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Animal Transport Systems
Blood Vessels
Blood Vessels
• There are three main types of blood vessels
i/ Arteries
ii/ Veins
iii/ Capillaries
ARTERIES
ARTERIES
ARTERIOLES
ARTERIES
ARTERIOLES
CAPILLARIES
ARTERIES
ARTERIOLES
CAPILLARIES
VENULES
ARTERIES
ARTERIOLES
CAPILLARIES
VENULES
VEINS
Blood VesselsARTERIES• Carry blood away from the heart• Thick muscular walls• Lots of elastic tissue in wall• Relatively small lumen• Blood under high pressure• Blood flow rapid• Blood flows in pulses• No valves
ARTERIES
ARTERIESartery outer layer
ARTERIESartery outer layer
thick smooth muscle
ARTERIESartery outer layer
thick smooth muscle
elastic white fibrous tissue
ARTERIESartery outer layer
thick smooth muscle
elastic white fibrous tissue
inner lining (endothelium)
Arteries
• The elastic tissue in the artery wall allows the vessel to ‘give’ as blood surges through.
• So, the artery wall first stretches as a result of the high blood pressure,
• before an elastic recoil of the wall pushes the blood on its way.
• This swelling can be felt as a pulse where arteries travel near the skin surface.
Blood VesselsVEINS• Carry blood back to the heart• Thin muscular walls• Little elastic tissue in the wall• Relatively large lumen• Blood under low pressure• Blood flow is slow• No pulse• Valves prevent backflow of blood
Vein
Vein
outer layer
Vein
outer layer
thin smooth muscle
Vein
outer layer
thin smooth muscle
inner lining (endothelium)
Vein
outer layer
thin smooth muscle
inner lining (endothelium)valve
VEINS
How the semi-lunar valve works in a vein:
• The blood has just enough pressure to force the valve open as it flows towards the heart
• Backflow of blood causes the valves to close
Blood VesselsCAPILLARIES• Link up arteries and veins in the tissues• No muscle• Wall made up of one cell thick endothelium• Small lumen – just large enough for a red blood cell to squeeze
through• Pressure falls as blood passes along capillary• Blood flowing is slowing down• No pulse• No valves
