Blood Vessels

Main types of blood vessels:

  1. Arteries: Carry blood away from the heart

  2. Arterioles: Carry blood from arteries into capillaries

  3. Capillaries: Site of diffusion between blood and body tissues

  4. Venules: Carry blood for capillaries into veins

  5. Veins: Returns blood to the heart.

Arteries & Arterioles

  • Arteries carry blood at high pressure away from the heart.

  • Arterioles are smaller than arteries but with a comparatively larger lumen.

    • Their walls have more smooth muscle and less elastin as they do not need to withstand such high pressures.

  • Adaptations of arteries

    • Collagen: Provided strength t prevent the vessel from bursting adn to maintain vessel shape.

    • Elastic fibres: Contain elastin that let's them stretch and recoil to minimise changes in pressure.

    • Thick smooth muscle layer: contracts/relaxes to constrict/dilate the lumen and control the blood flow.

  • Vasoconstriction:

    • Smooth muscle contracts

      • Constricting the blood vessel

      • Decreasing blood flow.

  • Vasodilation:

    • Smooth muscle relaxes

      • Dilating the blood vessel

      • Increasing blood flow

Capillaries

  • Form extensive networks between arterioles and Venules

    • providing an area between blood and tissues where exchange of substance like gases and nutrients occur.

  • Adaptations:

    • Lumen is very narrow

      • Allows red blood cells to be close to body cells

    • Walls are thin

      • Substances can be exchanged across a short stance by diffusion

    • Highly branched

      • This provides a large surface area for diffusion

Veins & Venules

  • Veins are adapted to cary blood towards the heart at low pressure

  • Venules are smaller than veins.

    • They have very thin walls

    • They also have very little smooth muscle

  • Both veins and Venules have valves

  • Adaptation

    • Collagen

      • Provides strength to prevent the vessel from bursting and maintain vessel shape.

    • Little smooth muscle and elastic fibre

      • Not much needed due to low blood pressure

      • Thinner walls allow views to be easily compressed aiding the flow of blood

    • Valves

      • Pocket valves shut to prevent the back flow of blood when veins are a queried by surrounding skeletal muscle

      • The pocket valves in veins are similar in structure to valve in the heart

        • But pocket valves are the only type of velvet controlled by skeletal muscle.