Integumentary System CN 2 PDF

Skin Types of Skin Thick: covers palms of hands and soles of feet. Thin: covers rest of body, mostly hairy Thin Thick  Layers of Skin 1- Epidermis Stratified squamous keratinizing epithelium 2- Dermis Papillary layer of loose connective tissue and reti...

Skin Types of Skin Thick: covers palms of hands and soles of feet. Thin: covers rest of body, mostly hairy Thin Thick  Layers of Skin 1- Epidermis Stratified squamous keratinizing epithelium 2- Dermis Papillary layer of loose connective tissue and reticular layer of dense irregularly arranged Connective Tissue(CT) Hypodermis Subcutaneous tissue, loose CT, contains adipose tissue A. Epidermis – Stratified Squamous Keratinized Epithelium 5 4 Five Layers 2 1. Stratum basalis 2. Stratum spinosum 3 3. Stratum granulosum 4. Stratum lucidum 5. Stratum corneum 1 1. Stratum Basalis Consists of a single layer of columnar epithelial cells which rests on a well-developed basement membrane. Hemidesmosomes and desmosomes and many mitotic cell mitotic figures are detected. The cytoplasm contains tono-filaments. Cells containing melanin may be either melanocytes or keratinocytes cells with melanin 2. Stratum Spinosum It is formed of polygonal cells with central nuclei. The cells attached to each other by desmosomes. The attachment sites give spiny appearance. Another cytoplasmic feature is the appearance of membrane-coating granules (Odland bodies) 3. Stratum Granulosum Consists of flattened elongated cells containing in their cytoplasm irregularly shape non-membrane bound keratohyalin granules. Membrane-coating granules are discharged into the intercellular spaces (forming a skin barrier). 4. Stratum lucidum Stratum lucidum This layer is prominent in thick skin not in thin skin. Thin poorly staining clear layer consisting of flattened non-nucleated cells 5. Stratum Corneum This is the outermost layer of the epidermis. Consists of 15-20 layers of dead, flattened, anucleate, keratin-filled keratinocytes. protects against friction and water loss.  09:49 Thin Skin It covers all the body except the palms of hands & soles of feet. It differs from thick skin in: It contains hairs, hair follicles and sebaceous glands. Stratum lucidum is absent. Stratum spinosum& granulosum and corneum are thinner than those of thick skin. Principles of Skin  The Cell Types in Epidermis  1. Keratinocytes: Keratinocytes are the predominant cell type of epidermis and originate in the basal layer, produce keratin, and are responsible for the formation of the epidermal water barrier by making and secreting lipids.  2. Melanocyte : in the basal epidermis synthesize dark melanin pigment in melanosomes and transport these to adjacent keratinocytes, which accumulate them to protect nuclear DNA from UV damage.  3. Langerhan’s cells : Located in stratum spinosum. They are branched star shaped cells. The most characteristic feature of these cells are the Birbeck granules in their cytoplasm. Functions: Act as an antigen- presenting cells. It comprise a major component of the skin immunity.  4. Merkel’s cells : Located in the basal layer of epidermis. Their cytoplasm contain small dense neurosecretory granules near the basolateral cell membrane, which is in direct contact with the expanded, disc-like ending of a sensory nerve. Functions: mechanoreceptor for tactile sensation.  B. Dermis Layers of the Dermis Papillary layer  Underlies epidermis Dermal Papillae  Aerolar connective tissue  Supports, nourishes epidermis  Provides sensory nerves, lymphatics, and capillaries Reticular layer  Tough, dense, fibrous layer  Dense irregular connective tissue  Collagen fibers - limit stretch  Elastic fibers - provide flexibility Structures in the dermis The dermis consists of many structures in it. Most of these structures are ingrowths from the epidermis. The structures are, 1) Blood vessels 2) Sensory (touch) nerve endings 3) Sweat glands and their ducts 4) Hair follicles 5) Sebaceous glands 6) Arrector pili muscles  Structures in dermis Sebaceous glands :- These consist of secretory epithelial cells which secrete an oily secretion called sebum. Their ducts open into the hair follicle and soften the hair. These glands are present in hairy areas mostly Sweat glands :- These glands are widely distributed in skin. Each gland has a coiled body under the skin and duct opens on pores on the skin. The glands are Arrector pili muscles:- most numerous in palms of hands, These are small bundles of smooth muscles soles of feet, axilla and groin. attached to hair follicles. Contraction causes the hair to stand and causes goose flesh. Finger prints The surface of the epidermis is ridged by projections from the cells in the dermis called papilla. The pattern of these ridges is different in every person. These impression made by these ridges form the fingerprints.