IntroductionAccording to Foex and Sear (2004), hypertension refers to the sustained elevation of blood pressure in the systemic arteries, which will often lead to morbidity and mortality increased in the long term. A patient with hypertension is said to have a systolic blood pressure above 140 mmHg or a diastolic blood pressure above 90 mmHg (Stedman, 2005). According to statistics obtained by Morbidity and Mortality Weekly Report (2012), approximately 31% of the 67 million American adults have hypertension. This astonishing figure indicates that hypertension has become one of the most prevalent health problems in today's society. There are a myriad of possible factors that may contribute to hypertension, such as the cardiovascular system, the reninangiotensin-aldosterone system, and the sympathetic nervous system (Foex and Sear, 2004). This research paper aims to investigate the dysfunction of the renin-angiotensin-aldosterone system in the pathophysiology of hypertension and the effects of an antihypertensive drug, losartan, on angiotensin II type 1 receptors in response to disease. Pathophysiology of Hypertension Renin is a type of protein enzyme secreted by the juxtaglomerular apparatus of the kidneys when blood pressure is low in the arteriole. It is produced and stored in an inactive form called prorenin in juxtaglomerular cells (Hall, 2010). Abnormalities in the renin-angiotensin-aldosterone system pathway, such as overproduction of renin or excessive release of angiotensin II, can lead to hypertension (Williams and Lemke, 2008). For example, when renin secretion is abnormally high, a large amount of angiotensinogen (renin substrate) secreted by the liver will be converted to angiotensin I by renin. ...... middle of paper ......-S6. doi: 10.1016/j.annemergmed.2007.11.004Kaplan, N.M. (2006). Kaplan's clinical hypertension. (9th ed.). Colombia: Lippincott Williams and Wilkins. Lemke, TL and Williams, DA (2008). Foye's principles of medicinal chemistry. (6th ed.). United States: Lippincott Williams & Wilkins. Morbidity and Mortality Weekly Report. (September 7, 2012). Vital signs: awareness and treatment of uncontrolled hypertension in adults—United States, 2003-2010. Centers for Disease Control and Prevention. Retrieved from http://www.cdc.gov/mmwr/preview/mmwrhtml/mm6135a3.htm Stedman, T. L. (2005). Stedman's Medical Dictionary. (5th ed.). Philadelphia: LippincottWilliams & Wilkins. Shankie, S. (2001). Hypertension in point. London: Pharmaceutical Press. Silverthorn, D.U. (2009). Human physiology: an integrated approach. (5th ed.). United States: Benjamin Cummings.