Question

6) A decrease in MAP is detected by baroreceptors, which initiate a reflexive increase in sympathetic
activity. This results in generalized vasoconstriction of arterioles throughout the body. Among the
arterioles that constrict are the afferent arterioles of the kidneys (which are innervated to a much
greater extent than the efferent arterioles). What effect does this have on GFR? And how does this
counteract the drop in blood pressure? What is the consequence of sympathetic stimulation of the beta-
1 receptors on JG cells?

Answer 1

the afferent arteriole has more and larger diameter than the efferent arterioles. So there is high resistance as the blood flows from a wider vessel to a narrower one.

the constriction of the afferent arteriole decreases and reduces blood flow and filtration pressure that is glomerular filtration rate where as constricting the efferent arteriole decreases only blood flow .

Auto regulation.

When arterial blood pressure increases then resistance in afferent arteriole also increases and the opposite happens if blood pressure falls.

• Stretching of blood vessels occurs due to increase in blood pressure results in the decreased dimater of blood vessel.
  • Resulting in an increased resistance to blood flow.
  • keeping the GFR constant.

The JG cells in the kidney  synthesize the enzyme called renin. These cells help in renin–angiotensin system and in autoregulation of the kidney.

JG cells secrete renin when blood pressure drops drop which is detected by stretch receptors present in the vascular walls.

JG cells have β1 adrenergic receptors and when these are stimulated by sympathetic, these receptors bring the secretion of renin. These cells often respond to decrease in systemic blood pressure which then these renin stimulates the angiotensin l to angiotensin ll by the amgioangiot converting enzyme ,which then regulates the blood pressure and arterial blood flow .

α1-adrenoreceptors contribute to vasoconstriction, thus increasing the blood pressure and the several subtypes of adrenoreceptors, α1A-receptors are responsible for regulating renal blood flow and sodium and water reabsorption .