USMLE Step 1 Renal Physiology Review 59 17 Angiotensin 2

USMLE Step 1 Renal Physiology Review 59 17 Angiotensin 2

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Play USMLE Audio MP3   59 17 Angiotensin 2  Below

Begin  59 17 Angiotensin 2  Transcription

Let’s look at how angiotensin II works. How long does angiotensin II persist? Just one to three minutes. Angiotensin II has two principal actions. One has to do with blood vessels.

What is it?

  • Vasoconstriction of the renal arterioles an increased smooth muscle tension of arterioles throughout the body.

What does this lead to?

  • Increased systemic blood pressure.

What is the second primary action of angiotensin II, having to do with aldosterone?

Angiotensin II stimulates the zona glomerulosa cells to produce and secrete aldosterone.

What do the zona glomerulosa cells comprise?

  • The outer layer of the adrenal cortex.

What do the zona glomerulosa cells produce aldosterone from? It starts with C.

  • Corticosterone.

What does the aldosterone do?

  • Aldosterone increases sodium reabsorption in the kidneys.

How does increased sodium reabsorption affect water reabsorption?

  • Water reabsorption also increases.

And what does this cause an increase in?

  • Extracellular fluid volume.

What does increased extracellular fluid volume lead to?

  • Increased blood pressure.

Student doctor, please pause the tape and summarize what we’ve discussed about the principal actions of angiotensin II.

One of the principal actions of angiotensin II is vasoconstriction of the renal arterioles and increased smooth muscle tension of arterioles throughout the body which leads to increased systemic blood pressure. The second primary action of angiotensin II is to stimulate the zona glomerulosa cells which comprise the outer layer of the adrenal cortex to produce and secrete aldosterone which is produced from corticosterone. Aldosterone increases sodium and therefore water reabsorption in the kidneys. This leads to increased extracellular fluid volume which in turn leads to increased blood pressure.

Angiotensin II has two secondary functions. First it stimulates the release of what hormone by the posterior pituitary?

  • One of the secondary functions of angiotensin II is to stimulate the release of ADH by the posterior pituitary.

What else does angiotensin II stimulate? The answer starts with HTC.

  • Another secondary function of angiotensin II is stimulation of the hypothalamic thirst centers.

The released ADH has two effects. First what does ADH cause to happen in the late distal tubule and collecting duct?

  • Water permeability is increased.

Which causes what to increase?

  • Water reabsorption.

And what ultimately increases because of this?

  • Blood pressure.

In addition to this, what effect does the released ADH have on vascular smooth muscle?

  • ADH increases constriction of vascular smooth muscle.

What effect does this have?

  • Blood pressure is increased. Thus the end result of both the principal and secondary actions of angiotensin II is increased blood pressure.

What does the increased blood pressure caused by all these mechanisms do?

  • It feeds back to inhibit further renin secretion by the juxtaglomerular cells.

Student doctor, please pause the tape and summarize what we’ve discussed about the secondary functions of angiotensin II.

The two secondary functions of angiotensin II are to stimulate the release of antidiuretic hormone by the posterior pituitary and the stimulation of the hypothalamic thirst centers. The released ADH has two effects. First, water permeability in the late distal tubule and the collecting duct is increased which also increases water reabsorption. This ultimately increases blood pressure. In addition to this the released ADH increases constriction of vascular smooth muscle which increases blood pressure. Thus, the end result of both the principal and secondary actions of angiotensin II is to increase blood pressure which then feeds back to inhibit further renin secretion by the juxtaglomerular cells.

 


 

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