The human heart is an important muscular organ involved in pumping blood to different parts of the body with the help of three segments of the circulatory system:
- The pulmonary circulation ( heart and lungs ),
- The systemic circulation (body systems) and
- The coronary circulation (blood vessels of the heart).
The coronary circulation is an essential system to the heart as it circulates blood from the main artery – that comes from the heart. It also plays a vital role in supplying oxygen, nutrients and removing carbon dioxide and other wastes through the circulatory system.
Structure of the Human Heart
The human heart is about the size of our 0wn fist and is mainly divided into four chambers namely two ventricles and two atria. The ventricles are the chambers that pump blood and atrium are the chambers that receive blood. Among which both right atrium and ventricle make up the “right heart, and the left atrium and ventricle make up the “left heart.” The right and the left region of the heart are separated by the wall of muscle called septum. The right ventricle pumps the blood to the lungs for re-oxygenation when it gets filled up by the pulmonary arteries. The right semilunar valves close and prevent the blood from the pulmonary veins after blood passes through the pulmonary arteries. Then the oxygenated blood is received by the left atrium from the lungs via pulmonary veins.
1. The Pericardium
As we all know our heart is situated to the left side of our chest and is present within a fluid-filled cavity described as the pericardial cavity. The walls and lining of the pericardial cavity are a special membrane known as the pericardium.
The pericardium is a fiber membrane found as an external covering around the heart. It protects the heart by producing serous fluid to lubricate the heart and prevent friction between the heart and its surrounding organs. Apart from the lubrication, the pericardium also helps by holding the heart in its position and by maintaining a hollow space for the heart to expand itself when it is full. The pericardium has 2 exclusive layers—
- Visceral layer directly covers outside of the heart.
- Parietal layer forms a sac around the exterior region of the heart that contains the fluid in the pericardial cavity.
2. The Structure of the Heart Wall
The heart wall is made up of 3 layers:
- Epicardium – This is the outermost layer of the heart and a thin layer of membrane that protects and lubricates the outer its section.
- Myocardium – This is a muscular layer and consists of muscle tissue. It contributes to the thickness and responsible for the pumping action.
- Endocardium – It is the innermost layer that lines within the heart and keeps blood from sticking and prevents the formation of harmful blood clots.
3. Chambers of the Heart
The four chambers are as mentioned below:
- Left atrium
- Right atrium
- Left ventricle
- Right ventricle
Atria are thin, less muscular walls and smaller than ventricles. These are the blood-receiving chambers that are carried to the heart by the large veins.
Ventricles are larger and more muscular chambers of pumping and push blood out to the circulation. These are connected to larger arteries that deliver blood for circulation.
The right ventricle and right atrium are smaller than left chambers. Their walls consist of fewer muscles compared to the left portion and the size difference is based on their functions. The blood from the right side flows through the pulmonary circulation while blood from the left chambers is pumped to the complete body.
4. Blood Vessels
- The blood vessels are the tubes that deliver blood to all parts of a body.
- Veins supply deoxygenated blood to the heart via inferior and superior vena cava that drains into the right atrium.
- Capillaries are very small, tube-like vessels which form a network between the arteries to veins.
- Arteries are muscular-walled tubes, mainly involved in supplying oxygenated blood away from the heart to all other parts of the body. Aorta is the longest artery that leaves the heart and gives off smaller branches.
These are the fibrous flaps of tissues that are present in cardiac chambers between the veins. They ensure unidirectional flow and prevent backflow of blood. There are two types of valves.
- Atrioventricular valves are present in every ventricle and atrium. The valve between the ventricle and right atrium is the tricuspid valve, and the one which is found between the left ventricle and atrium is known as the mitral valve.
- Semilunar valves are present in the large arteries and ventricles. An aortic valve is present between the aorta and left ventricle, and a pulmonary valve exists between the pulmonary artery and right ventricle.
Facts about Human Heart
- The Heart pumps around 5.7 liters of blood in a day throughout the body.
- The heart is situated at the center of the chest and points slightly towards the left.
- On an average, the heart beats about 100,000 times a day i.e, around 3 billion beats in a lifetime.
- The heart weight is around 280 to 340 grams (10 to 12 ounces) in male and 230 to 280 grams (8 to 10 ounces) in the female.
- An adult heart beats about 60 to 80 times per minute and newborn babies heart beats faster than an adult which is about 70 to 190 beats per minute.
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