The Integumentary System Chapter 5

The Skin A surface area of square meters Weighs approximately 4-5 kg (9-11 lbs.) Every square centimeter contains: –70 cm of blood vessels –55 cm of nerves –100 sweat glands –15 oil glands –230 sensory receptors –Half million cells that are constantly dying and being replaced

The Skin Called the integument or covering, its function is primarily protective Forms the boundary between our internal and the external environment It is a pliable, tough, organ that is constantly regenerating Without skin we would succumb to infection, water loss, or heat loss

Skin Layers Epidermis –Outermost protective shield of the body – mm in thickness depending on location –Composed of epithelial cells –Avascular receives nutrients that diffuse from dermis Dermis –Underlying skin layer making up the bulk of the skin –A tough leathery layer deep to the epidermis –Composed of fibrous connective tissue –Vascular

Hypodermis or superficial fascia A subcutaneous tissue deep to the skin Not considered a part of the skin, but it shares some of the skins protective functions Consists mostly of adipose tissue and areolar connective tissue It functions to store fat, anchor the skin to the underlying muscles, allowing for movement Hypodermis thickens markedly when one gains weight

Hypodermis Fat Deposition Female –Breasts –Thighs Saddle bags Male –Anterior abdomen Beer belly –Waist Spare tire

Epidermis A thick keratinized layer of stratified squamous epithelium Consists of four distinct cell types Arranged in four or five distinct cell layers

Cells of the Epidermis Keratinocytes Melanocytes Merkel cells Langerhans’ cells

Keratinocyte Principle cell of the epidermis Seen here migrating upward through various layers of the epidermis

Keratinocytes Most of the epidermal cells are keratinocytes The chief role of keratinocytes is to produce keratin, the tough fibrous protein that gives the epidermis its protective qualities Tightly connected by desmosomes Keratinocytes arise from constant cell mitosis at the deepest layer of the epidermis Keratinocyte cells manufacture keratin during their migration to the skin surface

Keratinocytes (continued) As cells migrate to the surface their contents become dominated by keratin The cells will deform to become flattened, dead structures that are keratin filled Million of cells on the free surface rub off daily A totally new epidermis every days Cell reproduction is higher in areas subject to friction (hands, feet)

Melanocytes Spider shaped cells found in Stratum basale or basal layer

Melanocytes Specialized epithelial cells that synthesize the pigment melanin Cells are found in the deepest layer of the epidermis Melancytes have many branching processes that touch all keratinocytes in the basal layer Processes carry melanin to keratinocytes Melanin granules accumulate on the super- ficial side of the nucleus of the ketatinocytes

Melanocytes Melanin granules form a pigment shield that protects the nucleus from ultraviolet (UV) radiation in sunlight All humans have the same amount of melanocytes Racial differences in skin coloring is thought to reflect the kind and amount of melanin made and retained

Langerhan’s Cells Star shaped cells among keratinocytes

Langerhan’s Cells Cells arise from bone marrow and migrate to the epidermis The cells are macrophages that help to activate the immune system Their cell processes extend among surrounding keratinocytes From a continuous network

Merkel Cells Spiky shaped hemispheres found at the epidermal - dermal junction

Merkel Cells Each Merkel cell is associated with a disc shaped sensory nerve ending The combined structure is called a Merkel disc Merkel discs function as a sensory nerve receptor for touch

Epidermal layers Four layers in “thin skin” Covers most of the body

Epidermal Layers Five layers found in “thick skin” Stratum lucidum is extra layer Found on fingertips, palms and soles of feet

Stratum basale Deep layer attached to underlying dermis Singe row of youngest cells Ongoing cell mitosis

Stratum spinosum Several cell layers thick Cells contain a web-like system of filaments Abundant Langerhan’s cells in this layer

Stratum granulosum Area of 3-5 cell layers Ketatinocytes flatten and begin to disintegrate Release of glycolipid slows water loss Cell binding

Stratum lucidum Consist of a few rows of clear, flat, dead cells Present only in thick skin

Stratum corneum Broad zone cell layers thick 3/4 of epidermal thickness Protects skin from abrasion & penetration

Dermis

The dermis is the second major skin region Layer of strong, flexible connective tissue Cells are typical of connective tissue –Fibroblasts, macrophages, mast cells, and white blood cells Semifluid matrix is heavily embedded with collagen, elastin, and reticular fibers It is your “hide”

