Section 6 Flashcards
How is the high demand for oxygen by cardiac muscle cells met?
Through coronary arteries.
Explanation: Cardiac muscle cells, rich in mitochondria and myoglobin, require a constant supply of oxygen to produce ATP. This demand is met by coronary arteries, which branch off the aorta, including the right and left coronary arteries. The left coronary artery further branches into the left anterior descending artery and the circumflex artery, ensuring adequate blood supply to the cardiac muscles.
When does the majority of blood flow in the coronary circulation occur?
During ventricular diastole.
Explanation: Unlike other circulatory systems, such as systemic and pulmonary, the coronary circulation experiences the majority of blood flow during ventricular diastole.
During systole, when the ventricle is contracted, vasculature within the heart walls constricts, and the open aortic valve partially obstructs the entrance to the coronary circulation, reducing blood flow. However, during diastole, when the ventricular walls relax and the aortic valve closes, blood can freely flow into the coronary circulation, with about 70% of the total blood flow occurring at this time. This ensures that coronary blood flow meets the heart’s demands for oxygen.
What happens to coronary circulation during systole and diastole?
Systole:
- During systole, when the ventricle is contracted, the vasculature within the walls of the heart constricts due to the force generated.
- The open aortic valve during this phase partially obstructs the entrance to the coronary circulation.
- These combined events result in a reduction of the amount of blood that can flow into the coronary circulation during systole.
Diastole:
- In contrast, during diastole, when the ventricular walls relax and the aortic valve closes, conditions favor blood flow into the coronary circulation.
- Approximately 70% of the total blood flow to the coronary arteries occurs during diastole.
- This time frame is crucial as coronary blood flow is matched to the heart’s demands for oxygen, ensuring an adequate oxygen supply to the cardiac muscles.
The dynamics of coronary circulation are influenced by the cardiac cycle. Systole, characterized by ventricular contraction, leads to vasoconstriction in the heart walls and obstruction by the open aortic valve, reducing blood flow. Diastole, marked by ventricular relaxation and a closed aortic valve, facilitates free blood flow into the coronary circulation, with a significant proportion occurring during this phase to meet the heart’s oxygen demands.
How much oxygen do most tissues in the body extract at rest?
Most tissues in the body only extract around 25% of delivered oxygen at rest.
How much oxygen does the heart extract while at rest?
The heart extracts about 65% of the oxygen while at rest.
Why do most tissues have a larger reserve for oxygen extraction compared to the heart?
Most tissues have a larger reserve for oxygen extraction (around 25%) in case conditions change and they need to extract more. The heart, however, has a smaller reserve as it extracts about 65% of the oxygen at rest.
What triggers the dilation of the coronary circulation to increase oxygen delivery to the heart?
Adenosine, a metabolic product from ATP, triggers the dilation of the coronary circulation. When metabolic activity in the heart increases, more ATP is consumed, leading to the creation and release of adenosine. Adenosine acts as a paracrine hormone, causing the coronary circulation to dilate.
How is cardiac oxygen delivery matched to its metabolic demand?
Cardiac oxygen delivery is matched to its metabolic demand by the dilation of the coronary circulation triggered by adenosine. This allows more blood and oxygen to flow to the heart when metabolic activity increases.
What is a paracrine hormone?
A hormone that has an effect only in the vicinity of the gland which is secreting it
We have already discussed that the heart needs plenty of oxygen as it is dependent upon aerobic
metabolism to meet its energy demands but what about its fuel source?
The heart, understandably, is incredibly adaptable and will use what is available. It’s primary fuel
source, though, is free fatty acids. When necessary it will switch to ketones, glucose, and even lactate.
From what you have learned in this course and from others, explain why you think free fatty
acids are the preferred source of fuel for the heart?
Unlike skeletal muscle, the heart functions continuously in a regular rhythm of contraction and
relaxation that is almost exclusively aerobically. Free fatty acids are slow burning and easily stored
making them the ideal fuel for the heart.
What is the formula for calculating Cardiac Output (CO)?
Heart Rate (HR) x Stroke Volume (SV) = Cardiac Output (CO)
What is the formula for calculating Ejection Fraction?
Stroke Volume (SV) / End Diastolic Volume (EDV) = Ejection Fraction
