One-way valves separate the four chambers. The heart is composed of three layers: the epicardium, the myocardium, and the endocardium. The inner wall of the heart is lined by the endocardium. The myocardium consists of the heart muscle cells that make up the middle layer and the bulk of the heart wall. The outer layer of cells is called the epicardium, the second layer of which is a membranous layered structure the pericardium that surrounds and protects the heart; it allows enough room for vigorous pumping, but also keeps the heart in place, reducing friction between the heart and other structures.
The heart has its own blood vessels that supply the heart muscle with blood. The coronary arteries branch from the aorta, surrounding the outer surface of the heart like a crown. They diverge into capillaries where the heart muscle is supplied with oxygen before converging again into the coronary veins to take the deoxygenated blood back to the right atrium, where the blood will be re-oxygenated through the pulmonary circuit.
Atherosclerosis is the blockage of an artery by the buildup of fatty plaques. The heart muscle will die without a steady supply of blood; because of the narrow size of the coronary arteries and their function in serving the heart itself, atherosclerosis can be deadly in these arteries. The slowing of blood flow and subsequent oxygen deprivation can cause severe pain, known as angina. Complete blockage of the arteries will cause myocardial infarction—death of cardiac muscle tissue—which is commonly known as a heart attack.
Blood vessels include arteries, capillaries, and veins which are responsible for transporting blood throughout the body. The blood from the heart is carried through the body by a complex network of blood vessels. Arteries take blood away from the heart. The main artery is the aorta that branches into other major arteries, which take blood to different limbs and organs. These major arteries include the carotid artery, which takes blood to the brain; the brachial arteries, which take blood to the arms; and the thoracic artery, which takes blood to the thorax and then into the hepatic, renal, and gastric arteries for the liver, kidneys, and stomach, respectively.
The iliac artery takes blood to the lower limbs. The major arteries diverge into minor arteries, and then into smaller vessels called arterioles, to reach more deeply into the muscles and organs of the body. Major arteries and veins : The blood from the heart is carried through the body by a complex network of blood vessels. This diagram illustrates the major human arteries and veins of the human body. Arterioles diverge into capillary beds. Capillary beds contain a large number 10 to of capillaries that branch among the cells and tissues of the body.
Capillaries are narrow-diameter tubes that can fit red blood cells in single-file lines and are the sites for the exchange of nutrients, waste, and oxygen with tissues at the cellular level.
Fluid also crosses into the interstitial space from the capillaries. The capillaries converge again into venules that connect to minor veins, which connect to major veins that take blood high in carbon dioxide back to the heart.
The major veins drain blood from the same organs and limbs that the major arteries supply. Fluid is also brought back to the heart via the lymphatic system. The structure of the different types of blood vessels reflects their function or layers. There are three distinct layers, or tunics, that form the walls of blood vessels. The inner, tunica intima is a smooth, inner lining of endothelial cells that are in contact with the red blood cells.
This tunic is continuous with the endocardium of the heart. The cardiac cycle is the coordination of the filling and emptying of the heart of blood by electrical signals that cause the heart muscles to contract and relax. The human heart beats over , times per day. In each cardiac cycle, the heart contracts systole , pushing out the blood and pumping it through the body; this is followed by a relaxation phase diastole , where the heart fills with blood.
The atria contract at the same time. Following a brief delay, the ventricles contract at the same time forcing blood through the semilunar valves into the aorta and the artery transporting blood to the lungs via the pulmonary artery. During a cardiac diastole, the heart muscle is relaxed and blood flows into the heart. During b atrial systole, the atria contract, pushing blood into the ventricles.
During c atrial diastole, the ventricles contract, forcing blood out of the heart. The pumping of the heart is a function of the cardiac muscle cells, or cardiomyocytes, that make up the heart muscle. Cardiomyocytes are distinctive muscle cells that are striated like skeletal muscle but pump rhythmically and involuntarily like smooth muscle; they are connected by intercalated disks exclusive to cardiac muscle.
They are self-stimulated for a period of time and isolated cardiomyocytes will beat if given the correct balance of nutrients and electrolytes. Cardiomyocytes are striated muscle cells found in cardiac tissue. Girod, Anton Becker; scale-bar data from Matt Russell. The electrical signals and mechanical actions are intimately intertwined.
The internal pacemaker starts at the sinoatrial SA node , which is located near the wall of the right atrium. Electrical charges spontaneously pulse from the SA node causing the two atria to contract in unison. The pulse reaches a second node, called the atrioventricular AV node, between the right atrium and right ventricle where it pauses for approximately 0.
From the AV node, the electrical impulse enters the bundle of His, then to the left and right bundle branches extending through the interventricular septum. People who smoke often have cold hands and feet. What might explain this condition in terms of Is the vertebral artery a branch of the aortic arch? What conditions contribute to elevated blood levels of alkaline phosphatase? Are lymphocytes produced in the bone marrow and then migrate to the thymus gland and lymph nodes The waste product of this process, carbon dioxide, is carried away from your cells in your blood.
Your heart is a single organ, but it acts as a double pump. The first pump carries oxygen-poor blood to your lungs, where it unloads carbon dioxide and picks up oxygen. It then delivers oxygen-rich blood back to your heart. The second pump delivers oxygen-rich blood to every part of your body. Blood needing more oxygen is sent back to the heart to begin the cycle again. In one day your heart transports all your blood around your body about times.
Your right ventricle pumps blood to your lungs and your left ventricle pumps blood all around your body. The muscular walls of the left ventricle are thicker than those of the right ventricle, making it a much more powerful pump. For this reason, it is easiest to feel your heart beating on the left side of your chest. Unlike skeletal muscle cells that need to be stimulated by nerve impulses to contract, cardiac muscle cells can contract all by themselves.
However, if left to their own devices, cardiac muscle cells in different areas of your heart would beat at different rates. Muscle cells in your ventricles would beat more slowly than those in your atria. Without some kind of unifying function, your heart would be an inefficient, uncoordinated pump.
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