubule?
It increases as it is weakly absorbed. This means as water leaves the tubule the concentration of chlorine will increase.
How do the concentrations of sodium and potassium change along the tubules?
They remain the same as they leave the tubule in proportion to water.
How does the concentration of bicarbonate ions change along the tubule?
It decreases as it is strongly absorbed. This means that it is absorbed faster than water so the HCO3- remaining in the tubule becomes more dilute.
How do the concentrations of amino acids and glucose change along the tubule?
They decrease as the are strongly absorbed. This means that they are absorbed faster than water so become more dilute in the tubule.
How is sodium reabsorbed?
The Na/K ATPase on the basolateral membrane actively transports sodium out of the cells causing an electrochemical gradient to be set up. This causes sodium to move in by the Na/H exchanger on the apical membrane. This is secondary active transport.
How is bicarbonate reabsorbed in the proximal tubule?
H+ and Hco3- combine to form h2co3. Carbonic anhydrase which is in the brush border of the epithelial cells converts the h2co3 to H2O and CO2. The small uncharged co2 can easily move into the cell and recombine with h2o under the action of carbonic anhydrase to reform h+ and Hco3-. hco3- is cotransported with na out of the basolateral membrane.
How is chlorine- reabsorbed in the proximal tubule?
It is secondary actively transported as an antiporter against HCOO-. HCOO- reacts with H+ to form formic acid, as this is uncharged it can easily pass into the cell and dissociate into its ions. The HCOO- can then antiport with Cl- and H+ is recycled out of the cell by Na+ antiporting.
Also have passive paracellular transport of Cl- due to it increasing in concentration along the tubule.
How is glucose reabsorbed along the proximal tubule?
90% of the glucose is transported by the SGLT2 cotransporter on the apical membrane and 10% on the SGLT1 cotransporter. They both cotransport with sodium. SGLT2 is in the earlier part and only requires 1 Na+ whereas SGLT1 is in the later part where glucose is less concentrated and requires 2 Na+.
On the basolateral membrane either GLUT1 or GLUT2 transports it out.
