Blood vessels and their functions

Function:

• Carry blood away from the heart and into the arterioles

Structure:

• Tough fibres outer layer- resists pressure changes within and outside
• Muscle layer is thicker than veins- can be constricted and dilated in order to control the volume of blood passingthrough them.
• Elastic layer is thicker than veins- able to stretch and recoil to maintain high BP
• Thin inner layer- smooth to reduce friction and thin for short diffusion pathway.
• No Valves- due to constant high pressure
• Lumen 

Function:

• Smaller arteries that control blood flow from arteries to capillaries

Structure:

• Tough fibrous outer layer- resists pressure changes
• Muscle layer is relatively thicker than arteries- Retricts blood flow and so controls its movement
• Elastic layer (tinner than arteries)- because the BP is lower.
• Thin enothelium- smooth, reduces friction, short diffusion pathway
• Lumen- blood flows through here.

Function:

• Tiny vessels that link arterioles to veins

Structure:

• Walls consist of epithelium lining- extremely thin for short diffusion pathway
• Hughly branched- large surface area for exchange
• Narrow diameter- short diffusion pathway
• Lumen  is narrow- red blood cells are squeezed flat against the side reduces diffusion distance.

Function: 

• Carry blood from the capillaries back to the heart

Structure:

• Tough fibrous outerlayer
• Thin muscle layer- carry blood away from tissues doesnt cannot control flow of blood
• Elastic layer relatively thin- BP too low to cause recoil action
• Thin epithelium layer- Smooth, and short diffususion pathway
• Valves at intervals throughout to prevent backflow of blood
• Lumen