The Structure of Blood Vessels (AQA GCSE Physical Education (PE))

Blood Vessels: Structure

• Blood flows within three main types of blood vessel:

  • Arteries

  • Veins

  • Capillaries

Arteries

• Arteries carry blood away from the heart at high pressure

• The blood within arteries is oxygenated

  • With the exception of the pulmonary artery

• The structure of arteries is adapted to their function as follows:

  • Thick muscular walls withstand the high pressure of blood

  • Elastic tissue within the walls allows arteries to stretch and recoil to their original shape; this maintains high blood pressure

  • A narrow lumen helps to maintain high pressure

Redistribution of blood during exercise

• The muscle in the walls of small arteries (arterioles), can contract or relax to alter the diameter of the blood vessel lumen; this allows blood to be redistributed to different organs, e.g.

  • Arterioles supplying the digestive system constrict during exercise, resulting in a reduced diameter that restricts blood flow

    • This is known as vasoconstriction

  • Arterioles supplying the muscles dilate during exercise, resulting in an increased diameter and increased blood flow

    • This is known as vasodilation

    • Vasodilation increases the quantity of oxygen and glucose being delivered to the respiring cells

Veins

• Veins carry blood towards the heart at low pressure

• The blood within veins is deoxygenated

  • With the exception of the pulmonary vein

• The walls of veins are thinner than the walls of arteries as they do not need to withstand high blood pressure

• The structure of veins is adapted to their function as follows:

  • They have a wide lumen to allow large volumes of blood to flow

  • The presence of valves prevents blood from flowing backwards

Arteries and veins diagram

Arteries have thick walls to withstand high blood pressure, while veins contain valves to prevent backflow of blood

Capillaries

• These are very small blood vessels that carry blood to the cells of the body at low pressure

  • Oxygen and nutrients diffuse out of capillaries to the cells

  • Carbon dioxide diffuses from the cells into capillaries

• The blood in capillaries may be either oxygenated or deoxygenated

• The structure of capillaries is adapted to their function as follows:

  • Capillaries have walls that are one cell thick, reducing the diffusion distance for gas exchange

  • Capillaries have a very narrow lumen; this forces red blood cells to flow one at a time and allows diffusion to occur

  • There are many capillaries, providing a very large surface area

Capillaries diagram

Capillaries have thin walls, reducing the diffusion distance between the blood and surrounding tissues

Types of blood vessel table

Blood vessels of the heart

• The blood vessels that carry blood to and from the heart are as follows:

  • The vena cava

    • The main vein that carries deoxygenated blood from the body to the heart

  • The pulmonary artery

    • Carries deoxygenated blood from the heart to the lungs

  • The pulmonary vein

    • Carries oxygenated blood from the lungs to the heart

  • The aorta

    • The main artery that carries oxygenated blood from the heart to the body