Blood Vessels D. Matesic
Blood VesselsBranching of arteries and veins and relation to lymphatic
system
Fig. 19.2
Figure 19.1
Blood Vessels
General structure of arteries and veins 3 layers- “tunics”
1.tunica intima-tunica intima-endothelium + loose CT2.2.tunica media-tunica media-smooth muscle + elastic fiber
sheets 3.3.tunica externa-tunica externa-connective tissue (mostly
collagen fibers)
Most arterioles and venules also have 3 layers, but tunica media is thinner and smallest ones lack tunica externa
Capillary structure and transport mechanismsCapillaries allow exchange of materials between the blood and tissues
Comprised of 2 layers: Endothelium, and basal lamina.
pericytes surround and help support the capillaries
Transport of materials across capillaries occurs via: 1. diffusion across endothelial cell membranes 2. intercellular clefts – space between tight junctions 3. fenestrations – pores 4. vesicular transport –
Fig. 19.16
Fig. 19.3 (optional)
Functions of endothelium
1. Physical lining of heart and blood vessels2. Permeability barrier for exchange of substances
between plasma and tissue interstitial fluid3. Secrete paracrine agents that act as vasodilators
and vasoconstrictors4. Mediate angiogenesis (new capillary growth)5. Regulate platelet clumping, clotting and
anticlotting
Capillary Beds –interwoven networks of capillaries that branch from terminal arterioles (via metarterioles)
precapillary sphincters control flow of blood
through the capillary bed
after exchange of nutrients/fluids between the blood in the capillary bed and the tissue, blood flows into the postcapillary venules and ultimately
back to the heart.
Capillary Beds
Fig 19.4Not required
Vascular anastomosesRegions where vessels interconnect; provide alternate routes for blood to reach a given body part