Endothelial Physiology

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Endothelial Physiology

• Readings Klabunde, pp. 54-6
• Ross Pawlina, pp. 409-414
• Functions
• Maintenance of a selective permeability barrier
• Maintenance of a nonthrombogeneic barrier
• Modulation of blood flow and vascular resistance
• Trigger blood coagulation
• Regulate traffic of inflammatory cells
• Oxidation of lipoproteins and foam cell formation

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Endothelium
Simple squamous epithelium lining BVs, lymphatic
vessels, heart Tight junctions (zonula
occludens) between adjacent endothelial
cells. Damage to capillary endothelium ?
increased permeability and tissue edema
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Endothelial Permeability

• Permeability of capillary endothelium is
  tissue-specific! Ex, liver sinusoids are more
  perm to albumin than caps in kidney glomerulus
• Due to difference in tight junctions b/ adjacent
  endothelial cells
• Topographic permeability post-cap venules (1)
  have the greatest perm

Diapedesis in post-cap venules the passage of
blood or any of its cells through the walls of
intact BVs
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I. Maintenance of a Selective Permeability
Barrier to things entering or leaving the
bloodstream
Pinocytotic
Water-soluble proteins
Glucose, Amino acids
Klabunde, Cardiovascular Physiology Concepts, 2005
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Transcytosis

• a combo of enodcytosis exocytosis
• Only in continuous capillaries, esp of muscle
• Transfers a signif amt of albumin from blood ?
  tissue fluid
• Macromolecules LDLs, insulin.
• Viruses hepatitis, polio, AIDS

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Receptor-Mediated Endocytosis
Ingestion of specific particles via binding to
specific receptors on PM ex, LDL, cholesterol,
growth factors, antibodies, etc
Hepatitis, polio, and AIDS viruses trick our
cells into engulfing them by RME
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II. Maintenance of a Nonthrombogenic Barrier

• Endothelium normally coated with prostacyclin
  (PGI2), a platelet repellant
• In an injured area, platelets and endothelial
  cells secrete platelet-derived growth factor
  (PDGF) to repair damaged BV
• Stims the synthesis of collagen
• Stims mitosis of smooth muscle cells and their
  migration from t. media ? t. intima

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Platelet Adhesion to Injured BV
Kierszenbaum, Histology and Cell Biology

• Damage ? platelet adhesion to exposed collagen
• Platelet pseudopods aid adhesion to BV and other
  platelets

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III. Modulation of Blood Flow Vascular
Resistance

• Endothelial cells secrete vasoactive substances
• 1. Nitric oxide ? relaxation of smooth muscle ?
  vasodilation
• 2. Endothelin very potent vasoconstrictor
• (also stims proliferation of endothelial cells
  fibroblasts for BV repair)
• 3. Prostacyclin vasodilator

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Summary Endothelial products
PGl2 prostacyclin ET-1 endothelin-1 NO
nitric oxide
Klabunde, Cardiovascular Physiology Concepts, 2005
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Other Endothelial Functions
IV. Trigger Blood Coagulation Damaged ? Tissue
Factor von Willebrand factor V.
Regulate Traffic of Inflammatory Cells Leukocyte
rolling ? adhesion, margination
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V. Regulation of traffic of inflammatory cells
Ross Pawlina, Histology A Text and Atlas, 5th
ed.
Selectin receptors cell-adhesion molecules that
induce WBCs to adhere to endothelial surface
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VI. Oxidation of Lipoproteins and Foam Cell
Formation
Ross Pawlina, Histology, 5th ed.
Atherosclerosis - often assc w/ elevated levels
of blood cholesterol (esp LDL). Monocytes remove
the excess cholesterol once engorged with this
lipid foam cells. Endothelial cells smooth
muscle cells can also accumulate lipid ? foam
cells. Fatty cells forms a plaque, bulges into
the lumen ? occlude the vessel. Continued plaque
formation produces gaps in the endothelial lining
exposing collagen fibers which circulating
platelets can adhere to, forming a clot.
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Typical BV Atherosclerosis
- Assc w/ high levels of cholesterol (esp. LDL)
Foam Cells
Saladin, Anatomy Physiology, 5th ed.
Coronary arteries are very susceptible to this
process.