Flashcards in Specific Tubule Functions Along the Nephron Deck (43)
What does the proximal tubule mainly absorb?
It absorbs around 2/3 of the water, sodium, potassium and chloride ions. It also absorbs nearly all of the glucose and amino acids that are filtered.
What is the main mechanism for the proximal tubule absorption?
Na-K ATPase in the membrane as every substance has its reabsorption linked to this pump.
Describe sodium reabsorption in the first half of the proximal tubule.
Na uptake is coupled with either H+ or organic solutes using the Na-H+ anti porter
What does the Na-H+ anti porter secrete and reabsorb?
It secretes H+ and absorbs NaHCO3
What are the two mechanisms for Na reabsorption in the first half of the proximal tubule?
What type of transport occurs with Na in the first half of the proximal tubule?
How is the Na transported out of the basolateral membrane after its uptake via a Na-Glucose Symporter?
Passive Transport Mechanisms
How is Na transported out after its uptake with the Na-H+ Antiporter?
Uses the Na-K ATPase
How is Na reabsorption related to that of water?
It creates an osmotic gradient that provides the driving force for the passive reabsorption of water
Describe Na reabsorption in the second half of the proximal tubule.
It is reabsorbed coupled with Cl- in the second half primarily, rather than HCO3- or other solutes like it was in the first half of the tubule
What type of transport occurs with Na in the second half of the proximal tubule?
Both paracellular and transcellular
What is the mechanism for Na transport in the second half of the proximal tubule?
It is transported via the parallel operation of Na-H and Cl-Anion anti porters. Na is transported in and H+ and Cl is transported in and an anion is transported out.
How does Na leave the cell in the second half of the proximal tubule?
Na leaves via the Na-K ATPase
How does Cl leave the cell in the second half of the proximal tubule?
Cl leaves via a K-Cl symporter that transports both ions out from the cell
How is water reabsorption occurring in the proximal tubule?
It is a passive process that is driven by the osmotic gradient that is generated from the active solute reabsorption (mainly Na)
What is the meaning of isosmotic absorption?
It means that water reabsorption occurs in equal proportion with that of the reabsorbed solutes.
What type of transport occurs with water in the proximal tubule?
Both transcellular and paracellular
What is the importance of solvent drag in water reabsorption?
Solutes that are trapped in the water are also reabsorbed as a result and this is most important for K and Ca
How much of filtered protein is reabsorbed by the proximal tubule?
What happens to reabsorbed proteins that makes it different form other reabsorbed substances?
They are degraded into amino acids rather than taken up in their original forms.
What happens when the protein reabsorption process is saturated?
Proteinuria - that is protein begins to appear in the urine
What happens with organic ions in the proximal tubule?
The ones that are necessary are reabsorbed with the rest of them being actively secreted into the proximal tubule.
What is a possible danger of organics that share the same carrier?
The can elevate the plasma concentration of the other and lead to drug toxicity
What happens to urine with a low osmolality ratio ( <1.0 )?
Low [ADH] and urine is pale and dilute
What happens to urine with a high osmolality ratio ( >1.0 )?
High [ADH] and urine is dark and concentrated
What is absorbed in the thick ascending loop of Henle?
25% of Na and other solutes are absorbed, with no water absorbed as it is H2O impermeable
What is the main transporter in the loop of Henle?
What is absorbed in the thin descending loop of Henle?
H2O is absorbed passively and it is impermeable to ions like Na and Cl
What is absorbed in the thin ascending loop of Henle?
Na and Cl are reabsorbed and it is impermeable to H2O