Heart : A powerful muscle slightly larger than a clenched fist. It is composed of four chambers, two upper (the atria) and two lower (the ventricles). It works as a pump to send oxygen-rich blood through all the parts of the body. A human heart beats an average of 100,000 times per day. In that time, it pumps more than 4,300 gallons of blood throughout the entire body. The heart's cycle starts when oxygen-poor blood from the body flows into the right atrium. Next the blood flows through the right atrium into the right ventricle, which serves as a pump that sends the blood to the lungs. Within the lungs, the blood releases waste gases and picks up oxygen. This newly oxygen-rich blood returns from the lungs to the left atrium. Then the blood flows through the left atrium into the left ventricle. Finally, the left ventricle pumps the oxygen-rich blood to all parts of the body.
The human body has about 5.6 liters (6 quarts) of blood, all of which circulates through the body three times every minute.
Atria: The two upper cardiac chambers that collect blood entering the heart and send it to the ventricles. The right atrium receives blood from the superior vena cava and inferior vena cava. The left atrium receives blood from the pulmonary veins. Unlike the ventricles, the atria serve as collection chambers rather than as primary pumps, so they are thinner and do not have valves at their inlets.
Ventricles: The two lower cardiac chambers that collect blood from the upper chambers (atria) and pump it out of the heart. Because the ventricles pump blood away from the heart, they have thicker walls than the atria so that they can withstand the associated higher blood pressures. The right ventricle pumps oxygen-poor blood through the pulmonary artery and to the lungs. The left ventricle pumps oxygen-rich blood through the aorta and to the rest of the body.
Left Ventricle:The lower left chamber of the heart. During the normal cardiac cycle, the left ventricle receives oxygenated blood through the mitral valve from the left atrium as it contracts. At the same time, the aortic valve leading to the aorta is closed, allowing the ventricle to fill with blood. Once both ventricles are full, they contract. As the left ventricle contracts, the mitral valve closes and the aortic valve opens. The closure of the mitral valve prevents blood from returning to the left atrium, and the opening of the aortic valve allows the blood to flow into the aorta and from there throughout the body.
The left and right ventricles contract simultaneously; however, because the left ventricle is thicker than the right, it produces a higher presure than the right when contracting. This higher pressure is necessary to pump the oxygenated blood throughout the body
Right Ventricle:The lower right chamber of the heart. During the normal cardiac cycle, the right ventricle receives deoxygenated blood as the right atrium contracts. During this process the pulmonary valve is closed, allowing the right ventricle to fill. Once both ventricles are full, they contract. As the right ventricle contracts, the tricuspid valve closes and the pulmonary valve opens. The closure of the tricuspid valve prevents blood from returning to the right atrium, and the opening of the pulmonary valve allows the blood to flow into the pulmonary artery toward the lungs for oxygenation of the blood
The right and left ventricles contract simultaneously; however, because the right ventricle is thinner than the left, it produces a lower pressure than the left when contracting. This lower pressure is sufficient to pump the deoxygenated blood the short distance to the lungs.
Right Atrium:The upper right chamber of the heart. During the normal cardiac cycle, the right atrium receives deoxygenated blood from the body (blood from the head and upper body arrives through the superior vena cava, while blood from the legs and lower torso arrives through the inferior vena cava). Once both atria are full, they contract, and the deoxygenated blood from the right atrium flows into the right ventricle through the open tricuspid valve.
Left Atrium:The upper left chamber of the heart. During the normal cardiac cycle, the left atrium receives oxygenated blood from the lungs through the pulmonary veins. Once both atria are full, they contract, and the oxygenated blood from the left atrium flows into the left ventricle through the open mitral valve.
Pulmonary trunk:A vessel that conveys deoxygenated blood from the right ventricle of the heart to the right and left pulmonary arteries, which proceed to the lungs. When the right ventricle contacts, the blood inside it is put under pressure and the tricuspid valve between the right atrium and right ventricle closes. The only exit for blood from the right ventricle is then through the pulmonary trunk.
Inferior Vena Cava:One of the two main veins bringing deoxygenated blood from the body to the heart. Veins from the legs and lower torso feed into the inferior vena cava, which empties into the right atrium of the heart.
Superior Vena Cava:One of the two main veins bringing deoxygenated blood from the body to the heart. Veins from the head and upper body feed into the superior vena cava, which empties into the right atrium of the heart.
pulmonary veins: The vessels that transport oxygenated blood from the lungs to the left atrium. A common misconception is that all veins carry deoxygenated blood. It is more appropriate to classify veins as vessels carrying blood to the heart.
MRI anatomy of the Horse heart
The three-dimensional horse and heart on the left can be rotated, zoomed, and panned by clicking and moving the mouse as indicated.
The three-dimensional Rabbit and heart on the left can be rotated, zoomed, and panned by clicking and moving the mouse as indicated.
Rabbit heart MRI (long axis view)
MRI anatomy of the Dog heart