06+Cardiology

Cardiology Chapter 14

__//**Content Summary **//__ //According to dictionary.com, cardiology is the study of the heart in health and in disease. In essence, when it comes down to the study of the heart it all revolves around the blood that the heart is constantly pumping. The blood flow to the various parts of the body and the organs is a major part of the cardiology study. Along with the flow, the pressure and the volume are two more vital aspects of the cardiology as a whole. A few of the specific diseases that directly affect heart and cardiology are hypertension, shock, and congestive heart failure. // //Cardiology focuses on the blood flow in a few different areas. The heart pumps the blood to and from various places in the body. An important factor when discussing the blood flow is the vascular resistance. In Poiseuille’s Law, blood flow is directly proportional to a couple of different things. First off it is proportional to the length of the vessel and also the thickness, or the viscosity, of the blood. Next is the radius of the vessel, which is equally important when trying to discover the exact vascular resistance. The blood flow in the body runs to a few main places that are important in cardiology. The four areas introduced and discussed in this chapter are the heart, skeletal muscles, skin, and the brain. // Source (Physiology Book)

[|Poiseuille's Law]



//The first two of these four topics to be discussed are the blood flow to the heart and the skeletal muscles. The most vital organ is the heart because it is the motor that drives the flow of blood. It respires aerobically because of its high hemoglobin and enzyme levels along with the fact that it contains an abundant supply of capillaries. The heart goes through some interesting changes during exercise. The coronary vessels are effect by vasodilation when the heart’s metabolism is boosted and metabolic mechanism triggers this action. The flow during exercise differs from that directly before and right at the start of the exercise. Before and right at the onset of the exercise the blood flow through the skeletal muscles is increased by the vasodilation which is a result of cholinergic sympathetic nerve fibers actions. Obviously during exercise the heart and the skeletal muscles need more blood, so they receive up to five times, or higher, total blood flow. There are a few reasons for the heart rate, and therefore blood flow, to increase. First off, an increase in the activity of the sympathetic nerves or a decline in the activity of the vagus nerve can cause a rise in cardiac rate. Next, there is the greater activity of the skeletal muscles and increased breathing which in turn raise the level of venous return to the heart. And lastly, there is the possibility of a decrease in total resistance, or the increased contractility of the heart, which can cause an increase in stroke volume. // Source (Physiology Book)

[|//The Cardiovascular System and Exercise//]

//﻿ // //The skin and the brain are the two organs in the body that there blood flow is controlled by a very unique process. The blood flow to the brain is controlled by two different methods, myogenically and metabolically. If there is a rise in systemic blood pressure, this causes the blood flow to the cerebral vessels to constrict. When there is an area that needs more blood, the metabolic actions cause the vessels to dilate so that more blood can reach these specific regions. The rare arteriovenous anastomoses is the regulator mechanism for the skin that can redirect the route of blood away from a certain capillary loop. This often happens when the body gets cold. The blood is rerouted to stay towards the inner more precious organs. Activities of the sympathetic nerve fibers can constrict the cutaneous arterioles. As a reverse of what I previously said about the body trying to keep itself warm, it can reverse this process to cool down as well. The flow of blood through the surface capillaries can be increased in order to try to cool the blood down in order to ultimately cool down the rest of the body as well. // Source (Physiology Book)

__//**Application **//__ //This is an application that all of us share because we all get hot and cold. Through this application section I chose to discuss how the blood flow affects all of our bodies if we were to get hypothermia. When our bodies get to cold the blood flow throughout the body retreats from the capillary loops that are in the skin and returns to the organs. Instead it stays deeper in the body to continue to keep the organs warm, because we depend on them more than the skin. The effect of this on the skin is that it is the first thing to be affected by prolonged exposure to the elements. This is when hypothermia sets in and frostbite can occur. When rescue arrives and they process of warming an individual who has hypothermia begins, certain precautions must be taken. It is advised that the body be warmed immediately and removed from the cold environment. It is very important that the heat be returned as soon as possible to reduce the risk of a heart attack. Rapid re-warming, however, can still cause a rapid decrease in blood pressure and a drop in cardiac output. //

__//**Essential Questions **//__ //The three most important aspects of controlling blood pressure are the heart rate, stroke volume, and the peripheral resistance. These variables are all controlled by a range of negative feedback mechanisms in order to maintain homeostasis. If any of these variables increase for any reason, and this is not countered by another action, the blood pressure will increase accordingly. First off the heart rate can vary greatly depending on what the body is doing. For example during exercise the heart’s metabolism increases, causing vasodilation and therefore increasing coronary blood flow. This action is to be able to deliver the products through the blood that the muscles need more of during exercise. The cardiac control center located in the medulla controls the cardiac rate. Stroke volume plays a toll on the blood pressure as well. At rest the stroke volume is about equal to the amount of blood that is currently in the veins. During a stressful situation however, the heart can increase the stroke volume to compensate for the stress and this is caused by the nervous system. The peripheral resistance of the veins and arteries also plays an important part in blood pressure. Too much resistance can cause an increase in blood pressure, and not enough can cause a drop as well. The vasomotor control center located in the medulla controls the resistance. // //The baroreceptor reflex that helps maintain homeostasis. The reflex, however, is more sensitive to a decrease in pressure than to an increase in the blood pressure. A decrease in blood pressure spurs an increase in the sympathetic nervous system, and a related decrease in the parasympathetic division. The peripheral resistance then increases along with the cardiac output. Inversely, a rise in blood pressure can cause the parasympathetic system to increase in activity, and the opposite for the sympathetic system. The roles are reversed in order to maintain homeostasis. // //<span style="color: #000080; font-family: Verdana,Geneva,sans-serif; font-size: 18pt;">Another reflex that is important in regulation of blood pressure is the atrial stretch reflexes. This reflex is performed by the atrial stretch receptors located in the atria of the heart. A venous return that is to high causes the response. These receptors are activated to lower the venous return and also stimulate the tachycardia and the resulting increase in sympathetic nerve activity. Next is the inhibition of ADH, which causes an increase in the amount of urine excreted and lowering the blood volume. Last is the promotion of the atrial natriuretic peptide, or ANP. ANP lowers the blood volume by increasing urinary salt and water excretion. //