Angiotensin

[Jenny_94]

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I am totally mixed up right now. Please help me!

Does angiotensin2 contract afferent or efferent arteriole of the glomerulus? In some writings, it says that in the case of blood loss, the renal blood flow decreases therefore raa system is activated to contract the afferent arteriole and prevent more loss. However in some writings about AKI, it says that when ace inhibitor is used, the function of angiotensin2 to contract the efferent arteriole is decreased so gfr is decreased and therefore the kidney is damaged..

1. What happens to the raa system when blood loss occurs?
2. What does angiontensin2 do to the afferent and efferent arteriole?

 

[jqueb29]

I am totally mixed up right now. Please help me!

Does angiotensin2 contract afferent or efferent arteriole of the glomerulus? In some writings, it says that in the case of blood loss, the renal blood flow decreases therefore raa system is activated to contract the afferent arteriole and prevent more loss. However in some writings about AKI, it says that when ace inhibitor is used, the function of angiotensin2 to contract the efferent arteriole is decreased so gfr is decreased and therefore the kidney is damaged..

1. What happens to the raa system when blood loss occurs?
2. What does angiontensin2 do to the afferent and efferent arteriole?

1. RAA system is activated due to decreased renal perfusion detected by macula densa which signals juxtaglomerular cells to secrete renin

2. Angiotensin 2 preferentially constricts the efferent arterioles when there are low levels of it. At higher levels (such as with response to hemorrhage), it constricts both afferent and efferent arterioles.

 

[Jenny_94]

1. RAA system is activated due to decreased renal perfusion detected by macula densa which signals juxtaglomerular cells to secrete renin

2. Angiotensin 2 preferentially constricts the efferent arterioles when there are low levels of it. At higher levels (such as with response to hemorrhage), it constricts both afferent and efferent arterioles.[/QUOTE

 

[Jenny_94]

1. RAA system is activated due to decreased renal perfusion detected by macula densa which signals juxtaglomerular cells to secrete renin

2. Angiotensin 2 preferentially constricts the efferent arterioles when there are low levels of it. At higher levels (such as with response to hemorrhage), it constricts both afferent and efferent arterioles.

Thank you sooooo much! I think I get it now🙂

 

[worldbeater]

1. RAA system is activated due to decreased renal perfusion detected by macula densa which signals juxtaglomerular cells to secrete renin
.

2. Angiotensin 2 preferentially constricts the efferent arterioles when there are low levels of it. At higher levels (such as with response to hemorrhage), it constricts both afferent and efferent arterioles.

1) Yup, but this takes 20 minutes to occur in a low volume state (low BP). From 0 seconds to 2 seconds its your carotid reflex (decreased carotid stretch -> decreased CN IX -> decreased CN X(inhibitory)-> increased HR (CO = SV x HR). From 2 seconds to 20 minutes is your alpha 1 constriction of your veins to deliver 60% of your pooled blood to the heart. >20 minutes is as your RAA system as your described

2) Yup. Addition point: Increased constriction of your efferent arteriole causes a backpedaling, leading to an increase in your glomerular filtration rate(GFR) and your filtration fraction (which is your GFR/RPF).

 

[Jenny_94]

I am confused again..it says that when hemorrage occurs the angiotension2 will constrict the afferent arteriole not to lose blood. But normally when the GFR is low, angiontensin constricts the efferent arteriole to maintain the GFR, right? Why is hemorrhagic situation different? I mean, i do understand the part that angiotensin has other mechanisms to increase BP so it definitely is needed in the situation, but it just doesnt get to me the fact that angiotensin constricts the afferent arteriole to save blood...it is written in my textbook like this.

 

[worldbeater]

I am confused again..it says that when hemorrage occurs the angiotension2 will constrict the afferent arteriole not to lose blood. But normally when the GFR is low, angiontensin constricts the efferent arteriole to maintain the GFR, right? Why is hemorrhagic situation different? I mean, i do understand the part that angiotensin has other mechanisms to increase BP so it definitely is needed in the situation, but it just doesnt get to me the fact that angiotensin constricts the afferent arteriole to save blood...it is written in my textbook like this.

Angiotensin 2 constricts both the afferent and efferent arterioles, but it constricts the efferent arteriole more. That's why the backpedaling of the efferent causes an increase in GFR. Hemorrhagic is a low volume profile, it shouldn't be different.