Human Heart: Anatomy, Functions, Circulation & Facts

The heart is the most essential organ of our body. The muscular organ is roughly about the size of a human fist and is responsible for pumping blood throughout our body that sustains life. It pumps around 5-6 liters of blood every day. In this article, we will discuss the position of the heart, its functions, structure, and some common heart diseases. 

Human Heart

The heart is generally referred to as the body's power engine. It is mainly required for the smooth functioning of the human body due to its function of circulating blood in all organs. While humans have been blessed with only one heart, certain animals or mammals may have more than one heart that functions differently than the human heart.

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Location of Heart in Human Body

The heart sits at the center of the chest, which is between the lungs(in the thoracic cavity) and is situated towards the left breastbone, also known as the sternum. It is protected all around by the rib cage as it is a delicate organ and needs to be left undisturbed.

Functions of the heart

The heart has a primary role to play when it comes to taking care of several aspects of the body. A few of its functions are as follows:

• The heart is responsible for supplying fresh oxygen and nutrients to the tissues and eliminating carbon dioxide and other forms of wastes from the cells.
• It also plays a great role in maintaining stable blood pressure in the human body. 
• It also regularly pumps oxygen-rich blood to other parts of the body for better functioning. 
• The heart is concerned with the function of releasing certain hormones and transferring them to different parts of the body. 

Structure of the human heart

The internal cavity of the heart forms two separate pumps on each side of the heart. These pumps are separated by the Septum, which is a wall formed of muscles. The upper chambers are known as Atrium while the lower chambers are called Ventricles. The right and left atria receive blood from either the body or the lungs and the ventricles pump blood into the lungs or the body. A person’s heartbeat is felt more strongly on the left side of the chest because of the left ventricle pumping forcefully. The chambers of the heart become smaller when it contracts, hence forcing the blood out of the atria into the ventricles and later from each ventricle into a blood vessel that is connected to the top of the heart.

• The pulmonary artery transfers blood to the lungs.
• The aorta is responsible for transporting oxygen-rich blood to the rest of the body. 

The blood vessels that help in supplying the blood to the heart are known as veins, while the two main veins that connect to the heart are called the vena cava.

Internal Structure of the Heart

Various valves and chambers are responsible for controlling the blood flow in the heart.

Valves 

The valves are flap-like structures, present at the end of two ventricles. These flaps are made up of thin tissues called cusps. They are responsible for maintaining a stable direction of blood flow. The basic function of our valves is to prevent the backflow of blood at any cost. From one side of the ventricle, the blood enters, while it leaves from the other side. The sound of the beating of our hearts comes from the opening and closing of these valves. There are four major valves -

• ?Aortic valve - It prevents blood from flowing back to the left ventricle and is located between the aorta and the left ventricle. 
• Mitral valve - A mitral valve happens to have two flaps and is situated between the left atrium and left ventricle. 
• Tricuspid valve - It is present between the right atrium and the right ventricle and makes sure blood flows forward.
• Pulmonary valve - The pulmonary valve is in between the pulmonary artery and the right ventricle.

Chambers of the heart

The heart has four chambers that are further associated with their respective functions. These include:

• Right atrium
• Right ventricle
• Left atrium
• Left ventricle

Right Atrium

The right atrium gets blood, lacking in oxygen, from the systemic veins and pushes it towards the right ventricle via the tricuspid valve. The tricuspid’s valve is solely concerned with preventing blood backflow. 

Right Ventricle

The right ventricle pumps deoxygenated blood to the pulmonary artery after receiving it from the right atrium. The tricuspid valve closes itself up when the right ventricle contracts. In return, blood is pumped through the pulmonary artery and is transported to the lungs. At this point of time, when the right ventricle relaxes, blood tends to come back. However, this fills the valve flaps and closes the pulmonary valve to stop the blood from flowing back into the right ventricle.

Left Ventricle 

The left ventricle pumps fresh oxygenated blood. The left ventricle contracts more strongly than any other chamber. This is what creates blood pressure in the body. The left ventricle connects almost all organ systems. A breakdown of the left ventricular would likely result in the impairment of all other organs. 

