Lesson Notes By Weeks and Term v5 - Grade 11

Lesson Video

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Performance objectives

• Describe the structure and function of arteries, veins, and capillaries.
• Identify the components of blood and their roles.
• Explain how haemoglobin transports oxygen.
• Describe the transport of nutrients, wastes, and hormones.
• Understand the importance of healthy blood pressure.

Lesson summary

The transport system in humans is vital for our survival. It’s how our cells receive oxygen and nutrients, and how waste products are removed. Without an efficient transport system, we would quickly become ill. Imagine trying to deliver food or medicine across South Africa without roads or vehicles – that’s what life would be like for our cells without a functioning circulatory system! Issues like high blood pressure, heart disease, and anaemia are common in South Africa, often linked to lifestyle and diet. Understanding how our transport system works is the first step in taking care of our health.

Lesson notes

2.1 Blood Vessels: Our circulatory system is a network of vessels through which blood travels.

There are three main types: Arteries: These vessels carry blood away from the heart. They have thick, muscular walls with elastic fibres. This allows them to withstand the high pressure of blood being pumped from the heart and to stretch and recoil, maintaining blood flow even when the heart is not contracting. The thick walls also prevent the arteries from bursting under pressure. Arteries branch into smaller vessels called arterioles, which help regulate blood flow into capillaries.

Structure: Tunica adventitia (outer layer): Made of connective tissue, providing support and protection.

Tunica media (middle layer): Thick layer of smooth muscle and elastic fibres, allowing for vasoconstriction (narrowing) and vasodilation (widening) of the artery.

Tunica intima (inner layer): Thin layer of endothelium (single layer of cells), providing a smooth surface for blood flow.

Veins: These vessels carry blood back to the heart. They have thinner walls than arteries because the blood pressure is lower. Veins also contain valves to prevent the backflow of blood, especially in the limbs where gravity works against blood flow. Veins originate as small vessels called venules which collect blood from capillaries.

Structure: Tunica adventitia (outer layer): Made of connective tissue, thinner than in arteries.

Tunica media (middle layer): Thin layer of smooth muscle and elastic fibres.

Tunica intima (inner layer): Thin layer of endothelium, with valves present.

Capillaries: These are the smallest blood vessels, forming a vast network throughout the body. Their walls are only one cell thick, allowing for the efficient exchange of substances (oxygen, nutrients, waste products) between the blood and the body's cells through diffusion.

Structure: Single layer of endothelial cells. Extremely thin walls to facilitate diffusion.

Example: Imagine a tap supplying water to a garden. The main pipe from the municipality is like an artery – thick and strong. Smaller pipes branching off to different sections of the garden are like arterioles. The thin, porous pipes dripping water directly onto the plants are like capillaries, delivering water (nutrients and oxygen) to the plants (body cells). The pipes draining excess water back to a reservoir are like veins, carrying waste products away. 2.2 Blood Components: Blood is a complex fluid made up of several components: Plasma: This is the liquid part of blood, making up about 55% of its volume. It's mostly water but also contains dissolved substances such as: Nutrients: Glucose, amino acids, lipids Waste products: Urea, carbon dioxide Hormones: Chemical messengers Proteins: Albumin (maintains osmotic pressure), globulins (antibodies), fibrinogen (involved in blood clotting).

Red Blood Cells (Erythrocytes): These are responsible for carrying oxygen. They contain haemoglobin, a protein that binds to oxygen. Red blood cells are biconcave in shape, increasing their surface area for oxygen diffusion and allowing them to squeeze through narrow capillaries. They lack a nucleus, maximising space for haemoglobin.

White Blood Cells (Leukocytes): These are part of the immune system, defending the body against infection. There are different types of white blood cells, each with a specific role.

Examples include: Neutrophils: Phagocytose (engulf) bacteria and other pathogens.

Lymphocytes: Produce antibodies and attack infected cells.

Platelets (Thrombocytes): These are small cell fragments that play a crucial role in blood clotting. When a blood vessel is damaged, platelets aggregate at the site of injury and help form a clot to stop the bleeding. 2.3 Haemoglobin and Oxygen Transport: Haemoglobin is the protein in red blood cells that binds to oxygen. Each haemoglobin molecule can bind to four oxygen molecules. This binding is affected by factors such as: Partial pressure of oxygen: Higher oxygen concentration (e.g., in the lungs) promotes oxygen binding. pH: Lower pH (more acidic) reduces oxygen binding (Bohr effect). This is important in tissues with high metabolic activity, where carbon dioxide production lowers pH, causing haemoglobin to release oxygen.

Temperature: Higher temperature reduces oxygen binding.

Example: A person living in the high-altitude areas of Lesotho might have a higher concentration of red blood cells and haemoglobin compared to someone living at sea level. This adaptation helps them to compensate for the lower partial pressure of oxygen at higher altitudes and ensure sufficient oxygen delivery to their tissues. 2.4 Transport of Nutrients, Waste Products, and Hormones: Nutrients: Glucose, amino acids, and lipids are absorbed from the small intestine into the blood and transported to cells throughout the body for energy production and building new tissues.