chemistry

Renin–angiotensin system

Renin–angiotensin system is a chemistry topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Renin–angiotensin system rather than just read about it. In short: The renin–angiotensin system (RAS), or renin–angiotensin–aldosterone system (RAAS), is a hormone system that regulates blood pressure / fluid / electrolyte balance, and systemic vascular resistance. When renal blood flow is reduced, juxtaglomerular cells in the kidneys convert the precursor prorenin (already present in the blood) into renin and secrete it directly into the circulation.

Key takeaways

Renin–angiotensin system belongs to chemistry; place it in that map before memorising details.
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Reference excerpt

The renin–angiotensin system (RAS), or renin–angiotensin–aldosterone system (RAAS), is a hormone system that regulates blood pressure / fluid / electrolyte balance, and systemic vascular resistance. When renal blood flow is reduced, juxtaglomerular cells in the kidneys convert the precursor prorenin (already present in the blood) into renin and secrete it directly into the circulation. Plasma renin then carries out the conversion of angiotensinogen, released by the liver, to angiotensin I, which has no biological function on its own. Angiotensin I is subsequently converted to the active angiotensin II by the angiotensin-converting enzyme (ACE) found on the surface of vascular endothelial cells, predominantly those of the lungs. Angiotensin II has a short life of about 1 to 2 minutes. Then, it is rapidly degraded into angiotensin III by angiotensinases which are present in red blood cells and vascular beds in many tissues. Angiotensin III increases blood pressure and stimulates aldosterone secretion from the adrenal cortex; it has 100% of the adrenocortical stimulating activity and 40% of the vasopressor activity of angiotensin II. Angiotensin IV also has adrenocortical and vasopressor activities. Angiotensin II is a potent vasoconstrictive peptide that causes blood vessels to narrow, resulting in increased blood pressure. Angiotensin II also stimulates the secretion of the hormone aldosterone from the adrenal cortex. Aldosterone causes the renal tubules to increase the reabsorption of sodium which in consequence causes the reabsorption of water into the blood, while at the same time causing the excretion of potassium (to maintain electrolyte balance). This increases the volume of extracellular fluid in the body, which also increases blood pressure. If the RAS is abnormally active, blood pressure will be too high. There are several types of drugs that affect the RAS, which include ACE inhibitors, angiotensin II receptor blockers (ARBs), and renin inhibitors that interrupt different steps in this system to improve blood pressure. These drugs are one of the primary ways to control high blood pressure, heart failure, kidney failure, and the harmful effects of diabetes.

Activation

The system can be activated when there is a loss of blood volume or a drop in blood pressure (such as in hemorrhage or dehydration). This loss of pressure is interpreted by baroreceptors in the carotid sinus. It can also be activated by a decrease in the filtrate sodium chloride (NaCl) concentration or a decreased filtrate flow rate that will stimulate the macula densa to signal the juxtaglomerular cells to release renin.

If the perfusion of the juxtaglomerular apparatus in the kidney's macula densa decreases, then the juxtaglomerular cells (granular cells, modified pericytes in the glomerular capillary) release the enzyme renin. Renin cleaves a decapeptide from angiotensinogen, a globular protein. The decapeptide is known as angiotensin I. Angiotensin I is then converted to an octapeptide, angiotensin II by angiotensin-converting enzyme (ACE), which is thought to be found mainly in endothelial cells of the capillaries throughout the body, within the lungs and the epithelial cells of the kidneys. One study in 1992 found ACE in all blood vessel endothelial cells. Angiotensin II is the major bioactive product of the renin–angiotensin system, binding to receptors on intraglomerular mesangial cells, causing these cells to contract along with the blood vessels surrounding them; and to receptors on the zona glomerulosa cells, causing the release of aldosterone from the zona glomerulosa in the adrenal cortex. Angiotensin II acts as an endocrine, autocrine/paracrine, and intracrine hormone.

Cardiovascular effects

Angiotensin I may have some minor activity, but angiotensin II is the major bioactive product. Angiotensin II has a variety of effects on the body:

… excerpt ends here. Continue reading the full article.

Illustrations

Renin–angiotensin system: Flowchart showing the clinical effects of RAAS activity and the sites of action of ACE inhibitors and angiotensin receptor blockers. — Flowchart showing the clinical effects of RAAS activity and the sites of action of ACE inhibitors and angiotensin receptor blockers.

Worked examples

Example 1 — a first encounter with Renin–angiotensin system

Start with the simplest possible case. Write down what Renin–angiotensin system claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Renin–angiotensin system before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Renin–angiotensin system ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Renin–angiotensin system

In research: Renin–angiotensin system appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Renin–angiotensin system in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Renin–angiotensin system is common in secondary-school and first-year university syllabi. It links to neighbouring topics Biochemical reactions, Cardiovascular physiology, Endocrinology, so understanding it makes those chapters shorter.
In everyday life: Look for Renin–angiotensin system outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Renin–angiotensin system in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Renin–angiotensin system means in your own words.
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Frequently asked questions

What is Renin–angiotensin system in simple terms?

Why does Renin–angiotensin system matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Renin–angiotensin system?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Renin–angiotensin system.