1.2 : The Circulatory System (Blood Vessels)

Biology Form 5 

Chapter 1 : Transport

Subtopic 1.2 : The Circulatory System (Blood Vessels)

The Structure of Human Blood Vessels

Hand blood vessels

Hand blood vessels

 

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  • Blood vessels are the tubes for the medium to flow through
  • Three main types of blood vessels are
    1. Arteries
    2. Capillaries
    3. Veins
  • Each type of blood vessels has different structure according to their functions

 

 

 

 

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a) Arteries

  • Functions: carry blood away from the heart towards other tissues and organs
  • When an artery enters an organ, it divides into smaller branches called arterioles

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  • The wall of an artery has three layers
    • Endothelium
      • Innermost layer
      • consists of a single layer of endothelial cells
    • Tunica media
      • Thick middle layer
      • consist of elastic fibres & smooth muscles
    • Tunica Externa
      • Outermost layer
      • Consists of collagen fibres
  • Thick walls can withstand the high pressure of blood inside the arteries

b) Veins

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  • are large vessels which carry blood back to the heart
  • receive blood from small blood vessels called venules
  • possesses less smooth muscle tissues than an artery
  • have thinner walls than arteries because blood pressure in the veins is  much lower than in the arteries
  • lumen in the centre of a vein is larger in diameter than in an artery
  • semilunar valves in the vein prevent backflow of blood, thereby maintaining a one-way flow of blood towards the heart

 

 

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c) Capillaries

capillary

  • the smallest and most numerous blood vessels
  • comprises of a single layer of endothelial cells
  • tiny gaps between the endothelial cells allow water, ions and small solute molecules to leak out of the capillaries
  • the site of exchange of materials between the tissues and the blood
  • erythrocytes and large protein molecules are unable to leak out of the capillaries
  • leucocytes can squeeze through the capillary wall into the tissue spaces

 

Compare and contrast arteries, veins and capillaries

Similarities

  • Walls consist of epithelial tissues, smooth muscles and connective tissues (except capillaries)
  • Carry blood

Differences

1.2 The Circulatory Sytem (Blood Vessels & Heart)

 

 

 

 

 

 

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