Cardiac Physiology Walkthrough

Cardiac physiology refers to the study of the heart's function, including how it pumps blood, regulates blood flow, and maintains the circulatory system. It encompasses understanding the electrical and mechanical activities of the heart.

The heart's primary function is to pump blood throughout the body, supplying oxygen and nutrients to tissues and removing carbon dioxide and other waste products. It does this through a coordinated sequence of muscle contractions and relaxations.

The heart pumps blood through a series of rhythmic contractions known as heartbeats. Blood flows from the atria (upper chambers) into the ventricles (lower chambers) and is then pushed into the arteries during systole (contraction phase) and fills the heart during diastole (relaxation phase).

The SA node, located in the right atrium, is known as the heart's natural pacemaker. It creates electrical impulses that initiate each heartbeat, causing the atria to contract and send blood into the ventricles.

The AV node is located between the atria and ventricles and acts as a gatekeeper. It slows down the electrical signal before it enters the ventricles, ensuring that the atria have enough time to contract and empty their blood into the ventricles before they contract.

The cardiac cycle consists of two main phases: systole, when the heart muscle contracts to pump blood out, and diastole, when the heart muscle relaxes to fill with blood. These phases ensure continuous blood circulation.

Cardiac output is the volume of blood the heart pumps per minute. It is crucial because it determines how much blood – and thus how much oxygen and nutrients – reaches the body's tissues. It's calculated by multiplying heart rate by stroke volume.

Heart rate can be influenced by various factors including physical activity, emotions, temperature, body position, medication, and overall health. The autonomic nervous system plays a significant role, with the sympathetic system increasing heart rate and the parasympathetic system decreasing it.

The Frank-Starling law states that the strength of the heart's contraction is directly proportional to the length of its muscle fibers at the end of diastole. In simpler terms, the more the heart is filled with blood during diastole, the stronger the contraction during systole.

Blood pressure is the force exerted by circulating blood on the walls of blood vessels, and it reflects how hard the heart has to work to pump blood. It is an important measure of heart health, as both high and low blood pressure can indicate underlying cardiac issues.

Coronary arteries supply oxygen-rich blood to the heart muscle itself. Since the heart works continuously, it requires a consistent supply of oxygen and nutrients, provided by these arteries, to function properly.

An electrocardiogram (ECG) is a medical test that records the electrical activity of the heart over a period. It helps in diagnosing heart conditions by showing the heart's rhythm, detecting heart attacks, and identifying abnormalities in heart structure and function.

Heart valves maintain unidirectional blood flow through the heart's chambers. They open to allow blood to flow forward and close to prevent it from flowing backward. The four main valves are the mitral, tricuspid, aortic, and pulmonary valves.

The myocardium is the muscular layer of the heart wall responsible for contracting and generating the force needed to pump blood. This cardiac muscle tissue is unique in its endurance and ability to keep functioning continuously without fatigue.

Exercise enhances cardiac physiology by improving heart muscle function, increasing cardiac output, and promoting better blood circulation. Regular physical activity strengthens the heart, reduces resting heart rate, and lowers the risk of cardiovascular diseases.