BLOOD VESSELS

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BLOOD VESSELS

• By Ms. Reis

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Arterial System

• Arteries vessels that carry blood away from the
  heart to arterioles. The aorta is the largest
  artery in the body carrying blood from the heart
  to the tissues.
• Arteries have elastic walls that allow it to
  first expand as blood passes through then snap
  back again. This movement keeps blood flowing in
  the right direction, and provides an additional
  pumping motion to help force the blood through
  the blood vessels.

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Aneurysm

• An aneurysm occurs when the inner wall of the
  artery begins to bulge. When a rupture or
  blockage occurs in the arterial wall, parts of
  the brain don't get the blood and oxygen they
  need which may lead to stroke.
• Blood from the arteries passes into smaller
  arteries called arterioles.

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Arterioles

• Blood from the arteries passes into smaller
  arteries called arterioles.
• Vasoconstriction occurs when the arterioles
  contract decreasing blood flow to the tissues.
  Ex turning pale when in a state of fear
• Vasodilation occurs when the arterioles dilate
  increasing blood flow to the tissues. Ex
  blushing when in a state of nervousness

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Capillaries

• Arterioles carry blood to capillaries.
• Capillaries smaller blood vessels that carry
  blood to larger venules. Because of their small
  diameter red blood cells must travel through
  capillaries in single file. Nearly every tissue
  within the body is within 0.1 mm of a capillary.

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Capillaries the Site of Gas and Fluid Exchange

• Capillaries are the site of fluid and gas
  exchange between the blood and cells.
• Capillaries are composed of a single layer of
  cells. This allows capillaries to provide cells
  with oxygen, glucose, and amino acids via
  diffusion through the thin capillary walls.
• Endocytosis and exocytosis result in the exchange
  of protein.

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Capillaries

• Oxygenated blood, which appears red in colour,
  takes on a purple-blue colour as it leaves the
  capillary. The deoxygenated blood collects in
  small veins called venules.

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Venous System

• Venules merge into veins with an even greater
  diameter.
• Veins vessels larger than venules that return
  blood back to the heart.
• Once blood reaches the veins after passing the
  fine network of capillaries it is travelling very
  slowly.
• Unlike arteries veins are unable to contract and
  thus another mechanism must be used to move blood
  back to the heart.

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Blood Vessels

• How then does blood flow get back to the heart?
• 1) Veins have valves that open in only 1
  direction helping push the blood toward the heart
  and overcoming the force of gravity.
• 2) Muscles surrounding the veins exert pressure
  on the veins which also helps push blood toward
  the heart.

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Blood Vessels A Comparison

• Arteries have strong walls capable of
  withstanding great pressure. Veins are not able
  to withstand great pressure.
• Veins have thinner walls but a larger inner
  circumference. As a result veins lack the
  elasticity of the artery, but have a greater
  capacity to carry blood.
• The venous system contains twice as much blood as
  the arterial system.

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ARTERY CAPILLARY VEIN
Wall is composed of 3 layers of cells Wall is one cell thick Thinner wall than artery
High elasticity No elasticity Little elasticity but has valves
Smaller diameter than veins very narrow diameter Larger diameter than arteries
Carries blood away from the heart Site of gas exchange with tissue cells Carries blood toward the heart
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Varicose Veins

• If valves do not function properly gravity
  carries blood to the feet and blood pooling
  occurs. This results in veins distending/expandin
  g.
• Both genetics and lifestyle are factors.