Lesson Notes By Weeks and Term v5 - Grade 11

Lesson Video

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Performance objectives

• Describe the structure of the human heart and relate it to its function.
• Explain the structure and function of arteries, veins, and capillaries.
• Distinguish between pulmonary and systemic circulation.
• Apply this knowledge to understand cardiovascular health.

Lesson summary

The efficient transport of essential substances (oxygen, nutrients, hormones) and the removal of waste products (carbon dioxide, urea) are vital for the survival and proper functioning of the human body. This intricate process is orchestrated by the circulatory (blood, heart, blood vessels) and lymphatic systems. Understanding these systems is not only crucial for grasping basic human physiology but also for appreciating the impact of lifestyle choices and diseases on our health. Many health challenges in South Africa, such as hypertension, heart disease, and lymphatic disorders, are directly linked to the functioning of these transport systems.

Lesson notes

2.1 The Human Heart: Structure and Function The heart is a muscular organ responsible for pumping blood throughout the body. It's located in the thoracic cavity, protected by the rib cage.

Structure: The heart is composed of four chambers: Atria (Right and Left): The upper chambers that receive blood returning to the heart. The right atrium receives deoxygenated blood from the body, while the left atrium receives oxygenated blood from the lungs.

Ventricles (Right and Left): The lower chambers that pump blood out of the heart. The right ventricle pumps deoxygenated blood to the lungs, while the left ventricle pumps oxygenated blood to the body. The left ventricle has a thicker muscular wall than the right ventricle because it needs to generate more force to pump blood over a greater distance and against higher resistance.

Valves: These ensure unidirectional blood flow, preventing backflow.

Atrioventricular Valves (AV Valves): These are located between the atria and ventricles. The tricuspid valve is on the right side, and the bicuspid (mitral) valve is on the left side. They are attached to chordae tendineae and papillary muscles, which prevent the valves from inverting back into the atria during ventricular contraction.

Semilunar Valves: These are located at the exit of the ventricles. The pulmonary valve is between the right ventricle and the pulmonary artery, and the aortic valve is between the left ventricle and the aorta.

Cardiac Muscle (Myocardium): The heart wall is primarily composed of cardiac muscle, which is specialized for rhythmic contractions. Cardiac muscle cells are interconnected by intercalated discs, which allow for rapid and coordinated spread of electrical impulses.

Pericardium: A double-layered sac that surrounds the heart, providing protection and reducing friction during heartbeats.

Coronary Arteries: These supply the heart muscle itself with oxygenated blood. Blockage of these arteries can lead to a heart attack (myocardial infarction).

Function: The heart functions as a double pump: Pulmonary Circulation: The right side of the heart pumps deoxygenated blood to the lungs via the pulmonary artery. In the lungs, carbon dioxide is exchanged for oxygen, and the oxygenated blood returns to the left atrium via the pulmonary veins.

Systemic Circulation: The left side of the heart pumps oxygenated blood to the rest of the body via the aorta. Oxygen and nutrients are delivered to the body's tissues, and carbon dioxide and waste products are picked up. The deoxygenated blood returns to the right atrium via the superior and inferior vena cava.

Cardiac Cycle: The sequence of events that occur during one heartbeat.

It involves two phases: Systole: Contraction phase. Atrial systole is followed by ventricular systole.

Diastole: Relaxation phase. The atria and ventricles fill with blood.

Worked example

Imagine a person running a Comrades marathon. Explain how the structure of their heart helps them in this strenuous activity.

Solution: The heart's structure is perfectly adapted to the demands of strenuous activity like the Comrades. The left ventricle's thick, muscular wall allows it to forcefully pump oxygenated blood to the working muscles. The valves ensure that this blood flows in one direction only, preventing backflow and maintaining efficient circulation. The coronary arteries provide the heart muscle itself with the increased oxygen it needs during exercise. The pericardium protects the heart from damage during the repetitive pounding of running.

Therefore, the structural integrity of the heart is critical for supporting the sustained physical exertion of running a marathon.

2.2 Blood Vessels: Structure and Function

There are three main types of blood vessels: arteries, veins, and capillaries.

Arteries: Carry blood away from the heart.

Structure: Thick, elastic walls with smooth muscle. The elasticity allows them to stretch and recoil, maintaining blood pressure.

Function: Transport blood under high pressure. The smooth muscle allows for vasoconstriction (narrowing) and vasodilation (widening) to regulate blood flow.

Example: Aorta (the largest artery) carries oxygenated blood from the left ventricle to the rest of the body. Pulmonary artery carries deoxygenated blood from the right ventricle to the lungs.