Exam 3 Lecture: Tubular Reabsorption Flashcards
What does the ultrafiltrate contain?
contains stuff the kidney wants to expel in the urine but also important stuff that it needs to retain and to return to the blood stream
What is reabsorption defined as?
the movement of desired solutes from the lumen of the nephron back to the blood
How can a molecule move from the lumen fluid into the blood?
either through the epithelial cells or between the epithelial cells
What is the key molecule for reabsorption?
NaKATPase
Where is the Na K ATPase pump located?
in the basolateral membrane
Why is NaKATPase important?
3 Na move out, 2 K moves in creating a low intracellular concentration that creates an electrochemical gradient that was not otherwise there
What is reabsorbed in the proximal tubule?
67% of H2O, Na, and solutes
99% of glucose and AA
90% of Bicarb
What mechanisms are involved in reabsorption of Na and other solutes in the 1st 1/2 of the proximal tubule?
NaH antiporter, and Na symporters all on the luminal membrane
How does the NaH antiporter work in the proximal tubule?
The Na moves into the cell due to the Na electrochemical gradient and H moves into the tubular fluid
How do Na symporters work in the proximal tubule?
Na, glucose, and AA move via facilitated diffusion into the cell from the tubular fluid
How is water reabsorbed in the proximal tubule?
The Na, AA, and glucose that enters the cell creates an osmotic gradient that brings H2O into the cell
What are the reabsorption mechanisms in the second 1/2 of the proximal tubule?
Na H antiporter, Cl- anion antiporter, paracellular movement all on the luminal membrane
What is reabsorbed paracellularly in the second half of the proximal tubule?
Chlorine and sodium, because the gaps are leaky
How is reabsorbed Cl removed?
a K Cl symporter at the basolateral membrane
What allows the Na and Cl reabsorption mechanisms to work?
the constant circulating of H and anions in and out of the epithelium
How are proteins reabsorbed in the proximal tubule?
proteins are partially degraded by enzymes in the luminal membrane and reabsorbed by endocytosis, then degraded further into amino acids and leave via the basolateral membrane
What is reabsorbed in the descending limb of the loop of Henle?
15% of the filtered water
What is reabsorbed in the ascending limb of the loop of henle?
25% of filtered NaCl
What are the reabsorption methods of the initial part of the distal tubule?
NaH antiporter, NKCC2, paracellular reabsorption - all on the luminal membrane
How does the Na H antiporter work in the early part of the distal tubule?
Na enters the cell via facilitated diffusion
Why can water not enter the cell when ADH is not present in the early part of the distal tubule?
because the tight junctions are too tight and water cannot follow Na into the cell
What enters the cell via the NKCC2 transporter in the early part of the distal tubule?
Na, K, and 2 Cl
What is absorbed paracellularly in the early part of the distal tubule?
Na, K, Ca
What are the reabsorptive methods in the later part of the distal tubule?
NaCl symporter on the luminal membrane; Na and Cl enters the cell
What inhibits the NaCl symporter?
thiazide diuretics inhibit it
What are the reabsorptive methods of the principle cells in the collecting duct?
Amiloride sensitive Na channels, paracellular
How does K leave the collecting ducts?
via K channels on both the laminal and basolateral membrane
What enters the cell paracellularly in the principle cells of the collecting ducts?
Cl
How does Na enter into the principle cells of the collecting ducts?
Na enters via amiloride sensitive Na channels
Where is Na K ATPase the principle molecule for reabsorption in the nephron?
Proximal and distal tubules and the collecting ducts
