Understanding:
• Veins collect blood at low pressure from the tissues of the body and return it to the atria of the heart
Structure and Function
The function of veins is to collect the blood from the tissues and convey it at low pressure to the atria of the heart
To this end, veins have a specialised structure in order to accomplish this task:
- They have a very wide lumen (relative to wall thickness) to maximise blood flow for more effective return
- They have a thin wall containing less muscle and elastic fibres as blood is flowing at a very low pressure (~ 5 – 10 mmHg)
- Because the pressure is low, veins possess valves to prevent backflow and stop the blood from pooling at the lowest extremities
Structure of a Typical Vein
Understanding:
• Valves in veins and the heart ensure circulation of blood by preventing backflow
Flow of Blood
Blood is at very low pressure in the veins which can make it difficult for the blood to move against the downward force of gravity
- The veins contain numerous one-way valves in order to maintain the circulation of blood by preventing backflow
Veins typically pass between skeletal muscle groups, which facilitate venous blood flow via periodic contractions
- When the skeletal muscles contract, they squeeze the vein and cause the blood to flow from the site of compression
- Veins typically run parallel to arteries, and a similar effect can be caused by the rhythmic arterial bulge created by a pulse
The Role of Skeletal Muscles in Venous Blood Flow
