Systemic Circulation

Question 1

Elasticity of blood vessel

Answer 1

• blood vessel walls contain elastic elements (elastin and collagen fibers) that act to maintain steady tension and hold the wall in equilibrium
• smooth muscle is arranged circumferentially, producing an active tension by constricting the vessel and thus changing the radius
• the endothelium is very elastic
• blood vessels resist stretch more strongly the more they are stretched

Question 2

Pressure tension on blood vessel walls

Answer 2

• for most arteries and veins, the dynamic pressure is small and they act like balloons with one pressure (lateral/static) throughout
• the pressure exerts a force on the blood vessel walls
• since the extra-lumenal pressure is equal to atmospheric the pressure across the vessel wall, termed the transmural pressure, is equal to the blood pressure
• the transmural pressure gives rise to the development of tension within the vessel wall
• tension is a force exerting its effect along the wall circumference and is often described as the force that would pull apart a longitudial slit in wall

Question 3

Elasticity of blood vessels

Answer 3

• total tension in circulation varies ~10^4 from the large arteries to capillaries
• capillaries experience a very small transmural pressure that is how they can function without supporting structures