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Transport in Animals - Blood and lymphatic vessels

Grade 11IGCSEBiology

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Arteries: Transport blood away from the heart at high pressure. They feature thick walls containing muscle and elastic fibers to withstand and maintain high pressure, ensuring O2O_2 reaches tissues efficiently.

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Veins: Transport blood towards the heart at low pressure. They have thinner walls and a larger lumen than arteries, and contain valves to prevent the backflow of blood against gravity.

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Capillaries: Microscopic vessels with walls only one cell thick (approximately 1μm1 \mu m) to provide a short diffusion distance for the exchange of gases such as O2O_2 and CO2CO_2, and nutrients like glucose (C6H12O6C_6H_{12}O_6).

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Tissue Fluid Formation: At the arterial end of a capillary, high hydrostatic pressure forces water and small solutes out of the blood plasma into the surrounding spaces to form tissue fluid.

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Lymphatic System: A network of vessels that drains excess tissue fluid (lymph) and returns it to the circulatory system via the subclavian veins. It also transports fats from the small intestine via lacteals.

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Lymph Nodes: Small structures located along the lymphatic vessels that filter lymph and contain lymphocytes to produce antibodies for immune defense.

📐Formulae

Cardiac Output=Stroke Volume×Heart RateCardiac\ Output = Stroke\ Volume \times Heart\ Rate

Rate of Diffusion∝Surface Area×Concentration GradientDiffusion Distance\text{Rate of Diffusion} \propto \frac{\text{Surface Area} \times \text{Concentration Gradient}}{\text{Diffusion Distance}}

SA:V=Surface AreaVolumeSA:V = \frac{\text{Surface Area}}{\text{Volume}}

💡Examples

Problem 1:

Explain the difference in the partial pressure of oxygen (PO2P_{O_2}) between the blood entering the pulmonary artery and the blood leaving the pulmonary vein.

Solution:

PO2P_{O_2} in Pulmonary Artery << PO2P_{O_2} in Pulmonary Vein.

Explanation:

The pulmonary artery carries deoxygenated blood from the heart to the lungs. After gas exchange in the alveoli, the blood becomes oxygenated, increasing the PO2P_{O_2} before it returns to the heart via the pulmonary vein.

Problem 2:

A capillary has a diameter of approximately 8μm8 \mu m. Why is this significant for the transport of Red Blood Cells (RBCs)?

Solution:

The diameter of an RBC is also approximately 7−8μm7-8 \mu m, meaning cells must pass through in single file.

Explanation:

This slows down blood flow and brings the RBCs into close contact with the capillary wall, minimizing the diffusion distance for O2O_2 and CO2CO_2 according to Fick's Law.

Blood and lymphatic vessels - Revision Notes & Key Diagrams | IGCSE Grade 11 Biology