Skin Anatomy PDF
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This document provides an overview of the integumentary system, including the structure, functions, and components of the skin. It describes the different layers, cells, and glands. The document also covers topics such as hair, nails, and various types of skin glands, including their functions.
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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