Question

RAAS involve (a) JGA apparatus (b) Angiotensinogen (c) Adrenal cortex (d) All of these

Short answer

(d) All of these

Step-by-step solution

Analyze each option in the context of RAAS

The Juxtaglomerular Apparatus (JGA) is the location where renin is produced. Renin works with angiotensinogen to produce angiotensin I, thus JGA apparatus is involved.

Analyzing the second and third option

Angiotensinogen, a protein produced by the liver is part of RAAS. It is acted upon by renin (from JGA apparatus) to produce Angiotensin I. Adrenal cortex is involved as it is the site where aldosterone (an hormone) is produced which is also a part of RAAS.

Conclusion

As all the options given JGA apparatus, Angiotensinogen, and Adrenal cortex are all part of RAAS, the correct answer is (d) all of these.

Key concepts

Juxtaglomerular Apparatus (JGA)

The Juxtaglomerular Apparatus (JGA) plays a critical role in the regulation of blood pressure and fluid balance in the body. It is a specialized structure formed by the cells lining the distal convoluted tubule and the afferent arteriole of the kidney nephron. The JGA is primarily responsible for sensing changes in blood pressure and sodium content in the blood, triggering a compensatory mechanism to correct any imbalance.

When the blood pressure falls or sodium levels are low, the JGA releases an enzyme called renin. Renin acts on angiotensinogen, a protein secreted by the liver, converting it to angiotensin I. Angiotensin I is then converted to angiotensin II, a powerful vasoconstrictor, by the angiotensin-converting enzyme (ACE) found in the lungs. Angiotensin II not only constricts blood vessels to increase blood pressure but also stimulates the secretion of aldosterone from the adrenal cortex.

Through the release of renin, the JGA initiates the Renin-Angiotensin-Aldosterone System (RAAS), a primary regulatory pathway for blood pressure and fluid balance, validating its key involvement in the process.

Angiotensinogen

Angiotensinogen is an alpha-2-globulin protein synthesized by the liver and continually released into the bloodstream. As the substrate for renin, which the JGA releases in response to low blood pressure, angiotensinogen is critical to the RAAS. The interaction between renin and angiotensinogen leads to the production of angiotensin I, which is relatively inactive but serves as the precursor for the potent angiotensin II.

Angiotensin II has multiple effects on the body, including vasoconstriction, which increases blood pressure, and stimulation of the adrenal cortex to release aldosterone. Aldosterone prompts the kidneys to reabsorb sodium and excrete potassium, leading to an increase in blood volume and blood pressure. This sequence of events highlights the centrality of angiotensinogen in the RAAS, bridging the initial signal of low blood pressure to the systemic response aimed at restoring homeostasis.

Adrenal Cortex

The adrenal cortex, the outer region of the adrenal glands, located atop the kidneys, is integral to the RAAS through the secretion of the hormone aldosterone. Aldosterone is a steroid hormone that plays a crucial role in regulating blood pressure and electrolyte balance.

Upon stimulation by angiotensin II, the adrenal cortex increases the production of aldosterone. This hormone acts on the distal tubules and collecting ducts of the kidneys, promoting the reabsorption of sodium and water, which in turn increases blood volume and pressure. Additionally, aldosterone causes the renal excretion of potassium, further aiding in the regulation of electrolytes in the body.

The interplay between angiotensin II and aldosterone secretion by the adrenal cortex ensures that the RAAS precisely controls blood pressure and maintains electrolyte homeostasis, underscoring the necessity of the adrenal cortex in this complex regulatory system.