Physiology 2 Flashcards
How much of the original filtrate is reabsorbed?
20% of plasma is filtered, 19% is reabsorbed.
How much water, glucose, sodium and urea are reabsorbed?
100% glucose (usually)
99% water
99.5% Na
50% urea
what is carrier mediated transport mechanism?
When some molecules need a carrier protein to transport them from the tubule lumen back into the intracellular fluid.
What is the Tm value?
This is the maximum amount of a molecule that can be reabsorbed due to the transport carriers being at full capacity.
What is the Tm value of glucose?
10mmoles/l.
What is the normal plasma level of glucose?
5mmoles/l.
Which molecules are reabsorbed using active transport?
Sodium - via sodium-potassium ATPase pump.
How is sodium transported?
Sodium - potassium ATPase pumps potassium into the cell and sodium out of the cell into the interstitial fluid.
this creates low sodium concentration inside the cell - so sodium from the tubule lumen can enter the cell moving down its concentration gradient - this sodium is then pumped out into the interstitial fluid back into the blood via Na-K-ATPase.
Which ion follows sodium to maintain the electrochemical gradient?
Chlorine (passive transport)
What follows sodium and chlorine as they are reabsorbed?
Water (due to the oncotic effect)
As water is reabsorbed, what happens to the other ions in the tubule lumen?
They become more concentrated - they are now more concentrated in the tubule lumen than in the cell, so they can move down their concentration gradient and be reabsorbed.
How does sodium increased glucose reabsorption?
Sodium-potassium-ATPase pumps sodium out of the cell. sodium then enters the cell from the tubule lumen side moving down its concentration gradient - using a sodium-glucose transporter. Glucose concentration is higher inside the cell but using the transporter it can still enter the cell. It then does down its concentration gradient and is reabsorbed into the blood.
does the kidneys control glucose reabsorption?
No this is controlled via hormones.
Which ions is the kidney directly responsible for their reabsorption?
Sulphate and phosphate
What happens to an excess of a substance if it has exceeded its Tm value?
it remains in the filtrate and is excreted into the urine.