Chapter 5

skin cancer

basal cell carcinomas account for about 78% of all skin cancers - squamous cell carcinomas, which account for about 20% of all skin cancers - most arise from preexisting lesions of damaged tissue on sun-exposed skin - malignant melanomas arise from melanocytes and account for about 2% of all skin cancers

carotene

antioxidant precursor of vitamin A, which is needed for synthesis of pigments needed for vision - yellow-orange pigment present in the stratum corneum of the epidermis - accounts for the yellowish coloration of skin

sudoriferous gland

apocrine or eccrine exocrine gland in the dermis or subcutaneous layer that produces perspiration - 3 to 4 million - release sweat into hair follicles or onto the skin surface through pores - divided into two main types, eccrine and apocrine, based on their structure, location, and type of secretion

reticular region

attached to the subcutaneous layer, consists of dense irregular connective tissue containing fibroblasts, bundles of collagen, and some coarse elastic fibers - the collagen fibers in the reticular region interlace in a netlike manner - spaces between cells contain hair follicles, sweat glands, nerve endings, etc.

stratum spinosum

8 to 10 layers of many-sided keratinocytes fitting closely together - Langerhans cells and projections of melanocytes are also present in this layer - each spiny projection in a prepared tissue section is a point where bundles of tonofilaments are inserting into a desmosome, tightly joining the cells to one another - provides both strength and flexibility to the skin

melanocyte

8% of the epidermal cells - develop from the ectoderm of a developing embryo and produce the pigment melanin

epidermal wound healing

basal cells of the epidermis surrounding the wound break contact with the basement membrane - cells enlarge and migrate across the wound until advancing cells from opposite sides of the wound meet

inflammatory phase

blood clot forms in the wound and loosely unites the wound edges - inflammation,helps eliminate microbes, foreign material, and dying tissue in preparation for repair - the vasodilation and increased permeability of blood vessels associated with inflammation enhance delivery of helpful cells

excretion and absorption

certain lipid-soluble materials penetrate the skin - about 400 mL of water evaporates through stratum corneum daily - sweat is the vehicle for excretion of small amounts of salts, carbon dioxide, and two organic molecules that result from the breakdown of proteins—ammonia and urea

migratory phase

clot becomes a scab, and epithelial cells migrate beneath the scab to bridge the wound - fibroblasts migrate along fibrin threads and begin synthesizing scar tissue (collagen fibers and glycoproteins), and damaged blood vessels begin to regrow

cerumen

combined secretion of the ceruminous and sebaceous glands - provides a sticky barrier that impedes the entrance of foreign bodies and insects, waterproofs the canal and prevents bacteria and fungi from entering cells

hair

composed of columns of dead, keratinized epidermal cells bonded together by extracellular proteins - shaft and root of the hair both consist of three concentric layers of cells: medulla, cortex, and cuticle

hair follicle

composed of epithelium and surrounding the root of a hair from which hair develops - made up of an external root sheath and an internal root sheath

subcutaneous layer - hypodermis

consists of areolar and adipose tissues - fibers extend from the dermis anchor the skin to the subcutaneous layer attaches to underlying fascia, the connective tissue around muscles and bones - serves as a storage depot for fat, contains large blood vessels that supply the skin - contains nerve endings called pacinian corpuscles that are sensitive to pressure

stratum corneum

consists on average of 25 to 30 layers of flattened dead keratinocytes - cells are continuously shed and replaced by cells from the deeper strata - cells contain mostly keratin

skin or cutaneous membrane

covers an area of about 2 square meters (22 square feet), weighs 4.5-5 kg (10-11 lb), about 16% of total body weight - ranges in thickness from 0.5 mm (0.02 in.) on the eyelids to 4.0 mm (0.16 in.) on the heels - over most of the body it is 1-2 mm (0.04-0.08 in.)

stratum basale or stratum germinativum

deepest layer - single row of cuboidal or columnar keratinocytes - some cells in this layer are stem cells that undergo cell division to continually produce new keratinocytes - includes scattered intermediate filaments called tonofilaments

free nerve ending

dendrites that lack any apparent structural specialization - different free nerve endings initiate signals that give rise to sensations of warmth, coolness, pain, tickling, and itching

hair colour

due primarily to the amount and type of melanin in its keratinized cells - dark-colored hair contains mostly eumelanin; blond and red hair contain variants of pheomelanin - hair becomes gray because of a progressive decline in melanin production - contains only a few melanin granules - white hair results from the lack of melanin and the accumulation of air bubbles in the shaft.

skin wound healing

epidermal wound healing occurs following wounds that affect only the epidermis; deep wound healing occurs following wounds that penetrate the dermis

sebaceous gland

exocrine gland in the dermis of the skin, almost always associated with a hair follicle, that secretes sebum - the secreting portion lies in the dermis and usually opens into the neck of a hair follicle

proliferative phase

extensive growth of epithelial cells beneath the scab, deposition by fibroblasts of collagen fibers in random patterns, and continued growth of blood vessels

dermal papilla

fingerlike projection of the papillary region of the dermis that may contain blood capillaries or corpuscles of touch (Meissner corpuscles)

acne

inflammation of sebaceous glands - occurs predominantly in sebaceous follicles that have been colonized by bacteria

eczema

inflammation of the skin characterized by patches of red, blistering, dry, extremely itchy skin. It occurs mostly in skin creases in the wrists, backs of the knees, and fronts of the elbows

albinism

inherited inability of an individual to produce melanin - melanocytes are unable to synthesize tyrosinase - melanin is missing from their hair, eyes, and skin.

