Strands of hair originate in the hair follicle. It is primarily made of dead, keratinized cells. Hair is a keratinous filament growing out of the epidermis. These structures embryologically originate from the epidermis and can extend down through the dermis into the hypodermis. Media 5.2 The Integumentary System, Part 2-Skin Deeper: Crash Course A&P #7 Copyright 2015 by CrashCourse.Īccessory structures of the skin include hair, nails, sweat glands, and sebaceous glands. In the presence of sunlight, a form of vitamin D3 called cholecalciferol is synthesized from a derivative of the steroid cholesterol in the skin. The epidermal layer of human skin synthesizes vitamin D when exposed to UV radiation. (Credit a: “Trysil”/flickr credit c: Ralph Daily.) From Betts, et al., 2013. In contrast, the dermal blood vessels constrict to minimize heat loss in response to low temperatures (b). These mechanisms prevent the body from overheating. During strenuous physical activities, such as skiing (a) or running (c), the dermal blood vessels dilate and sweat secretion increases (b). The sympathetic nervous system is continuously monitoring body temperature and initiating appropriate responses.įigure 7.2 Thermoregulation. The integumentary system helps regulate body temperature through its tight association with the sympathetic nervous system. These receptors are more concentrated on the tips of the fingers, which are most sensitive to touch, especially the Meissner corpuscle (tactile corpuscle), which responds to light touch, and the Pacinian corpuscle (lamellar corpuscle), which responds to vibration. The skin acts as a sense organ because the epidermis, dermis, and the hypodermis contain specialized sensory nerve structures that detect touch, surface temperature, and pain. Sweat excreted from sweat glands deters microbes from over-colonizing the skin surface by generating dermcidin, which has antibiotic properties. It acts as a protective barrier against water loss, and it also is the first line of defense against abrasive activity such as grit, microbes, or harmful chemicals. The skin protects the body from wind, water, and UV sunlight. Physiology of the Integumentary System Basic Physiology of the System Protection
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