The Circulatory System

Name the three blood components that carry out transport, defence, and clotting functions, and state what each of them does.

Look at the cross-sectional image of the heart. State which numbers point to the two atria and which point to the two ventricles, and explain one difference between their walls.

In the image of the heart, the numbered valves between the chambers can be seen. Explain the function of these valves and reason what problem a person would have if the valve between the left atrium and the left ventricle did not close properly.

Complete the sentence with the correct terms: "$\dots$ carry blood from the heart to the organs, $\dots$ return it from the organs to the heart, and $\dots$ are very thin vessels where the exchange of substances with tissues takes place."

Describe the complete pathway of blood through the two circuits of the circulatory system: the pulmonary circuit (or minor circuit), indicating which heart chamber it begins in, which vessel carries it out, what happens to it in the lungs, and through which vessel and to which chamber it returns; and the systemic circuit (or major circuit), indicating which chamber it leaves from, through which major artery, to which parts of the body it carries blood, and through which major vein it returns to the heart.

A child takes their pulse at the wrist and counts $72$ beats in one minute; after running during break time, they count $115$ beats in one minute. Explain why the heart rate increases during exercise, linking it to the needs of muscle cells.

A patient goes to the doctor and is diagnosed with severe pulmonary hypertension (the resistance of the vessels leading to the lungs is abnormally high), while the pressure in the rest of the body is normal. Two years later, an ultrasound reveals that the muscular wall of one of their two ventricles has doubled in thickness to compensate for this extra workload.

1. a) Reasonably justify which of the two ventricles will have increased in thickness.
2. b) Predict what consequences it would have for gas exchange in the alveoli and for the body if that ventricle were to eventually fail due to muscular exhaustion.

If a person's heart expels about $70\ \text{mL}$ of blood with each beat and beats $75$ times per minute, calculate the volume of blood it pumps in one day, express it in liters, and comment on why the figure seems so large given that the body only contains about $5\ \text{L}$ of blood.

A student raises the following question in class: "The heart's chambers are constantly filled with oxygen-rich blood coming from the lungs. Therefore, it makes no sense that a blockage in the coronary arteries causes a heart attack, since the cardiac muscle could absorb nutrients directly from the blood it pumps."

1. a) Refute this argument by justifying why myocardial cells cannot obtain nutrients directly by diffusion from inside the heart chambers and depend exclusively on the coronary arteries.
2. b) Explain the "domino effect" that occurs in the rest of the body when an area of the heart muscle undergoes necrosis, comparing it to what would happen if the blocked artery were in an arm.