Bloodvessels

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