Structure, Function, and Regulation of the Heart

Cardiac Muscle Contractions

- Cardiac muscle can contract without any signal from the nervous system.

Average Cardiac Output

- Humans have an average cardiac output of about 5.25 L/min. - Heavy exercise can increase cardiac output up to five times. - Epinephrine and increased body temperature also increase heart rate and, thus, the cardiac output.

Stroke Volume

- The amount of blood pumped by the left ventricle each time it contracts.

Atria and Ventricles

- The atria are the chambers that receive blood returning to the heart and the ventricles are the chambers that pump blood out of the heart.

Atrioventricular Node

- The atrioventricular node briefly delays the electrical impulse to ensure the atria empty before the ventricles contract.

Cardiac Output

- The cardiac output is the volume of blood per minute that the left ventricle pumps. - This output depends on the heart rate and stroke volume.

Cardiovascular System

- The function of the closed circulatory system (cardiovascular system) is to carry oxygenated blood and nutrients to all cells of the body and return carbon dioxide waste to the lungs for expulsion. - The heart, blood vessels, and blood make up the cardiovascular system.

Heart Rate

- The heart rate is the number of times the heart beats per minute.

Sinoatrial Node

- The sinoatrial node is the pacemaker of the heart. - It is located on the wall of the right atrium and generates electrical impulses that make cardiac muscle cells contract in unison.

Valves

- There are four vales, two atrioventricular (AV) valves and two semilunar valves. - The AV valves are located between each atrium and ventricle. - The contraction of the ventricles closes the AV valve to keep blood from flowing back into the atria. - The semilunar valves are located where the aorta leaves the left ventricle and the pulmonary artery leaves the right ventricle. - Ventricular contraction opens the semilunar valves, pumping blood out into the arteries, and ventricular relaxation closes the valves.