Lesson Notes By Weeks and Term v5 - Grade 11

Lesson Video

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Performance objectives

• Describe the structure and function of the human heart.
• Explain the cardiac cycle and its relation to blood pressure.
• Compare and contrast arteries, veins, and capillaries.
• Describe the composition and functions of blood.
• Explain the importance of the lymphatic system.

Lesson summary

The human transport system, primarily the circulatory system, is vital for maintaining life. It functions like a complex highway network, delivering essential substances like oxygen, nutrients, and hormones to every cell in the body and removing waste products like carbon dioxide and urea. Understanding this system is crucial because its proper functioning directly impacts our overall health and wellbeing. Problems within the transport system, such as heart disease or blood disorders, are prevalent in South Africa and worldwide.

Lesson notes

2.1 The Heart: The Central Pump The heart is a muscular organ responsible for pumping blood throughout the body.

It consists of four chambers: Right Atrium: Receives deoxygenated blood from the body via the superior and inferior vena cava.

Right Ventricle: Receives deoxygenated blood from the right atrium and pumps it to the lungs via the pulmonary artery.

Left Atrium: Receives oxygenated blood from the lungs via the pulmonary veins.

Left Ventricle: Receives oxygenated blood from the left atrium and pumps it to the body via the aorta. The left ventricle has the thickest walls because it needs to generate enough force to pump blood to the entire body.

Valves: The heart contains valves that ensure blood flows in one direction only.

Atrioventricular Valves (AV valves): These valves are located between the atria and ventricles. The tricuspid valve is on the right side (between the right atrium and ventricle), and the bicuspid (mitral) valve is on the left side (between the left atrium and ventricle).

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

Major Blood Vessels: Aorta: The largest artery in the body, carrying oxygenated blood from the left ventricle to the body.

Pulmonary Artery: Carries deoxygenated blood from the right ventricle to the lungs.

Pulmonary Veins: Carry oxygenated blood from the lungs to the left atrium.

Vena Cava (Superior and Inferior): The superior vena cava carries deoxygenated blood from the upper body to the right atrium, and the inferior vena cava carries deoxygenated blood from the lower body to the right atrium. 2.2 The Cardiac Cycle The cardiac cycle refers to the sequence of events that occur during one complete heartbeat.

It consists of two phases: Systole: The contraction phase of the heart, during which the ventricles pump blood out.

Diastole: The relaxation phase of the heart, during which the atria fill with blood. The cardiac cycle involves the following steps: Atrial Systole: The atria contract, pushing blood into the ventricles.

Ventricular Systole: The ventricles contract, closing the AV valves (tricuspid and bicuspid) and opening the semilunar valves (pulmonary and aortic). Blood is ejected into the pulmonary artery and aorta.

Diastole: The atria and ventricles relax. The semilunar valves close, preventing backflow of blood into the ventricles. The AV valves open, and the atria begin to fill with blood.

Blood Pressure: Blood pressure is the force of blood pushing against the walls of the arteries. It is measured as systolic pressure (pressure during ventricular systole) over diastolic pressure (pressure during diastole). A normal blood pressure is around 120/80 mmHg. High blood pressure (hypertension) can damage the heart, blood vessels, and other organs.

Example: A patient with a blood pressure reading of 140/90 mmHg is considered to have hypertension and might be advised to reduce their salt intake and increase physical activity. 2.3 Blood Vessels: Arteries, Veins, and Capillaries There are three main types of blood vessels: Arteries: Carry blood away from the heart. They have thick, elastic walls to withstand the high pressure of blood pumped from the heart. The aorta is the largest artery.

Veins: Carry blood back to the heart. They have thinner walls than arteries and contain valves to prevent backflow of blood, especially in the legs. The vena cava is the largest vein.

Capillaries: Tiny, thin-walled vessels that connect arteries and veins. They are the site of exchange of gases, nutrients, and waste products between the blood and the body's cells. Their walls are only one cell thick, facilitating diffusion.

Comparison Table: | Feature | Arteries | Veins | Capillaries | |------------------|---------------------------------------------|----------------------------------------------|------------------------------------| | Direction of flow | Away from the heart | Towards the heart | Connect arteries and veins | | Wall thickness | Thick, elastic, muscular | Thin, less elastic, less muscular | One cell thick | | Blood pressure | High | Low | Low | | Valves | Absent (except in the aorta and pulmonary artery) | Present (to prevent backflow) | Absent | 2.4 Composition of Blood Blood is a complex fluid consisting of: Plasma: The liquid portion of blood, containing water, proteins, nutrients, hormones, and waste products. It makes up about 55% of blood volume.

Red Blood Cells (Erythrocytes): Contain hemoglobin, a protein that binds to oxygen. They transport oxygen from the lungs to the body's cells and carry carbon dioxide back to the lungs. They have no nucleus in mammals to maximize space for hemoglobin.

White Blood Cells (Leukocytes): Part of the immune system, defending the body against infection.