L25 Proximal Tubular Function and Renal Clearance Flashcards
True or false: Molecules up to 70,000 daltons can be filtered in the glomerulus
True
Movement of useful substances from the tubule lumen into the blood is known as __?__
reabsorption
Movement of less useful substances from the blood into the tubule lumen is known as __?__
secretion
This process is selective, whereas filtration is non-selective
Secretion and reabsorption can be __1__cellular or __2__cellular
1) trans
2) para
Where does the majority of reabsorption take place?
Proximal convoluted tubule
What type of transporters are mainly involved in the process of reabsorption in the proximal convoluted tubule?
Sodium symporters and antiporters
These transporters require energy (ATP) - active transport
What does Tm symbolise?
Transport maximum (refers to maximum transport capacity of transporters)
True or false: H2O reabsorption in the proximal tubule is facultative
False
In the PCT, H2O is reabsorbed with solutes. This reabsorption is obligatory.
In the collecting duct, H2O is reabsorbed according to needs (i.e. facultative)
True or false: Na transporters in proximal tubule can achieve near 100% reabsorption of organic solutes (such as glucose, amino acids)
True
What proportion of bicarbonate can be reabsorbed by Na transporters in proximal tubule?
A) Near 100%
B) 80-90%
C) 65%
D) 50%
B) 80-90%
What proportion of chloride can be reabsorbed by Na transporters in proximal tubule?
A) Near 100%
B) 80-90%
C) 65%
D) 50%
D) 50%
What proportion of H2O can be reabsorbed by Na transporters in proximal tubule?
A) Near 100%
B) 80-90%
C) 65%
D) 50%
C) 65%
What proportion of sodium can be reabsorbed by Na transporters in proximal tubule?
A) Near 100%
B) 80-90%
C) 65%
D) 50%
C) 65%
What proportion of potassium can be reabsorbed by Na transporters in proximal tubule?
A) Near 100%
B) 80-90%
C) 65%
D) 50%
C) 65%
True or false: Sodium-potassium pumps are located on the apical surface of tubular cells
False
Na-K pumps are located basolaterally
True or false: The main function of the tubular cell Na-K pumps is to keep the intracellular levels of sodium high
False
Na-K pumps move Na out of the cell and K in
What is the sodium concentration in the:
- Tubule lumen
- Tubular cell
- Basal lamina
- 140mM
- <30mM
- 140mM
True or false: The same carrier protein that allows sodium to leave the tubule lumen also transports glucose into the tubular cell
True
Na and glucose use the same symporter when being reabsorbed
How is sodium bicarbonate reabsorbed from the tubule lumen?
- Filtered NaHCO3 dissociates into Na and HCO3
- The sodium enters the tubular cell using an antiporter, which throws out a H ion into the tubule lumen
- The H ion binds with HCO3 to form carbonic acid (H2CO3)
- The enzyme carbonic anhydrase splits H2CO3 into CO2 and H2O, which can easily diffuse into the cell
- Inside the cell, carbonic anhydrase reforms H2CO3, which then dissociates into H+ and HCO3-
- H+ is used again in to pump another sodium ion in, while the bicarbonate diffuses out of the cell and into the capillary
What is the clinical significance of para aminohippuric acid (PAH) as it relates to the kidneys?
PAH can be given to a patient via IV infusion and then their urine is tested to see how much has been filtered out.
It is a good indicator of renal blood flow because it is freely filtered in the glomerulus, and also secreted into the tubule but it isn’t reabsorbed. So, if kidneys have a good blood supply, there should be plenty of PAH in their urine.
What is this formula measuring:
(urine conc. x urine flow) / plasma conc.
Renal clearance
True or false: Inulin is a polysaccharide used to test GFR
True
Is inulin secreted into the tubule?
No
Is inulin reabsorbed?
No
What is the key benefit to using creatinine instead of inulin as a measure of GFR?
Creatinine is endogenous, therefore you don’t need to infuse it into the patient.
Inulin is not endogenous, therefore infusion is required
