What happens to bloop pressure during vasoconstriction?

Question

According to my understanding, when there is constriction, blood flow is slowed, which leads to increased blood pressure. Is this correct?

If so, then there seems to be a discrepancy. According to my book, macula densa in the kidneys dilates the afferent arteriole which leads to an increase in blood pressure. Shouldn't dilation of a blood vessel lead to increased flow rate, ultimately leading to a decrease in blood pressure?

Answer 1

What Blue boy and Peter S are right.  

The kidneys work in "high" pressure.  The arterioles that are dilated lead to the Cortex. By dilating the arterioles there is less flow resistance in them causing less pressure drop, allowing more pressure drop across the cortex.

The cortex is the outer part of the kidney. This is where blood is filtered. We call this process "ultra-filtration" or "high pressure filtration" because it only works if the blood entering the kidney in the renal artery is at high pressure.

Billions of glomeruli are found in the cortex. A glomerulus is a tiny ball of capillaries. Each glomerulus is surrounded by a "Bowman's Capsule". Glomeruli leak. Things like red blood cells, white blood cells, platelets and fibrinogen stay in the blood vessels. Most of the plasma leaks out into the Bowman's capsules. This is about 160 litres of liquid every 24 hours.

Check Ref 1 for simplified answer ans 2 for doctoral answer and experimental process.

Answer 2

IN the kidney the afferent arteriole feeds into the glomerulus(Ball of blood capillaries) in Bowman's Capsule and blood leaves via the efferent arteriole. In order to assist in ultrafiltration in the glomerulus the afferent arteriole has a larger diameter than the efferent arteriole thus increasing the pressure in the glomerulus.(In simple terms more blood is entering the glomerulus than can leave via the efferent arteriole and the pressure causes ultrafiltration of the blood). Increasing the diameter of the afferent arteriole will bring in even more blood and since the efferent arteriole diameter remains the same the blood pressure in the glomerulus will increase resulting in an increased ultrfiltration

Hope that helps.

Answer 3

your correct ur book is wrong, when the blood vessel dilates it will enlarge decreasing the blood pressure

Answer 4

Bloop pressure should not affect anything at all, it is a frequency and changing the pressure it is in should not change too much.

Answer 5

This is actually true.

A decrease in blood pressure leads to the secretion of Renin by the kidneys.

Renin, is needed to turn Angiotensinogen into angiotensin I, and angiontensin conversion enzyme (ACE) converts angiotenin I into angiotensin II.

Angiotensin II creates a systemic (body) vasocontriction and increases Aldosterone secretion, which increases ADH, which increases H20 uptake, which increase blood pressure.

PROBLEM!!! Now that there is increased pressure everwhere in the body, both effarent and affarent atrioles of the kidney are constricted, there is no capillary pressure in the GLOMERULUS. With out a presssure difference there is no pressure gradient to allow for exchange of fluid therefore filtration.  

SOLUTION!!! The distal tube has osmoreceptors which monitors the amount of filtrate. If it is low, it will stimulate the affarent artrole to secrete more renin and at the same time dialate the affarent atriole to increase blood flow to the glomerulus. This is done by the juxtaglomerulus aparatus (a link between the affarent atriole and distal tube). An increase blood flow towards the glomerulus and a contricted effarent atriole increases blood pressure in the glomerulus, thus increase the rate of filtration.