According to Foex and Sear (2004), hypertension refers to the sustainable elevation of blood pressure in systemic arteries which will often lead to increased morbidity and mortality in the long-term. A patient with hypertension is said to have a systolic blood pressure that is above 140 mmHg or a diastolic blood pressure of more than 90 mmHg (Stedman, 2005). According to the statistics obtained by Morbidity and Mortality Weekly Report (2012), about 31% of the total 67 million adults in America have hypertension. This astounding figure indicates that hypertension has become one of the most prevalent health problems in the current society. There is a myriad of possible factors that can contribute to hypertension, such as the cardiovascular system, reninangiotensin-aldosterone system and sympathetic nervous system (Foex & Sear, 2004). This research paper aims to study the dysfunction of renin-angiotensin-aldosterone system in pathophysiology of hypertension and the effects of an antihypertensive drug, losartan on the angiotensin II type 1 receptors in response to the disease.
Pathophysiology of hypertension
Renin is a type of protein enzyme secreted by the juxtaglomerular apparatus of the kidneys when the blood pressure is low in the arteriole. It is produced and stored as an inactive form which is known as prorenin in the juxtaglomerular cells (Hall, 2010). Anomalies in the renin-angiotensin-aldosterone system pathway such as overproduction of renin or excessive release of angiotensin II can lead to hypertension (Williams & Lemke, 2008). For instance, when the secretion of renin is abnormally high, a high amount of angiotensinogen (renin substrate) secreted by the liver will be converted to angiotensin I by renin. The conversion of angiotensin I to angiotensin II will then follow with the aid of angiotensin-converting enzyme (ACE) found in the lungs (ibid). Therefore, this explained that the overproduction of angiotensin II is indirectly caused by an inordinate amount of renin secreted from the kidneys. Angiotensin II is known as one of the most potent vasoconstrictors in human body. It mediates its effects by binding to the angiotensin II type 1 receptors to induce vasoconstriction in the arterioles which then results in a rise in blood pressure (Silverthorn, 2010). Besides, angiotensin II also acts on the adrenal glands to secrete aldosterone which in turn causes sodium and water reabsorption in the tubules of the kidneys and this process further elevates the blood pressure. Multiple researches have shown that patients with higher blood pressure have high risks of developing stroke, heart failure, myocardial infarction, and renal disease (Heilpern, 2008). Therefore, hypertension is a disease that should not be taken lightly. Fortunately, various antihypertensive drugs had been successfully developed by the researchers to cure hypertension. One of them is losartan, a type of angiotensin receptor blocker (ARB) (Silverthorn, 2010)....