Skin Anatomy PDF

 Skin (Integument) Consists of three major regions Epidermis – outermost superficial region Dermis – middle region Hypodermis – deepest region  Functions of the Skin Functions of Skin Resistance...

 Skin (Integument) Consists of three major regions Epidermis – outermost superficial region Dermis – middle region Hypodermis – deepest region  Functions of the Skin Functions of Skin Resistance to trauma and infection – Keratin – defensins – Acid mantle Other barrier functions – Water – UV radiation – Harmful chemicals Vitamin D synthesis – Skin carries out first step – Liver and kidneys complete process 6 - 6 Functions of the Skin Sensation – Skin is an extensive sense organ – Receptors for temperature, touch, pain, and more Thermoregulation – Thermoreceptors – Vasoconstriction/vasodilation – Perspiration Nonverbal communication – Facial expression – Importance in social acceptance and self image 6 - The SkinThe andSkiTissuehe SkinTissues and 7 Subcutaneous Subcutaneous Skin is body’s largest and Tissue heaviestand organ – Covers 1.5 to 2.0 m2 ; composes 15% of body weight Layers Subcutaneous Tissue – Epidermis: stratified squamous epithelium – Dermis: deeper connective tissue layer – Hypodermis—connective tissue layer below dermis (not part of skin, but associated with it) Skin thickness ranges from 0.4mm on the eyelid to 6.0 mm thick on the heels feet. – Thick skin covers front of hands, bottoms of feet Has sweat glands, but no hair follicles or sebaceous (oil) glands Epidermis 0.5 mm thick – Thin skin covers rest of the body Possesses hair follicles, sebaceous glands, and sweat glands Epidermis about 0.1 mm thick  Cells of the Epidermis Types of Cells Keratinocytes – produce the fibrous protein keratin Melanocytes – produce the brown pigment melanin Langerhans’ cells – epidermal macrophages that help activate the immune system Merkel cells – function as touch receptors in association with sensory nerve endings 6 - 1 7 The Dermis Papillary layer—superficial zone of dermis – Thin zone of areolar tissue in and near the dermal papilla – Allows for mobility of leukocytes and other defense cells – Rich in small blood vessels Reticular layer—deeper and thicker layer of dermis – Consists of dense, irregular connective tissue – Stretch marks (striae): tears in the collagen fibers caused by stretching of the skin due to pregnancy or obesity 6 - 1 9 The Dermis Figure 6.5 6 - 2 3 Structure of the Hair and Follicle Three layers of the hair in cross section – Medulla Core of loosely arranged cells and air spaces – Cortex Constitutes bulk of the hair Consists of several layers of elongated keratinized cells – Cuticle Composed of multiple layers of very thin, scaly cells that overlap each other Free edges directed upward 6 - 2 4 Structure of the Hair and Follicle Copyright © The McGraw-Hill Companies, Inc. 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Hair is divisible into three zones along its length – Bulb: a swelling at the Hair shaft base where hair originates in dermis or hypodermis Only living hair cells are in or near bulb Sebaceous Piloerector gland muscle – Root: the remainder of the hair in the follicle Hair receptor Bulge Hair root Hair matrix – Shaft: the portion above Hair bulb Apocrine sweat gland Dermal Blood capillaries papilla the skin surface in dermal papilla (a) Figure 6.7a 6 - 2 7 Nails Nails Fingernails and toenails—clear, hard derivatives of stratum corneum – Composed of thin, dead cells packed with hard keratin Functions: – Improve grooming, picking apart food, other manipulations – Provide a counterforce to enhance sensitivity of fleshy fingertips to tiny objects Nail plate—hard part of the nail – Free edge: overhangs the fingertip – Nail body: visible attached part of nail – Nail root: extends proximally under overlying skin Nails 6-44 Figure 6.10 6 - 3 0 Cutaneous Glands Figure 6.11a Figure 6.11b Figure 6.11c The skin has five types of glands: merocrine sweat glands, apocrine sweat glands, sebaceous glands, ceruminous glands, and mammary glands 6 - 3 1 Sweat Two kinds of sweat Glands (sudoriferous) glands: apocrine and merocrine – Apocrine sweat glands Locations: groin, anal region, axilla, areola, beard area in men – Inactive until puberty Ducts lead to nearby hair follicles Produce sweat that is milky and contains fatty acids Respond to stress and sexual stimulation – Believed to secrete pheromones—chemicals that can influence behavior of others Bromhidrosis—disagreeable body odor produced by bacterial action on sweat from apocrine glands 6 - 3 2 Sweat (Continued) Glands – Merocrine (eccrine) sweat glands Most numerous skin glands—3 to 4 million in adult skin – Especially dense on palms, soles, and forehead Simple tubular glands Watery perspiration that helps cool the body – Myoepithelial cells—contract in response to stimulation by sympathetic nervous system and squeeze perspiration up the duct Found in both apocrine and merocrine glands 6 - 3 3 Sweat Sweat—begins as a Glands protein-free filtrate of blood plasma produced by deep secretory portion of gland – Some sodium chloride and other small solutes remain in the sweat Some sodium chloride reabsorbed by duct – Some drugs are excreted in sweat – On average, 99% water, with pH range of 4 to 6 Acid mantle—inhibits bacterial growth – Insensible perspiration—500 mL/day Does not produce visible wetness of skin – Diaphoresis—sweating with wetness of the skin Exercise—may lose 1 L sweat per hour 6 - 3 4 Sebaceous Sebaceous glandsGlands are flask-shaped and have short ducts opening into hair follicles Holocrine secretion style Sebum—oily secretion of sebaceous glands – Keeps skin and hair from becoming dry, brittle, and cracked – Lanolin—sheep sebum 6 - 3 5 Ceruminous Ceruminous glandsGlands are simple, coiled, tubular glands in external ear canal Their secretion combines with sebum and dead epithelial cells to form earwax (cerumen) – Keeps eardrum pliable – Waterproofs the canal – Kills bacteria – Makes guard hairs of ear sticky to help block foreign particles from entering auditory canal 6 - 3 6 Mammary Glands glands that Mammary glands—milk-producing develop only during pregnancy and lactation – Modified apocrine sweat glands – Rich secretion released through ducts opening at nipple Mammary ridges or milk lines – Two rows of mammary glands in most mammals – Primates kept only two glands, but a few people have additional nipples along the milk line (polythelia) 6 - 3 Cutaneous Glands 7