Heart
Diagram Identification Cues:
When looking at a diagram of the heart, remember that diagrams are drawn from the perspective of the person whose heart it is. Therefore, the right side of the heart is on the left side of the page, and the left side of the heart is on the right side of the page.
- Muscular Wall: The thick outer layer surrounding the chambers. It is made of cardiac muscle tissue.
- Septum: The vertical wall separating the left and right sides of the heart. It prevents mixing of blood.
- Left Ventricle: The chamber on the right side of the diagram (patient's left). It has the thickest muscular wall because it pumps blood to the whole body.
- Right Ventricle: The chamber on the left side of the diagram (patient's right). It has a thinner wall than the left ventricle because it only pumps blood to the lungs.
- Left Atrium: The upper chamber on the right side of the diagram. It receives oxygenated blood from the lungs.
- Right Atrium: The upper chamber on the left side of the diagram. It receives deoxygenated blood from the body.
- One-way Valves: Flaps of tissue located between the atria and ventricles (atrioventricular valves) and between the ventricles and arteries (semilunar valves). They ensure blood flows in only one direction.
Veins: Blood vessels that carry blood towards (back to) the heart. They have thinner walls and contain valves to prevent backflow.
The left ventricle pumps blood to the entire body (systemic circulation), which requires generating high pressure to overcome resistance in distant vessels. The right ventricle only pumps blood to the lungs (pulmonary circulation), a short distance with low resistance. Therefore, the left ventricle needs more muscular tissue to contract with greater force.
Why are atrial walls thinner than ventricular walls?
The atria only need to pump blood a short distance into the ventricles below them. This requires much less pressure and force than pumping blood out of the heart into arteries.
Correction: While this is true for most of the body, the pulmonary artery carries deoxygenated blood to the lungs, and the pulmonary vein carries oxygenated blood from the lungs to the heart. Always define arteries/veins by their direction relative to the heart (away/towards), not by oxygen content.
Correct Phrasing: You should state that heart activity is monitored by:
- ECG (Electrocardiogram): Measures the electrical impulses that trigger muscle contraction.
- Pulse rate: The number of times the heart beats per minute, felt at arteries like the wrist or neck.
- Listening to sounds: The 'lub-dub' sound is caused by the closing of the one-way valves.
Why examiners accept this: These methods directly address different aspects of cardiac function: electrical activity (ECG), mechanical output (pulse), and valve integrity (sound).
The heartbeat is a coordinated cycle of contraction and relaxation:
- Atrial Systole: The muscles in the atria contract, pushing blood down into the ventricles. This opens the atrioventricular valves.
- Ventricular Systole: The muscles in the ventricles contract. This increases pressure, forcing the semilunar valves open and pushing blood out of the heart into the arteries. The high pressure also forces the atrioventricular valves shut to prevent backflow into the atria.
- Diastole: All chambers relax. Pressure drops, allowing blood to flow passively from veins into the atria and then through the open atrioventricular valves into the ventricles.
Importance: It ensures that oxygenated blood (from the lungs) and deoxygenated blood (from the body) do not mix. Mixing would reduce the efficiency of oxygen transport to tissues.
Description of CHD: Coronary heart disease occurs when the coronary arteries become blocked or narrowed. This blockage is usually caused by a buildup of fatty deposits (atheroma).
Consequence: The blockage reduces the supply of oxygen and glucose to the heart muscle cells. Without sufficient oxygen, the heart muscle cannot perform aerobic respiration effectively, leading to reduced energy production and potential heart attack.
Risk Factors:
- Diet: High intake of saturated fats increases cholesterol levels, promoting plaque buildup.
- Lack of Exercise: Leads to obesity and poor cardiovascular health.
- Smoking: Chemicals damage artery walls and increase blood pressure.
- Stress: Increases heart rate and blood pressure, damaging arteries over time.
- Genetic Predisposition: Family history can influence cholesterol levels and arterial health.
- Age and Sex: Risk increases with age; men are generally at higher risk at younger ages than women.
Correct Phrasing:
- Diet: A balanced diet low in saturated fats and salt helps maintain healthy blood pressure and cholesterol levels, preventing atheroma formation. Controlling calorie intake prevents obesity, which reduces strain on the heart.
- Exercise: Regular exercise strengthens the heart muscle, allowing it to pump more efficiently with fewer beats. It also helps maintain a healthy weight and improves circulation.
Why examiners accept this: This directly links lifestyle choices to physiological mechanisms (cholesterol levels, blood pressure, muscle strength) rather than just stating 'it is good for you'.
Observation: During physical activity, heart rate increases.
Explanation:
- Muscles require more energy for contraction.
- To produce this energy, muscles need more oxygen and glucose for aerobic respiration.
- The heart pumps faster to deliver more oxygenated blood (carrying oxygen and glucose) to the muscles.
- The heart also pumps faster to remove waste products like carbon dioxide and lactate from the muscles more quickly.