The cardiac cycle and its control

Stages 1, 2a, and 2b together comprise the "Diastole" period; stages 3 and 4 together comprise the "Systole" period.

The cardiac cycle and its control

Photograph of a human heart Computer-generated animation of a beating human heart Location and shape Real-time MRI of the human heart The human heart is in the middle of the thoraxwith its apex pointing to the left.

A double-membraned sac called the pericardium surrounds the heart and attaches to the mediastinum. The upper part of the heart is located at the level of the third costal cartilage. Because the heart is between the lungsThe cardiac cycle and its control left lung is smaller than the right lung and has a cardiac notch in its border to accommodate the heart.

The atria open into the ventricles via the atrioventricular valves, present in the atrioventricular septum. This distinction is visible also on the surface of the heart as the coronary sulcus. Similarly, the left atrium and the left ventricle together are sometimes referred to as the left heart.

It forms the atrioventricular septum which separates the atria from the ventricles, and the fibrous rings which serve as bases for the four heart valves.

The interatrial septum separates the atria and the interventricular septum separates the ventricles. Heart valves With the atria and major vessels removed, all four valves are clearly visible. The white arrows show the normal direction of blood flow.

Frontal section showing papillary muscles attached to the tricuspid valve on the right and to the mitral valve on the left via chordae tendineae.

The cardiac cycle and its control

One valve lies between each atrium and ventricle, and one valve rests at the exit of each ventricle. Between the right atrium and the right ventricle is the tricuspid valve. The tricuspid valve has three cusps, [21] which connect to chordae tendinae and three papillary muscles named the anterior, posterior, and septal muscles, after their relative positions.

It is also known as the bicuspid valve due to its having two cusps, an anterior and a posterior cusp. These cusps are also attached via chordae tendinae to two papillary muscles projecting from the ventricular wall.

These muscles prevent the valves from falling too far back when they close. As the heart chambers contract, so do the papillary muscles. This creates tension on the chordae tendineae, helping to hold the cusps of the atrioventricular valves in place and preventing them from being blown back into the atria.

The pulmonary valve is located at the base of the pulmonary artery. This has three cusps which are not attached to any papillary muscles. When the ventricle relaxes blood flows back into the ventricle from the artery and this flow of blood fills the pocket-like valve, pressing against the cusps which close to seal the valve.

The semilunar aortic valve is at the base of the aorta and also is not attached to papillary muscles. This too has three cusps which close with the pressure of the blood flowing back from the aorta.

A small amount of blood from the coronary circulation also drains into the right atrium via the coronary sinuswhich is immediately above and to the middle of the opening of the inferior vena cava.

The cardiac cycle and its control

In addition to these muscular ridges, a band of cardiac muscle, also covered by endocardium, known as the moderator band reinforces the thin walls of the right ventricle and plays a crucial role in cardiac conduction. It arises from the lower part of the interventricular septum and crosses the interior space of the right ventricle to connect with the inferior papillary muscle.

The pulmonary trunk branches into the left and right pulmonary arteries that carry the blood to each lung. The pulmonary valve lies between the right heart and the pulmonary trunk.

The left atrium has an outpouching called the left atrial appendage.


Like the right atrium, the left atrium is lined by pectinate muscles. Like the right ventricle, the left also has trabeculae carneaebut there is no moderator band. The left ventricle pumps blood to the body through the aortic valve and into the aorta.

Two small openings above the aortic valve carry blood to the heart itself, the left main coronary artery and the right coronary artery.

Cardiac muscle Layers of the heart wall, including visceral and parietal pericardium. The heart wall is made up of three layers:63 Physiologic Responses and Long-Term Adaptations to Exercise is generally much higher in these patients, likely owing to a lesser reduction in total peripheral resistance.

Cardiovascular Health Cardio- Vascular Health. In the U.S., every 34 seconds, someone has a heart attack and every 60 seconds, someone dies from a heart disease-related event.

Cardiovascular System I: The Beating Heart

A cardiac arrest happens when your heart suddenly stops pumping blood around your body. Learn what the causes are and what you should do if you witness a cardiac arrest. There are no proven relationships between coronary artery calcification and the probability of plaque rupture.

Some advocates have argued that EBCT scores could be an effective substitute for standard risk factors in predicting the risk of coronary artery disease.

What are the stages of the cardiac cycle? How do valves control the flow of blood through the heart? What is myogenic stimulation of the heart?

What are the roles of the sinoatrial node, the atrioventricular node and the bundle of His in controlling the cardiac cycle? Regulation of the Cardiac Cycle – controlled by the cardiac center within the medulla oblongata.

The cardiac center signals heart to increase or decrease its rate according to many factors that the brain constantly monitors.

Cardiac Catheterization - procedure, recovery, test, blood, tube, pain, complications, time