Regulation of Renin Secretion

An inadequate dietary intake of salt (NaCl) is always accompanied by a fall in blood volume. This is because the decreased plasma concentration (osmolality) inhibits ADH secretion. With

Glomerulus

Glomerular capsule

Glomerulus

Region of the juxtaglomerular apparatus

Glomerular capsule

Juxtaglomerular Apparatus

Efferent arteriole

Region of the juxtaglomerular apparatus

Afferent arteriole w

Distal tubule

Efferent arteriole

Glomerulus m

Granular cells

Efferent arteriole

Macula densa

Thick ascending limb

Granular cells

Macula densa

Juxtaglomerular apparatus

Thick ascending limb

■ Figure 17.25 The juxtaglomerular apparatus. (a) The location of the juxtaglomerular apparatus. This structure includes the region of contact of the afferent arteriole with the last portion of the thick ascending limb of the loop. The afferent arterioles in this region contain granular cells that secrete renin, and the tubule cells in contact with the granular cells form an area called the macula densa, seen in (b).

less ADH, less water is reabsorbed through the collecting ducts and more is excreted in the urine. The fall in blood volume and the fall in renal blood flow that result cause increased renin secretion. Increased renin secretion is believed to be due in part to the direct effect of blood pressure on the granular cells, which may function as baroreceptors in the afferent arterioles. Renin secretion is also stimulated by sympathetic nerve activity, which is increased by the baroreceptor reflex (chapter 14) when the blood volume and pressure fall.

An increased secretion of renin acts, via the increased production of angiotensin II, to stimulate aldosterone secretion. Consequently, less sodium is excreted in the urine and more is retained in the blood. This negative feedback system is illustrated in figure 17.26.

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  • karin
    What cells secrete renin?
    8 years ago

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