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How Does Blood Travel Through the Body? The circulatory system is a network of blood vessels that transport blood throughout the body.
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The circulatory system
Your circulatory system is made up of your heart and blood vessels. Your heart pumps blood through your arteries and veins to all parts of your body.
Your arteries carry oxygen-rich blood from your heart to the rest of your body. Your veins carry oxygen-poor blood from the rest of your body back to your heart.
Blood is red because it contains a lot of oxygen. Oxygen is needed by all the cells in your body to help them work properly.
The heart
The heart is a muscular organ that pumps blood through the body. The left side of the heart pumps blood to the body, and the right side pumps blood to the lungs. The right side of the heart receives oxygen-poor blood from the body and pumps it to the lungs, where it picks up oxygen. The left side of the heart receives oxygen-rich blood from the lungs and pumps it to the body.
Arteries
The arteries are the roads of the circulatory system. They are responsible for carrying oxygen-rich blood away from the heart to the body’s cells. The walls of the arteries are made up of three layers of tissue. The inner layer, called the endothelium, is a single layer of smooth cells that helps blood flow smoothly through the artery. The middle layer, called the smooth muscle layer, is made up of muscle tissue that contract and relax to help regulate blood flow. The outer layer, called the connective tissue layer, is made up of collagen and elastin fibers that provide support and strength to the artery wall.
Capillaries
Capillaries are tiny blood vessels that connect the smallest arteries to the smallest veins. They are about 5 µm in diameter (5 µm = 0.005 mm). Red blood cells (erythrocytes) are able to pass through capillaries because of their small size. The average red blood cell is 7 µm in diameter.
When red blood cells reach the capillaries, they release oxygen and pick up carbon dioxide and waste products such as lactic acid. The walls of the capillaries are only one cell layer thick, so gases and waste products can diffuse easily through them.
Blood flow through capillaries is slow, about 5 cm/second, which gives ample time for exchange to occur.
Veins
Veins are the blood vessels responsible for carrying blood back to the heart. Most veins are found just beneath the skin, and are relatively close to the surface. This allows for easy access when drawing blood or starting an IV. There are three types of veins — superficial, pulmonary, and systemic.
Superficial veins are found close to the surface of the skin and are not usually connected to other veins. These veins are often used for blood tests or IVs because they are easy to access.
Pulmonary veins carry blood from the lungs back to the heart. These veins are located deep in the body and are not easily accessed from the outside.
Systemic veins carry blood from various organs back to the heart. These veins are located deep in the body and can be difficult to access.
Blood pressure
Blood pressure is a measure of the force that blood applies to the walls of arteries as it circulates through the body. The higher the blood pressure, the higher the force. The force is created by the heart as it pumps blood through the body. When blood pressure is measured, there are two numbers for each reading. The higher or systolic number represents the pressure when the heart contracts and pumps out blood. The lower or diastolic number represents the pressure when the heart relaxes and refills with blood.
Blood flow
In order to understand how blood travels through the body, it is important to first understand the basics of circulation. The heart is responsible for pumping blood through the body in a process known as circulation. Blood flows from the heart through a network of blood vessels, which include arteries, veins, and capillaries. Arteries carry oxygen-rich blood away from the heart, while veins carry oxygen-poor blood back to the heart. Capillaries are tiny blood vessels that connect arteries and veins and help to exchange oxygen and carbon dioxide between the bloodstream and tissues.
The lymphatic system
The lymphatic system is a network of tissues and organs that helps rid the body of toxins, waste and other unwanted materials. The main function of the lymphatic system is to transport lymph, a clear fluid that contains white blood cells, from the tissues to the bloodstream. Lymph travels through the body in a one-way direction and is eventually filtered by the kidneys and excreted as urine.
The lymphatic system is made up of a series of tubes that branch out into all parts of the body. These tubes are called lymphatic vessels. Lymphatic vessels are lined with smooth muscle tissue that contracts and relaxes to help move lymph through the body. The vessels are also equipped with valves that prevent the backward flow of lymph.
Lymphatic vessels empty into larger collecting vessels, which eventually drain into either the right side of the bloodstream or the left side, depending on their location in the body. Lymph from the right side of the body drains into veins near the right side of the heart, while lymph from the left side drains into veins near the left side of the heart.
Red blood cells
Red blood cells, or erythrocytes, are the most common type of blood cell and the vertebrate body’s principal means of delivering oxygen (O2) to the tissues — via blood flow through the circulatory system. Each red blood cell contains hemoglobin, an iron-containing protein, which facilitates oxygen transport by reversibly binding to this respiratory gas and greatly increasing its solubility in blood. In humans, mature red blood cells lack a nucleus and organelles in mammals other than mitochondria. They are biconcave disks and have a diameter of ~7 μm. Red blood cells are normally flexible and deform when passing through capillaries.
Platelets
Platelets are the smallest blood cells and they have no nucleus. Their main function is to help with blood clotting. When a blood vessel is damaged, platelets stick together and form a plug at the site of the injury to help stop the bleeding. Platelets also release chemicals that help attract more cells to the site of the injury.
