The document summarizes the structures of different types of veins in the cardiovascular system. Venules have three layers - the tunica intima, tunica media, and tunica adventitia. Small to medium veins also have these three layers, with the tunica media being thin and containing circular smooth muscle. Large veins like the vena cavae have a thicker tunica intima containing an internal elastic lamina, a thin tunica media containing mostly connective tissue, and a thick tunica adventitia with spirally arranged collagen fibers.

1. Cardio-vascular system II
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2. Venules
• Larger muscular venules
– Tunica intima - thin; endothelium surrounded by
outer sheath of loose connective tissue (collagen
fibers).
– Tunica media - thin; 1 - 3 layers of smooth muscle
(circular) with collagen and elastic fibers between
muscles
– Tunica adventita - thick; loose FECT containing
longitudinal collagen fibers and scattered elastic
fibers and fibroblasts

4. Small to medium veins
• Tunica intima – thin
– (1) Endothelium
– Thin subendothelial layer
– May be folded to form valves
• Tunica media - thin;
– circular smooth muscle, collagen fibers, some elastic
fibers
• Tunica adventita - well developed;
– loose FECT with longitudinally arranged collagen and
elastic fibers, bundles of longitudinal smooth muscle

10. Large veins - vena cavae and larger
branches
• Tunica intima - thicker
– Endothelium
– Thin subendothelial layer
– Internal elastic lamina - usually distinguishable
• Tunica media - thin,
– poorly developed; mostly FECT and smooth muscle
• Tunica adventita - thickest;
– moderately dense FECT with spirally arranged collagen fibers,
elastic laminae,
– longitudinal smooth muscle

17. Self-check: Identify the outlined structures. (advance slide for answer)

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21. Self-check: Identify the outlined structures. (advance slide for answer)

22. Self-check: Identify the outlined structures. (advance slide for answer)

23. Self-check: Identify the outlined structure (advance slide for answer)

24. Self-check: Identify the outlined structure (advance slide for answer)