The circulatory system is centred on the heart, an amazing organ that constantly works to pump blood around blood vessels in every part of the body. Blood carries all the things, like oxygen, that cells need to thrive and keep us healthy.
The heart is made up of four different blood-filled areas, and each of these areas is called a chamber. There are two chambers on each side of the heart. One chamber is on the top and one chamber is on the bottom.
The two chambers on top are called the atria. (If you're talking only about one, call it an atrium.) The atria are the chambers that fill with the blood returning to the heart from the body and lungs. The heart has a left atrium and a right atrium.
The two chambers on the bottom are called the ventricles. The heart has a left ventricle and a right ventricle. Their job is to squirt out the blood to the body and lungs. Running down the middle of the heart is a thick wall of muscle called the septum. The septum's job is to separate the left side and the right side of the heart.
The atria and ventricles work as a team — the atria fill with blood, then push it into the ventricles. The ventricles then squeeze, pumping blood out of the heart. While the ventricles are squeezing, the atria refill and get ready for the next contraction.
The blood moves through many tubes called arteries and veins, which together are called blood vessels. These blood vessels are attached to the heart. The blood vessels that carry blood away from the heart are called arteries. The ones that carry blood back to the heart are called veins.
The human body needs a steady supply of blood to keep it working right. Blood delivers oxygen to all the body's cells. To stay alive, a person needs healthy, living cells. Without oxygen, these cells would die. If that oxygen-rich blood doesn't circulate as it should, a person could die.
Remember that your heart is a muscle. In order for it to be strong, you need to exercise it. How do you do it? By being active in a way that gets you slightly out of breath, like skipping, dancing, or playing tennis or football. Try to be active every day for at least 30 minutes.
Words to know:
Aorta - the main artery in mammals that carries blood from the left ventricle of the heart to all the branch arteries in the body except those in the lungs.
Arteries - a blood vessel that is part of the system carrying blood under pressure from the heart to the rest of the body.
Atrium - one of the upper chambers of the heart that takes blood from the veins and pumps it into a ventricle.
Capillaries - an extremely narrow thin-walled blood vessel that connects small arteries arterioles with small veins to form a network throughout the body.
Carbon dioxide - a heavy, colourless, odourless gas.
Cells - the cell is the basic unit of life. Some organisms are made up of a single cell, like bacteria, while others are made up of trillions of cells. Human beings are made up of cells, too.
Circulatory - relating to the circulation of the blood.
Complex - made up of many interrelated parts.
Contractions - a tightening or narrowing of a muscle, organ, or other body part.
Nutrients - a substance that provides nourishment.
Organ - a complete and independent part of a plant or animal that has a specific function.
Oxygen - a colourless, odourless gas that is essential for plant and animal respiration.
Perish - to come to an end or cease to exist.
Pulse - the regular expansion and contraction of an artery, caused by the heart pumping blood through the body.
Transporting - to carry somebody or something from one place to another.
Veins - a blood vessel that carries blood to the heart.
Waste - unwanted or unusable remains, or by-products.
Although each organ has its specific functions, organs also function together in groups, called organ systems (see Table: Major Organ Systems). Doctors categorize disorders and their own medical specialties according to organ systems.
Some examples of organ systems and their functions include the digestive system, the cardiovascular system, and the musculoskeletal system.
The digestive (or gastrointestinal) system, extending from the mouth to the anus, is responsible for receiving and digesting food and excreting waste. This system includes not only the stomach, small intestine, and large intestine, which move and absorb food, but associated organs such as the pancreas, liver, and gallbladder, which produce digestive enzymes, remove toxins, and store substances necessary for digestion.
The cardiovascular system includes the heart (cardio) and blood vessels (vascular). The cardiovascular system is responsible for pumping and circulating the blood.
The musculoskeletal system includes the bones, muscles, ligaments, tendons, and joints, which support and move the body.
Major Organ Systems
Some Major Functions of the System
Pumps blood and circulates it throughout the body
Adds oxygen to the blood (and removes carbon dioxide from the blood)
Directs intentional (and many automatic) actions of the body
Enables thinking, self-awareness, and emotions
Provides barrier protection between the inside of the body and the external environment
Provides structure and allows motion of the body
Transports oxygen and nutrients to all the cells of the body (and removes carbon dioxide and waste products)
Extracts nutrients from foods
Excretes waste products from the body
Produces chemical messengers carried in the blood, which direct the activities of different organ systems
Filters waste products from the blood