Contents on the external surface the release of sweat

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contents on the external surface. The release of sweat is calledperspiration. Perspiration helpsthe body to regulate its temperature through a process calledthermoregulationby releasing heatfrom the body.
Figure 7.3 Sweat glands and sebaceous gland (blue) located within the skin.The EpidermisTheepidermis(outermost layer of skin) is made up ofstratified squamousepithelium.Stratifiedmeans layered andsquamousmeans flat). The epidermis isavascular, meaning it does not have adirect blood supply. The epidermis receives its nutrients from the basement membrane (basallamina).The epidermis is comprised of four distinct layers (listed from superficial to deep): the stratumcorneum, stratum granulosum, stratum spinosum and stratum basale(Figure 7.4). The stratumbasale is firmly adhered to thebasement membrane, which contains the blood supply for theepidermis.The cells of thestratum basaleare constantly dividing to rebuild the skin. As cells continue todivide, they are pushed towards the external surface until they are dead and slough off (areremoved through washing or friction). The most superficial layer of the epidermis is deadbecause it is far away from the blood and nutrient supply of the basement membrane. It takesabout 30 days for a single cell to move from the stratum basale to the external surface of thestratum corneum. Dead cells remain within the stratum corneum for about another two weeksbefore they slough off. The stratum basale formsepidermal ridges(notice the grooves present inFigure 7.4within the stratum basale). Epidermal ridges are unique to each person and areconsistent throughout a person’s lifetime. These projections extend all the way through theepidermis and form a distinct pattern which is commonly calledfingerprints.
Figure 7.4 Four layers of the epidermis.The stratum corneum, stratum spinosum and basementmembrane are highlighted in blue to show each layer's distinct shape and thickness.Some of the cells found in the epidermis are keratinocytes, Langerhans cells, fibroblast cells,melanocytes and Merkel cells(Figure 7.5).Melanocytesproduce a pigment calledmelanin.Langerhans cells are involved in the body’s immune responses.Langerhans cellsact as a firstline of defense for the body, helping to identify microorganisms before they reach thebloodstream.Merkel cells(see alsoFigure 7.2) are a type of sensory receptor which respond tolight touch.Keratinocytesproduce a tough substance calledkeratin. Cells within the epidermisundergokeratinizationwhich protects exposed surfaces of skin.Fibroblast cellsproducecollagen which helps to adhere the cells of the epidermis to each other and give the skinelasticity.Figure 7.5 Cells within the epidermis.The DermisSweat glands, oil glands and sensory organs are also found within the dermis. The dermiscontains the sensory organs ofMeissner corpusclesandPacinian corpuscles(as labeled inFigure 7.2). The dermis is comprised of a superficialpapillary regionand the deeperreticularregion

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Stratum Corneum

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