9.3 Blood Vessels

2026 Syllabus Objectives

  1. Describe the structure of arteries, veins and capillaries, limited to: relative thickness of wall, diameter of the lumen and the presence of valves in veins
  2. State the functions of capillaries
  3. Identify in diagrams and images the main blood vessels to and from the:
    • (a) heart, limited to: vena cava, aorta, pulmonary artery and pulmonary vein
    • (b) lungs, limited to: pulmonary artery and pulmonary vein
    • (c) kidney, limited to: renal artery and renal vein
  4. Explain how the structure of arteries and veins is related to the pressure of the blood that they transport
  5. Explain how the structure of capillaries is related to their functions
  6. Identify, in diagrams and images, the main blood vessels to and from the liver as: hepatic artery, hepatic veins and hepatic portal vein

Types of Blood Vessels 🔴

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The circulatory system contains three main types of blood vessels, each with distinct structures and functions:

Arteries carry blood away from the heart. They divide repeatedly and eventually form very tiny vessels called capillaries.

Capillaries deliver blood containing oxygen and nutrients close to every cell in the body. They are the smallest blood vessels in the body.

Veins carry blood towards the heart. The capillaries gradually join up with one another to form these larger vessels.

Structure of Arteries 💪

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Key Structural Features

Arteries are designed to withstand high-pressure blood flowing directly from the heart. When blood flows out of the heart, it enters the arteries at high pressure because it has just been forced out by the contraction of the ventricle muscles.

Wall thickness: Arteries have thick, strong walls containing muscle and elastic tissue to withstand the high pressure of blood flowing through them.

Lumen: The space inside the artery (the lumen) is relatively narrow. The width varies with the heartbeat because the walls can stretch and recoil.

Elastic tissue: Arteries contain elastic tissue in their walls which can stretch and recoil (bounce back) with the force of the blood.

Blood Flow in Arteries

The blood does not flow smoothly through arteries—it pulses through. The pressure of the blood is high when the muscles in the ventricles contract, and reduces as these muscles relax. The elastic walls help to make the flow of blood smoother by stretching and recoiling with each heartbeat.

Important: You can feel your arteries stretch and recoil when you feel your pulse in your neck or wrist.

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