Practical 2

• Vessels of circulatory system have three layers known as tunics
• Tunics form concentration rings surrounding the lumen
• Lumen is the hollow center of a vessel through which blood flows
• Tunica Intima -

  Innermost layer is composed of simple squamous epithelium

  Also called endothelium
• Tunica Intima -

  Endothelium is supported by basement membrane, or subendothelial layer
• Tunica Intima -

  Outer layer is the internal elastic lamina / membrane

  • Made of bands of elastic fibers.

  In large vessels, internal elastic lamina is thick
• Tunica Media -

  Middle layer is mainly composed of a thick sheet of smooth muscle
• Tunica Media -

  In elastic arteries, layer contains abundant elastic fibers scattered in smooth muscle, and has outer elastic band called the external elastic lamina / membrane
• Tunica Externa -

  Outermost layer contains collagen fibers that help support the vessels
• Tunica Externa -

  In large vessels that are exposed to higher pressures, this layer can be very thick
• Tunica Externa -

  Tunica externa of largest vessels are so thick they require their own blood supply by vessels called the vasa vasorum
• Introduction to Vessels

  A) Endothelium

  B) Subendothelial layer

  C) Internal elastic membrane

  D) External elastic membrane

  E) Vasa Vasorum

  F) Lumen

  G) Valve

  
• Vessel Types of Arterial System

  Conducting/ Elastic Arteries -

  Largest vessels in arterial portion of circulatory system
• Vessel Types of Arterial System

  Conducting/ Elastic Arteries -

  • Located near midline
  • Conduct blood very quickly from heart and through thoratic and abdominal cavities
  • Examples include ascending Aorta, aortic arch, and descending (thoratic and abdominal)
• Vessel Types of Arterial System

  Conducting/ Elastic Arteries -

  Can also be identified by large amount of elastin found within their tunica externa

  Tunica Externa of these vessels contain large amounts of collagen as well as vasa vasorum
• Vasa Vasorum : supply oxygen and nutrients to those portions of conducting artery that are distant from lumen
• Vessel Types of Arterial System

  Distributing/Muscular Arteries -

  Named after role they have in distributing blood to various organs or body regions.

  Typically named for the region, or organ, to which they supply blood
• Vessel Types of Arterial System

  Distributing/Muscular Arteries -

  Smallest of named vessels

  These arteries split into smaller and smaller branches - - smallest of which have no specific names
• Vessel Types of Arterial System

  Distributing/Muscular Arteries -

  Have thick tunica media

  display less elasticity than elastic arteries, but their large amounts of smooth muscle allows them to quickly change the diameter of their lumen
• Vasoconstriction : making lumen narrower
• Vasodilation : Making lumen wider
• Vessel Types of Arterial System

  Distributing/Muscular Arteries -

  Through Vasodilation and Vasconstriction, they determine how much blood flows into an organ or body region
• Vessel Types of Arterial System

  Arterioles -

  Large arterioles have all three vascular tunics

  As they branch and become smaller, tunica externa disappears and tunica media grows thinner
• Vessel Types of Arterial System

  Arterioles -

  Control blood flow on a microscopic level under direction of hormonal, neuronal and local factors.

  Terminal arteriole, smallest true arteriole, leads into capillary bed
• Blood from the terminal arteriole flows into the metarteriole,

  • has properties oof both terminal arterioles and true capillaries
• From metarteriole, blood can take two paths
• Capillaries

  If oxygen is needed, precapillary sphincters relax and allow blood to flow through the true capillaries until it arrives at the throughfare channel
• Capillaries

  After traveling through the throughfare channel, blood arrives at the post-capillary venule
• Capillaries

  if oxygen not needed, precapillary sphincters remain closed and blood flows directly from the metaarteriole to the throughfare channel.

  "Vascular shunt" represents a shortcut that allows blood to bypass areas where it is not needed
• Capillaries

  Wordbank

  Metaarteriole, Vascular Shunt, True capillaries, Terminal arteriole, Precapillary sphincters, Postcapillary venule, Thoroughfare channel

  A) Vascular Shunt

  B) True capillaries

  C) Precapillary sphincters

  D) Postcapillary venule

  E) Metarteriole

  F) Terminal arteriole

  G) Thoroughfare channel

  
• Capillaries

  Walls of true capillaries consist of only endothelial cells and subendothelial

  • site of gas and nutrient exchange with surrounding tissues
• Capillaries

  • vessels are quite delicate and can be ruptured if experience high pressure
  • wide enough for formed elements to travel in a single filed line
• Vessels Types of Venous System

  Venules

  From post capillary venule, blood makes its way through a series of progressivly large vessels called venules
• Vessels Types of Venous System

  Venules

  Pathway back to heart is referred to as venous return
• Vessels Types of Venous System

  Venules

  Smaller venules only have tunica intima

  • as they grow larger they add tunica media and tunica externa
  • Too small to have valves
• Vessels Types of Venous System

  Veins

  Typically have all three tunica layers

  • wall of a vein is much thinner than walls of arteries
  • thin flimsy walls of veins allows them to easily expand and fill with blood
• Vessels Types of Venous System

  Veins

  relatively little smooth muscle in tunica media

  • largenst veins (like superier/inferior vena cava, have bands of smooth muscle embedded in tunica externa
  • bands run along length of vessels and helps push blood towards heart
• Vessels Types of Venous System

  Veins

  Many veins in limbbs have valves, only allow blood to flow in one direction
• Identify features of arteries/veins

  A) Tunica Media

  B) Lumen

  C) Tunica Interna

  D) Tunica externa

  
• Photograph of adipose tissue

  A.its a arterioles

  C. Capillary