Chapter 19: Blood Vessels

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Chapter 19 Blood Vessels

• Part I Anatomy and vessel names

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General

• Arteries carry blood away from the heart, toward
  the capillaries
• Veins carry blood from the capillaries, toward
  the heart
• Capillaries are the smallest vessels and interact
  directly with the bodys cells

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Vessel structure

• Internal cavity lumen (carries blood)
• Large vessels have 3 layers, or tunics
• Tunica internal (or intima) innermost, forms
  lumen, composed of endothelium, in larger vessels
  there is also a loose connective tissue basement
  membrane

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• Tunica media middle layer, composed of smooth
  muscle and elastin protein, thick in arteries,
  innervated with sympathetic nerve fibers which
  cause vasoconstriction/dilation
• Tunica externa (adventitia) outermost mostly
  collagen, also elastin, nerve fibers, lymph
  vessels thickest layer in veins, largest vessels
  contain vasa vasorum (vessels of vessels)

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Arteries

• Elastic arteries aorta and major branches
• Also called conducting arteries
• Contain elastin in every tunic, elastic tissues
  almost equal smooth muscle (Table 19.1)

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• Expand and recoil as heart pumps out blood
• Recoil helps to push blood along when heart is
  diastole

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Arteries, part 2

• Muscular arteries found b/t elastic arteries and
  arterioles
• Also called distributing arteries
• Deliver blood to most organs
• Contains thickest tunica media, has more collagen
  and less elastin than elastic arteries
• Involved in vasoconstriction/dilation

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Arteries, part 3

• Arterioles (little artery) smallest arteries
• Have all 3 tunics, nearer to capillaries, the
  media and externa are very thin
• Control blood flow into capillary beds, dilation
  allows more into beds

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Capillaries

• Possess only tunica interna one cell layer thick
• Most tissues have capillaries, exceptions
  cartilage, epithelia, tendons, ligaments, cornea
  lens
• Blood flow through capillaries called
  microcirculation
• Pericytes are smooth-muscle like cells that help
  stabilize the cap walls

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Types

• Continuous found in skin and muscle
• Endothelial cells that form walls are tightly
  packed against one another
• Small gaps called intercellular clefts allow some
  fluid to be exchanged
• Exception brain capillaries do not contain
  clefts forms blood-brain barrier

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Notice cells of walls packed relatively close or
tight
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• Fenestrated found in small intestine, kidneys,
  and endocrine organs
• Involved with secretion, absorption, filtration
• In addition to clefts, walls contain
  fenestrations (pores)
• Membranes (diaphragms) cover the pores, but
  still very permeable

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Notice the porous openings called fenestrations
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• Sinusoid(al) found in liver, bone marrow,
  spleen, and endocrine organs
• Involved in secretion or filtration of large
  compounds (proteins, etc.)
• Very leaky (porous)
• Irregular shaped lumens, walls have large clefts
  and pores

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Notice very large pores and clefts
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Capillary beds

• Capillaries are more correctly termed beds
  because they form interconnected networks
• Beds receive blood from terminal arteriole
  (precapillary vessel)
• Beds empty blood into postcapillary venule
  (venule small vein)

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Capillary vessels

• Vascular shunt directly connects arteriole to
  venule
• Also called metarteriole-thoroughfare channel
• True capillaries (10-100 / bed) allow exchange
  with tissues/cells
• Precapillary sphincters (sphincter circular
  muscle) located in metarteriole can close off
  blood flow to capillaries

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Veins, part 1

• Venules form from capillaries
• Smallest venules possess only internal tunic,
  larger ones have thin other tunics
• The venules closest to the capillaries are very
  porous

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Veins, part 2

• Veins have all three tunics, the media is very
  thin and the externa thicker
• Large lumen that possesses semilunar-like valves
  that prevent back flow
• Veins contain 65 of total blood volume
• As a result, veins also called capacitance
  vessels or blood reservoirs

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Names

• Be able to identify/locate the following
  arteries
• Head common, internal, and external carotid
• Upper body/extremities ascending/descending/thora
  cic aorta, aortic arch, brachiocephalic,
  subclavian, common carotid, axillary, brachial,
  deep brachial, ulnar/radial, circumflex humeral,
  intercostal, thoracic

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• Abdominal abdominal aorta, celiac trunk, common
  hepatic, gastric, superior mesenteric, renal
• Lower extremities common, internal, external
  iliac femoral, deep femoral, circumflex femoral,
  tibial/fibular

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Veins

• Head external internal jugular
• Upper cephalic, ulnar, radial, basilic,
  axillary, brachial, subclavian, brachiocephalic,
  azygos, superior vena cava
• Abdominal inferior vena cava, renal, hepatic
  portal, hepatic, mesenterics, gastric

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• Lower tibial, fibular, femoral,
  internal/external/common iliac, saphenous

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Sinuses and anastomoses

• Venous sinuses are specialized, flattened, thin
  wall veins
• Found in the brain and heart
• Anastomoses are interconnected vessels (network
  like)
• Arterial anastomoses occur where arteries supply
  organs (brain, digestive tract, heart) and around
  joints

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• Venous anastomoses are numerous
• Vascular shunts/capillary beds are example of
  arteriovenous anastomoses
• Anastomoses are important because if one vessel
  is damaged or blocked, the blood can flow through
  collateral channels