Anatomy
Fact-checked

At WiseGEEK, we're committed to delivering accurate, trustworthy information. Our expert-authored content is rigorously fact-checked and sourced from credible authorities. Discover how we uphold the highest standards in providing you with reliable knowledge.

Learn more...

What is an Angiotensin?

Dulce Corazon
Dulce Corazon

Angiotensin, which is a protein, is a component of the renin-angiotensin-aldosterone system (RAAS), which performs important functions in the regulation of fluid balance and blood pressure in the human body. It has two forms: angiotensin I (AI) and angiotensin II (AG II). Generally, the function of angiotensin is to raise the blood pressure.

Formation of AI is brought about by the reactions between renin, produced by the kidneys, and angiotensinogen, produced by the liver. A specific enzyme produced in the lungs, called angiotensin-converting enzyme (ACE), then acts on AI, converting it to AG II. The first form, AI, does not commonly exert any functions in the body, while AG II has numerous effects.

Angiotensins in the body contribute to high blood pressure.
Angiotensins in the body contribute to high blood pressure.

AG II causes blood vessels to constrict, concentrating more blood flow to vital areas of the body. In the adrenal cortex, it stimulates the release of aldosterone, which makes the kidneys reabsorb more sodium and preserve water. The thirst center in the brain is also stimulated, thereby promoting an individual to drink more fluids. It also promotes the release of vasopressin, otherwise known as antidiuretic hormone, from the posterior pituitary gland. Vasopressin also increases retention of fluids by the kidneys and decreases urine volume.

Angiotensin-II causes blood vessels to constrict, concentrating more blood flow to vital areas of the body.
Angiotensin-II causes blood vessels to constrict, concentrating more blood flow to vital areas of the body.

Renin production in the kidneys is usually stimulated by low blood pressure or low blood volume, caused by factors such as inadequate intake of salt, bleeding, obstruction, or shock. Angiotensin II acts to make blood vessels in the kidneys and other organs constrict, limiting blood flow to these areas and diverting more blood flow towards the heart and the brain. Aldosterone and vasopressin mostly contribute in fluid retention and limiting urination. Sodium reabsorption in the kidneys increases, as sodium also aids in the retention of more fluids.

Some people with hypertension take angiotensin-converting enzyme (ACE) inhibitors.
Some people with hypertension take angiotensin-converting enzyme (ACE) inhibitors.

Atherosclerosis due to the accumulation of cholesterol in the blood often causes narrowing of the arteries. When arteries supplying the kidneys become narrowed and blood flow decreases, the kidney usually interpret this as low blood pressure, thereby activating the RAAS and eventually raising the blood pressure. Through this mechanism, renal hypertension develops.

Renin production in the kidneys is usually stimulated by low blood volume.
Renin production in the kidneys is usually stimulated by low blood volume.

Treatment of hypertension frequently includes the use of ACE inhibitors or angiotensin II receptor blockers (ARBs). ACE inhibitors mostly block the action of ACE on AI, thus preventing the formation of AG II. ARBs, on the other hand, block AG II from binding with receptors in the blood vessels, thus causing the arteries to dilate instead of constricting.

Discuss this Article

Post your comments
Login:
Forgot password?
Register:
    • Angiotensins in the body contribute to high blood pressure.
      By: Monkey Business
      Angiotensins in the body contribute to high blood pressure.
    • Angiotensin-II causes blood vessels to constrict, concentrating more blood flow to vital areas of the body.
      By: Balint Radu
      Angiotensin-II causes blood vessels to constrict, concentrating more blood flow to vital areas of the body.
    • Some people with hypertension take angiotensin-converting enzyme (ACE) inhibitors.
      By: dambuster
      Some people with hypertension take angiotensin-converting enzyme (ACE) inhibitors.
    • Renin production in the kidneys is usually stimulated by low blood volume.
      By: 7activestudio
      Renin production in the kidneys is usually stimulated by low blood volume.
    • The accumulation of cholesterol in the blood can narrow the arteries, which may activate RAAS.
      By: hywards
      The accumulation of cholesterol in the blood can narrow the arteries, which may activate RAAS.
    • AG II stimulates the thirst center of the brain, prompting someone to drink more fluids.
      By: mallivan
      AG II stimulates the thirst center of the brain, prompting someone to drink more fluids.
    • Renin is secreted in response to low blood pressure or volume.
      By: Wellford Tiller
      Renin is secreted in response to low blood pressure or volume.
    • Aldosterone affects the movement of sodium, potassium and water through the kidney.
      By: snapgalleria
      Aldosterone affects the movement of sodium, potassium and water through the kidney.
    • The adrenal cortex—the outer part of the gland—produces cortisol (to regulate metabolism) and aldosterone (to control blood pressure).
      By: CLIPAREA.com
      The adrenal cortex—the outer part of the gland—produces cortisol (to regulate metabolism) and aldosterone (to control blood pressure).