Left atrium

The function of the left atrium is that it receives blood, rich in oxygen, from the lungs through the pulmonary veins. These are blood receiving chambers and their muscular walls are comparatively thinner than the ventricles. Here, the blood flows through the atrioventricular valve into the left ventricle, also called the mitral valve or bicuspid valve.

The mitral valve prevents blood from the left ventricle to the left atrium when the ventricles contract. This atrium is associated with an important function of producing a hormone so as to maintain blood pressure. When an increased amount of blood is stretched along the atria's wall, atrial natriuretic peptide (ANP) is produced which decreases kidney reabsorption of sodium ions to excrete more sodium ions in urine and causes water loss. As a result, loss of water causes a reduction in the volume of blood and possible blood pressure. 

Blood Vessels

Blood vessels can be referred to as the channels through which blood passes and moves around in the whole human body. These contain a network of arteries, arterioles, capillaries, venules, and veins, each of them associated with a unique function.

However, there are three major types of blood vessels. These are -

• Arteries
• Capillaries, and
• Veins 

Arteries 

These are muscular tubes and are red in color. Their function is to nourish our body tissues with oxygen and necessary nutrients. These arteries carry oxygenated blood away from the heart and towards the tissues of the body. As they move on away from the heart, they keep breaking into minute branches. 

Capillaries 

Capillaries are the smallest blood vessels in the human body, which connect the arteries to veins. They have a very thin wall which allows them enough elasticity to exchange oxygen, carbon dioxide, certain nutrients, and waste material between the blood and tissues. The largest capillaries can be found in the liver. There are mainly three major types of capillaries -

• Continuous

• Fenestrated, and 

• Sinusoidal

Veins 

These are the blood vessels that are responsible for carrying the deoxygenated blood back to the heart. These are blue in color and keeps increasing in size as they reach towards their target organ, that is the heart. It has been found that the superior vena cava and the inferior vena cava are the largest veins present in the body. The superior vena cava carries blood to the heart from the upper half of the body, while the inferior vena cava brings blood from the lower half of the body and supplies it to the heart.

External Structure of the Heart

The pericardium is the first thing that can be observed while viewing the human heart.

Pericardium

The human heart is located in the left of the chest within the pericardial cavity. The pericardium is the membrane that makes up the lining of the pericardial activity. It is referred to as the outer covering of our hearts. It maintains a hollow space for the heart to expand when full, maintaining its position. It also produces a fluid that reduces the friction between the heart and its surrounding organs, thus protecting the heart. It has two layers:

• The Visceral layer directly covers the heart from the outside.
• The Parietal layer forms a sac around the heart’s outer region that contains the fluid in the pericardial cavity.

Walls of the Heart

The three layers of the heart's wall are separated into the epicardium, the myocardium, and the endocardium.

• Epicardium - It's the outermost layer of the heart and is composed of a thin-layered membrane. The prime function of this membrane is to provide enough lubrication and protect the outer section. 

• Myocardium - It's the middle layer wall of the heart. Its sole function is to provide thickness and is responsible for pumping action.
• Endocardium – It is the innermost layer of the heart lining across the inner heart chambers and covers the heart valves. In addition to this, it prevents the blood from sticking to the inner walls, thereby preventing the chance of fatal blood clots.

Types of circulation

Pulmonary circulation

• In this circulation, it carries the deoxygenated blood from the heart and transports it to the lungs. 
• As a response, this blood gets filled with oxygen so that it can be ready for systemic circulation. 
• This waste blood present in the bottom half of the body enters the heart through the inferior vena cava whereas the blood present in the upper half of the body enters through the superior vena cava.
• The blood of both these channels is released into the right atrium where it flows into the target organ, that is the right ventricle. 
• Once it contains a sufficient amount of oxygen from the lungs it gives out carbon dioxide. 
• This blood now is transferred to the left atrium and eventually into the left ventricle. 
• The oxygenated blood is pushed from the left ventricle into the aorta where further processes take place regarding the systemic circulation. 

