Cardiac cycle and blood loops worksheet - Free Printable

Solution and Explanation for the Worksheet

#### Activity 1: The Cardiac Cycle
The cardiac cycle involves the phases of contraction (systole) and relaxation (diastole) of the heart. Let's analyze the images and complete the sentences:

Image A:
- This image shows the atria contracting, pushing blood into the ventricles. The semilunar valves are closed, preventing backflow into the arteries, while the atrioventricular (mitral and tricuspid) valves are open to allow blood flow from the atria to the ventricles.

Image B:
- This image shows the ventricles contracting, pushing blood out into the arteries. The atrioventricular (mitral and tricuspid) valves are closed to prevent backflow into the atria, while the semilunar valves are open to allow blood to flow into the arteries.

Now, let’s fill in the blanks:

1. Image A represents: Diastole
- During diastole, the heart relaxes, allowing blood to fill the chambers.

2. Image B represents: Systole
- During systole, the heart contracts, pumping blood out of the chambers.

3. In A mitral and tricuspid valves are: Open
- These valves allow blood to flow from the atria to the ventricles during diastole.

4. In A semilunar valves are: Closed
- These valves prevent backflow from the arteries into the ventricles during diastole.

5. In A blood flows from the: Atria to the Ventricles
- Blood moves from the atria to the ventricles during diastole.

6. In B mitral and tricuspid valves are: Closed
- These valves prevent backflow from the ventricles to the atria during systole.

7. In B semilunar valves are: Open
- These valves allow blood to flow from the ventricles into the arteries during systole.

8. In B blood flows from the: Ventricles to the Arteries
- Blood moves from the ventricles to the arteries during systole.

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#### Activity 2: Characteristics of Human Circulation
Human circulation is a double-circuit system where oxygenated and deoxygenated blood do not mix. Here are the answers:

1. Oxygenated blood does not mix with deoxygenated blood. Our circulation is: Double Circulation
- In humans, there are two separate circuits: the pulmonary circuit (to the lungs) and the systemic circuit (to the body).

2. Blood passes through the heart twice. Our circulation is: Double Circulation
- Blood enters the heart once in the right atrium, goes to the right ventricle, then to the lungs, returns to the left atrium, and finally goes to the left ventricle before being pumped to the body.

3. Our blood never leaves the blood vessels and recirculates over and over again. Our circulation is: Closed Circulation
- In closed circulation, blood remains within the blood vessels and continuously circulates throughout the body.

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#### Activity 3: Blood Flow in the Heart
This activity focuses on the movement of blood through the heart and the oxygen content at different stages.

1. Blood rich in …… enters the left atrium because it comes from ……
- Answer: Blood rich in O₂ enters the left atrium because it comes from the lungs.
- Explanation: Oxygen-rich blood returns to the heart via the pulmonary veins after gas exchange in the lungs.

2. Blood flows from the left atrium to the left ventricle.
- This is straightforward as blood moves from the atrium to the ventricle during diastole.

3. Blood rich in …… leaves the left ventricle through the aorta artery to ……
- Answer: Blood rich in O₂ leaves the left ventricle through the aorta artery to the body tissues.
- Explanation: Oxygen-rich blood is pumped to the body tissues via the aorta and systemic arteries.

4. Blood rich in …… from cells enters the right atrium.
- Answer: Blood rich in CO₂ from cells enters the right atrium.
- Explanation: Deoxygenated blood, rich in carbon dioxide, returns to the heart via the superior and inferior vena cava after delivering oxygen to the tissues.

5. Blood flows from the right atrium to the right ventricle.
- This is straightforward as blood moves from the atrium to the ventricle during diastole.

6. Blood rich in …… leaves the right ventricle through the pulmonary artery to the ……
- Answer: Blood rich in CO₂ leaves the right ventricle through the pulmonary artery to the lungs.
- Explanation: Carbon dioxide-rich blood is pumped to the lungs for gas exchange.

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#### Activity 4: Systemic and Pulmonary Circulation
This activity involves labeling parts of the circulation system. Since the image is not provided, I will describe what should be labeled:

- Systemic Circulation:
- Aorta: Carries oxygenated blood from the left ventricle to the body.
- Arteries: Carry oxygenated blood away from the heart.
- Capillaries: Site of exchange between blood and tissues.
- Veins: Carry deoxygenated blood back to the heart.
- Superior and Inferior Vena Cava: Return deoxygenated blood to the right atrium.

- Pulmonary Circulation:
- Pulmonary Artery: Carries deoxygenated blood from the right ventricle to the lungs.
- Lungs: Site of gas exchange (O₂ in, CO₂ out).
- Pulmonary Veins: Carry oxygenated blood from the lungs to the left atrium.

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Final Answer Summary

1. Activity 1:
- Image A: Diastole
- Image B: Systole
- Valves and flow directions as explained above.

2. Activity 2:
- Double Circulation
- Double Circulation
- Closed Circulation

3. Activity 3:
- O₂, Lungs
- O₂, Body tissues
- CO₂, Cells
- CO₂, Lungs

4. Activity 4:
- Labeling of systemic and pulmonary circulation components as described.

Final Answer Boxed:
\boxed{
\text{See detailed explanations above.}
}