Ĭardiovascular diseases are the most common cause of death globally as of 2008, accounting for 30% of deaths. Exercise temporarily increases the rate, but lowers it in the long term, and is good for heart health. The heart beats at a resting rate close to 72 beats per minute. Oxygenated blood then returns to the left atrium, passes through the left ventricle and is pumped out through the aorta into systemic circulation, traveling through arteries, arterioles, and capillaries-where nutrients and other substances are exchanged between blood vessels and cells, losing oxygen and gaining carbon dioxide-before being returned to the heart through venules and veins. From here it is pumped into pulmonary circulation to the lungs, where it receives oxygen and gives off carbon dioxide. In humans, deoxygenated blood enters the heart through the right atrium from the superior and inferior venae cavae and passes to the right ventricle. These generate an electric current that causes the heart to contract, traveling through the atrioventricular node and along the conduction system of the heart. The heart pumps blood with a rhythm determined by a group of pacemaker cells in the sinoatrial node. The wall of the heart is made up of three layers: epicardium, myocardium, and endocardium. The heart is enclosed in a protective sac, the pericardium, which also contains a small amount of fluid. In a healthy heart blood flows one way through the heart due to heart valves, which prevent backflow. Fish, in contrast, have two chambers, an atrium and a ventricle, while most reptiles have three chambers.
Commonly the right atrium and ventricle are referred together as the right heart and their left counterparts as the left heart. In humans, other mammals, and birds, the heart is divided into four chambers: upper left and right atria and lower left and right ventricles. In humans, the heart is approximately the size of a closed fist and is located between the lungs, in the middle compartment of the chest, called the mediastinum.
The pumped blood carries oxygen and nutrients to the body, while carrying metabolic waste such as carbon dioxide to the lungs. This organ pumps blood through the blood vessels of the circulatory system. The heart is a muscular organ in most animals.
0 kommentar(er)