Dermis Dermis is richly supplied with nerve endings, blood vessels, and lymphatic vessels Hair follicles, oil and sweat glands, are located in the dermis Dermis has two main layers –Papillary layer –Reticular layer

Papillary layer A thin superficial connective tissue layer in which the fibers form a loosely woven mat heavily invested with blood vessels Superior surface has projections called dermal papillae that indent the overlying epidermis Many papillae contain capillary loops, in others are free nerve endings (pain), and Meissner’s corpuscles (touch)

Dermal ridges On the hands and soles of the feet the papillae lie atop dermal ridges The dermal ridges produce conspicuous looped and whorled ridges on the epidermal surface which increase the grip of the fingers and feet Sweat pores open along the crests of the epidermal ridges leaving a film of sweat we know as fingerprints

Reticular layer

This layer accounts for 80% of the dermis Tissue is dense irregular connective tissue Its extracellular matrix contains thick collagen bundles running in various planes Collagen fibers of the dermis give the skin its strength and resiliency Collagen binds water helping to maintain hydration Elastin provides stretch-recoil properties

Tension lines Collagen fibers tend to run parallel to the skin surface Separations in fibers yield lines of tension Tension lines are significant for surgeon’s and their patients Incisions parallel to lines of tension gape less than those made across the line of tension

Dermal stretching During pregnancy dermal tearing may occur indicated by silvery white scars or “stretch marks” Blisters are the separation of the epidermal and dermal layers with the resulting development of a fluid filled pocket

Flexure lines Flexure lines are dermal folds that occur at or near joints where the dermis is secured to deeper structures Folds occur on the surface of the wrists, palms, soles of the feet, fingers and toes Since the skin cannot slide to accommodate joint movement in such regions, the dermis folds and skin creases form

Skin Color Three pigments contribute to skin color; melanin, carotene, and hemoglobin Melanin ranges in color from yellow to reddish brown Racial differences in skin coloring reflect the relative kind and amount of melanin Dark skinned people produce much more and darker melanin than those of fair skinned individuals and their ketatinocytes retain it longer

Melanin Freckles and pigmented moles are local accumulations of melanin Melanocytes are stimulated to greater activity when exposed to sunlight Prolonged sun exposure causes a substantial melanin buildup, which helps protect DNA of viable skin cells from UV radiation A speed up of melanin production resulting in a darkening of the skin (a tan)

Carotene Carotene is a yellow to orange pigment found in plant products such as carrots It tends to accumulate in the stratum corneum and the fatty tissue of the epidermis It is most obvious on the palms and soles of the feet where the stratum corneum is thickest Color is more intense when large amount of carotene rich foods are eaten

Hemoglobin The crimson color of oxygenated hemoglobin gives fair skin its pinkish hue The hemoglobin is located in red blood cells circulating in the dermal capillaries Caucasians have only a small amount of melanin, the dermis is nearly transparent and the hemoglobin’s color shows through When hemoglobin is poorly oxygenated the blood and skin of light skinned people appears blue

Skin color anomalies Redness - embarassment, fever, allergy, inflammation or hypertension Blanching - emotional stress, anemia, or low blood pressure Jaundice - liver disorder resulting in a buildup of bile pigments Bronzing - metallic appearance if skin is due to hypofunction of the adrenal cortex Black and blue - clotted blood masses under the skin are called hematomas

Appendages of the Skin Sweat (Sudoriferous) glands Sebaceous (oil) glands Hair and hair follicles Nails

Sweat Glands Sweat glands are distributed over the entire body surface except the nipples and parts of the external genitalia Approximately 2.5 million per individual Two major types –Eccrine sweat glands –Apocrine sweat glands

Eccrine sweat glands The most numerous sweat gland Particularly abundant on the palms, soles of the feet, and forehead Each is a simple, coiled, tubular gland The secretory part lies coiled in the dermis and the duct extends to open in a funnel shaped pore

Sweat Sweat is a hypotonic filtrate of the blood that passes through the secretory cells of the sweat glands and is release by exocytosis It is 99% water with some salt (NaCl), vitamin C, antibodies, traces of metabolic wastes and lactid acid Composition depends on heredity and diet Normally sweat is acidic with a pH between 4 and 6

