Blood Vessels

• Blood Vessels


  A closed system of tubes that transport blood
• Tunics


  • Wall consists of 3 layers: Tunica Externa (Adventia), Tunica Media, Tunica Interna (Intima)
• Tunica Externa (Adventia)


  Connective tissue outer covering, outermost layer, helps anchor vessels to surrounding tissues
• Tunica Media


  Middle layer of blood vessels with smooth muscle, has high elastic fiber called elastic lamellae
• Vasospasm


  Limits blood loss
• External Elastic Lamina


  Elastic fibers separating tunica media from externa
• Tunica Interna (Intima)


  Epithelial inner lining, innermost layer/tunic
• Tunica Intima (Interna) Layers

  • Endothelium
  • Basement Membrane
  • Internal Elastic Lamina
• Endothelium


  Passive barrier between blood and the remainder of the vessel wall
• Basement Membrane


  Provides physical support, framework of collagen fibers
• Internal Elastic Lamina


  Outermost part, forms the boundary between tunica interna and media, thin sheet of elastic fibers with variable number of window openings
• Types of Blood Vessels

  • Arteries
  • Arterioles
  • Capillaries
  • Venules
  • Veins
• Arteries


  • Wall has the three layers, plentiful elastic fibers that have high compliance
• Types of Arteries


  • Elastic Arteries
  • Muscular Arteries
• Elastic Arteries


  Largest diameter and thin vessel walls, pressure reservoir, conducting arteries (aorta, pulmonary trunk, subclavian, etc.)
• Muscular Arteries


  Medium sized arteries, maintain vessel pressure and efficient blood flow (a.k.a. Distributing Arteries)
• Anastomosis


  Collateral circulation, end arteries
• Arterioles


  Regulate blood flow into the capillary networks of the body's tissue (a.k.a. Resistance Vessels)
• Metarteriole


  Terminal end of the arteriole
• Precapillary Sphincter


  At end of metarteriole, monitors the blood flow into the capillary
• Capillaries


  • Found near almost every cell in the body, smallest blood vessel 5-10 diameters, forms the u turn - connect the arterial outflow to venous return, exchange substances between the blood and interstitial fluid, thus called "exchange vessels"
• Pericytes


  Help stabilize the walls and help control permeability
• Capillary Bed


  Network of 10-100 capillaries that arises form a single metarteriole
• Vasomotion


  Blood flows intermittently through capillaries due to alternating contraction and relaxation of the smooth muscle and precapillary sphincters
• Thoroughfare Channel


  Distal end of metarteriole that has no smooth muscle, a channel that bypass capillaries
• Types of Capillaries


  • Continuous Capillaries
  • Fenestrated Capillaries
  • Sinusoids
• Continuous Capillaries


  Most common type of capillary but least permeable, plasma membranes of endothelial cells form a continuous tube that is interrupted only by intercellular clefts, tight junctions and desmosomes of epithelial cells, found in CNS, lungs, skin, muscle tissue
• Fenestrated Capillaries


  Plasma membrane of the endothelial cells have many fenestrations or small pores, function in absorption or filtration, found in kidneys, endocrine glands
• Sinusoids


  Wider and more winding than other capillaries, specialized lining cells, large fenestrations, seen at red bone marrow, liver, spleen
• Muscular Venules


  Have thicker wall where exchange with the interstitial fluid can no longer occur
• Postcapillary Venule


  Smallest venules that initially receive blood from capillaries, have loosely organized intercellular junction
• Venules


  Thin walls that do not readily maintain their shape, drain the capillary blood and begin the return flow of blood back to the heart
• Veins


  • Blood vessels carrying blood back to the heart, thin walls (<1/10) and are more numerous than arteries, a.k.a CAPACITANCE VESSEL accomodates 65% of the blood
• Vascular (Venous) Sinus


  A vein with a thin endothelial wall; no smooth muscle to alter its diameter
• Blood Distribution on the CVS

  • 64% Systemic Veins and Venules
  • 13% Systemic Arteries and Arterioles
  • 9% Pulmonary Vessels
  • 7% Heart
  • 7% Systemic Capillaries
• Blood Reservoirs


  Systemic Veins and Venules contain more than half the total blood volume
• Capillary Exchange Mechanisms


  • Diffusion
  • Transcytosis
  • Bulk Flow
• Diffusion


  Substances in blood can cross the walls of a capillary by diffusing through the intercellular clefts, more important for solute exchange between blood and interstitial fluid
• Transcytosis


  Substance enclosed in a pinocytic vesicles -endocytosis & exocytosis- mainly for large, lipid-insoluble molecules
• Bulk Flow


  Passive process in which large number of ions, molecules, or particles in a fluid move together in the same direction, more important for regulation of the relative volumes of blood