Specific Tubule Functions Along the Nephron Flashcards
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?
- Na-H Antiporter
- Na-Glucose Symporter
What type of transport occurs with Na in the first half of the proximal tubule?
Transcellular
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?
100% ideally
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?
Na-K ATPase
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
What is the transporter into the cell for the thick ascending loop of Henle?
1 Na - 2 Cl - 1 K Symporter
What transports Na out of the cell in the thick ascending loop of Henle?
Na-K ATPase
What transports K and Cl out of the cell in the thick ascending loop of Henle?
K - Cl Symporter
What is reabsorbed in the distal tubule?
Remaining 8% of Na in the urine
How much of Na is reabsorbed by the time it reaches the distal tubule?
99.9%
What is the role of principal cells?
Absorbs NaCl and secretes K+
What is the role of intercalated cells?
Secrete H+ and HCO3-
What happens with a decrease in the extracellular fluid volume in regards to the RAA system?
The Renin-Angiotensin-Aldosterone system is activated and angiotensin-II is increased leading to increased reabsorption of Na/Cl/H2O in the proximal tubule.
What happens with an increase in the extracellular fluid volume in regards to atrial natriuretic peptide?
It will lead to atrial stretch which increases atrial natriuretic peptide and leads to increased natriuresis and the decrease in total peripheral resistance and decreased reabsorption of Na/Cl in the proximal tubule. There is a decrease in ADH.
What happens with a decrease in the extracellular fluid volume in regards to sympathetics?
Sympathetic activity will increase and release NE and E leading to increased reabsorption of Na/Cl in the proximal tubule.
What happens with an increase in the ECFV in regards to dopamine?
It will increase dopaminergic activity and lead to the decreased reabsorption of Na/Cl in the proximal tubule.
What is the effect of ADH?
With a decrease in the ECFV, ADH will increase and lead to increased H2O reabsorption in the collecting duct with little effect on the Na and Cl excretion.
What is glomerulotubular balance?
Despite variations in GFR it is the fact that a constant fraction of Na and H2O are still reabsorbed from the proximal tubule.
How does increased GFR affect reabsorption?
It will increase the amount of H2O and Na reabsorbed
