Edexcel IGCSE Biology 复习笔记 2.8.11 Blood Vessels & the Circulatory System

Edexcel IGCSE Biology 复习笔记 2.8.11 Blood Vessels & the Circulatory System

Blood Vessels

 

  • There are three main types of blood vessel:
    • Arteries
    • Veins
    • Capillaries

     

  • Smaller vessels that branch off from arteries are called  arterioles (small arteries) and those that branch into veins are called venules (small veins)
  • Each vessel has a particular function and is specifically adapted to carry out that function efficiently

 

 

Arteries

  • Key features:
    • Carry blood at high pressure away from the heart
    • Carry oxygenated blood (except the pulmonary artery)
    • Have thick muscular walls containing elastic fibres
    • Have a narrow lumen
    • Blood flows through at a fast speed

     

  • The structure of an artery is adapted to its function in the following ways
    • Thick muscular walls containing elastic fibres withstand the high pressure of blood and maintain the blood pressure as it recoils after the blood has passed through
    • A narrow lumen also helps to maintain high pressure

     

 

 

 

Veins

  • Key features:
    • Carry blood at low pressure towards the heart
    • Carry deoxygenated blood (other than the pulmonary vein)
    • Have thin walls
    • Have a large lumen
    • Contain valves
    • Blood flows through at a slow speed 

     

  • The structure of a vein is adapted to its function in the following ways:
    • A large lumen reduces resistance to blood flow under low pressure 
    • Valves prevent the backflow of blood as it is under low pressure

     

 

Comparing-arteries-and-veins

 

Comparing the structure of arteries and veins

 

 

 

Capillaries

  • Key features:
    • Carry blood at low pressure within tissues
    • Carry both oxygenated and deoxygenated blood
    • Have walls that are one cell thick
    • Have ‘leaky’ walls
    • Speed of blood flow is slow

     

  • The structure of a capillary is adapted to its function in the following ways:
    • Capillaries have walls that are one cell thick (short diffusion distance) so substances can easily diffuse in and out of them
    • The ‘leaky’ walls allow blood plasma to leak out and form tissue fluid surrounding cells

     

 

 

 

Structure-of-a-capillary

 

Structure of a capillary

 

 

 

Arterioles and venules

  • As arteries get further away from the heart, they divide more and get narrower
  • The narrow vessels that connect arteries to capillaries are called arterioles
  • Veins also get narrower the further away they are from the heart
  • The narrow vessels that connect capillaries to veins are called venules

 

 

The-blood-vessel-network

 

The blood vessel network

 

 

Circulatory System

 

  • The circulatory system consists of a closed network of blood vessels connected to the heart
    • Oxygenated blood is carried away from the heart and towards organs in arteries
    • These narrow to arterioles and then capillaries as they pass through the organ
    • In the organs, respiring cells use up the oxygen from the blood
    • The capillaries widen to venules and finally veins as they move away from the organs
    • Veins carry deoxygenated blood back towards the heart

     

  • A different network of lymphatic vessels collect all the excess tissue fluid that leaks out of the capillaries and delivers it back to the circulatory system

 

 

 

The-circulatory-system

 

The circulatory system

 

 

 

Main Blood Vessels of the Circulatory System Table

 

 

Important-Blood-Vessels-table

转载自savemyexam

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