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How does blood travel around the body? The heart pumps blood around the body through a system of tubes called arteries and veins.
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The circulatory system
The circulatory system is a network of vessels that transport blood around the body. It is made up of the heart, which pumps blood, and the arteries and veins, which transport it.
The circulatory system has two main parts: the lymphatic system and the cardiovascular system. The lymphatic system helps to fight infection and drains fluid from tissues. The cardiovascular system transports oxygen and nutrients to cells and gets rid of carbon dioxide and other waste products.
The heart pumps blood around the body through a network of arteries. Arteries are blood vessels that carry blood away from the heart. The blood flows through the arteries to the smaller blood vessels called capillaries. Capillaries are found in all tissues of the body, where they exchange oxygen and nutrients for carbon dioxide and waste products. The blood then flows through veins back to the heart. Veins are blood vessels that carry blood towards the heart.
The heart
The heart is a muscular organ that pumps blood around the body. The blood carries oxygen and nutrients to the cells, and carbon dioxide and other waste products away from them. The heart is located in the chest, between the lungs. It is about the size of a fist.
Arteries
Arteries are the blood vessels that carry blood away from the heart. They are muscular tubes lined with smooth muscle cells and endothelial cells. The smooth muscle cells are arranged in layers that can contract and relax. This allows the arteries to adjust their diameter to regulate blood flow. Arteries branch into smaller and smaller vessels called arterioles until they reach the capillaries.
The walls of arteries are thicker than those of other blood vessels because they have to withstand the high pressure of blood as it is pumped from the heart. The outer layer (the tunica externa) is made of connective tissue and protects the artery from injury. The middle layer (the tunica media) is made up of smooth muscle cells and elastic fibers. This layer can contract or relax to help regulate blood flow. The innermost layer (the tunica intima) is made up of endothelial cells that line the artery and prevent blood from clotting inside it.
Capillaries
The smallest blood vessels in the body are called capillaries. They are only one cell thick and are found in between the cells of the body. Each capillary is connected to a larger blood vessel, called an arteriole (artery + taper). The arteriole carries oxygen-rich blood from the heart to the capillaries. Then, the capillaries deliver the oxygen-rich blood to all of the cells in the body.
After delivering oxygen to the cells, the capillaries pick up carbon dioxide and other wastes from the cells. The carbon dioxide and waste-filled blood from the capillaries flows into venules (vein + taper), which are small veins. The venules then connect to larger veins that carry carbon dioxide and waste-filled blood back to the heart.
Veins
Your veins are the blood vessels that take blood back to your heart. They are usually blue in color and are found just beneath your skin. Your veins have valves to keep your blood flowing in the right direction. Blood flow is helped along by the muscles in your body, which squeeze the veins and push the blood toward your heart.
Blood pressure
Blood pressure is the force that pushes blood through the body. It is created by the heart as it pumps blood through the arteries. The higher the pressure, the harder the heart has to work. Over time, this can lead to heart disease.
Blood flow
Your heart is a pump that sends blood around your body. Blood flows from your heart through a network of arteries and veins. Arteries carry blood away from your heart, and veins carry blood back to your heart.
Your arteries are made up of smooth muscle cells. These cells contract and relax to squeeze blood through your arteries. The force generated by the contracting muscle cells is called hydrostatic pressure. Hydrostatic pressure drives blood flow through your arteries and veins.
Blood flow is also affected by another type of pressure, called oncotic pressure. Oncotic pressure is created by the proteins in your blood plasma. Proteins are attracted to each other, and this attraction creates oncotic pressure. Oncotic pressure pulls fluid back into your blood vessels, which helps to keep blood flowing smoothly.
Blood flow slows as it travels through your arteries and veins. This happens because the walls of your arteries and veins create resistance to blood flow. The longer the distance that blood has to travel, the more resistance it encounters, and the slower its flow becomes.
The lymphatic system
The lymphatic system is a network of tissues and organs that help rid the body of toxins, waste and other unwanted materials. The system includes the lymph nodes, thymus, spleen, tonsils and bone marrow. These organs work together to produce and store white blood cells, which are critical for fighting infections.
The lymphatic system also helps maintain fluid balance in the body by collecting excess fluid and returning it to the circulatory system. This fluid, called lymph, is collected in a network of tiny vessels called lymphatics. Lymphatics are found throughout the body but are most concentrated in the neck, armpits and groin.
Lymphatic vessels are similar to veins but have thinner walls and no valves. Lymph flows through these vessels by a process called filtration. As fluid passes through the walls of the lymphatics, small particles such as bacteria and viruses are filtered out. The filtered fluid then enters the lymph nodes where it is cleansed before being returned to circulation.
Red blood cells
Red blood cells are the most common type of blood cell and they play a vital role in transporting oxygen and carbon dioxide around the body. They are produced in the bone marrow and released into the bloodstream when they are mature.
Red blood cells are shaped like discs and have a smooth, flexible membrane. The cell is filled with hemoglobin, a protein that contains iron. This gives the cell its red color and enables it to carry oxygen.
Red blood cells are constantly being produced and released into the bloodstream. They have a lifespan of around 120 days before they are broken down and replaced.
Platelets
Platelets are small, round, white blood cells that help with blood clotting. When you cut yourself, your body forms clots to stop the bleeding. Platelets and a protein in your blood called fibrin team up to form these clots.
