Human Heart

Contents:

Introduction to the Human Heart

The human heart is one of the most important organs responsible for sustaining life. It is essentially a muscle, about the size of a clenched fist. 

The human heart functions throughout a person’s lifespan, pumping almost 200 million litres of blood. A  human heart roughly beats 2.5 billion times during a human lifespan, making it one of the most robust and hardest working muscle in the human body.

Besides humans, most other animals also possess a heart that pumps blood throughout their body. Even invertebrates such as grasshoppers possess a “heart”, though they do not function the same way a human heart does.

Position of Heart in Human Body

The human heart is located between the lungs,  behind and slightly towards the left of the sternum (breastbone). Two-thirds of the heart is situated on the left side of the chest, and the remaining part is balanced on the right side of the chest.

The Function of Heart

The function of the heart in any organism is to maintain a constant flow of blood throughout the body. This replenishes oxygen and circulates nutrients among the cells and tissues. Also, because the human heart is a homologous organ, it functions no differently from any other vertebrates that possess a heart. Following are the main functions of the heart:

  • One of the primary function of the human heart is to pump blood throughout the body.
  • Blood delivers oxygen, hormones, glucose and other components to various parts of the body, including the human heart.
  • The heart also ensures that adequate blood pressure is maintained in the body

There are two types of circulation within the body, namely pulmonary circulation and systemic circulation.

Pulmonary circulation and Systemic circulation

Pulmonary circulation (blue) and Systemic circulation (red)

Types of Circulation

  • Pulmonary circulation is a portion of circulation responsible for carrying deoxygenated blood away from the heart, to the lungs and then brings oxygenated blood back to the heart.
  • Systemic circulation is another portion of circulation where the oxygenated blood is pumped from the heart to every organ and tissue in the body, and then back again to the heart.

Now, the heart itself is a muscle and therefore, it needs a constant supply of oxygenated blood. This is where another type of circulation comes into play, the coronary circulation.

  • Coronary circulation is an essential portion of the circulation, where oxygenated blood is supplied to the heart. This is important as the heart is responsible for supplying blood throughout the body. Moreover, organs like the brain need a steady flow of fresh, oxygenated blood to ensure functionality.

In a nutshell, the circulatory system plays a vital role in supplying oxygen, nutrients and removing carbon dioxide and other wastes from the body. Let us gain a deeper insight into the various anatomical structures of the heart:

Structure of the Human Heart

The human heart is about the size of a human fist and is 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 structure of the heart also houses the biggest artery in the body – the aorta.

Human Heart

Human heart diagram highlighting the various anatomical structures.

 

The right and the left region of the heart are separated by a wall of muscle called the septum. The right ventricle pumps the blood to the lungs for re-oxygenation through the pulmonary arteries. The right semilunar valves close and prevent the blood from flowing back into the heart. Then, the oxygenated blood is received by the left atrium from the lungs via the pulmonary veins.  Read on to explore more about the structure of heart.

External Structure of Heart

One of the very first structures which can be observed when the external structure of the heart is viewed is the pericardium.

Pericardium

The human heart is situated to the left of the chest and is enclosed within a fluid-filled cavity described as the pericardial cavity. The walls and lining of the pericardial cavity are made up of a membrane known as the pericardium.

The pericardium is a fibre membrane found as an external covering around the heart. It protects the heart by producing a serous fluid, which serves to lubricate the heart and prevent friction between the 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 two exclusive layers—

  • Visceral Layer: It directly covers the outside of the heart.
  • Parietal Layer: It forms a sac around the outer region of the heart that contains the fluid in the pericardial cavity.

Structure of the Heart Wall

The heart wall is made up of 3 layers, namely:

  • Epicardium – Epicardium is the outermost layer of the heart. It is composed of a thin-layered membrane that serves to lubricate and protect the outer section.
  • Myocardium – This is a layer of muscle tissue, and it constitutes the middle layer wall of the heart. It contributes to the thickness and responsible for the pumping action.
  • Endocardium – It is the innermost layer that lines the inner heart chambers and covers the heart valves. Furthermore, it prevents the blood from sticking to the inner walls, thereby preventing potentially fatal blood clots.

Internal Structure of Heart

The internal structure of the heart is rather intricate with several chambers and valves that control the flow of blood.

Chambers of the Heart

Vertebrate hearts can be classified based on the number of chambers present. For instance, most fish have two chambers, reptiles and amphibians have three chambers. Avian and mammalian hearts consists of four chambers. Humans are mammals; hence, we have four chambers, namely:

  • 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 fed by the large veins.

Ventricles are larger and more muscular chambers responsible for pumping and pushing blood out to the circulation. These are connected to larger arteries that deliver blood for circulation.

