The heart and circulatory system
The circulatory (cardiovascular) system is made up of the heart, blood vessels and the blood. But what does the circulatory system do? And how do its parts work together to keep your body healthy? Explore the circulatory system in this engaging and informative article.
Athletes, trainers, bodybuilders and even regular gym-goers need to understand exactly how the heart and circulatory system in their body function, so that they can work them properly to make them stronger and healthier.
The heart is the most appreciated part of the circulatory system. This is with good reason. In your lifetime, your heart will beat more than 2 billion times! Leg muscles may tire after a run. And, arm muscles may grow weary after swimming laps. But, your heart’s cardiac muscle keeps going.
Here are the main functions of the circulatory system:
- transport – carrying blood, water, oxygen and nutrients throughout the body and the transport and removal of waste;
- body temperature control – the blood absorbs the body heat and carries it to the lungs and to the skin, where it is then released;
- protection – it helps to fight disease, e.g. antibodies which fight infection are carried in the blood; also the clotting of blood seals cuts and wounds.
The heart – body’s hardest-working muscle
The heart is a vital organ which pumps blood around the body delivering oxygen to working muscles and transporting waste products, eg carbon dioxide back to the heart and lungs for removal from the body. The heart of a healthy adult (70 kg) pumps approximately 1,900 gallons of blood each day.
Cardiac muscle is different from the other muscle types in that it is striated like skeletal muscle, but automatic like smooth muscle. Unlike other muscles, heart muscle does not need to rest. It operates constantly. Heart pumps blood every second, every day and every night. It pumps blood when we eat, when we sleep or when we exercise. It never rests. Your heart beats o its own. You don’t have to think about making it pump blood.
Location and size
The heart is a hollow muscular organ shaped like a blunt cone and located in the chest behind the sternum (breast bone). It is supported by ligaments attached to the sternum, or breastbone, and hangs slightly to the left of the center of the chest .A healthy heart weighs less than a pound (.45 kilograms), and is approximately 5.5 inches (14 centimeters) tall by 3.5 inches (9 cm) wide by 2.5 inches (6 cm) thick.
Inner chambers: atria and ventricles
The heart is a hollow organ with four flexible and resilient inner chambers. The upper two chambers are called the atria. Singly, one is called an atrium, from the Latin word meaning “entrance.”
The lower chambers are called the ventricles, from the Latin word for “belly.” The heart is also divided into two sides—left and right.
Atria fill with the blood returning to the heart from the body and lungs. When full, the atria contract. This action squeezes the blood into the two lower chambers called ventricles.
Ventricles are larger and more muscular than atria. Their walls are thicker because they have a harder task. They push blood out of the heart and back into blood vessels.
The left ventricle is stronger than the right as it pumps blood round the whole body (all the way to your feet), whereas the right ventricle only has to pump blood to the lungs via the pulmonary artery.This is where the process of gaseous exchange (diffusion of oxygen) takes place.
Pulmonary circulation is the transportation of blood from the right side of the heart to the lungs, returning to the left side of the heart. Systemic circulation is the transportation of blood from the left ventricle through the aorta, arteries and capillaries to the body tissues, returning via veins to the right atrium.
Wall of muscle tissue: Septum
The two sides are separated by a wall of muscle tissue called the septum. The septum prevents blood on one side from mixing with blood on the other. It is critical that the two sides remain apart because the two sides of the heart perform completely separate functions.
Each half of the heart has special flaps made of muscle. The flaps separate the atrium from the ventricle. These flaps are called valves. Each valve is like a door. It opens only one way. When the valve opens, blood flows from the atrium to the ventricle. Then the valve closes quickly. It does not let the blood flow back into the atrium.
On the outside wall of each ventricle is another valve. When the ventricles are full of blood, these valves open. The blood flows from the ventricles into the blood vessels. Then the valves close again.
The sound of the valves opening and closing is what one hears when listening for a heartbeat.
How blood flows through the heart?
The main function of the heart is to act as a pump. It beats over and over and over again. However, it always beats in the same way. This is how it works:
- The blood enters the right atrium. It is now dark red with little oxygen but mainly waste products such as carbon dioxide.
- The right atrium pumps the blood into the right ventricle, through a one-way valve.
- The right ventricle pumps the blood through the pulmonary artery to the lungs where oxygen is picked up and carbon dioxide is deposited. The blood now changes color to bright red because it is carrying extra oxygen.
