Integumentary System 2009 - 1 Integumentary...

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1 Integumentary System (Skin) -2009 Integumentum is Latin for covering or enclosure. 1. The skin is the largest organ of our bodies. (Liver is second largest). The skin has many functions in addition to containment. These functions include protection (both physical and immunological) and formation of a barrier to water loss or bacterial invasion. The skin is vital for thermoregulation, formation of Vitamin D, protection from ultraviolet radiation, and for communication with the outside environment through the sensory organs contained in the skin and by releasing visual and pheromonal signals (blushing, nervous sweating). 2. Structure: The skin has two main layers the epidermis and the dermis . The hypodermis is a layer underneath the dermis; it is composed of CT and frequently has a lot of adipose tissue. There is no clear boundary between the dermis and hypodermis but the hypodermis rests on the underlying muscle tissue. a. The epidermis is keratinized stratified squamous epithelium. This stratified squamous epithelium is divided into five layers of cells. Beginning from the outside and going in, these layers of cells are: Stratum Corneum : consists of very flat, dead, non nucleated cells filled with keratin; these cells are shed in a process called desquamation. This layer is usually very thin in thin skin but can be very thick as on the palms and soles of feet. (Note – so called thick skin is normally found only on palms and soles of feet; all the rest of our skin is thin skin). Stratum Lucidum : is found only in thick skin (palms, soles); again dead cells. Stratum Granulosum: is 2 – 5 cells thick; the cells are flat and contain keratohyalin granules. These granules are very basophilic and they are not membrane bound and they do not leave the cells. Cells in this granular layer, however, do contain another granule (lamellar granules) which is membrane bound and this granule secretes a lipid (waxy) substance which acts as an intercellular cement and protective barrier. (Note: Blue Histology tries to trick you by asking a lot about the keratohyalin
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2 granules being secreted; they are not; it is the lamellar granules that are secreted). Note also, that the cells in this layer are beginning to die as keratin builds up in the cytoplasm. Stratum Spinosum:
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Integumentary System 2009 - 1 Integumentary...

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