structure and function of blood vessels - yale...
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Structure and Function of Blood Vessels
Peter TakizawaDepartment of Cell Biology
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What we’ll talk about…
• Structure of blood vessels and their appearance in histological samples
• Endothelium and structures that control permeability
• Increasing endothelial permeability and leukocyte transmigration
• Smooth muscle and vascular repair
• Angiogenesis
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Blood vessels comprise three functional layers.
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Endothelial cells perform a variety of structural and biochemical functions.
• Permeability
• Immune response
• Angiogenesis
• Modulate vascular resistance
• Antihaemostatic and haemostatic control
• Enzymatic action on plasma proteins
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The aorta is an elastic artery that contains numerous elastic fibers in the media.
MediaAdventitiaIntima
Smooth Muscle Cell
Elastic Fiber
Internal Elastic Lamina
Vasa Vasorum
Endothelial Cell
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Muscular arteries contain more smooth muscle and fewer elastic fibers in the media layer.
MediaAdventitia
Intima
Internal Elastic Lamina
Endothelial Cell
External Elastic Lamina
Smooth Muscle Cell
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Small muscular arteries contain fewer layers of smooth muscle.
Endothelial Cell
Smooth Muscle Cell
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Arterioles control blood flow into capillaries and create the highest resistance in the circulatory system.
Endothelial Cell
Smooth Muscle Cell
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Arterioles have one or two layers of smooth muscle cells.
Endothelial Cell
Smooth Muscle Cell
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Capillaries contain a single layer of endothelial cells and the occasional pericyte.
Endothelial Cell Capillary Lumen
Pericyte
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Permeability of capillaries
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Small molecules and ions diffuse across capillaries but proteins are restricted in most capillaries.
s
Sugars
Small Protein Large Protein
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Capillaries restrict the diffusion of protein to maintain oncotic pressure.
Protein Protein
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Primary components that regulate permeability of capillaries.
• Structure of endothelial cells
• Basement membrane
• Intercellular junctions between endothelial cells
• Glycocalyx
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Structure of Endothelial Cells
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Continuous capillaries contain endothelial cells that only allow passage through intercellular junctions.
Endothelial Cell
Intercellular Junctions
Pericyte
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Fenestrated capillaries have endothelial cells with several gaps for diffusion of solutes.
Endothelial Cell
Fenestrae
Pericyte
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Discontinuous capillaries contain large pores and lack a basement membrane.
Endothelial Cell
FenestraeLumen
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Basement membrane is a negatively-charged barrier on the basal surface of endothelial cells.
Basement Membrane
Red Blood Cell
Endothelial Cell
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Junctional complexes restrict paracellular diffusion between endothelial cells.
Lumen
Lumen
Interstium
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Glycocalyx restricts diffusion of large, negatively charged molecules.
Glycocalyx Glycocalyx Removed
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Transcytosis of Proteins
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Receptor-mediated endocytosis transports specific proteins across endothelium via transcytosis.
Blood
Interstitium
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Transcytosis mediates movement of proteins across endothelial cells.
Lumen
Lumen
Endocytic Vesicle
Endocytic Vesicle
Interstitium
Release of Material
Release of Material
Intercellular Junction
Interstitium
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Increasing the Permeability of Blood Vessels
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Inflammatory molecules and immune cells activate signaling pathways that disrupt junctions.
Kinases
Myosin
Disrupt Junctions
Increase Tension
Modify Cadherins
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Thrombin increase vascular permeability through tension on adhesion junctions.
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Immune cells must pass across endothelial cells to reach sites of infection.
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Rolling Adhesion Emigration
Timothy Springer Lab, Harvard Medical School
Leukocyte transmigration consist of three distinct steps.
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Selectins and integrins mediate rolling and adhesion of immune cells.
Capture Rolling Arrest Transmigration
Selectins Integrins
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Leukocytes disrupt adhesion junctions to migrate across endothelium.
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Venules and Veins
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Venules have an endothelium and relatively thin layer of smooth muscle.
Endothelial Cell
Smooth Muscle Cell
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Venules have thinner medial layers than arteries and tend to lose their shape.
Endothelial Cell Smooth Muscle Cell
Artery
Venule
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The vena cava has a thinner media than the aorta with mostly smooth muscle cells and collagen.
Smooth Muscle Cell
Intima
Media
Adventitia
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Lymphatic vessels have thin walls and lack red blood cells.
Endothelial Cell
Lymphatic Vessel
Venule
Arteriole
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Vascular Repair
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Damage recruits smooth muscle cell progenitors to the intima.
Damage
Endothelial Cell
Smooth Muscle Cell
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Smooth muscle proliferation can lead to occlusion of arteries after insertion of stents.
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Angiogenesis
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VEGF triggers morphological changes in endothelial tip cells.
High O2 Low O2
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Tip cells follow guidance cues to connect to existing vessels.
Semaphorins
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Tumor cells initiate angiogenesis to increase their blood supply.
VEGF VEGF
Tumor cells Stromal cells