PHYL3002 Lecture Notes - Lecture 12: Skeletal Muscle, Neutrophil, Ultrafiltration
LECTURE TWELVE: Endothelial Function
Functions of Endothelium:
• Non-thrombogenic surface
• Control of vascular smooth muscle → e.g. via NO and endothelin
• Permeability barrier
• Metabolism of blood-born substances
o Angiotensin I converting enzyme (ACE)
o Lipoprotein lipase (LPL)
• Adhesion and extravasation of leukocytes
• Angiogenesis
Structure of Endothelium:
• Endothelial cells are the only components of vascular wall continuous
with circulation → from artery level to capillary level
• Also continuous on venous side of vascular tree
• 10-20um in diameter
• 1-2um thick to allow diffusion of solutes
• Flat structures wrap around and form a tube
• Intercellular junctions between individual endothelial cells
• Junctions overlap with each other → some fuse to form tight junctions
• Limits diffusion of substances
• Changes in permeability of endothelial cells in capillaries can occur → i.e.
inflammation and disease states
Pericytes:
• Small mesenchymal-like stem cells
• Main function → support the small blood vessels/capillaries
• Relatively undifferentiated cells but can differentiate into
o Fibroblast
o Smooth muscle cell
o Macrophage
• Important in angiogenesis and stability of blood brain barrier
• Have been implicated in regulation of blood flow in capillaries
Microcirculation:
• Macrocirculation → large vessels that transport blood to and from the
organs
• Microcirculation → smaller vessels responsible for blood flow within
tissues (arterioles, capillaries, venules, lmphatic capillaries)
• Functions
o Delivery of O2/nutrients and removal of waste products
o Regulation of blood flow and pressure
o Regulation of intra-tissue fluids (swelling or oedema)
o Role in inflammation
• Blood flow through capillaries is regulated by pre-capillary sphincter →
sensitive to local metabolic changes
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