Angiotensin-renin-aldosterone system: a scheme, functions and its role
The renin-angiotensin-aldosterone system is a complex of enzymes and hormones that support homeostasis. Regulates the balance of salt and water in the body and the level of blood pressure.
Mechanism of operation
The physiology of the renin-angiotensin-aldosterone system originates at the border of the cortical and medullary substance of the kidney, where there are juxtaglomerular cells that produce peptidase( enzyme) - renin.
Renin is the hormone and the initial link of the RAAS.
Situations in which renin is released into the blood
There are several conditions in which a hormone enters the bloodstream:
- Reduction of blood flow to the kidney tissue - in inflammatory processes( glomerulonephritis, etc.), with diabetic nephropathy, kidney tumors.
- Decrease in the volume of circulating blood( with bleeding, repeated vomiting, diarrhea, burns).
- Drop in blood pressure. In the arteries of the kidneys there are baroreceptors, which react to changes in systemic pressure.
- Change in the concentration of sodium ions. In the human body there are accumulations of cells that respond to changes in the ionic composition of the blood by stimulation of renin production. Salt is lost with heavy sweating, and also with vomiting.
- Stresses, psychoemotional loads. The juxtaglomerular apparatus of the kidney is innervated by sympathetic nerves, which are activated with negative psychological influences.
In the blood renin occurs with protein - angiotensinogen, which is produced by the cells of the liver and takes a fragment from it. Angiotensin I is formed, which is the source of exposure for the angiotensin-converting enzyme( ACE).As a result, angiotensin II is obtained, which serves as the second link and is a potent vasoconstrictor of the arterial system( narrows the vessels).
Effects of angiotensin II
The goal: to raise blood pressure.
- Promotes the synthesis of aldosterone in the glomerular zone of the adrenal cortex.
- Affects the center of hunger and thirst in the brain, causing a "salt" appetite. Human behavior becomes motivated by the search for water and salty foods.
- Affects the sympathetic nerves, promoting the release of norepinephrine, which is also a vasoconstrictor, but less weak in action.
- Affects the vessels, causing their spasm.
- Participates in the development of chronic heart failure: promotes proliferation, fibrosis of blood vessels and myocardium.
- Reduces the rate of glomerular filtration.
- Brakes the production of bradykinin.
Aldosterone is the third component that acts on the terminal tubules of the kidneys and promotes the release of the ions of potassium, magnesium and the reverse absorption( reabsorption) of sodium, chlorine, water. Due to this, the volume of circulating fluid rises, blood pressure figures rise, and renal blood flow increases. Receptors to aldosterone are available not only in the kidneys, but also in the heart, vessels.
When the body reaches homeostasis, vasodilators( substances that dilate the blood vessels) - bradykinin and callidinum - begin to be produced. And the components of RAAS are destroyed in the liver.
Scheme of the renin-angiotensin-aldosterone system
Like any system, RAAS can fail. The pathophysiology of the renin-angiotensin-aldosterone system manifests under the following conditions:
- Adrenal cortex lesions( infection, hemorrhage and trauma).The state of aldosterone deficiency develops, and the body begins to lose sodium, chlorine and water, which leads to a decrease in the volume of the circulating fluid and a decrease in blood pressure. The state is compensated by the administration of saline solutions and receptor stimulators to aldosterone.
- Tumor of the adrenal cortex leads to an excess of aldosterone, which realizes its effects and increases the pressure. Also, processes of cell division become more active, hypertrophy and fibrosis of the myocardium develop, and heart failure develops.
- Liver pathology, when destruction of aldosterone is disrupted and its accumulation takes place. Pathology is treated with receptor blockers to aldosterone. Stenosis of the renal artery.
- Inflammatory diseases of the kidneys.
The importance of RAAS for life and medicine
The renin-angiotensin-aldosterone system and its role in the body:
- takes an active part in maintaining a normal blood pressure value;
- provides a balance of water and salts in the body;
- maintains the acid-base balance of the blood.
The system may fail. Influencing its components, you can fight hypertension. The mechanism of the onset of renal hypertension is also closely related to RAAS.
Highly effective groups of drugs that are synthesized through the study of RAAS
- "Prilys".Inhibitors( blockers) of ACE.Angiotensin I does not pass into angiotensin II.No vasoconstriction - no increase in blood pressure. Drugs: Amprilan, Enalapril, Captopril, etc. ACE inhibitors significantly improve the quality of life of diabetic patients, providing prevention of kidney failure. Preparations are taken in a minimal dosage, which does not cause a decrease in pressure, but only improves local blood flow and glomerular filtration. Medications are indispensable in renal failure, chronic heart disease and serve as one of the means of treatment of hypertension( if there are no contraindications).
- "Sartans".Blockers of receptors for angiotensin II.Vessels do not react to it and do not shrink. Preparations: Losartan, Eprosartan, etc.
The opposite renin-angiotensin-aldosterone system is kinin. Therefore, the blocking of RAAS leads to an increase in the blood components of the kinin system( bradykinin, etc.), which favorably affects the heart tissue and vessel walls. Myocardium does not suffer from starvation, because bradykinin strengthens the local blood flow, stimulates the production of natural vasodilators in the cells of the medulla of the kidneys and microcytomas of the collecting tubules - prostaglandins E and I2.They neutralize the pressor action of angiotensin II.The vessels are not spazmirovany, which provides adequate blood supply to the organs and tissues of the body, blood does not stay and reduces the formation of atherosclerotic plaques and blood clots. Kininy favorably affects the kidneys, increase diuresis( daily urine output).