A Closer Look at Blood Vessels

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A Closer Look at Blood Vessels

• Key Concepts
• What are the structures and functions of
  arteries?
• What are the structures and functions of
  capillaries and veins?
• What causes blood pressure?

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Key Terms

• Coronary artery
• Pulse
• Diffusion
• Blood pressure

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Blood vessels

• Blood vessels can be as wide as your thumb, but
  most are much finer than a human hair
• If all were hooked together end to end they would
  stretch almost 100,000 kilometers long enough
  to wrap around the earth twice, with a lot left
  over!

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Arteries

• When blood leaves the heart it travels through
  arteries
• Aorta is the largest artery in the body
• Aorta soon branches into smaller arteries
• First branches called the coronary arteries go
  to the heart muscle itself to supply the heart
  with O2 and nutrients
• Others branch out to brain, intestines and other
  organs

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Artery Structure

• Walls are generally very thick, consist of three
  layers
• Innermost layer is made of epithelial cells and
  is smooth lets blood flow freely
• Middle layer is muscle tissue
• Outer wall made of flexible connective tissue
• Arteries have both strength and flexibility to
  withstand the tremendous pressure of blood as it
  is pumped by the heart

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Pulse

• Caused by the alternating expansion and
  relaxation of the artery wall.
• Every time the hearts ventricles contract, they
  send a spurt of blood out through arteries. It
  pushes on the artery wall and makes them expand,
  After the spurt of blood passes the artery wall
  becomes narrower again
• When you count the number of times an artery
  pulses, you are determining how fast the heart is
  beating.

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Regulating Blood Flow

• Layer of muscle in an artery acts as a control
  gate, adjusting the amount of blood sent to
  different organs
• When the muscle contracts the opening of the
  artery becomes smaller. When it relaxes the
  opening becomes larger
• The arteries leading to areas that need more
  blood relax and open up allowing more blood to
  flow through

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Capillaries

• Blood flows through smaller and smaller arteries
  until it gets to extremely thin-walled blood
  vessels known as capillaries
• Only room for 1 cell at a time
• Transferring O2 and food to cells and taking CO2
  and other wastes from cells occur in capillaries.
  This happens by diffusion

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Veins

• After capillaries blood starts its
• journey back to the heart
• Enters blood vessels known as veins
• Veins have 3 layers like arteries, but veins are
  thinner walled than arteries
• Pushing force of the heart is much less in veins
• Contraction of skeletal muscles help the blood
  return to the heart
• Valves help the blood from flowing backwards
• Breathing movements squeeze against veins and
  force blood towards the heart

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Blood Pressure

• Pressure is the force that something exerts over
  an area
• Blood exerts a force called blood pressure
  against the walls of blood vessels
• Blood pressure is caused by the force with which
  the ventricles contract
• As blood moves away from the heart, blood
  pressure decreases
• Blood flowing near the heart arteries exerts the
  highest pressure

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Measuring Blood Pressure

• Blood pressure is measured with an instrument
  called a sphygmomanometer
• Cuff is wrapped around the persons arm and
  inflated until blood flow from the artery is
  stopped
• The examiner listens to the pulse and records 2
  numbers.
• Pressure when the ventricle contracts and the
  pressure when the ventricle relaxes
• The 2 numbers are expressed as a fraction
• 120/80 or lower is typical for a healthy adult

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Sources

• http//www.landholt.com/Graphics/Images/arteries_v
  eins_01.jpg