Why ventricles larger than atria

The heart gets messages from the body that tell it when to pump more or less blood depending on a person's needs. For example, when we're sleeping, it pumps just enough to provide for the lower amounts of oxygen needed by our bodies at rest. But when we're exercising, the heart pumps faster so that our muscles get more oxygen and can work harder.

How the heart beats is controlled by a system of electrical signals in the heart. The sinus or sinoatrial node is a small area of tissue in the wall of the right atrium. It sends out an electrical signal to start the contracting pumping of the heart muscle. This node is called the pacemaker of the heart because it sets the rate of the heartbeat and causes the rest of the heart to contract in its rhythm.

These electrical impulses make the atria contract first. Then the impulses travel down to the atrioventricular or AV node , which acts as a kind of relay station. From here, the electrical signal travels through the right and left ventricles, making them contract. Let the doctor know if your child has any chest pain, trouble breathing, or dizzy or fainting spells; or if your child feels like the heart sometimes goes really fast or skips a beat.

Note: All information is for educational purposes only. For specific medical advice, diagnoses, and treatment, consult your doctor. Search KidsHealth library. What Does the Heart Do?

What Does the Circulatory System Do? What Are the Parts of the Heart? The heart has four chambers — two on top and two on bottom: The two bottom chambers are the right ventricle and the left ventricle. These pump blood out of the heart. A wall called the interventricular septum is between the two ventricles. The two top chambers are the right atrium and the left atrium. They receive the blood entering the heart.

A wall called the interatrial septum is between the atria. The atria are separated from the ventricles by the atrioventricular valves: The tricuspid valve separates the right atrium from the right ventricle. The mitral valve separates the left atrium from the left ventricle. Your heart is located between your lungs in the middle of your chest, behind and slightly to the left of your breastbone. A double layered membrane called the pericardium surrounds your heart like a sac.

The outer layer of the pericardium surrounds the roots of your hearts major blood vessels and is attached by ligaments to your spinal column, diaphragm and other parts of your body. The inner layer of the pericardium is attached to the heart muscle. A coating of fluid separates the two layers of membrane, letting the heart move as it beats, yet still be attached to your body. Your heart has 4 chambers.

The upper chambers are called the left and right atria and the lower chambers are called the left and right ventricles. A wall of muscle called the septum separates the left and right atria and the left and right ventricles. These are referred to as the atrial and ventricular septum. 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.

The ventricles of the heart have thicker muscular walls than the atria. This is because blood is pumped out of the heart at greater pressure from these chambers compared to the atria. 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. 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 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 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.