Physiology 2

Question 1

How much of the original filtrate is reabsorbed?

Answer 1

20% of plasma is filtered, 19% is reabsorbed.

Question 2

How much water, glucose, sodium and urea are reabsorbed?

Answer 2

100% glucose (usually)
99% water
99.5% Na
50% urea

Question 3

what is carrier mediated transport mechanism?

Answer 3

When some molecules need a carrier protein to transport them from the tubule lumen back into the intracellular fluid.

Question 4

What is the Tm value?

Answer 4

This is the maximum amount of a molecule that can be reabsorbed due to the transport carriers being at full capacity.

Question 5

What is the Tm value of glucose?

Answer 5

10mmoles/l.

Question 6

What is the normal plasma level of glucose?

Answer 6

5mmoles/l.

Question 7

Which molecules are reabsorbed using active transport?

Answer 7

Sodium - via sodium-potassium ATPase pump.

Question 8

How is sodium transported?

Answer 8

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.

Question 9

Which ion follows sodium to maintain the electrochemical gradient?

Answer 9

Chlorine (passive transport)

Question 10

What follows sodium and chlorine as they are reabsorbed?

Answer 10

Water (due to the oncotic effect)

Question 11

As water is reabsorbed, what happens to the other ions in the tubule lumen?

Answer 11

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.

Question 12

How does sodium increased glucose reabsorption?

Answer 12

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.

Question 13

does the kidneys control glucose reabsorption?

Answer 13

No this is controlled via hormones.

Question 14

Which ions is the kidney directly responsible for their reabsorption?

Answer 14

Sulphate and phosphate

Question 15

What happens to an excess of a substance if it has exceeded its Tm value?

Answer 15

it remains in the filtrate and is excreted into the urine.

Question 16

Why is only some urea reabsorbed?

Answer 16

The tubule membrane is only partly soluble to urea.

Question 17

which type of substances are secreted?

Answer 17

Substances which are protein bound and not filtered well.

Question 18

What is true about the Tm mediated secretion molecules?

Answer 18

They are unspecific so can be used to secrete lots of things - eg lactic acid and penicillin.

Question 19

What is hyperkalaemia?

Answer 19

> 5.5mmoles

this decreases resting membrane potential, less energy is needed to depolarise the cells.

Question 20

What is hypokalaemia?

Answer 20

<3.5mmHg

increases resting membrane potential, more energy is needed to depolarise the cells - cardiac arrhythmias.

Question 21

What effect does aldosterone have on potassium?

Answer 21

increased aldosterone causes an increased potassium secretion.