CH 19: Anatomy of the Blood Vessels J. F. Thompson

Vessel Structure All vessels have the same basic structure 3 layers in the wall –Tunica adventitia (externa) - elastic and laminar fibers –Tunica media thickest layer smooth muscle fibers and elastic fibers –Tunica interna (intima) endothelium – non-stick layer basement membrane internal elastic lamina lumen = opening

Elastic (conducting) arteries –near the heart –the largest diameter with the thickest walls –more elastic fibers, slighty less smooth muscle –lose elasticity with aging Arteries

Aorta and elastic arteries –can vasoconstrict or vasodilate –large arteries expand to absorb the force of each pressure wave, then release it with elastic recoil – (Windkessel effect ) –help to move blood along during diastole –with aging elastic arteries have less expansion and recoil

Arteries Muscular (distributing) arteries –deliver blood to most organs –more smooth muscle cells –fewer elastic fibers

Arteries Arterioles –distribution of blood within organs –wall composition varies depending on position - less smooth muscle, more elastic fibers distal from the heart –regulate flow from arteries to capillary beds Flow = Δ P/R vary resistance by changing vessel diameter –sites for blood pressure regulation

Vessel Structure - Capillaries Microcirculation – located between arteries and veins Found in almost every tissue in the body –the higher the metabolic activity, the more capillaries in a tissue –skeletal muscle has many capillaries (> 600/mm 2 ) –epidermis, cartilage and tooth enamel have none

Capillaries Allow exchange of nutrients and wastes between the blood and the tissue cells Capillary structure – simple squamous epithelium –basal lamina - connective tissue –endothelial cells Details of structure determine specific functions

Capillary Types 1. Continuous capillaries continuous lining of endothelial cells except for the clefts between cells tight junctions between the endothelial cells most of the capillaries in the body

Capillary Types 2. Fenestrated capillaries fenestrations (“windows”) are not true holes, but rather where the cell membrane is compressed to permit greater fluid transmission glomerular capillaries in the kidney

Capillary Types 3. Sinusoid capillaries some wider intercellular gaps permit increases exchange with surrounding tissues may have a larger diameter more irregular in cross section found in liver, bone marrow, lymphoid tissue, some endocrine glands Intercellular clefts permit WBCs to migrate in or out

Vessel Structure - Veins Venules –collect blood from capillary beds to carry it to veins –structure changes with distance from the heart –become more vessel-like as one moves away from the capillaries

Venous Structure Veins –interna thicker than arteries –media thinner, less smooth muscle –externa thick –valves –pressure low –high compliance = change the volume easily with a small change in pressure –varicose veins

Vessel Structure - Histology very different morphology under light microscopy tunica media thickness distinguishes arteries from veins

Vessel Structure - Histology Vein Artery

End CH 19 Vessel Anatomy