Human Anatomy, First Edition McKinley

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Human Anatomy, First EditionMcKinley
O'Loughlin

• Chapter 23
• Vessels and Circulation

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Blood Vessels

• An efficient mode of transport for oxygen,
  nutrients, and waste products to and from body
  tissues.
• Heart is the mechanical pump that propels the
  blood through the vessels.
• Heart and blood vessels form a closed-loop
  system.
• Blood is continuously pumped to and from the
  tissues.
• Are not rigid and immobile.
• Can pulsate and change shape in accordance with
  the bodys needs.

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Blood Vessels

• Naming
• Often share names with either the body region
  they traverse or the bone next to them.
• Some are named for the structure they supply.
• Arteries and veins that travel together sometimes
  share the same name.
• Systemic circulation
• consists of the blood vessels that extend to and
  from the body tissues.
• Pulmonary circulation
• consists of the vessels that take the blood to
  the lungs for gas exchange.
• Work continuously and in tandem with each other.

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Three Main Classes of Blood Vessels

• Arteries convey blood away from the heart to the
  body tissues.
• Arteries branch, or bifurcate, into smaller and
  smaller vessels (arterioles) until they feed into
  the capillaries, where gas and nutrient exchange
  occurs.
• From the capillaries, veins return blood to the
  heart.

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Three Main Classes of Blood Vessels

• Arteries become progressively smaller as they
  divide and get further from the heart.
• Veins become progressively larger as they merge
  and get closer to the heart.
• Anastomosis Site where two or more vessels
  merge to supply the same body region.
• arterial anastomoses alternate route
• Veins tend to form many more anastomoses than do
  arteries.

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Three Main Classes of Blood Vessels

• End arteries
• Arteries that do not form anastomoses
• Only one route
• E.g. renal artery, splenic artery
• Functional end arteries
• Have small anastomoses
• E.g. coronary arteries

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Blood Vessel Tunics

• Tunica Intima, or Tunica Interna
• innermost layer
• composed of
• an endothelium (simple squamous epithelium)
• subendothelial layer (areolar CT)
• Tunica Media
• middle layer of the vessel wall
• composed of
• circularly arranged smooth muscle cells
• Sympathetic innervation
• Increase vasoconstriction (narrowing of the
  blood vessel lumen)
• Decrease vasodilation (widening of the blood
  vessel lumen)

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Blood Vessel Tunics

• Tunica Externa, or Tunica Adventitia
• outermost layer
• composed of
• areolar connective tissue that contains elastic
  and collagen fibers
• helps anchor the vessel to other tissues
• Term adventitia is used to specify outer layer in
  blood vessels that are buried in CT
• Vasa vasorum blood vessels that supply large
  blood vessels
• In the externa
• Arteries vs Veins
• Media largest in arteries, externa largest in
  veins
• Lumen is smallest in arteries
• Artery wall have more elastic and collagen fibers
• Capillaries only the Interna

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Arteries

• In the systemic circulation, carry oxygenated
  blood to the body tissues.
• Pulmonary arteries carry deoxygenated blood to
  the lungs.
• Three basic types of arteries
• elastic arteries, muscular arteries, and
  arterioles
• as an arterys diameter decreases
• corresponding decrease in the amount of elastic
  fibers
• relative increase in the amount of smooth muscle

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Capillaries

• Contain only the tunica intima, but this layer
  consists of a basement membrane and endothelium
  only.
• Allow gas and nutrient exchange between the blood
  and the body tissues to occur rapidly.
• Smallest blood vessels, connect arterioles to
  venules.
• Are called the functional units of the
  cardiovascular system.
• A group of capillaries (10100) functions
  together and forms a capillary bed.

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The Three Basic Kinds of Capillaries

• Continuous capillaries
• the most common type
• Fenestrated capillaries
• Sinusoids, or discontinuous capillaries

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Veins

• Drain capillaries and return the blood to the
  heart.
• Walls are relatively thin and the vein lumen is
  larger.
• Systemic veins carry deoxygenated blood to the
  right atrium of the heart, while pulmonary veins
  carry oxygenated blood to the left atrium of the
  heart.
• Blood pressure is substantially reduced by the
  time blood reaches the veins.
• Hold about 60 of the bodys blood at rest.
• Veins function as blood reservoirs.

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From Venules to Veins

• Venules merge to form veins.
• Venule becomes a vein when its diameter is
  greater than 100 micrometers.
• Blood pressure in veins is too low to overcome
  the forces of gravity.
• To prevent blood from pooling in the limbs, most
  veins contain one-way numerous valves to prevent
  blood backflow in the veins.
• As blood flows superiorly in the limbs, the
  valves close to prevent backflow.
• Numerous valves along its length to assist in
  moving blood back to the heart.

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From Venules to Veins

• Many deep veins pass between skeletal muscle
  groups.
• As the skeletal muscles contract, veins are
  squeezed to help pump the blood toward the heart.
  
• This process is called the skeletal muscle pump.

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Blood Pressure

• Force/unit area blood places on the inside wall
  of a blood vessel.
• Measures in mmHg
• Sphygmomanometer device to measure blood
  pressure.
• Systolic blood pressure
• Diastolic blood pressure
• 120/80 mmHg

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Circle of Willis

• An important anastomosis of arteries around the
  sella turcica.
• Formed from posterior cerebral arteries and
  posterior communicating arteries (branches of the
  posterior cerebral arteries), internal carotid
  arteries, anterior cerebral arteries, and
  anterior communicating arteries (which connect
  the two anterior cerebral arteries).
• Equalizes blood pressure in the brain and can
  provide collateral channels should one vessel
  become blocked.

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Hepatic Portal System

• A venous network that drains the GI tract and
  shunts the blood to the liver for processing and
  absorption of transported materials.
• Blood exits the liver through hepatic veins that
  merge with the inferior vena cava.
• Is needed because the GI tract absorbs digested
  nutrients, and these nutrients must be processed
  and/or stored in the liver.

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Pulmonary Circulation

• Responsible for carrying deoxygenated blood from
  the right side of the heart to the lungs, and
  then returning the newly oxygenated blood to the
  left side of the heart.
• Blood is pumped out of the right ventricle into
  the pulmonary trunk.
• This vessel bifurcates into a left pulmonary
  artery and a right pulmonary artery that go to
  the lungs.

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Aging and the Cardiovascular System

• Heart and blood vessels become less resilient.
• Elastic arteries are less able to withstand the
  forces from the pulsating blood.
• Systolic blood pressure may increase with age.
• Apt to develop an aneurysm, whereby part of the
  arterial wall thins and balloons out.
• Wall is more prone to rupture, which can cause
  massive bleeding and death.
• Incidence and severity of atherosclerosis
  increases.

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Fetal Circulation

• Oxygenated blood from the placenta enters through
  the umbilical vein.
• Blood is shunted away from the liver and directly
  toward the inferior vena cava through the ductus
  venosus.
• Oxygenated blood in the ductus venosus mixes with
  deoxygenated blood in the inferior vena cava.
• Blood empties into the right atrium.
• Most of the blood is shunted to the left atrium
  via the foramen ovale.
• Blood flows into the left ventricle and out the
  aorta.
• A small amount of blood enters the right
  ventricle and pulmonary trunk, but much of this
  blood is shunted to the aorta through ductus
  arteriosus.
• Blood travels to the rest of the body, and the
  deoxygenated blood returns to the placenta
  through umbilical arteries.

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