- From the lungs the blood returns to the left atrium through the pulmonary vein.
- The left atrium pumps the blood into the left ventricle and the blood leaves here through the aorta to be distributed to the rest of the body.
Blood vessels are the system of hollow tubes that carry blood to and from the heart. If they could be set end to end, they would extend for more than 60.000 miles. Some blood vessels are big. Others are tiny. There are three types of blood vessels:
- veins, and
Arteries are the strongest, thickest, and most elastic of all the vessels. They carry the blood at high pressure away from the heart. The arteries divide into smaller vessels called arterioles.
Aorta is the largest artery. It rises upward after leaving the left ventricle of the heart, and forms an arch that extends downward to the abdomen and separates into two arteries. All major arteries leaving the heart, except the pulmonary artery, branch off from the aorta.
The first to do so are the left and right coronary- arteries. These vessels are connected to the upward, or ascending, aorta. Coronary arteries carry oxygen-rich blood to the heart itself. Other arteries that stem from the aortic arch are the brachiocephalic artery, the left common carotid artery, and the left subclavian artery.
Arteries that branch from the descending aorta are the thoracic and abdominal arteries, which split into large arteries that branch into medium sized arteries. Arteries branch off into smaller arteries – arterioles. Arterioles control the flow of blood into the smallest vessels, the capillaries.
The veins carry blood towards the heart. This blood is usually low in oxygen and so is a deep purplish-red colour. They have much thinner walls than arteries and the blood in them is under much lower pressure because it is a long way away from the thrust of the heart. They do not have a pulse, but they often have valves to prevent the back-flow of blood as it moves from the various parts of the body back to the heart.
The two main veins near the heart are the inferior vena cava and the superior vena cava, which empty into the right atrium. The inferior vena cava carries blood from the legs and trunk. The superior vena cava carries blood to the head and arms. Venous blood is dark red in color, because it has little oxygen with significant amounts of carbon dioxide.
Between the arteries which bring blood from the heart and the veins which collect it up lo take back to the heart are very narrow, thin–walled blood vessels called capillaries. These take the blood into all the organs and tissues of the body.
The capillaries are narrow with very thin ( ‘semi-permeable’) walls so that substances needed by body cells, such as oxygen and glucose, can easily pass out of the blood and into the cells by diffusion. In the same way substances produced by the cells, such as carbon dioxide, pass easily into the blood through the walls of the capillaries.
Blood is always moving through the body. It takes 20 to 30 seconds for the blood to circulate through the body and return to the heart. It moves in two big circles. One circle runs from the heart to the lungs and back again. The other circle runs from the heart to the rest of the body and back to the heart. Blood is the only human connective tissue that is fluid.
The main function of the blood is to circulate oxygen, carbon dioxide, digested and absorbed food, water and other substances around the body. It helps in the body’s defence against infection and plays an important part in maintaining a constant body temperature.
Blood is made up of red and white blood cells and platelets which help in the process of blood clotting. It is responsible for the:
- delivery of oxygen to muscles and organs;
- removal of carbon dioxide and waste products;
- distribution of hormones;
- regulation of body temperature;
- defence against infection and disease;
- clotting of blood;
- transportation of digested and absorbed foods
How the heart and circulatory system work in sport?
During physical exercise, muscles demand oxygen at a faster rate. The heart responds to this need by beating more rapidly to transport more blood and oxygen to the working muscles.
At rest, the heart beats approximately 72 times per minute. During physical activity, the heart rate increases according to the intensity (difficulty) of exercise.
Your resting heart rate is greatly influenced by the amount of exercise you do. As you do more exercise and become fitter, the resting heart rate decreases.
The heart rate can be measured during exercise to estimate a person’s aerobic fitness (the fitness of the circulatory and respiratory systems). Regular endurance training will reduce the resting heart rate, strengthen the heart muscle and improve stroke volume, the amount of blood pumped with each beat of the heart.
Summing up: The heart and circulatory system
The cardiovascular system is made up of the blood, heart, and blood vessels. The main responsibility of the cardiovascular system is transportation of blood to all parts of the body.
During exercise. the muscles that are contracting require a continual supply of nutrients and oxygen to support energy production. These requirements are over and above those required to support normal activities at work or rest. As a result, the heart has to beat harder and faster to meet these increased demands. If these demands are repeated frequently as a result of a systematic training programme, over time the heart becomes stronger. The heart and blood vessels of the circulatory system adapt to repeated bouts of exercise.