Aldosterone

[jeppuda]

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Hi, I have a question that should be fairly simple. It says in my Kaplan book that Adolsterone increases blood pressure by allowing the blood to reabsorb sodium...this leads the body to reabsorb more water....this increases blood volume...the increase in blood volume increases blood pressure?...I thought pressure and volume were inversely proportional. Therefore if blood volume increases, then blood pressure should decrease....can anyone clear this up for me? thanks in advance

 

[blasterx]

Hi, I have a question that should be fairly simple. It says in my Kaplan book that Adolsterone increases blood pressure by allowing the blood to reabsorb sodium...this leads the body to reabsorb more water....this increases blood volume...the increase in blood volume increases blood pressure?...I thought pressure and volume were inversely proportional. Therefore if blood volume increases, then blood pressure should decrease....can anyone clear this up for me? thanks in advance

Yep, as blood volume increases, blood pressure also increases.

 

[queenskillers]

yes i agree also........a common sense way of looking at it is that as blood volume increases and the area in the veins, arteries, etc. stays the same, the excess blood volume will push against the artery and vein walls and will cause an increase in pressure.....im not sure if this explanation is good enough but thats how i look at it since blood pressure is dependent on surface area

 

[Lipoxygenase]

yes i agree also........a common sense way of looking at it is that as blood volume increases and the area in the veins, arteries, etc. stays the same, the excess blood volume will push against the artery and vein walls and will cause an increase in pressure.....im not sure if this explanation is good enough but thats how i look at it since blood pressure is dependent on surface area

Another way of looking at it is using the good-old cardiac output formula. You've probably seen this in physiology class or in intro bio.

Mean Arterial Pressure (MAP) = Total Peripheral Resistance (TPR) x Cardiac Output (CO)
Cardiac Output (CO) = Stroke Volume (SV) x Heart Rate (HR)
Thus, MAP = SV x HR x TPR

So, if you increase the blood volume (SV) or increase resistance (TPR) by vasoconstriction, MAP increases. These two methods are employed by angio-tensin system which includes aldosterone as the intermediate player, but aldosterone contributes to SV route only. It does not affect TPR. I don't know the details of how, but angiotensinII somehow knows how to tell the arteries to constrict and tell adrenal cortex to secrete aldosterone.

Another way of increasing MAP is by causing the SA node in the heart to pump faster. This increases HR, thus MAP. Plasma epinephrine (a hormonal neurotransmitter) is the reagent that results in this response. This is the third method of increasing MAP.

edit: MAP = mean atrial pressure