Heart Structure

Question 1

External features:

Answer 1

Cardiac muscle: specialised muscle found in walls of heart chambers – dark red, firm muscle.
The coronary arteries lie over the surface of the heart, they supply oxygenated blood to the heart muscle. If these arteries become constricted it can have severe consequences for the health of the organ. Restricted blood flow reduces the delivery of oxygen and nutrients such as fatty acids and
glucose, which may cause angina or heart attacks (myocardial infarction).

Question 2

Internal features:

Answer 2

Left side – deoxygenated blood. Right side – oxygenated blood.
Atrioventricular valves: between atria and ventricles, ensure blood flows in right
direction (mitrial/bicuspid and tricuspid valves).
Semilunar valves: prevent blood re-entering the heart from the arteries as
ventricles relax (aortic and pulmonary valves).
Tendinous cords are attached to the valves and prevent them from turning inside
out when the ventricle walls contract.
(Interventricular) Septum: wall of muscle that separates ventricles from each other, ensuring oxygenated blood is not mixed with deoxygenated blood.

Question 3

Blood pressure:

Answer 3

The cardiac muscle in the walls of each chamber contracts to create pressure, the higher blood pressure created, the further blood will be pushed.

• Atria – the muscle of atrial walls is very thin; the chambers don’t need to create much pressure. They receive blood from veins and push it into the ventricles.
• Right ventricle – the walls are thicker than the atria, this enables the ventricle to pump (deoxygenated) blood out of the heart to the lungs. The lungs are in the chest cavity beside the heart, so blood doesn’t travel far. Also, the alveoli are very delicate and could be damaged by high pressure – pulmonary circulation.
• Left ventricle – 2/3 times thicker than the right ventricle walls. The blood is pumped out through the aorta to the whole body, a much longer distance. It needs sufficient pressure to overcome the resistance of the systemic circulation.

Question 4

Practical – Heart dissection:

Answer 4

Pig/cow heart, dissecting tray, scalpel, scissors, apron, gloves.
External examination: Identify vessels, arties are thick and rubbery.
Internal examination: cut the heart in a cross-section through each ventricle, not differences between ventricle walls. Cut open atria too and find semi-lunar and atrio-ventricular valves.
Draw sketches of internal and external views. Know how to draw sketches