a. Describe how heart contraction and relaxation influence coronary blood flow. b. Name the major branches of the coronary arteries, and note the heart regions served by each.

Verified step by step guidance

1. Step 1: Understand that coronary blood flow is primarily influenced by the phases of the cardiac cycle, which include systole (contraction) and diastole (relaxation).
2. Step 2: During systole, the heart muscle contracts, compressing the coronary vessels and reducing blood flow. This is because the increased pressure within the heart muscle during contraction limits the space available for blood to flow through the coronary arteries.
3. Step 3: During diastole, the heart muscle relaxes, allowing the coronary vessels to open and fill with blood. This phase is crucial for coronary blood flow as the pressure is lower, and the coronary arteries are not compressed, facilitating blood flow to the heart muscle.
4. Step 4: Identify the major branches of the coronary arteries: the left coronary artery (LCA) and the right coronary artery (RCA). The LCA further divides into the left anterior descending artery (LAD) and the circumflex artery (LCx).
5. Step 5: Note the regions served by each artery: the LAD supplies the front of the left side of the heart, the LCx supplies the left atrium and the side and back of the left ventricle, and the RCA supplies the right atrium, right ventricle, and bottom portion of both ventricles and back of the septum.

Key Concepts

Heart Contraction and Relaxation

Heart contraction (systole) and relaxation (diastole) are critical phases of the cardiac cycle that influence coronary blood flow. During systole, the heart muscles contract, which can temporarily reduce blood flow to the coronary arteries due to increased intramyocardial pressure. Conversely, during diastole, the heart relaxes, allowing the coronary arteries to fill with blood, thus supplying oxygen and nutrients to the heart muscle.

Coronary Arteries

The coronary arteries are the blood vessels that supply blood to the heart muscle itself. The major branches include the left main coronary artery, which divides into the left anterior descending artery and the circumflex artery, and the right coronary artery. Each branch serves specific regions of the heart: the left anterior descending artery primarily supplies the anterior wall, while the circumflex artery supplies the lateral wall, and the right coronary artery supplies the inferior wall.

Coronary Blood Flow Regulation

Coronary blood flow is regulated by various factors, including myocardial oxygen demand and local metabolic signals. During increased physical activity or stress, the heart requires more oxygen, leading to vasodilation of coronary vessels to enhance blood flow. This regulation ensures that the heart receives adequate blood supply to meet its metabolic needs, particularly during periods of increased workload.