The right ventricle and right atrium are comparatively smaller than the left chambers. The walls consist of fewer muscles compared to the left portion, and the size difference is based on their functions. The blood originating from the right side flows through the pulmonary circulation, while blood arising from the left chambers is pumped throughout the body.

Blood Vessels

In organisms with closed circulatory systems, the blood flows within vessels of varying sizes. All vertebrates, including humans, possess this type of circulation. The external structure of the heart has many blood vessels that form a network, with other major vessels emerging from within the structure. The blood vessels typically comprise of the following:

  • Veins supply deoxygenated blood to the heart via inferior and superior vena cava, and it eventually drains into the right atrium.
  • Capillaries are tiny, 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 largest of the arteries, and it branches off into various smaller arteries throughout the body.

Also refer: Difference between Arteries and Veins

Valves

Valves are flaps of fibrous tissues located in the cardiac chambers between the veins. They ensure that the blood flows in a single direction (unidirectional). Flaps also prevent the blood from flowing backwards. Based on their function, valves are of two types:

  • Atrioventricular valves are between ventricles and atria. The valve between the right ventricle and right atrium is the tricuspid valve, and the one which is found between the left ventricle and left atrium is known as the mitral valve.
  • Semilunar valves are located between the left ventricle and aorta. It is also found between the pulmonary artery and right ventricle.

Facts about Human Heart

Facts about Human Heart

  • The heart pumps around 5.7 litres of blood in a day throughout the body.
  • The heart is situated at the centre of the chest and points slightly towards the left.
  • On average, the heart beats about 100,000 times a day, i.e., around 3 billion beats in a lifetime.
  • The average male heart weights around 280 to 340 grams (10 to 12 ounces). In females, it weights around 230 to 280 grams (8 to 10 ounces).
  • 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.

To know more about the human heart structure and function, or any other related concepts such as arteries and veins, internal structure of heart, external structure of heart, etc. explore BYJU’S Biology. Also, discover concepts and relevant questions for human heart class 10 by downloading BYJU’S – The Learning App.

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Frequently Asked Questions

1. What is pulmonary circulation? Explain.

Pulmonary circulation is a type of blood circulation responsible for carrying deoxygenated blood away from the heart, and to the lungs, where it is oxygenated. The system then brings oxygenated blood back to the heart to be pumped throughout the body.

2. Define systemic circulation.

In the systemic circulation, the heart pumps the oxygenated blood through the arteries to every organ and tissue in the body, and then back again to the heart through a system of veins.

3. Elaborate coronary circulation and its significance.

The heart is a muscle, and it needs a constant supply of oxygenated blood to survive and work effectively. This is where coronary circulation fulfils this function through a network of arteries and veins in the heart. The coronary arteries supply oxygenated blood to the heart, and the cardiac veins drain the blood once it has been deoxygenated by the tissues of the heart.

4. Briefly explain the structure of the human heart.

The human heart is 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 the blood. Among which, the right atrium and ventricle make up the “right portion of the heart”, and the left atrium and ventricle make up the “left portion of the heart.”

5. Name the chambers of the heart.

  • Left atria
  • Right atria
  • Left ventricle
  • Right ventricle

6. What is pericardium? Explain its function.

The pericardium is a fibrous membrane that envelops the heart. It also serves a protective function by producing a serous fluid, which lubricates the heart and prevents friction between the surrounding organs. Furthermore, the pericardium also holds the heart in its position and provides a hollow space for the heart to expand and contract.

7. Explain the three layers of the heart wall.

The heart wall is made up of 3 layers, namely:

  • Epicardium – This is the outermost layer of the heart. It is composed of a thin layer of membrane that protects and lubricates the outer section.
  • Myocardium – This is a layer of muscle tissue that constitutes the middle layer wall of the heart. It is responsible for the heart’s “pumping” action.
  • Endocardium – The innermost layer that lines the inner heart chambers and covers the heart valves. Prevents blood from sticking, thereby avoiding the formation of fatal blood clots.

8. Explain the three major blood vessels of the human body.

The  blood vessels comprise of:

  • Veins – It supplies deoxygenated blood to the heart via inferior and superior vena cava, eventually draining into the right atrium.
  • Capillaries – They are minuscule, tube-like vessels which form a network between the arteries and veins.
  • Arteries – These are muscular-walled tubes responsible for supplying oxygenated blood away from the heart to all other parts of the body.

9. What is the function of the heart valves? Provide examples of various valves.

Valves are flaps of tissues that are present in cardiac chambers between the veins. They prevent the backflow of blood. Examples include the atrioventricular valves, tricuspid valves, mitral valves and the semilunar valves.

10. What is meant by myocardial infarction?

Myocardial infarction is a serious medical condition where the blood flow to the heart is reduced or entirely stopped. This causes oxygen deprivation in the heart muscles, and prolonged deprivation can cause tissues to die.

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