The Circulatory System
Created on September 29, 2020
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The circulatory system is an organ system which allows blood to circulate and transport nutrients like oxygen, carbon dioxide, amino acids, hormones, blood cells, and electrolytes to and from the cells in the body.
PARTS OF THE HEART
PARTS OF CIRCULATORY SYSTEM
THE HEART BEAT
“Heart and Circulatory System (for Teens) - Nemours KidsHealth.” Edited by Larissa Hirsch, KidsHealth, Nemours Children's Health System, Sept. 2018, kidshealth.org/en/teens/heart.html.
The circulatory system is comprised of blood vessels that bring blood away from and then back towards the heart. The blood vessels which carry blood away from the heart are called arteries, and the blood vessels which carry blood back to the heart are called veins. The circulatory system carries oxygen and nutrients to cells, and removes waste like carbon dioxide from the body.
The heart is a muscular organ which is at the center of the circulatory system. The heart is about the size of a fist, and it serves as a pump. The heart pumps blood throughout the body, using beating from 60 to 100 times per minute. The blood that the heart sends throughout our bodies carries oxygen to our cells, and once the blood has delivered the oxygen, it returns to the heart. This blood is then sent by the heart back to the lungs where it picks up more oxygen, and then the cycle repeats.
There are 4 chambers in the heart - two on top and two on the bottom. The two bottom chambers are the ventricles, and you have a right ventricle and a left ventricle. The ventricles pump blood out of the heart. The two chambers on top are the atria, and you have a right atrium and a left atrium. The atria are responsible for receiving the blood entering the heart. The inter ventricular septum is a wall which separates the ventricles, and the intertribal septum is a wall which separates the atria. The atria and the ventricles are separated from each other by the atrioventricular valve. There are also two valves which separate the ventricles from large blood vessels carrying blood leaving the heart: the pulmonic valve and the aortic valve.
The heart can pump more or less blood depending on what a person needs. When you’re resting, for example, it pumps just enough to provide the lower oxygen levels needed at rest. However, when you run or exercise, the heart pumps faster so your muscles can get more oxygen. The heartbeat is controlled by a system of electrical signals in the heart. A small area of tissue in the right atrium called the sinus node sends out an electrical signal to start pumping the heart muscle. The sinus node sets the rate of the heartbeat. The heartbeat is made of two phases: systole and diastole. In systole, the ventricles contract and pump blood into the aorta and pulmonary artery. The atrioventricular valves close to prevent blood from going back into the atria. The aortic and pulmonary valves open to allow blood into the aorta and pulmonary artery. Then these valves close to prevent blood from going back into the ventricles. The opening and closing of these valves is what creates the sound of a heartbeat. In diastole, the atrioventricular valves open and the ventricles relax, allowing them to fill with blood from the atria and prepare for the next heartbeat.
The circulatory system is comprised of blood vessels that bring blood away from and then back towards the heart. There are two pathways from the heart. Pulmonary circulation is a loop from the heart to the lungs and back to the heart. Systemic circulation brings blood from the heart to all other parts of the body and back to the heart. In pulmonary circulation, the pulmonary artery is used to bring blood from the heart to the lungs. The blood picks up oxygen at the lungs and drops off carbon dioxide to be exhaled, and then the blood returns to the heart through the pulmonary veins. In systemic circulation, blood which has returned from the lungs and now has oxygen is sent to the rest of the body. There is a large artery called the aorta which leaves the heart carrying oxygenated blood. The aorta has lots of smaller branches which send blood to the muscles of the heart and all other parts of the body. There are capillaries, or tiny blood vessels, at each body part, and capillaries connect arteries to the veins. Nutrients and oxygen are delivered to the cells through the thin walls of the capillaries, and waste is brought into the capillaries. The capillaries then lead into small veins, which lead to larger and larger veins, until the blood approaches the heart. When the blood gets back to the heart, it re-enters pulmonary circulation and goes back to the lungs so it can drop off the carbon dioxide and waste and pick up more oxygen.