Reabsorption and Secretion

Question 1

Where does reabsorption primarily occur?

Answer 1

Peritubular capillaries

Question 2

What are many substances reabsorbed by?

Answer 2

Carrier mediated transport systems

Question 3

Carriers have a maximum transport capacity, what happens if this is excedded?

Answer 3

Excess substrates go into urine

Question 4

Describe briefly how carrier mediated transporters allow for reabsorption.

Answer 4

There is a binding site for the transported solute and when it binds, there is conformational change.
The outer side closes, meaning the substrate is momentarily trapped in the membrane. The inner side opens, allowing the substrate to pass into the cell

Question 5

Carrier protein enable larger molecules to cross the membrane.
Give an example.

Answer 5

Glucose

Question 6

Renal threshold?

Answer 6

Plasma threshold at which saturation occurs

Question 7

If plasma glucose concentration is increased, what happens to reabsorption?

Answer 7

Reabsorbed until plasma threshold is reached and then rest is excreted in urine

Question 8

If there is glucose in the urine, what is this due to the failure of?

Answer 8

Insulin

->not the kidneys, do not regulate glucose levels

Question 9

There are some examples in which the kidneys do regulate the concentration in the plasma. Give some examples.

Answer 9

Sulphate and phosphate ions

Question 10

Which type of ion is the most abundant in the ECF?

Answer 10

Sodium ions

Question 11

Where does the majority of sodium reabsorption take place?

Answer 11

Proximal tubule

Question 12

What % of sodium is reabsorped?

Answer 12

99.5%

Question 13

Through which mechanism is sodium reabsorbed?

Answer 13

Active transport

Question 14

What allows the uptake of sodium into the cell?

Answer 14

The sodium-potassium pump, sodium leaving the cell and potassium entering establishes a gradient for sodium. Low sodium in cells facilitates the uptake of sodium

Question 15

Reabsorption of which ion is key to the reabsorption of other filtrate components?

Answer 15

Sodium

Question 16

How does water get into the cell through the lipid membrane if it isn’t lipid soluble?

Answer 16

Through aquaporins

Question 17

What is the normal counter ion for sodium?

Answer 17

Chloride

Question 18

How do chloride ions get into the cell?

Answer 18

Diffuse passively down the electrical gradient established and maintained by the active transport of sodium.

Question 19

What happens as a result of the active transport of sodium followed by the chloride ions?

Answer 19

An osmotic force is created which draws out water from the tubules

->by water being taken out, this concentrates the substances left in the tubule creating outgoing concentration gradients

Question 20

What does the rate of reabsorption of non-actively reabsorbed solutes depend on?

Answer 20

-Amount of water removed, as determines extent of concentration gradient
-Permeability of the membrane to the particular solute

Question 21

Is the tubule membrane permeable to urea?

Answer 21

Moderately- only 50% is reabsorbed and the rest stays in the tubule

Question 22

Name some substances in which the tubular membrane is impermeable.

Answer 22

Inulin and mannitol

Question 23

Active transport of which ion establishes the gradients in which other ions, water and solutes can pass passively?

Answer 23

Sodium

Question 24

Anything that decreases active transport has what effect on renal function?

Answer 24

Disrupts renal function

Question 25

What is tubular secretion?

Answer 25

Secretory mechanism used to transport substances from the peritubular capillaries into the tubule lumen and therefore provide a second route into the tubule

Question 26

Why is tubule secretion important?

Answer 26

Potentially harmful substances can be removed more quickly
Important for protein-bound substances

Question 27

What level of potassium could lead to hyperkalaemia?

Answer 27

> 5.5mmoles/L

-> 4mmoles/L is normal

Question 28

What level of potassium could lead to hypokalaemia?

Answer 28

<3.5,,oles/L

Question 29

What happens as a result of hyperkalaemia?

Answer 29

Decrease in resting membrane potentials, ventricular fibrillation and death

Question 30

What happens as a result of hypokalaemia?

Answer 30

Increase in resting membrane potential, cardiac arrhythmias and death

->therefore, potassium balance is essential for life

Question 31

RECAP- what part of the kidney does the filtering?

Answer 31

Glomerulus

Question 32

What hormone has a role in the regulation of potassium secretion?

Answer 32

Aldosterone

Question 33

RECAP- where is aldosterone released from?

Answer 33

Zona glomerulosa of the adrenal cortex