The cutaneous blood vessels are involved in the control of body temperature and provide a conduit for the supply of nutrients and oxygen to the skin and for the rapid disposal of metabolic waste products. The vascular system of the skin consists of a superficial and a deep vascular plexus with additional vascular networks surrounding sweat glands and hair follicles . Consistently, blood vessels are found immediately below the nonvascularized epidermis and surrounding anagen (growth phase) hair follicles. Whereas the richness of the follicular blood supply depends on the size of the hair follicles, recent studies suggest that, conversely, the extent of perifollicular vascularization may directly influence the size of hair follicles .
All cutaneous blood vessels contain a continuous inner monolayer of flat endothelial cells that are surrounded by a continuous basement membrane. Smaller vessels contain a second, sometimes discontinuous layer of pericytes that can be visualized by staining for alpha-smooth muscle actin and desmin. The walls of most cutaneous arterioles and larger venules and veins contain contractile smooth muscle cells that are surrounded by a basement membrane. Vascular basement membranes contain collagen type IV, collagen type XVIII, laminin, fibronectin, and other extracellular matrix proteins.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.