[7.6] (1/2) blood vessels and their functions Flashcards
what is the function of arteries?
to carry blood away from the heart into arterioles
what is the function of arterioles?
smaller arteries that control blood flow from arteries to capillaries
what is the function of capillaries?
to link arterioles to veins
what is the function of veins?
to carry blood from the capillaries back to the heart
what are 4 structural adaptations of arteries that improve its function?
- muscle layer thicker > veins
- elastic layer thicker > veins
- overall thickness of wall is great
- no valves
why do arteries have a thicker muscle layer (than veins)?
smaller arteries can be constricted and dilated to control volume of blood passing through them
why do arteries have a thicker elastic layer (than veins)?
- arteries must be able to withstand high blood pressure so blood can reach extremities of the body
- elastic wall stretches at each heart contraction (systole) and recoils when heart relaxes (diastole)
- stretching and recoil action helps maintain high pressure and smooth pressure surges from heart beating
why do arteries have an overall thick wall?
stops it bursting under pressure
why do arteries not have valves?
blood is under constant high pressure due to heart pumping blood into arteries so tends not to flow backwards
which arteries do have valves?
arteries leaving the heart
how is arteriole structure related to function?
- muscle layer is thicker than in arteries
- elastic layer is thinner than in arteries
why do arterioles have a thicker muscle layer (than arteries)?
- contraction of this muscle layer allows constriction of the lumen of the arteriole
- this restricts the flow of blood and so controls its movement into the capillaries that supplies the tissue with blood
why do arterioles have a thinner elastic layer (than arteries)?
because blood pressure is lower
how is vein structure related to function?
- muscle layer is thinner than in arteries
- elastic layer is thinner than in arteries
- overall thickness of wall is small
- valves at intervals throughout
why do veins have a thinner muscle layer (than arteries)?
- veins carry blood away from tissues (towards heart)
- their constriction and dilation cannot control the flow of blood to the tissues
why do veins have a thinner elastic layer (than arteries)?
- low pressure of blood in veins means they won’t burst
- pressure is too low to create a recoil action
why do veins have an overall thin wall?
- no need for thick wall as pressure within veins is too low to create any risk of bursting
- allows them to be flattened easily, aiding the flow of blood within them
why do veins have valves at intervals throughout?
- ensures blood does not flow backwards, which it might otherwise do as the pressure is so low
- when body muscles contract, veins are compressed, pressuring blood within them
- valves ensure that this pressure directs the blood in one direction only: towards the heart
how is capillary structure related to function?
- walls consist mostly of the lining layer
- numerous and highly branched
- narrow diameter
- lumen is narrow
- spaces between the lining (endothelial cells)
why do capillary walls consist mostly of the lining layer?
- makes them extremely thin, so there is a short diffusion distance
- this allows for rapid diffusion of materials between the blood and cells
why are capillaries numerous and highly branched?
provides a larger cumulative surface area for exchange
why do capillaries have a narrow diameter?
- permeates tissues
- no cell is far away from a capillary
- short diffusion pathway
why do capillaries have a narrow lumen?
- RBC are squeezed flat against the side of a capillary
- this brings them closer to the cells they supply oxygen to
- this reduces the diffusion distance
why do capillaries have spaces between the lining (endothelial cells)?
allows WBC to escape to attack infections within tissues
