Renin-angiotensin system
You don't need to be Editor-In-Chief to add or edit content to WikiDoc. You can begin to add to or edit text on this WikiDoc page by clicking on the edit button at the top of this page. Next enter or edit the information that you would like to appear here. Once you are done editing, scroll down and click the Save page button at the bottom of the page.
| Cardiology Network |
 Discuss Renin-angiotensin system further in the WikiDoc Cardiology Network |
| Adult Congenital |
|---|
| Biomarkers |
| Cardiac Rehabilitation |
| Congestive Heart Failure |
| CT Angiography |
| Echocardiography |
| Electrophysiology |
| Cardiology General |
| Genetics |
| Health Economics |
| Hypertension |
| Interventional Cardiology |
| MRI |
| Nuclear Cardiology |
| Peripheral Arterial Disease |
| Prevention |
| Public Policy |
| Pulmonary Embolism |
| Stable Angina |
| Valvular Heart Disease |
| Vascular Medicine |
| WikiDoc Cardiology News |
 Read more about Renin-angiotensin system in the WikiDoc Cardiology News |
| All News Articles |
|---|
| Acute Coronary Syndromes |
| Biomarkers |
| Cardiovascular Imaging |
| CT Surgery |
| Diabetes |
| Electrophysiology |
| General Cardiology |
| Guidelines |
| Health Policy |
| Heart Failure |
| Hypertension |
| Interventional |
| Peripheral Arterial Disease |
| Prevention |
| Valvular Heart Disease |
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Phone:617-525-6884
Please Take Over This Page and Apply to be Editor-In-Chief for this topic: There can be one or more than one Editor-In-Chief. You may also apply to be an Associate Editor-In-Chief of one of the subtopics below. Please mail us [2] to indicate your interest in serving either as an Editor-In-Chief of the entire topic or as an Associate Editor-In-Chief for a subtopic. Please be sure to attach your CV and or biographical sketch.
The renin-angiotensin system (RAS) or the renin-angiotensin-aldosterone system (RAAS) is a hormone system that helps regulate long-term blood pressure and extracellular volume in the body.
Activation
The system can be activated when there is a loss of blood volume or a drop in blood pressure (such as in a hemorrhage).
- If the perfusion of the juxtaglomerular apparatus in the kidneys decreases, then the juxtaglomerular cells release the enzyme renin.
- Renin cleaves an inactive peptide called angiotensinogen, converting it into angiotensin I.
- Angiotensin I is then converted to angiotensin II by angiotensin-converting enzyme (ACE),[1] which is found mainly in lung capillaries.
- Angiotensin II is the major bioactive product of the renin-angiotensin system. Angiotensin II acts as an endocrine, autocrine/ paracrine, and intracrine hormone.
Effects
Angiotensin I may have some minor activity, but angiotensin II is more potent. Angiotensin II has a variety of effects on the body:
- Throughout the body, it is a potent vasoconstrictor.
- In the kidneys, it constricts glomerular arterioles, having a greater effect on efferent arterioles than afferent. As with most other capillary beds in the body, the constriction of afferent arterioles increases the arterioler resistance, raising systemic arterial blood pressure and decreasing the blood flow. However, the kidneys must continue to filter enough blood despite this drop in blood flow, necessitating mechanisms to keep glomerular blood pressure up. To do this, Angiotensin II constricts efferent arterioles, which forces blood to build up in the glomerulus, increasing glomerular pressure. The glomerular filtration rate (GFR) is thus maintained, and blood filtration can continue despite lowered overall kidney blood flow.
- In the adrenal cortex, it acts to cause the release of aldosterone. Aldosterone acts on the tubules (i.e. the distal convoluted tubules and the cortical collecting ducts) in the kidneys, causing them to reabsorb more sodium and water from the urine. Potassium is secreted into the tubule in exchange for the sodium, which is reabsorbed. Aldosterone also acts on the central nervous system to increase a person's appetite for salt, and to make them feel thirsty.
- Release of Anti Diuretic Hormone (ADH) -- also called vasopressin -- ADH is made in the hypothalamus. ADH is stored and released from the pituitary gland.
These effects directly act to increase the amount of fluid in the blood, making up for a loss in volume, and to increase blood pressure.
Clinical significance
The renin-angiotensin system is often manipulated clinically to treat high blood pressure.
- Inhibitors of angiotensin-converting enzyme (ACE inhibitors) are often used to reduce the formation of the more potent angiotensin II. Captopril is an example of an ACE inhibitor.
- Alternatively, angiotensin receptor blockers (ARBs) can be used to prevent angiotensin II from acting on angiotensin receptors.
- A new drug called Aliskiren is being released in 2007 which directly inhibits renin.
Other uses of ACE
Interestingly, ACE cleaves a number of other peptides, and in this capacity is an important regulator of the kinin-kallikrein system.
Fetal renin-angiotensin system
In the fetus, the renin-angiotensin system is predominantly a sodium-losing system, as angiotensin II has little or no effect on aldosterone levels. Renin levels are high in the fetus, while angiotensin II levels are significantly lower — this is due to the limited pulmonary blood flow, preventing ACE (found predominantly in the pulmonary circulation) from having its maximum effect.
References
External links
Cardiovascular system, physiology: cardiovascular physiology | |
|---|---|
| Volumes | Preload - Afterload - End-systolic volume - End-diastolic volume - Frank-Starling law of the heart |
| Interactions | Cardiac output - Wiggers diagram - Pressure volume diagram |
| Tropism | Chronotropic - Dromotropic - Inotropic |
| Hemodynamics | Baroreflex - Kinin-kallikrein system - Renin-angiotensin system - Vasoconstrictors - Vasodilators - Compliance - Vascular resistance |
| Other | Electrical conduction system of the heart (Cardiac action potential) |
da:Renin-angiotensin-aldosteron-systemet de:Renin-Angiotensin-Aldosteron-System fr:Système rénine-angiotensine-aldostérone he:מערכת הרנין-אנגיוטנסין-אלדוסטרון it:Sistema renina-angiotensina nl:Bloeddrukregulatiesk:Systém renín-angiotenzín-aldosterón sv:Renin-angiotensinsystemet
Acknowledgement and Attribution Regarding Sources of Content
Some of the initial content on this page may be incorporated in part from copyleft sources in the public domain including wikis such as Wikipedia and AskDrWiki. Drug information for patients came from the The National Library of Medicine. Infectious disease information may have come from the Centers for Disease Control (CDC). Differential Diagnoses are drawn from clinicians as well as an amalgamation of 3 sources: 1.The Disease Database; 2. Kahan, Scott, Smith, Ellen G. In A Page: Signs and Symptoms. Malden, Massachusetts: Blackwell Publishing, 2004:3; 3. Sailer, Christian, Wasner, Susanne. Differential Diagnosis Pocket. Hermosa Beach, CA: Borm Bruckmeir Publishing LLC, 2002:7 .
