The skin system aids in heat homeostasis. When the external temperature is too cold, the hairs on your skin stands up. This is results in what we call goose bumps. When it’s cold, vasoconstriction of arterioles reduce blood supply to skin capillaries, which leads to less heat loss at the skin surface. When the external temperature is too hot it results in sweating, which facilitates evaporative cooling. The sweat glands are located in the dermis and they are the organs that produce sweat. When it is hot, vasodilation of arterioles increase blood supply to the skin capillaries, which leads to more heat loss at skin surface. Hairs help insulate the body by trapping air in them. Normally hair lies at an angle to the skin, with erectile muscle attaching to it. When it is cold, the erectile muscles contract, and the hair stands up. This erect position helps hair to trap more air, providing better insulation. The skin also aids in water homeostasis. It insulates the body against water loss. It is involved in osmoregulation as the sweat excretes salts and nitrogenous wastes such as trace urea and uric acid. Some other functions of the skin includes protection against ultraviolet radiation by making melanin to absorbs UV radiation, it makes vitamin D upon exposure to sunlight and it acts as blood reservoir. Vasoconstriction in the skin also shunts blood to other organs. It is sensitive to touch, pressure, pain, heat and cold. It also provides protection as a physical barrier to outside organisms, abrasion and chemicals. Keratin in the skin protects skin against abrasion and the tight seal made from keratin-packed cells and glycolipids form a barrier against pathogens. The skin has a fat layer in hypodermis which acts as insulation.
Sweat is acidic and contains antibodies as well as antimicrobial agents. Sebum, or skin oil, also kills bacteria. The skin has natural flora on the surface of skin that doesn’t cause harm to the body, and they fight off bad bacteria that can harm you. The skin is differentiated into several layers. The epidermis is made up of stratified squamous epithelial tissue and it is involved in protection. Keratinocytes, or cells that produce keratin, dominates the epidermis. Keratinocytes start off like normal cells at the bottom of the epidermis, but gets flatter as you go up, and eventually die to become hardened keratin plates at the surface of the skin. Melanocytes are cells that make melanin, the skin pigment. Dendritic cells (Langerhans cells) are phagocytes that eat pathogen and present foreign antigens to activate immune response. The dermis is connective tissue with blood and nerve supply. Fibroblasts are cells that make fiber and ground substance (glue) for the extracellular matrix that makes up connective tissue. Hypodermis contains adipose tissue and absorbs shock and provides insulation. The skin has relative impermeability to water due to layer of dead, keratin-packed cells sealed with glycolipids. Keratin is water insoluble, and layers of dead, keratin-packed cells reside on the skin surface. Glycolipids seal the space between the dead keratin-packed cells. Sebum helps to contribute to the sealing as well. But oil glands are not present everywhere, as they are absent from the palms and soles.
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