INTEGUMENTARY SYSTEM Produced by lecturer zahraa ahmed okhti

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) .

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

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

Dermis can recognize a division into two structully distinct layers . The papillary layer The reticular layer

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

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

Pacinian Corpuscle Skin contains many sensory receptors. Pacinian corpuscles are onion-like structures in the dermis and hypodermis. Pacinian corpuscles contain a myelinated nerve ending in the central core of the structure. The outer layers are composed of flattened cells, collagen fibers and a lymph-like fluid. Pacinian corpuscles are sensitive to mechanical and vibratory pressure.

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