Sweating Sweating is regulated by the sympathetic divisions of the autonomic nervous system Its major role is to assist in thermoregulation and prevent overheating of the body Heat induced sweating begins on the forehead and spreads inferiorly Emotional sweating “cold sweat” is brought on by fright, embarrassment, or nervousness and begins on the palms, soles, and axillae and then spreads over the body

Apocrine sweat glands Largely confined to the axillary and anogenital areas Apocrine sweat glands are larger than eccrine sweat glands and their ducts empty into hair follicles Apocrine secretions contain the same basic components as sweat plus some fatty substances and protein Bacteria upon our skin decompose these substances and produce body odor

Ceruminous glands Ceruminous glands are modified apocrine glands found in the lining of the external ear These glands secrete cerumen, or earwax, which because of its sticky texture deters insects and foreign material from entering the ear

Mammary glands Mammary glands are another variety of specialized sweat gland that secretes milk Lobules within the breast produce milk when a woman is lactating Compound alveolar glands pass the milk into the lactiferous ducts which open to the outside of the nipple

Sebaceous (oil) Glands Sebaceous glands are simple alveolar glands found all over the body except on the palms and soles The glands are small on the body trunk and limbs, but quite large on the face, neck and upper chest These glands secrete an oil called sebum Classified as holocrine glands they secrete into a hair follicle or pore on the skin surface

Sebaceous Glands (con’t) Sebum softens and lubricates the hair and skin, prevents hair from becoming brittle, and slows water loss from the skin Sebum is bactericidal and reduces the number of bacteria residing on the surface of the skin The glands are regulated by hormones and while relatively inactive in childhood become activated in both sexes during puberty

Hairs and Hair Follicles The main function of our sparse body hair is to sense insects on the skin before they sting Hair on the scalp protects against trauma, heat loss, and sunlight Eyelashes shield the eyes, and nose hairs filter large particles like lint and insects from the air

Structure of a Hair Hairs, or pili, are flexible strands produced by hair follicles that consist of largely keratinized cells Hard keratin found in hair is tougher and more durable than that found in epidermal layers and does not flake

Structure of a Hair The hair shaft projects from the skin The root is embedded in the skin The shape of the shaft determines whether the hair is straight or curly –Flat / kinky –Oval / smooth and silky –Round / coarse

Structure of a Hair A hair has three concentric rings –Medulla is the central core of large cells separated by air spaces –Cortex is the bulky layer surrounding the medulla –Cuticle is a single layer of overlapping cells Melanin colors hair

Structure of a Hair Follicle Hair follicles extend from the epidermal surface into the dermis The deep end of the follicle is expanded and forms a hair bulb A sensory nerve ending called a root hair plexus wraps each bulb

Structure of a Hair Follicle Papilla (a) protrudes into a hair bulb and supplies nutrients The wall of the follicle is made of an outer connective tissue (b) sheath and inner epithelial root sheath (c) A single layer of stratum basale cells (d) divide to form hair a c d b

Structure of a Hair Follicle Associated with each hair follicle is a bundle of smooth muscle fiber called arrector pili The muscle fibers pull the hair shaft into an upright position

Hair Distribution Millions of hair are scattered over the body 100,000 in the scalp and 30,000 in a beard Only lips, parts of external genitalia, and thick skin areas of hands and soles of feet are free of hair

Hair Type Hair is classified as vellus or terminal The body hair of children and women is the fine vellus variety Hair of the eyebrows and scalp is called terminal hair At puberty terminal hair appears in the axillary and pubic regions of both sexes Hair growth and density are influenced primarily by nutrition and hormones

Hair Development

Hair Growth The rate of hair growth varies from region to region and with sex and age, but averages 2 mm a week Hair follicles go through growth cycles A growth cycle (a) is followed by rest cycle where the follicle atrophies (b)

Hair Thinning and Baldness The rate of hair growth declines in the fourth decade and reflects an age related atrophy of hair follicles Hairs are not replaced as fast as they are shed and the result is a gradual thinning and some degree of baldness (alopecia) in both men and women Coarse terminal hair are replaced by vellus hair and the hair becomes increasingly wispy

