Lecture 6: Integration of Salt and Water Balance

Question 1

What happens with dehydration

Answer 1

To get EC osmolarity back to normal

Question 2

What physiological factors regulates ADH release?

Answer 2

1. Osmolarity changes <1%. (osmoreceptors) *lower threshold and higher sensitivity
2. Changes in blood volume >10% (cardiopulonary receptors sense stretching of atria/ventricles → hypothalamus)

Question 3

What senses changes in osmolality?

Answer 3

Osmoreceptors in hypothalamus sense and stimulate ADH release.

Question 4

What non-physiological features stimulate ADH secretion

Answer 4

• Pain, stress
• Drugs
• Carcinomas
• Pulmonary disorders
• CNS disorders
• Acohol INHIBITS

Question 5

How is ADH made and released?

Answer 5

ADH is synthesized in the hypothalamus → Travels down axons to the posterior pit. (stored in granules in the nerve terminals) → Released into blood → acts on kidney

Question 6

How exactly does ADH have an affect on the kidneys?

Answer 6

ADH binds to V2 receptors of the Renal ISF side of the tubular cells. This stimulates the insertion of Aquaporin-2 channels on the tubular lumen side.

These are effectively water channels, allowing water reabsorption.

The more ADH, the less urine you make!

Question 7

Central and nephrogenic diabetes insipidus

Answer 7

Inability to respond or produce ADH no matter the osmolarity! Extremely large urine output.

Central: head injury, infection, tumor
Damage with hypothalamus or post. pit.
No ADH produced

Nephrogenic: issue with V2 receptors in the kidney or drugs
collecting tubule unresponsive to ADH

Question 8

How do you distinguish between Central and Nephrogenic DI?

Answer 8

Via the Water Deprivation Test.

Dehydrate patient, then give them a ADH-replacement. Only those with a central ADH will go up, as there issue is not with the receptors, but that there is no ADH produced!

Question 9

Syndrome of inappropriate ADH secretion SIADH.

What is it? How is it caused? Treatment?

Answer 9

• Plasma ADH levels higher then should be for the individuals EC osmolarity and volume, so patient inappropriately retains water
• Posm. significately lower then normal.
• If patients water intake is not controlled → hypo-osmolal state with possible dire consequences

Caused by: brain injury/tumor, some anti-cancer drugs

Treatment: Restrict water intake

Question 10

Under what conditions is Renin release increased?

Answer 10

• Increased Sympathetic Stimulation
• Decreased afferent arteriole BP
• Decreased macular densa NaCl delivery.

Question 11

Once released, draw what Renin does via a flow diagram

Answer 11

Can be blocked via ACE inhibitors or angiotension receptor blockers

Question 12

What does Angiotensin II do?

Answer 12

1. increased aldosterone production
2. Constriction of efferent arteriole
3. Bind to AT1 receptor, allowing Na+ reabsorption

Question 13

If the right renal artery becomes abnormally constricted, what will happen to renin secretion by the right and left kidney?

Answer 13

Right kidney: gets lower renal PP via the intrarenal baroreceptor and → increased renin output → elevated angiotensin II and arterial BP

These both inhibit renin secretion from the left kidney. Acutely you will have overall higher renin levels for the first month