The Cardiovascular System Blood Vessels

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The Cardiovascular SystemBlood Vessels
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The Vessels

• Functions
• Distribution of blood
• Exchange of materials with tissues
• Return of blood to the heart
• Structure
• Most have the same basic structure
• 3 layers surrounding a hollow lumen

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General Structure of Blood Vessels

• Arteries and veins are composed of three tunics
• tunica interna
• tunica media
• tunica externa
• Capillaries are composed of endothelium.

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General Structure
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The Vessels

• 1. Tunica Intima
• innermost smooth layer
• simple squamous epithelium
• continuous with the endocardium
• present in all vessels

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The Vessels

• 2. Tunica Media
• layer of smooth muscle - circular arrangement
  contains elastin
• supplied by sympathetic division of the ANS
• depending on bodys needs lumen is narrowed
  (vasoconstriction) or widened (vasodilation)

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The Vessels

• 3. Tunica Externa (Adventitia)
• thin layer of CT
• elastic collagen fibres

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The Vessels

• Types of Vessels
• Arteries carry blood away from the heart
• Veins carry blood towards the heart
• Capillaries the most important part of the
  vascular system site of exchange of materials

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Types of Blood vessels Arteries

• Elastic Arteries
• Thick-walled arteries near the heart the aorta
  and its major branches.
• Large lumen allows low-resistance conduction of
  blood.
• Contain lots of elastin in all three tunics.
• walls stretch and recoil to propel blood
• Withstand and regulate large blood pressure
  fluctuations.

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Types of Blood vessels Arteries

• Muscular (distributing) arteries
• medium sized vessels
• tunica media more smooth muscle less elastin
• major area of vaso-constriction dilation
  to regulate blood flow

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The Vessels

• Arterioles (diameter of 0.3 mm or less)
• - smallest arteries lead to capillary beds.
• - close to capillaries - single layer of muscle
  spiralling around the endothelial lining
• - regulates blood flow to capillary

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The Vessels

• Capillaries
• Smallest vessels diameter just large enough for
  a red blood cell
• walls consist of tunica intima only
• (i.e. layer of endothelium)
• thinness facilitates exchange of
• materials

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Capillary Beds
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Capillaries
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Types of Blood vessels Veins

• Venules
• Are formed when capillary beds unite.
• They merge to create veins.
• Veins
• Thin tunica media and a thick tunica externa
  consisting of collagen fibers and elastic
  networks.
• Capacitance vessels (blood reservoirs) that
  contain 65 of the blood supply.

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Venous Return

• Factors aiding venous return
• Large lumen which offers little resistance.
• Valves to prevent backflow
• Muscular pump skeletal muscles push blood
  toward the heart.
• Respiratory pump pressure gradient sucks
  blood into thorax

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Factors Aiding Venous Return
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The Vessels

• Control of Vessels
• is the responsibility of the vaso-motor centre
  in the medulla