BEFORE reabsportion, [Sodium] is (high, low) in the tubular lumen, (high, low) in intracellular fluid, and (high, low) in the interstitium.
1.) High (142 mEq/L)
2.) Low (14 mEq/L)
3.) High (139 mEq/L)
In the process of reabsorption, how does sodium in the tubule lumen enter the epithelial cells?
By diffusion using passive carriers and ion leak-channels.
In the process of reabsorption, how does sodium in the epithelial cells enter the interstitium?
By active transport with Na+/K+ pumps.
Once Na+ is pumped into the interstitium, is it hyper- or hypo- osmotic compared to the lumen/plasma?
1.) Hyper-osmotic
2.) Hyper-osmotic
Once pumped into the interstitium, how does Na+ enter the peritubular capillaries?
By passive diffusion.
True or False?
Starling forces cause solute movement.
False.
Starling forces cause fluid movement.
True or Fase?
A higher concentration of H2O, relative to another compartment, indicates a low osmolarity.
True.
A high concentration of water indicates a low concentration of solutes.
True or False?
The osmolarity of H2O is like the total omsolarity of all solutes.
True.
BEFORE reabsorption of sodium, total osmolarity of the tubule lumen is:
1.) >,<,= intracellular fluid
2.) >,<,= interstitium
3.) >,<,= plasma
1.) >
2.) >
3.) =
True or False?
BEFORE reabsorption of Na+, water diffuses passively into the tubule endothelial cells, the interstitium, and the PC's.
False.
Net movement is in the opposite direction (out of the interstitium and into the lumen or the peritubular capillaries).
What must first occur in order for water to diffuse passively out of the tubule lumen and ultimately into the interstitium?
Sodium reabsorption.
The resulting change in osmolarity creates a gradient for water to follow.
Once in the interstitium, what causes water to enter the peritubular capillaries?
A strong colloid osmotic pressure.
As water continues to enter down the length of the capillary, IIpc returns to normal.
True or False?
When water diffuses passively, it does so through transcellular and paracellular pathways.
True.
True or False?
Chloride diffuses passively by paracellular pathways only, in response to concentration gradients.
False.
It diffuses to maintain electroneutrality.
Concentrations of potassium are (high / low) in the tubule lumen, (high / low) within the cell, and (high / low) in the interstitium.
1.) Low
2.) High
3.) Low
How is K+ moved into the interstitium in order for it to be reabsorbed into the peritubular capillaries?
Since it cannot enter the cell due to the high cellular [K+], it diffuses passively to the interstium via paracellular pathways, due to a small concentration gradient.
What causes the small concentration gradient for K+ between the tubule lumen and the interstitium?
As water leaves the lumen to follow Na+, the concentration of lumenal K+ increases.
Is [glucose] higher in the tubule lumen or the cytoplasm of an endothelial cell?
The cytoplasm of an endothelial cell.
In the process of reabsoprtion, how does glucose cross the apical membrane of a tubule endothelial cell?
Na+/Glu sympoters (2' active) utilize a Na+ gradient to push glucose against its own gradient into the cell - no ATP is needed.
How does glucose cross the basolateral membrane of a tubule endothelial cell to enter the interstitium? The plasma?
[Glucose] is greater within the cell than the interstium, therefore it moves by diffusion.
Once in the ineterstitium, glucose follows water into the peritubular capillaries due to the high IIpc.
True or False?
Oral drugs must dissolve in the body's gastric juices in order to be absorbed.
True.
If a drug is lipid soluble, how do we modify it so it can be dissolved in our gastric juices?
We chemically modify them to exist as an organic acid or base.
Why must organic acids (drugs) be secreted rather than filtered?
Due to their charges, they could not pass through the glomerular capillaries.
Give some examples of organic acid drugs? Organic base drugs?
1.) Aspirin, PCN
2.) Histamine, Cimetidine
Where does the secretion of organic acids and bases take place in the nephron?
The proximal tubule.
How do organic acids and bases move from the interstitium into the tubular epithelial cell?
By active transport against their concentration gradient.
How do organic acids and bases move from the tubular epithelial cells into the tubule lumen?
By passive diffusion along a concentration gradient.
True or False?
There is an abundance of transporters for organic acids and bases on the basolateral membrane of tubular epithelial cells.
False.
A limited number of transporters leads to competition between various drugs.
