Electrolyte And Fluid Balance

Question 1

What is the main pathology caused by kidney problems?

Answer 1

Oedema

Question 2

What is the normal total intracellular fluid volume, and it’s most abundant ion?

Answer 2

25 litres and contains a lot of potassium

Question 3

What is the normal volume of the interstium and what is its most common ion?

Answer 3

12 litres

Sodium and chloride

Question 4

What is the normal volume of the plasma and what is its most common ion?

Answer 4

3 litres

Sodium and chloride

Question 5

Which two ways can the kidney control fluid and electrolytes?

Answer 5

Tubular reabsorption - active and passive

Tubular secretion - minimal

Question 6

What is the difference between osmolarity and osmolality?

Answer 6

Osmolarity is osmole per unit volume

Osmolality is osmole per unit mass - temperature independent

Question 7

6 functions of the kidneys?

Answer 7

Acid-base balance
Blood pressure regulation
EPO and vitamin D production 
Excretion of waste
Control of electrolytes and fluid balance 
Drug metabolism and excretion

Question 8

What transport occurs across the apical membrane of the proximal tubule cell?

Answer 8

Sodium hydrogen antiporter - the most important one
Sodium phosphate symporter
Sodium sulphate symporter
Sodium cotransport with glucose, amino acids, vitamins

Question 9

What is found in numerous quantities on the apical membrane of the PCT cells?

Answer 9

Microvilli, covered in aquaporins

Question 10

What covers the basolateral membrane of the PCT cells?

Answer 10

Infoldings covered in ATOase pumps

Question 11

Summarise the action of a PCT cells.

Answer 11

The ATPase pumps on the basolateral side increase the concentration gradient, so sodium enters the cell via an exchange with hydrogen. The numerous aquaporins on the apical surface allow water to flow after it.

Question 12

What are the loop rules of the countercurrent exchange multiplier?

Answer 12

1) thick ascending limb is impermeable to water, but active,y transports out sodium, potassium and chloride
2) thick ascending limb provides the concentration gradient to allow water reabsorption from the TDLH
3) thin descending limb is permeable to water and salt
4) vasa recto doesn’t wash away the concentration gradient

Question 13

How is sodium removed from the thick ascending limb?

Answer 13

NKCC2

• the sodium is transported out via the ATPase pump
• the chloride leaves via an ion channel
• the potassium is returned back to the lumen via ROMK
• magnesium and calcium travel paracellularly, following the gradient

Question 14

How does sodium get removed from the lumen in the DCT?

Answer 14

NCC pump
- one sodium and two chlorides are cotransported into the cell
Calcium is also being removed at this point

Question 15

What is the method of sodium excretion in the collecting duct?

Answer 15

ENaC channels
- sodium taken into the cells
At the same time potassium is being excreted in an ion pump

Question 16

How does ADH act?

Answer 16

• Binds to the V2 receptor on the principle cells of the CCD
• this activates cAMP
• cAMP stimulates vesicles containing aquaporin II to travel to the apical surface of the cell
• water is taken into the cell and released through the always present aquaporin I

Question 17

What is the action of aldosterone?

Answer 17

Inserts ENaC transporters into the apical membrane, to increase sodium absorption and blood pressure
It also stimulates the ROMK channels on the same cell to secrete more potassium

Question 18

What are the diuretics that affect the PCT, NKCC2, NCC and ENaC channels respectively?

Answer 18

PCT = acetazolamide
NKCC2 = loop
NCC = thiazides 
ENaC = K-sparing

Question 19

What produces urea?

Answer 19

Amino acid metabolism by the liver

Question 20

Adding one litre of fluid a person, will do what to the different body compartments?

Answer 20

The water will distribute equally across all of them and the concentration will therefore decrease in all of them

Question 21

What will happen to the different water compartments if you give someone a lot of sodium?

Answer 21

Sodium will only enter into the interstitial and intravascular compartments.

• this means the water in the body will redistribute to ensure the concentration doesn’t change too much
• volume of the IT and IV compartments will increase, while IC decreases
• concentration will increase slightly across all compartments

Question 22

What will happen to the different water compartments if you give someone a lot of sodium and water?

Answer 22

Because sodium will only stay in the IV and IT compartments, they will increase in size as the water enters them as well to keep the concentration level.
The IC compartment will remain unaffected because the isotonic solution means the concentration doesn’t change, and water doesn’t need to be redistributed

Question 23

What are the three basic processes of the nephron?

Answer 23

Glomerular filtration
Tubular reabsorption
Tubular secretion

Question 24

What is the glomeruluar filtration barrier composed of?

Answer 24

Endothelial cells of the capillary
Glomerular basement membrane
Podocytes

Question 25

What does the macula dense do when it senses increased tubular flow?

Answer 25

Secretes adenosine, causing the afferent arteriolar to constrict.
This causes a decrease in pressure in the bowmans capsule and the blood it filtered more slowly

Question 26

What does the macula densa do when it senses a decreased tubular flow?

Answer 26

In stimulates the granular cells of the JGA to secrete renin, because it means there is a circulatory failure
This leads to angiotensin II and aldosterone production, promoting vasoconstriction and increased sodium reabsorption. This will raise the blood pressure and hopefully tubular flow rate
Vasoconstric of the efferent arterial pressure in the bowmans capsule, and water should flow faster into the kidney