Structure of Vessels

Structure of Vessels

1. Overview cardiovascular system

2. General features of vessel

   • 3 layers
     • tunica intima
       • 3 components
         • endothelium
         • basal lamina
           • EC layer of endothelial cells
         • subendothelial layer
           • loose cnt
           • occasional smooth muscle cells
           • in arteries & arterioles> internal elastic membrane
       • inner most > facing lumen
     • tunica media
       • middle layer
       • distinguish btw different vessels
         • in arteries
           • thick
           • extend from internal > external elastic membrane
           • external elastic membrane = layer of elastin separating tunica media from tunica adventitia
       • smooth muscle
       • ECM components
         • fibers
           • elastin
           • collagen
           • reticular
         • ground substance
           • proteoglycans
         • all produced by smooth muscle cell!!!
     • tunica adventitia
       • outermost, connective tissue layer
         • longitudinally-arranged collagen
         • few elastic fibers
         • gradually merge w/ loose cnt layer surrounding vessel
       • various thickness
         • thin in arteries
         • thick in veins
       • blood supply & innervation
         • large arteries & veins
         • vasa vasorum
           • blood supply to super-thick vascular wall
         • nervi vasorum
           • contraction of smooth muscle
   • endothelium
     • simple squamous epithelium
       • from mesenchyme
       • intermediate filaments = vimentin
     • endothelial cells
       • surface receptors
         • ICAM 1/2 > extravasation
       • surface adhesion molecules
       • endothelial activation
     • structural & functional integrity of vessel wall
       • selective permeable barrier in capillaries
       • nonthrombogenic barrier (inhibit blood coagulation)
         • prevent aggregation of platelets
           • surface charge repulsive to
         • secretes anticoagulant & antithrombogenic factors
       • modulation of blood flow & vascular resistance (vessel diameter)
         • vasoconstrictors (endothelin, prostaglandins, ACE)
         • vasodilators (NO, prostacyclin)
       • regulation & modulation of immune response
         • cell surface adhesion molecules & their receptors (ICAM 1/2)
         • 3 classes of interleukins
       • hormonal & metabolic activity
         • growth factors (FGF, PDGF)
         • haemopoietic factors (GM-CSF)
       • modifications of lipoproteins
         • via oxydation by free radicals (produced by endothelial cells)
           • LDL & VLDL
           • products endocytocised by macrophages > foam cells
         • clinical: atherosclorosis

3. Arteries

   • overview
     • heart > organs/tissues
     • large arteries
       • elastic type
         • continuous blood flow
           • slow relaxation followed systole
       • muscular type (medium arteries)
         • diameter regulated by high smooth muscle content
         • regulate blood distribution + BP
     • small arteries & arterioles
       • wall like muscular type
   • elastic (large) arteries
     • 3 wall layers
       • tunica intima
         • endothelium
         • basal lamina
         • subendothelial layer
           • delicate reticular cnt
           • has smooth muscle + macrophages
             • macrophage for phagocytosis of oxydized lipoproteins
           • internal elastic membrane
             • not conspicuous (since there are a lot of elastic membranes in elastic arteries)
             • the first, innermost elastic membrane
       • tunica media
         • smooth muscle
           • produce ECM components (NO fibroblasts!!)
             • collagen, elastin fibers
             • ground substance (proteoglycans)
           • alternating layers w/ elastic lamellae
         • fenestrated elastic lamellae
         • external elastic membrane
         • thickest of 3!
       • tunica adventitia
         • loose cnt
           • components secreted by fibroblast!!
         • vasa vasorum
         • nervi vasorum
         • much thinner than tunica media
         • sharp border w/ media
     • nutrition of the wall
       • directly from blood
         • endothelium
       • vasa vasorum
         • outer layers (adventitia + outer half of media)
       • diffusion from outer layers
         • inner half of media
   • muscular (medium) arteries
     • maintain blood pressure
     • tunica intima
       • thinner than in elastic arteries
       • 3 components
       • prominent internal elastic membrane
     • tunica media
       • predominant: smooth muscle
         • contraction > maintain BP
         • produce ECM components (fibers + ground substance)
       • loose network of elastin + collagen
       • NO fibroblast!
     • tunica adventitia
       • relatively thick
       • external elastic membrane > separation from media
       • collagen predominantly + elastin in small amount
       • fibroblast!
   • Arterioles
     • only a few smooth muscle layers
     • weakly developed/missing internal elastic membrane
     • precapillary arteriole
       • 1 smooth muscle layer in media
       • precapillary sphincter
         • slight thickening of smooth muscle
     • regulate volume of blood flow into capillary beds

4. Capillaries

   • classification
     • continuous capillary
       • zonula occcludens
         • passage of small molecules @ Intercellular Cleft
       • most common: brain, skin, lung, muscle
       • uninterrupted vascular endothelium
       • continuous basal lamina
     • fenestrated capillary
       • endocrine organs, kidney, gallbladder
       • fenestrated vascular endothelium
         • fenestration pores = small, circular openings
         • diaphragm = thin, non-membranous across the opening
       • continuous basal lamina
       • filtration pores
         • WITHIN endothelium cells
     • discontinuous capillary
       • liver, bone marrow
       • large openings in endothelial cell CYTOPLASM
       • discontinuous basal lamina
       • intercellular gaps
         • passage of blood plasma proteins
   • only 1 layer: tunica intima
     • endothelium
     • basal lamina
     • perciytes
   • characteristics
     • selective permeability
     • diameter: 5-20 micrometer (max 3 RBCs)
     • material exchange between blood & tissue
   • transport
     • simple diffusion
       • gases, small hydrophobic molecules
     • paracellular
       • water, macromolecules, solutes
       • transported across tight junctions btw 2 adjacent endothelial cells
     • transcellular
       • pinocytosis
         • clarthrin-independent
         • bulk materials from into cell
       • receptor-mediated endocytosis
         • clarthrin-dependent
           • endothelial-specific membrane receptors
         • specific molecules (LDL, cholesterol, transferrin)
       • water, ions, organic molecules
   • perciytes
     • undifferentiated mesenchymal cells
     • structural stability to capillaries
     • differentiate into a wide variety of cells during angiogenesis
     • contractile > controlled by NO

5. veins

6. lymphatic vessels