veins

• What is the diameter of a vein?


  From 30 micrometers to 2.5 cm (SVC and IVC)
• What do veins do?


  Carry deoxygenated blood away from cells towards the heart (the blood has more CO2 than O2)
• What pressure is there in the veins?


  Low pressure, no pulse - large blood volume (60%)
• Which veins do NOT carry deoxygenated blood?

  pulmonary vein

  umbilical vein
• What does the outermost layer have?

  Lots of collagen but little elastic fibres
• What do veins have?


  •wide lumen

  •smooth endothelium
• Why do veins have valves?


  •in medium/small sized veins

  •valves are folds of the innermost layer strengthened by fibrous tissue

  •valves prevent backflow

  •when muscles contact, they press on the blood in veins and push it upwards

  •breathing movement of the chest (thorax) act as a pump to pull up blood

  •prevents pooling of blood

  •blood goes against gravity