Module 5: Section 6

Question 1

Cardiac Muscle Energy Demand

Answer 1

• Cardiac muscle cells have a high ATP demand and are rich in mitochondria (40% of cell volume) and myoglobin for oxygen storage
• The heart contracts about 70 times per minute to maintain blood and oxygen flow

Question 2

Coronary Artery Blood Supply

Answer 2

• The heart’s oxygen demand is met by the coronary arteries, which branch from the aorta
• he right coronary artery and left coronary artery supply the heart, with the left splitting into the left anterior descending and circumflex arteries

Question 3

Coronary Circulation

Answer 3

• The coronary circulation supplies oxygen-rich blood to cardiac muscle through the coronary arteries
• Unlike other systems, most coronary blood flow occurs during ventricular diastole, not systole

Question 4

Systole - coronary circulation

Answer 4

• The ventricle is contracted, the vasculature within the walls of the heart are also constricted due to the force
• The open aortic valve, partially obstructs the entrance to coronary circulation
• These events reduce the amount of blood flow during systole

Question 5

Diastole - coronary circulation

Answer 5

• The ventricle walls relax and aortic valve closes, blood can freely flow into the coronary circulation
• 70% of total blood flow to the coronary arteries occurs at this time
• Coronary blood flow is matched to the hearts demands for O2

Question 6

Cardiac Oxygen Extraction

Answer 6

Most tissues extract about 25% of oxygen at rest, but the heart extracts ~65%, leaving a smaller oxygen reserve and requiring increased blood flow to meet demand

Question 7

Regulation of Coronary Circulation

Answer 7

• When heart activity increases, adenosine (from ATP breakdown) acts as a paracrine hormone causing coronary vasodilation
• This increases blood and oxygen flow to match metabolic demand