Systemic Circulation

• Systemic circulation witnesses the movement of oxygenated blood from the left ventricle in the direction of the arteries, arterioles.
• It passes through the aorta and is supplied to the tissues of the body. 
• This circulation gives out essential nutrients and oxygen for growth and enhancement while sucking all the waste particles and carbon dioxide. 
• This waste blood now moves from the capillaries towards the systemic veins. 
• Further, these veins move into the inferior vena cava and superior vena cava. 
• The right atrium of the heart receives the deoxygenated blood from the vena cava.

Coronary circulation

• Here, blood rich in oxygen is supplied to the heart.

The circulation system ensures the removal of carbon dioxide and all other wastes and the supply of oxygen and other nutrients to the human body.

Cardiac Conduction Pathway

The cardiac conduction system is an electrical system whose main function is to control the heart rate. It releases electrical responses which are then transmitted throughout the heart walls so as to enable it to keep pumping blood. 

This pathway plays a very crucial part in the heart’s health and consists of 5 primary elements. These are - 

• The sinoatrial (SA) node: Also called the sinus node, it acts as a natural pacemaker for the heart and consists of a bundle of cells. Its main function is to create a signal, which in turn causes the upper chambers to have contractions
• The atrioventricular (AV) node: The AV node is responsible for keeping the heart rate in check. 
• The bundle of His: The Bundle of his are cells that are a part of the electrical conduction of the heart. It transfers the impulses from the AV node and delivers them to the ventricles. 
• The left and right bundle branches: Both of these bundle branches carry impulses. These signals make the heart beat.
• The Purkinje fibers: It sends signals to the ventricles and causes the heart to have contractions. They also enable the heart to pump blood.

Common heart diseases

1. Myocardial Infarction

More popularly known as ‘heart attack’, myocardial infarction involves an interruption of blood flow to the heart. This can lead to serious damage to the heart muscle. Chest pain and sweating are the most common symptoms of this disease. The most common cause of a heart attack is a blood clot, plaque, or both forming in a coronary artery. It also occurs if an artery suddenly constricts or spasms. However, it can be cured with the help of an early diagnosis.

2. Coronary artery disease

This is a very common heart disease affecting people. It occurs when plaque starts building up in the artery walls thus preventing them from supplying blood to the heart, thereby weakening it. Plaque consists of cholesterol. All of this can result in a heart attack. Smoking, lack of regular exercise, high cholesterol, and even high blood pressure are found to be the prime factors behind this heart disease. 

3. Arrhythmia 

When the heartbeats are irregular, beating too slow(bradycardia), or too quick(tachycardia), or don't have equal gaps between two heartbeats, then the person is said to be suffering from this disease. Popular reasons behind this disease include drinking, smoking, substance use disorder, stress, high blood pressure, drinking too much coffee, an overactive thyroid gland, etc. 

4. Heart Failure

It's a chronic condition in which the heart is unable to pump enough blood required to meet the needs of the body and tissues. Heart failure can result from high blood pressure, arrhythmias, diabetes, and other conditions. This prevents the heart’s ability to pump blood properly. 

Things to Remember

• The heart is generally referred to as the body's power engine. It is mainly required for the smooth functioning of the human body due to its function of circulating blood in all organs.
• Proper circulation of blood in the body is the key to maintaining sound health. There are two major types of circulation - Pulmonary circulation and Systemic circulation. They protect the body from infection and provide the organs with oxygen and essential nutrients. They also eliminate waste products like carbon dioxide.
• A man’s heart is nearly two ounces heavier and beats comparatively slower than a woman’s heart. 
• A newborn's heart beats faster than adults, around 70 - 190 beats per minute whereas for adults it's 60 to 80 times per minute.
• While we humans have only one heart, there are certain animals and mammals who happen to have more than one heart or even no heart at all. For example, the giraffe has a total number of three hearts functioning. Starfish and jellyfish don't have any heart. 
• Our heart pumps around 2000 gallons of blood each day. 
• The human heart beats about 100,000 times on a daily basis. 
• It weighs around 340 grams in men and 280 grams in women.
• The cardiac conduction system is an electrical system that helps take care of the heart. It helps the heart contract at regular intervals and keeps in check that it pumps blood effectively.