USMLE Step 1 Renal Physiology Review 59 12 Hypovolemia

USMLE Step 1 Renal Physiology Review 59 12 Hypovolemia

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Play USMLE Audio MP3  59 12 Hypovolemia Below

Begin  59 12 Hypovolemia Transcription

In the hypothalamic thirst center there are osmoreceptors that regulate thirst. The thirst mechanism is stimulated by the hormone angiotensin II.

What can override plasma osmolality as a stimulus for the release of ADH?

  • It has to do with blood volume and it starts with an H. Hypovolemia can override plasma osmolality as a stimulus for the release of ADH.

How much of a decrease in blood volume triggers ADH release?

  • A 10-25% decrease.

What immediate effect does this release of antidiuretic hormone have on blood pressure?

  • Blood pressure is regulated.

How does a decrease in blood volume affect atrial pressure?

  • Atrial pressure decreases.

What receptors respond to changes in atrial blood pressure? They start with AB.

  • Atrial baroreceptors.

When do these receptors fire?

  • These baroreceptors fire when blood pressure increases.

And what are they doing when they fire?

  • They are inhibiting the production and release of ADH.

What happens to these receptors as blood pressure decreases?

  • The baroreceptors fire less frequently as blood pressure decreases.

How does this affect antidiuretic hormone levels?

  • Production and release of antidiuretic hormone is stimulated. There are many other non-osmotic stimuli for ADH secretion besides hypovolemia.

Alphabetically list five diseases or disorders that stimulate the release of ADH. I’ll cue you with the first letter of each.

First, C.

Cirrhosis.

Second, HD.

Hypothalamic Disease.

Third, H.

Hypothyroidism.

Fourth, P.

Pneumonia

and fifth, T.

Tuberculosis.

What is the best thing to do to inhibit antidiuretic hormone production and release?

  • Drink water.

What condition, having to do with blood volume is an inhibitor of ADH release? It starts with an H.

  • Hypervolemia inhibits the release of ADH.

What are three more things that inhibit the release of ADH? The first one is a disease that starts with DI. What is it?

  • Diabetes insipidus. The second one has to do with body position. It starts with RP. A reclining posture inhibits the release of ADH. The third one is a special kind of breathing. It starts with NPB. Negative pressure breathing.

Student doctor, please pause the tape and summarize what we’ve discussed about non-osmotic stimuli for ADH release and inhibitors of ADH secretion. Hypovolemia can override plasma osmolality as a stimulus for the release of antidiuretic hormone.

A blood volume decrease of 10 to 25% triggers ADH release which has the immediate effect of regulating blood pressure. As blood volume decreases atrial pressure decreases which causes a response from the atrial baroreceptors. When blood pressure increases, these receptors fire and inhibit the production and release of ADH. As blood pressure decreases, the baroreceptors fire less frequently and production and secretion is stimulated. There are many non-osmotic stimuli for ADH secretion besides hypovolemia. Some diseases or disorders that stimulate ADH release are cirrhosis, hypothalamic disease, hypothyroidism, pneumonia, and tuberculosis. The best thing to do to inhibit the production and secretion of ADH is to drink water. Some other things that inhibit the release of ADH are hypervolemia, diabetes insipidus, a reclining posture, and negative pressure breathing.

 


 

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