OCR AS Biology Module 2 Circulatory systems/Blood Vessels

• All insects have an open circulatory system
• Blood is not always carried in blood vessels
• Blood fluid circulates through the body cavity, so tissues are bathed directly in blood.
• In some animals, the action of body muscles helps to circulate blood
• In many insects, there is a tubular heart, blood from the body enters the heart through pores called ostia
  

• In larger animals, the blood stay entirely in blood vessels

• Enables the heart to pump blood at higher pressure
• Therefore nuitrients are delivered quicker
• Fish closed circulation:

Heart->Arteries->Gills->Veins->Body Tissues->Veins->Heart

• Carries blood away from heart
• Lumen is relatively small to maintain high pressure
• Thick wall containing collagen to give it strength
• Elastic tissue which helps it to stretch and recoil
• Smooth muscle that can contract and constrict to limit blood flow to certain organs
• Endothelium is folded and can unfold when artery stretches

• Carry blood to the heart
• Large lumen to ease flow of blood
• Thinner layers of collagen, smooth muscle and elastic tissue
• Do not need to stretch and recoil
• Contain valves to help blood flow back up to the heart.

• Allow exchange of materals between bloodc and cells of tissues
• Very thin walls to reduce diffusion distance
• Narow lumen which makes sure the red blood cells are squeezed whilst passing through capillaries. Helps them to givbe up oxygen as pressed close to capillary wall.