A group of healthy volunteers embark on a study in which their dietary intake of sodium chloride is doubled over a period of one month. At the end of this period the average blood pressure of the group was found to be raised when compared to the control period before they started increasing their salt intake. What is the most likely physiological response to the raised salt intake?
A. Decreased release of Atrial Natriuretic Peptide (ANP) and dilation of afferent arterioles B. Afferent arteriolar dilation caused by decreased sympathetic nerve activity C. Increased ANP release and constriction of afferent arterioles D. Increased release of aldosterone E. Increased plasma oncotic pressure
Afferent arteriolar dilation caused by decreased sympathetic nerve activity-increased salt intake leads to volume expansion of the extracellular fluid and resultant increasedstretch in the walls of the afferent arteriole (as well as other baroreceptors elsewhere in thebody). the baroreceptor function of the afferent arteriole results in decreased sympatheticnerve activity which produces vasodilation of glomerular afferent arterioles. this increasesglomerular filtration rate by increasing glomerular capillary hydrostatic pressure. the proximaltubule receives direct innervation from the sympathetic nerves, which normally stimulate na+reabsorption. the decreased sympathetic nerve activity resulting from the baroreceptor reflexreduces reabsorption of nacl and water by the proximal tubule.anp is release is increased (not decreased) by volume expansion due to the increased venousreturn that occurs on volume expansion. however, anp causes dilatation of the afferentarteriole. not constriction.in the volume expanded state, delivery of nacl and water to the macula densa is increased. viathe tubuloglomerular feedback system, this results in suppression of renin release by thejuxtaglomerular apparatus and reduced circulating aldosterone.expansion of the plasma volume will dilute plasma proteins, so oncotic pressure will fall notincrease.further reading on the response to salt loading and the control of body fluid volume can befound in vanders renal physiology