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An angiotensin receptor is a protein found within the human body that responds to the angiotensin hormone as its ligand, or key. There are four different types of angiotensin receptors, and each one has a slightly different effect on the human body system. The A1 receptor is the most well-known and, in turn, the most thoroughly researched angiotensin receptor. It plays a major role in the body’s renin-angiotensin system (RAS), which is the major regulator of blood pressure and fluid levels within the body. A2 is implicated in the process of cell differentiation in the fetus and neonate, and the specific action of receptors A3-A4 is less known.
Angiotensin has two forms, type I and type II. While some effect has been observed from the first type, the majority of action that takes place at the receptor sites are in reaction to angiotensin II. An angiotensin receptor is a G protein-coupled receptor, meaning it has a protein that works specifically to transmit chemical signals between cells. As angiotensin II reacts at the A1 protein site, it starts a cascade of physiological processes that affect cell communication and help maintain homeostasis within multiple organ systems, most importantly, the circulatory and renal system via the RAS. The A2 receptor is vital for communication between cells when a fetus is developing inside the womb, and any breakdown in communication with angiotensin II can result in major birth defects.
The RAS is constantly in flux as fluid and blood levels move up and down within the body’s systems, and the angiotensin receptors play a major role in maintaining healthy homeostasis. Renin, the complimentary hormone to angiotensin, causes blood vessels to constrict, which causes increased blood pressure. Angiotensin II, in turn, causes blood vessels to dilate. Dehydration and certain conditions like diabetes can cause an imbalance in the system leading to high blood pressure, excessive thirst, and excessive urination. The RAS plays a prominent role in restoring balance and maintaining life when a person loses a significant volume of blood, like that experienced with a hemorrhage.
The cascade of physiological processes that happen after an angiotensin receptor is activated include the catalyzation of enzymes and other hormones. Tyrosine kinase, an enzyme, carries a phosphate group from ATP that transfers to a receiving protein within a cell, which then acts as on “off/on” switch for cellular processes. Aldosterone, one of the hormones activated by the process, increases the absorption of sodium and the release of potassium in the kidneys. Maintaining the balance between these two electrolytes is paramount for proper cardiac and renal functioning.