Only within the last hundred years has science been able to unravel many of the mysteries associated with the physiology of the body. Technological advances including the computer have enabled scientists to begin the quest for a complete understanding. Even with these abilities and skills knowledge continues to be limited in some areas. The human body is a complicated and integrated system that performs several hundred tasks each moment. Organs are interrelated and impact one another in a synchrony of ways that are still not yet completely known to or understood by medical science. Not only are organs interconnected via nerves and blood vessels, but they are also joined by the fluid that travels within the vessels or by the various blood components. Messages, as well as nutrients, are sent from organ to organ in an effort to maintain homeostasis of the system, which is the human body's primary goal. Because of this coordination among the many entities of the total human system, malfunction of one part of the system can impact various parts of the remaining system. In other words, there is a sort of ripple effect that eventually results in one difficulty influencing an assortment of other functions and the proper operation of many organs. An analysis of the renin-angiotensis system is an excellent example of how one biologic function may impact another. Additionally, it illustrates the progress made by medical science, which has allowed the advance to the level of knowledge that exists today.
The renin-angiotensin-aldosterone system (RAAS) is a system of bodily hormones that regulates fluid balance and blood pressure. As name suggests, there are three parts to RAAS.
- Renin comes mostly from the kidneys,
- In turn, this helps form angiotensin in our tissues and blood.
- Finally this stimulates the adrenal cortex to release aldosterone.
Aldosterone is a crucial hormone for sodium conversion in the kidneys, sweat glands, salivary glands, and the colon. As such, aldosterone helps maintain homeostatic blood pressure regulation, potassium levels, and plasma sodium levels. Renin is proteolytic enzyme whose stimulation depends on sympathetic nerve activation, decreases delivery of sodium to parts of the kidneys, and renal artery hypotension.
This system also regulates blood volume and systemic vascular resistance (SVR). Also known as total peripheral resistance, SVR can be exacerbated by vasoconstriction. When the amount of blood delivered to the kidneys (known as renal blood flow RBF) is reduced, specialized cells called juxtaglomerular cells convert prorenin that is already in the blood into renin and put it back into circulation. It should be noted that prorenin, the precursor of renin, occurs at higher level in diabetic patients. Prorenin levels can predict the existence of microvascular difficulties. Moreover, pregnant women have high levels of prorenin. This will have the same clearing effect.
Essentially, renin is a glycoprotein enzyme found in the juxtaglomerular cells of the afferent arteriole (Chappell et al., 2000). In these cells, renin is synthesized, stored, and released. Upon receiving a signal from individual nephrons, the kidney, or local effectors, the substance is released from the cells. Renin then combines with angiotensinogen, which is a protein. This combination results in angiotensin I, an inactive decapeptide. Angiotensin I can then be converted into angiotensin II, an octapeptide. This occurs when angiotensin I combines with angiotensin-converting enzyme. When the renin-angiotensin system in blocked intrarenally, the situation may evolve to include renal vasodilation, natriuresis, and diuresis. Consequently, angiotensin II, a substance found in the kidneys, is involved in adequate renal function and control of this system.
Thus, this system involves a sequence of reactions or a multi-step process, the end result of which is the products referred to above. The production of renin combines with angiotensinogen to form Angiotensin I. Angiotensin I combines with angiotensin-converting enzyme to form Angiotensin II. Angiotensin II is the end of this chain of events, and it is angiotensin II that produces all of the effects that are attributed to the renin-angiotensin system.
The angiotensin II then is circulated through the body by way of the blood stream. As it flows through the circulatory system, angiotensin II impacts arterial pressure and blood vessels. Recent research illustrates the high level of complexity of the interactions among elements of the renin- angiotensin system and various aspects of the cardiac system.