Lecture 22 - Renal physiology: salt and water

Question 1

What is the normal plasma (blood) osmolarity?

Answer 1

285-295mOsm/L.

Question 2

Define hyperosmolarity?

Answer 2

Too many positive ions in the blood.

Question 3

Define hypoosomolarity?

Answer 3

Not enough ions in the blood.

Question 4

Define hypertonic?

Answer 4

The cells don’t have enough water as there are too many positive ions in the cell. Cells shrink.

Question 5

Define hypotonic?

Answer 5

The cells have too much water as there could be not enough positive ions in the cell. Cells swell.

Question 6

Describe ADH?

Answer 6

Anti-diuretic hormone is made in the hypothalamus and secreted from the posterior pituitary. ADH is released if osmolarity in the blood is hyper-osmotic. ADH stimulates the insertion of aqua-porin-2 channels into the apical membrane of the principal cells in the collecting duct to reabsorb water. This decreases the osmolarity of blood.

Question 7

Describe aldosterone?

Answer 7

Mineralocorticoid hormone that acts on the distal convoluted tubule and collecting duct. It causes sodium to be reabsorbed into the blood and potassium to be excreted from the blood. By sodium being reabsorbed, subsequently water will follow to. This increases BP and blood volume.

Question 8

Define hypernatraemia?

Answer 8

Na+ is >145mmol/L.

Question 9

Define hyponatraemia?

Answer 9

Na+ is <135mmol/L.

Question 10

What happens in hypernatraemia?

Answer 10

ECF (blood) is hyper-osmotic because there are too many Na+ ions in the blood.

Question 11

What are the causes of hypernatraemia?

Answer 11

1. Impaired thirst/level of consciousness - basically you are not drinking enough water (so you could have normal levels of Na+ in your blood but the amount of water in the ECF is small, so osmatically you are hyper-osmotic). It can be even due to you being in a come (inability to communicate that you need water).
2. Burns/diarrhoea/blood loss - you are losing water.
3. Solute diuresis - this can be due to things such as DKA.
4. Diabetes insipidus.

Question 12

What are the sings of hypernatraemia?

Answer 12

1. Intense thirst.

2. Confusion.

Question 13

What happens in hyponatraemia?

Answer 13

There is not enough sodium in the blood.

Question 14

What are the causes of hyponatraemia?

Answer 14

1. Excessive sodium loss.

2. excess water retention.

Question 15

What are the types of hyponatraemia?

Answer 15

1. Hypovolaemia.
2. Euvolemia.
3. Hypervolaemia.

Question 16

Describe hypovolaemia hyponatraemia?

Answer 16

This is where there is water loss with more sodium being lost as well. It can be due to:

1. Diarrhoea.
2. Vomiting.
3. Bowel obstruction.
4. Burns.
5. Diuretics.
6. Addisons.
7. DKA.

Question 17

Describe euvolaemia hyponatraemia?

Answer 17

This is where there is excessive retention of water, so the water is retained and distributed back into the cells but not into blood (blood is hypotonic so water moves to cells which are hypertonic). But there is equal amount of water, just too much in blood compared to Na+ ions. It can be due to:

1. SIADH - increase ADH released.
2. Diuretics, endocrinopathies, fluid replacement.

Question 18

Describe hypervolaemia hyponatraemia?

Answer 18

This is where there is excessive water retention and less sodium retention. It can be due to:

1. Cirrhosis.
2. Nephrotic syndrome.
3. Heart failure.
4. Renal failure.

Question 19

What are the types of hyopantraemia symptoms?

Answer 19

1. Fast onset.

2. Slow onset.

Question 20

Describe slow onset?

Answer 20

This is where hyponatraemia symptoms gradually developed over a course of time. The persons brain adapts to these changes. The pt is typically confused and not quite themselves. The blood in their brain becomes hypotonic, so water goes into the hypertonic cells and the cells get bigger.

Question 21

What is the treatment for slow onset hyponatraemia?

Answer 21

You correct their hyponatraemia gradually and generally just fluid restrict them.

Question 22

What happens if you quickly correct hyponatraemia in slow onset patients?

Answer 22

Central Pontine Myelinosis occur - this is where if you add a whole lot of sodium into the blood, it will cause water to go out of the already big adapted brain cells to the hypertonic blood. This leads to compression of the myelin sheaths which can lead to rapid demyelination. This can lead to: quadraparesis, pseudobulbar palsy, locked in syndrome and irreversible damage.

Question 23

Describe fast onset?

Answer 23

This is where hyponatraemia symptoms quickly develop, they can cause: cerebral odema, confused states, seizures and even a coma.

Question 24

What is the treatment for fast onset hyponatraemia?

Answer 24

Fluid restriction is more vigorous than slow onset, can give normal saline or 3% hypertonic saline in ICU. You want to correct the hyponatraemia quickly.