CARDIOVASCULAR SYSTEM

INTRODUCTION TO CARDIOVASCULAR SYSTEM.

The heart is muscular organ about the size of a closed fist located in the chest between the lungs behind the sternum and above the diaphragm. It is surrounded by the pericardium.On its superior end, the base of the heart is attached to the aorta, pulmonary arteries and veins, and the vena cava. The inferior tip of the heart, known as the apex, rests just superior to the diaphragm. The base of the heart is located along the body’s midline with the apex pointing toward the left side. Because the heart points to the left, about 2/3 of the heart’s mass is found on the left side of the body and the other 1/3 is on the right.

Heart is the pump which is responsible for maintaining adequate circulation of oxygenated blood around the vascular network of the body. It takes in deoxygenated blood through the veins and delivers it to the lungs for oxygenation before pumping it into the various arteries.

Anatomy of the Heart 

Pericardium: The heart is placed within a fluid filled cavity called as periodically cavity. The walls and lining of the pericardial cavity are made up of a special membrane known as the pericardium. Pericardium is a type of serous membrane that produces serous fluid to lubricate the heart and prevent friction between the ever beating heart and its surrounding organs. Besides lubrication, the pericardium serves to hold the heart in position and maintain a hollow space for the heart to expand when it is full.The pericardium has two layers, a visually layer that covers the outside of the heart and a parietal layer that forms a sac around the outside of the pericardial cavity.The heart wall is made of three layers:

Epicardium: The epicardium is the outermost layer of the heart wall. It is also referred to as visceral pericardium, which is inner layer of pericardium. The epicardium is a thin layer of serous membrane that helps to lubricate and protect the outside of the heart.

Myocardium: Myocardium is the thick middle layer of heart wall and consists of numerous layers of cardiac muscle fibers that wrap around the heart. Contraction of myocardium pumps blood out of the heart into the aorta and pulmonary trunk arteries.

 Endocardium: Endocardium is the simple squamous endothelium layer that lines inside the heart. The endocardium is very smooth and is responsible for keeping blood from sticking to the inside of the heart and forming potentially deadly blood clots.The thickness of the heart wall varies in different parts of the heart. The atria of the heart have a very thin myocardium because they do not need to pump blood very far, but only to the nearby ventricles. The ventricles, on other hand, have a very thick myocardium to pump blood to the lungs or throughout the entire body. The right side of the heart has less myocardium in its walls than the left side because the left side has to pump blood through the entire body while the right side only has to pump to the lungs.

 Heart Chambers: The heart contains four chambers: the right atrium, left atrium, right ventricle and left ventricle. The atria are smaller than the ventricles and have thinner, less muscular walls than the ventricles. The atria act as receiving chambers for blood, so they are connected to the veins that carry blood to the heart.The ventricles are the larger, stronger pumping chambers that send blood out of the heart. The ventricles are connected to the arteries that carry blood away from the heart.

 Heart Valves: The heart functions by pumping blood both to the lungs and to the systems of the body. To prevent blood from flowing backwards or “regurgitating” back into the heart, a system of one way valves are present in the heart. The heart valves can be divided into two types: atrioventricular and semilunar valves.

 Atrioventricular Valves (AV): The AV valves are located in the middle of the heart between the atria and ventricles and only allow blood to flow from the atria into the ventricles. The AV valve on the right side of the heart is called the tricuspid valve because it is made of three cusps (flaps) that separate to allow blood to pass through andflow backward. The AV valve on the left side of the heart is called the mitral valve or the bicuspid valve because it has two cusps. The AV valves are attached on the ventricular side to tough strings called chordae tendineae. The chordae tendineae pull on the AV valves to keep them from folding backwards and allowing blood to flow backward. 

 Semilunar Valves: The semilunar valves, so named for the crescent moon shape of their cusps, are located between the ventricles and the arteries that carry blood away from the heart. The semilunar valve on the right side of the heart is the pulmonary valve, so named because it prevents the back flow of blood from the pulmonary trunk into the right ventricle. The semilunar valve on the left side of the heart is the aortic valve, named for the fact that it prevents the aorta from flowing blood back into the left ventricle. The semilunar valves are smaller than the AV valves and do not have chordae tendineae to hold them in place. Instead, the cusps of the semilunar valves are cup shaped to catch the backward flowing blood and use the blood pressure to snap shut.