Blood vessels

• Capillaries= microscopic blood vessels that link the arterioles with the venules.
• The lumen of a capillary is so small that red blood cells have to travel through in single file.
• Substances are exchanged through the capillary walls between the tissue cells and the blood.
• Artery walls contain elastic fibres, smooth muscle and collagen.
• The elastic fibres in artery walls enable them to withstand the force of the blood pumped out of the heart and stretch to take the larger blood volume.
• The lining of an artery is smooth so the blood flows easily over it.
• Arterioles link the arteries and capillaries.
• Arterioles have more smooth muscle and less elastin in their walls than artistries.
• Capillaries:

  • have a narrow diameter to slow blood flow
  • made of one single layer of squamous epithelial cells
• Capillaries have small gaps in their walls so that liquid and small molecules can be forced out- this forms tissue fluid.