HRR: renal tubule I and II Flashcards
What are the two big methods of transport across the tubule?
Transcellularly or paracellularly
What allows passive transport to be possible in the tubule?
Concentration gradient established by the sodium potassium pump
Describe the importance of the sodium potassium pump in the tubule.
It transports sodium from the interior of the cell through the basolateral membrane, creating negative intracellular potential that creates a favorable gradient for sodium entry for reabsorption.
What helps create different permeabilities to water in different parts of the tubule?
The presence/structure of the tight junctions and aquaporins in a given area.
Where is most solute reabsorption happening?
The proximal tubule
What is the segment of the tubule controlled by hormones?
The collecting duct
What are the main solutes reabsorbed in the proximal tubule?
Sodium, chloride, bicarb, phosphate, glucose
What is secreted by the proximal tubule?
Acids, bases, and hydrogen ions into the tubular lumen
Proximal tubule reabsorption is ___tonic with plasma.
Isotonic
What provides energy for reclamation in the proximal tubule?
The electrochemical gradient from the sodium potassium pump
What is solvent drag?
Passive paracellular reabsorption of solute and water due to leaky tight junctions of the proximal tubule. It results from a greater tonicity in the interstitial fluid compared to luminal fluid.
How is bicarb reabsorbed in the proximal tubule?
The sodium-proton exchanger
Describe the sodium-proton exchanger in relation to movement of bicarb.
- Filtrate enters the proximal tubule.
- Sodium-proton exchanger on the apical membrane brings sodium into the cell and puts proton into the lumen of the tubule.
- Proton in the tubule combines with bicarb to form carbonic acid, which converts to CO2 and water.
- CO2 diffuses into the epithelial cell, where it recombines with water to form carbonic acid.
- Carbonic acid dissociates into bicarb and a proton.
- Proton is exchanged for sodium via NHE3, and the bicarb is transported into the interstitial space.
How can declining kidney function lead to drug toxicity?
Usually, the kidneys secrete drugs and toxins through the tubular cells and into the lumen to clear them from the blood. When kidney function declines, they can’t clear these substances which can lead to toxicity.
Where does a lot of phosphate get reabsorbed?
The proximal tubule
Where is glucose reabsorbed?
The proximal tubule via SGLT
How much glucose should be in the urine?
Usually none, unless SGLT is saturated via issues with the transporter.
What is the thin descending limb of the loop of Henle permeable to?
Highly permeable to water, not super permeable to solute.
What happens to the concentration of urine as it travels down the thin descending limb?
It becomes more concentrated due to water moving out.
What is the thick ascending limb permeable to?
Salt and chlorine, but not water.
Where is there no reabsorption of water?
The thick ascending limb of the loop of Henle.
What is significant about the reabsorption of salt in the thick ascending limb of the loop of Henle?
It contributes to generating the hypertonic medullary interstitium, which is a pulling force for water later on!
What is the main drive for reabsorption of NaCl in the thick ascending limb?
The Na/K/Cl transporter (NKCC2)
Describe the role of potassium in the thick ascending limb of the loop of Henle.
Potassium becomes high in the cells and leaks back into the tubule via ROMK. This creates a positive charge in the lumen that drives paracellular reclamation of cations like calcium and magnesium.
