How many veins and arteries in the human body

Type 2 Diabetes. Arteries of the Body Medically reviewed by J. Arteries and your circulatory system. Major arteries of the body. Head and neck arteries. Share on Pinterest Arteries in the head and neck. Torso arteries. Share on Pinterest Arteries of the lungs, heart, pelvis, and the aorta in the abdomen. Abdomen arteries. Arteries of the arms. Arteries of the legs.

Quick guide to arteries vs. The bottom line. Medically reviewed by J. Automated vs. Read this next. Blood Pressure Readings Explained. Medically reviewed by Judith Marcin, M. Medically reviewed by Debra Sullivan, Ph. Medically reviewed by Alana Biggers, M. Medically reviewed by Deborah Weatherspoon, Ph. They can vary in size. The largest arteries have special elastic fibres in their walls. This helps to complement the work of the heart, by squeezing blood along when heart muscle relaxes.

Arteries also respond to signals from our nervous system, either tightening constricting or relaxing dilating. Arterioles are the smallest arteries in the body. They deliver blood to capillaries. Arterioles are also capable of constricting or dilating and, by doing this, they control how much blood enters the capillaries. Capillaries are tiny vessels that connect arterioles to venules.

They have very thin walls which allow nutrients from the blood to pass into the body tissues. Waste products from body tissues can also pass into the capillaries. For this reason, capillaries are known as exchange vessels. Groups of capillaries within a tissue reunite to form small veins called venules. Venules collect blood from capillaries and drain into veins. Veins are the blood vessels that carry blood back to the heart. They may contain valves which stop blood flowing away from the heart.

The heart works by following a sequence of electrical signals that cause the muscles in the chambers of the heart to contract in a certain order. If these electrical signals change, the heart may not pump as well as it should. The sequence then starts again for the next heartbeat. The closing of the valves in the heart make the 'lub-dub' sounds that a doctor can hear with a stethoscope.

If you exercise, your body tissues need more oxygen and will produce more carbon dioxide. This means your heart must speed up to meet those needs. How fast your heart beats your heart rate is controlled in a number of different ways. The brain controls the heart rate through the nervous system. A special part of the brain, called the medulla oblongata, receives information from many different systems of the body.

The brain then co-ordinates the information and either sends signals to increase or decrease the heart rate, depending on what is necessary. Even before physical activity begins, your heart may speed up in anticipation of what is to come. This is because a special part of the nervous system sends signals to the medulla. As physical activity starts, cells of the nervous system which monitor changes in the body receptors send signals about the position of your muscles to the brain.

This can increase your heart rate. The body also has other receptors which measure levels of chemicals, such as carbon dioxide, in your blood. If levels of carbon dioxide rise, signals are sent via the nervous system to the brain. The brain then sends electrical signals to the heart via nerves to speed it up.

The signals cause the release of hormones which make the SA node fire more often. This means the heart beats more frequently. The brain can also send signals to the heart to slow it down.

Other hormones, such as those from the thyroid gland, can also influence your heart rate, as can certain substances found in your blood. The most important function of the cardiovascular system the heart and blood vessels together is to keep blood flowing through capillaries. These layers surround the lumen, the hollow interior through which blood flows. The left ventricle of the heart pumps oxygenated blood into the aorta. From there, blood passes through major arteries, which branch into muscular arteries and then microscopic arterioles.

The arterioles branch into the capillary networks that supply tissues with oxygen and nutrients. The walls of arteries are thicker than the walls of veins, with more smooth muscle and elastic tissue. This structure allows arteries to dilate as blood pumps through them. After the capillaries release oxygen and other substances from blood into body tissues, they feed the blood back toward the veins.

First the blood enters microscopic vein branches called venules. The venules conduct the blood into the veins, which transport it back to the heart through the venae cavae. Vein walls are thinner and less elastic than artery walls. The pressure pushing blood through them is not as great. In fact, there are valves within the lumen of veins to prevent the backflow of blood. Capillaries are tiny vessels that branch out from arterioles to form networks around body cells.

In the lungs, capillaries absorb oxygen from inhaled air into the bloodstream and release carbon dioxide for exhalation. Elsewhere in the body, oxygen and other nutrients diffuse from blood in the capillaries to the tissues they supply.