Which chamber of heart has thickest wall

Health Library Heart Components

Índice Show

• Health Library Heart Components
• What Are the Heart's Main Components?
• Heart Chambers, Valves, Vessels, Wall and Conduction System
• Heart Valves
• Major Vessels
• Conduction System
• Chambers of the heart
• Valves of the heart
• How the heart beats

What Are the Heart's Main Components?

Heart Chambers, Valves, Vessels, Wall and Conduction System

The heart is made up of four chambers. The upper two chambers are called atria (singular: atrium) and the lower two are known as ventricles (singular: ventricle).

Muscular walls, called septa or septum, divide the heart into two sides.

On the right side of the heart, the right atrium and ventricle work to pump oxygen-poor blood to the lungs.

On the left side, the left atrium and ventricle combine to pump oxygenated blood to the body.

Heart Valves

There are four valves within the heart:

• The tricuspid valve is between the right atrium and the right ventricle.
• The pulmonary valve is between the right ventricle and the pulmonary artery.
• The mitral valve is between the left atrium and the left ventricle.
• The aortic valve is located between the left ventricle and the aorta.

These valves open when blood passes through them and then close to keep the blood from flowing in the wrong direction.

Major Vessels

The four chambers of the heart are attached to major veins or arteries that either bring blood into or carry blood away from the heart.

The atria are the receiving stations of the heart. The right atrium receives its supply of oxygen-poor blood from the two largest veins in the body, the superior and inferior vena cava.

The left atrium receives blood that has been oxygenated in the lungs from the pulmonary veins. Both atria then pump their supply of blood into the ventricles.

The ventricles are the shipping stations of the heart. The right ventricle pumps oxygen-poor blood into the lungs through the pulmonary artery while the left ventricle pumps oxygenated blood to the body through the aorta, the largest artery in the body.

Heart Wall

The heart wall consists of three layers: the endocardium, myocardium and epicardium.

The endocardium is the thin membrane that lines the interior of the heart.

The myocardium is the middle layer of the heart. It is the heart muscle and is the thickest layer of the heart.

The epicardium is a thin layer on the surface of the heart in which the coronary arteries lie.

The pericardium is a thin sac the heart sits in, often filled with a small amount of fluid, which separates the heart from the other structures in the chest such as the lungs.

Conduction System

The conduction system is the heart's own built-in pacemaker. This special tissue sets the heart rate and allows the upper and lower chambers to communicate with each other so they can function in a coordinated fashion.

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Contact Cincinnati Children's Heart Institute

Last Updated 04/2020

Reviewed by Marji Bretz, MSN, RN, CCRN, Education Specialist II

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Our own in-build mechanical pump that works 24/7 without taking a break! Check this page out to discover how this amazing organ works.

Chambers of the heart

The heart is made up of four chambers.  The chambers on the right side of the heart are the right atrium and right ventricle. 

The right atrium receives deoxygenated blood from the body via the superior and inferior vena cava (major veins). 

The blood then flows to the right ventricle where it is then pumped, via the pulmonary circuit, through the pulmonary artery to the lungs for gaseous exchange (CO2 out, O2 in).

The chambers on the left side of the heart are the left atrium and left ventricle.  The left atrium receives oxygenated blood from the lungs via the pulmonary veins. 

The blood then flows to the left ventricle where it is then pumped, via the systemic circuit, through the aorta and then pumped out to the to the organs and tissues of the body to supply them with oxygen and nutrients, and pick up waste products for expulsion.

Follow the arrows on the diagram above as this shows the direction of blood flow through the heart.

Being a muscle which requires nutrients for fuel, the heart also has its own blood supply. 

It receives the oxygenated, nutrient rich blood that it needs from the coronary arteries which branch off the aorta.  The deoxygenated blood is then returned to the right atrium through the cardiac veins. 

It is damage to the coronary arteries that often leads to heart problems such as heart attacks.

The left ventricle also has a thicker muscular wall than the right ventricle, as seen in the adjacent image.  This is due to the higher forces needed to pump blood through the systemic circuit (around the body) compared to the pulmonary circuit.

Valves of the heart

There are four valves within the heart which serve to prevent backflow of blood as it passes through the various chambers of the heart and out through the associated arteries.

The tricuspid valve and the mitral valve are known as ‘atrioventricular’ valves as they are situated between the atria and ventricles on both sides of the heart. 

The tricuspid valve is positioned between the right atrium and ventricle, and the mitral valve sits between the left atrium and ventricle, as seen in the adjacent image.

As blood is pumped out of the ventricles through the aorta and the pulmonary arteries, these valves close to ensure the blood does not get pumped back into the respective atria it came from.

The other two valves are the pulmonary and aortic valves, which are collectively known as the ‘semilunar’ valves. 

The pulmonary valve sits between the right ventricle and the pulmonary artery.  Its role is to prevent the backflow of blood into the right ventricle after it contracts.  The aortic valve sits between the left ventricle and the aorta and prevents backflow of blood into the left ventricle after it contracts.

How the heart beats

One heart beat consists of one contraction phase and one relaxation phase. 

The contraction phase, known as ‘systole’, occurs when blood is pumped out of the heart.  The relaxation phase, known as ‘diastole’, occurs when the heart is relaxing and filling with blood.  These phases can be seen in the following image.

There are two unique sounds associated with the heart beat (which you can hear through a stethoscope placed on a friend’s chest). 

There is a low pressure ‘lub’ sound which is the closing of the atrioventricular valves, followed quickly by a higher pressure ‘dub’ sound as the semilunar valves close.

The heart beat is controlled by the sympathetic and parasympathetic branches of the autonomic nervous system. 

The sympathetic system stimulates the heart to beat faster while the parasympathetic system returns the heart rate to its normal resting level.

Electrical impulses (action potentials) from both systems are sent to the sino-atrial (SA) node. The SA node, known as the hearts ‘pacemaker’, then sends out an impulse that stimulates both atria to contract and this stimulus is also sent to the atrioventricular (AV) node.  This is shown on the below image.

The AV node then further distributes the impulse from the SA node to both ventricles which contract a fraction of a second after the contraction of the atria. 

The rate at which the SA node sends out impulses determines the rate at which the heart beats.  As well as receiving impulses from the autonomic nervous system, the rate at which the SA node sends impulses can also be influenced by hormones such as adrenaline. 

When released into the system adrenaline stimulates the SA node to send impulses at a faster rate, thus increasing the rate at which the heart beats.