Male Pattern Baldness Male pattern baldness is a genetically determined sex-influenced condition Genes in adulthood changes the response of hair follicles to testosterone Follicle growth cycles shorten and many hair never emerge before they are shed by the follicle Any hair present are of the finer, vellus form

Nails Nails are scalelike modification of the epidermis that forms a clear protective covering of the distal part of the finger Nails contain hard keratin

Nails Nail components –Free edge –Body of nail –Nail folds –Lunula –Eponychium –Nail matrix The nail matrix lies deep to the lunula and is the site where nail growth is occurring

Integumentary System Functions Protection –Chemical barrier –Physical or Mechanical barrier –Biological barrier Body Temperature Regulation Cutaneous Sensation Metabolic Functions Blood Reservoir Excretion

Protection Chemical barrier –Skin secretions create an acid mantle that retard bacteria reproduction –Sebum from sebaceous glands is bactercidal –Skin cells secrete a natural antibiotic call human defensin –Melanin shields the skin from UV radiation

Protection Physical or mechanical barrier –Hard keratinized cells provide a continuous barrier –Glycolipids of the epidermis block the diffusion of water and water soluble substances from between cells –Substances that do penetrate the skin in limited amounts include Lipid soluble substances such as oxygen, carbon dioxide and fat soluble vitamins (A, D, E, and K) Natural and manufactured solvents, salts, and drugs

Protection Biological barrier –Langerhans’ cells of the epidermis “present” foreign substances (antigens) to the white blood cells (lymphocytes) which in tern activate our immune system –Macrophages of the dermis dispose of viruses and bacteria that have penetrate the epidermis but they also work as presenters

Body Temperature Regulation The body works best when its temperature remains within homeostatic limits Cooling occurs through radiation of heat and evaporation of water from the surface of the skin Heating occurs from metabolism, activity and shivering Extremes of environmental temperature threaten homeostatic balance

Cutaneous Sensation The skin is richly supplied with cutaneous sensory receptors Cutaneous receptors are classified as exteroreceptors because they respond to external stimuli Cutaneous receptors include –Meissner’s corpuscles (light touch) –Pacinian corpuscles (deep pressure –Root hair plexuses (displacement of hair shaft) –Free nerve endings (pain)

Metabolic Functions Sunlight bombarding modified cholesterol molecules in the epidermal cells are converted to a precursor of vitamin D Keratinocyte enzymes can “disarm” many cancer causing carcinogens Keratinocytes can also activate steroid hormones

Blood Reservoir The skin can hold about 5% of the body’s entire blood volume Blood volume can be diverted from the skin to other organs in need Blood volume can be diverted to the skin for temperature regulation

Excretion Limited amount of nitrogen-containing wastes (ammonia, urea, and uric acid) are eliminated from the body in sweat Sweating also excretes water and salt

Homeostatic Imbalances of the Skin Homeostatic imbalances of the skin range from mild to life-threatening Homeostatic imbalances are readily visible There are over 1000 different conditions and ailments affecting the skin A select few will be presented

Burns Burns are a devastating threat to the individual because of their effect on the skin The threat to life severe burns is loss of body fluids contain protein and electrolytes Fluid loss can cause dehydration and electrolyte imbalances These in turn can lead to renal shutdown and circulatory shock The amount of fluid volume lost is estimated using the rule of nines

Burns Estimating the area of a burn using the rule of 9’s

Classification of Burns Burns are classified according to their severity (depth) as first second or third degree –1st Only the epidermis is damaged –2ndEpidermis and the upper dermis –3rdEntire thickness of the skin Partial thickness and full thickness burns are a reference to the extent of skin layers damaged

Basal Cell Carcinoma Least malignant and most common skin cancer Cells of the stratum basale proliferate and invade the dermis Lesions appear as shiny dome shaped nodules Excision result in a 99% cure rate

Squamous Cell Carcinoma Lesions arise from the keratinocytes of the stratum spinosum Lesion appears as a scaly reddened rounded elevation Tends to grow rapidly and metastasize to adjacent lymph nodes

Malignant Melanoma Most dangerous form of skin cancer Melanoma can develop wherever there is pigment Appears as a brown to black patch that metastasizes rapidly to the adjacent lymph and blood vessels 50% survival rate

Skin Disorders - Anterior

Skin Disorders - Posterior

Medical Wounds

Developmental Aspects