Blood Vessels | Biology for GCSE/IGCSE - Year 11 PDF Download

Arteries

• Carry blood at high pressure away from the heart: Arteries are blood vessels that transport blood under high pressure from the heart to various parts of the body.
• Carry oxygenated blood (other than the pulmonary artery): Arteries carry oxygen-rich blood, except for the pulmonary artery which carries deoxygenated blood to the lungs for oxygenation.
• Have thick muscular walls containing elastic fibres: Arteries have thick walls composed of muscle and elastic fibers to withstand the pressure generated by the heart's pumping action.
• Have a narrow lumen: The lumen of arteries is relatively narrow, allowing for the maintenance of high blood pressure as blood flows through them.
• Speed of flow is fast: Blood flows rapidly through arteries due to the high pressure and muscular walls that propel it swiftly.

Veins

• Carry blood at low pressure towards the heart: Veins are blood vessels that transport blood at low pressure from various parts of the body back to the heart.
• Carry deoxygenated blood (other than the pulmonary vein): Veins carry deoxygenated blood, except for the pulmonary vein which carries oxygenated blood from the lungs to the heart.
• Have thin walls: Veins have thinner walls compared to arteries, as the pressure exerted by blood in veins is lower.
• Have a large lumen: The lumen of veins is wider compared to arteries, allowing for easier blood flow at a lower pressure.
• Contain valves: Veins are equipped with valves that prevent the backflow of blood, ensuring a unidirectional flow towards the heart.
• Speed of flow is slow: Blood moves more slowly in veins due to the lower pressure, thinner walls, and the presence of valves that regulate flow.

Comparing arteries and veins

Capillaries

• Carry blood at low pressure within tissues: Arteries and veins transport blood at different pressures. Arteries carry blood away from the heart at high pressure, while veins return blood to the heart at low pressure within tissues.
• Carry both oxygenated and deoxygenated blood: Arteries generally carry oxygenated blood (except for the pulmonary artery), while veins carry deoxygenated blood (except for the pulmonary vein).
• Have walls that are one cell thick: The walls of capillaries, not arteries or veins, are only one cell thick. This thin structure allows for the exchange of nutrients and waste products between blood and tissues.
• Have 'leaky' walls: Capillaries have permeable walls that allow for the exchange of substances between blood and surrounding tissues. This leakage is essential for processes like nutrient delivery and waste removal.
• Speed of flow is slow: Blood flow in capillaries is relatively slow, allowing more time for nutrient exchange and waste removal to occur at the cellular level.

Structure of a capillary