Produced by asistant lecturer: zahraa ahmed INTEGUMENTARY SYSTEM Produced by asistant lecturer: zahraa ahmed

Definition: The skin or integument is the largest organ in the mammalian body and is comprised of an epithelial covering, its derivatives (including hair, nails ,and several types of sweat and sebaceous glands) and its associated connective tissue. the surface of body are covered either by thin skin or thick skin

Layers Of The Skin Skin consist of two distinct regions Epidermis – outer Is non vascular and is lined by keratinized stratified squamous epithelium Dermis – inner Characterized by dense irregular connective tissue,blood vessels,nerves,and different gland Beneath the dermis is the hypodermis or subcutaneous layer of connective tissue and adipose tissue that forms the superficial fascia seen in gross anatomy

Epidermis Composed of stratified squamous epithelium Avascular as it has no blood supply of its own Oxygen and nutrients diffuse from the underlying dermis The most abundant epithelial cells, the keratinocytes form different layers. Thick skin (5) and thin skin (4)-refer only to the epidermis. Five structurally different layers can be identified:

Stratum Granulosum Stratum basale . Stratum Spinosum Stratum Lucidum EPIDERMAL LAYERS Stratum basale . Stratum Spinosum Stratum Granulosum Stratum Lucidum Stratum Corneum

The stratum basale(First Layer) is the deepest layer of the epidermis .It consists of a single layer of columnar or cuboidal cells which rest on the basement membrane Basal cells serve as stem cells for the epidermis.

Stratum Spinosum(second layer) This consists of 4-6 rows of cells Cells synthesize keratin filaments that become assembled into tonofilaments. Also contain Langerhans cells, part of the immune system (defense against microorganisms and cancers).

The stratum granulosum(Third Layer) Consists of 3-5 cell layers of flattened cells. Cells filled with dense keratohylaine granules( hence the name of the layer). and membrane-bound lamellar granules. Dendritic cells found throughout this stratum Nuclei already begin to degenerate in the outer part of the stratum granulosum.

stratum lucidum (fourth Layer) lucidum can usually not be identified in thin skin is translucent and barely visible (in thick skin of the palms and soles.) The tightly packed cells lack nuclei or organelles and are dead . The flatted cells contain densely packed keratin filaments

Stratum corneum (the fifth layer) All nuclei and organelles have disappeared from the cells . Consist of flatted , dead cells filled with soft keratin filaments Superficial cell from this layer are continually shed or replaced by new cells arising from the deep stratum basale. The protection of the body by the epidermis is due to the functional features of the stratum corneum

Dermis can recognize a division into two structully distinct layers . The papillary layer Basement membrane separate the dermis from the epidermis Is the superficial layer in the dermis and contain loose irregular C.T. Dermal papillae and epidermal ridges form evagination and interdigitations . Connective tissue filled with fiber ,capillaries,blood vessels ,fibroblasts , macrophages ,and another loose C.T. Senseory receptor are resent in the dermal papillae . dermal papillae, that project into the under surface of the epidermis .When it contain a blood vessel then called vascular papillae, but when it contain a nerve ending (Meissner corpuscle) . .

The reticular layer lies deep to the papillary layer; it characterized by thick , irregular bundles of collagen and elastic fibers. less cellular than papillary layer. No distinct boundary between the papillae and reticular layers. Accessory organs of epidermal origin, such as hair follicles and sweat glands extend into the dermis. contain Sensory receptors_ Meissner’s and Pacinian corpuscles The hypodermis contains variable amounts of adipose tissue.

Other skin cells Keratinocytes:represent the majority of cells Melanocytes:derived from neural crest cells,have long ,irregular cytoplasmic or extension that branch into the epidermis ,located between the stratum basal and stratum spinosum of epidermis ,and synthesize melanin which transferred from cytoplasmic extension to Keratinocytes in basal cell layer,and melanin darkens skin color and protects it from u.v.radation . Langerhans cells (dendritic cells ):originated from bone marrow ,migrate via blood stream to the skin in stratum spinosum , are- part of immune system of skin ,and are antigen-presenting cells of the skin. Merkel cells:found in stratum basal layer of epidermis and function as mechanoreceptor for sensation.

Thick versus Thin Skin: The terms thick and thin refer to the thickness of the epidermis. Most of the body is covered by thin skin. thin skin contains hair follicles, sebaceous glands, and arrector pili muscles. The epidermis in thick skin may be six times thicker than the epidermis that covers the general body surface. Thick skin does not have hair, smooth muscles, or sebaceous glands but contains sweat glands . Thick skin on the palms of the hands, the fingertips, and soles of the feet may be covered by many layers of keratinized cells that have cornified.

Major function of skin Protection through the keratinized epidermis from abrasion and the entrance of pathogen Impermeable to water ,owing to lipid layer in the epidermis Body temperature regulation as a result of sweating and changes in the vessel diameters. Sensory perception of touch ,pain ,pressure ,and temperature changes because of nerve endings Excretions through sweat of water ,sodium salts,urea,and nitrogenous waste . Formtion of vitamine D from precursore molecules produced in the epidermis when exposed to the sun

Skin derivatives Hair Developed from the epithelium of the epidermis and reside deep in the dermis Are hard cylindrical structure that arise from hair follicles Surrounded by external and internal root sheaths Grow from the expanded hair bulb of the hair follicle . Hair bulb indented by connective tissue(dermis) papilla that is highly vascularized

Functions of Hair Prevents heat loss, Decreases sunburn, Eyelashes help protect eyes Touch receptors senses light touch,

Skin derivatives sebaceous glands Numerous sebaceous associated with each hair follicle Cells in sebaceous glands grow ,accumlate secretion ,die and become oily secretion sebum . Smooth muscles arrector pili attach to the papillary layer of the dermis and to the sheath of the hair follicle Contraction of the arrector pili muscle stands hair up and for forces sebum into the lumen of the hair follicle

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