insensible and sensible perspiration

insensible - sweat that evaporates from the skin before it is perceived as moisture - sensible - sweat that is excreted in larger amounts and is seen as moisture on the skin

keratin

insoluble protein - tough, fibrous protein that helps protect the skin and underlying tissues from heat, microbes, and chemicals

protection

keratin protects underlying tissues from microbes, abrasion, heat, and chemicals, keratinocytes resist invasion by microbes - sebum keeps skin and hairs from drying out and contains bactericidal chemicals

Merkel cell

least numerous - located in the deepest layer of the epidermis - makes contact with a tactile (Merkel) disc, which functions in touch

cold sore

lesion, usually in oral mucous membrane, caused by Type 1 herpes simplex virus (HSV) transmitted by oral or respiratory routes - virus remains dormant until triggered by factors such as ultraviolet light, hormonal changes, and emotional stress

papillary region

makes up about one-fifth of the thickness of the total layer - consists of areolar connective tissue containing thin collagen and fine elastic fibers -

wart

mass produced by uncontrolled growth of epithelial skin cells; caused by a papillomavirus

basis of different skin colours

melanin, hemoglobin, and carotene are three pigments that impart a wide variety of colors to skin - the number of melanocytes is about the same in all people - differences in skin color are due mainly to the amount of pigment the melanocytes produce and transfer to keratinocytes

sebum

mixture of triglycerides, cholesterol, proteins, and inorganic salts - coats the surface of hairs and helps keep them from drying and becoming brittle - prevents excessive evaporation of water from the skin, keeps the skin soft and pliable, and inhibits the growth of some bacteria

lunula

moon-shaped white area at the base of a nail - appears whitish because the vascular tissue underneath does not show through due to a thickened region of epithelium

keratinocyte

most numerous of the epidermal cells (90%) - produces keratin - arranged in four or five layers - produce lamellar granules, which release a water-repellent sealant

layers or strata

most regions of the body the epidermis has four strata or layers—stratum basale, stratum spinosum, stratum granulosum, and a thin stratum corneum - thin skin - thick skin has one more layer, stratum lucidum, and a thick stratum corneum

corpuscle of touch - Meissner corpuscle

nerve endings that are sensitive to touch - tactile receptors

hair root plexus

network of dendrites arranged around the root of a hair as free or naked nerve endings that are stimulated when a hair shaft is moved

keratinization

new cells formed in the stratum basale are slowly pushed to the surface - as the cells move from one epidermal layer to the next, they accumulate more and more keratin, a process called keratinization

bulb

onion-shaped structure at the base of each hair follicle and its surrounding dermal root sheath - houses a nipple-shaped indentation, the papilla of the hair, which contains areolar connective tissue and many blood vessels that nourish the growing hair follicle

nail matrix

part of the nail beneath the body and root from which the nail is produced - cells divide by mitosis to produce growth - slower than toenails - 1mm a week

free edge

part of the nail body that may extend past the distal end of the digit - white because there are no underlying capillaries

root

portion of the hair deep to the shaft that penetrates into the dermis, and sometimes into the subcutaneous layer

nail root

portion of the nail that is buried in a fold of skin

stratum lucidum

present only in the thick skin - consists of three to five layers of flattened clear, dead keratinocytes that contain large amounts of keratin and thickened plasma membranes

epidermal ridge

produced during the third month of fetal development as downward projections of the epidermis into the dermis between the dermal papillae of the papillary region - increase the surface area of the epidermis and thus increase the grip of the hand or foot by increasing friction

melanin

protect keratinocytes - yellow-red or brown-black pigment that contributes to skin color and absorbs damaging UV light

hives

reddened elevated patches of skin that are often itchy - most commonly caused by infections, physical trauma, medications, emotional stress, food additives, and certain food allergies

maturation phase

scab sloughs off once the epidermis has been restored to normal thickness - collagen fibers become more organized, fibroblasts decrease in number, and blood vessels are restored to normal

Langerhans cell

small fraction of the epidermal cells - arise from red bone marrow and migrate to the epidermis - functions as an antigen-presenting cell during an immune response - help other cells recognize an invading microbe and destroy it

shaft

superficial portion of the hair, which projects above the surface of the skin

stratum granilosum

about the middle of the epidermis - 3 to 5 layers of flattened keratinocytes that are undergoing apoptosis (cell death) - tonofilaments become more apparent - marks the transition between the deeper, metabolically active strata and the dead cells of the more superficial strata - keratohyalin converts the tonofilaments into keratin- lipid rich water repelling secretions

deep wound healing

four phases: an inflammatory phase, a migratory phase, a proliferative phase, and a maturation phase

matrix

germinal layer of cells in the bulb - hair matrix cells arise from the stratum basale, the site of cell division - hair matrix cells are responsible for the growth of existing hairs, produce new hairs, give rise to the cells of the internal root sheath

hair growth

growth (anagen) stage, a regression (catagen) stage, and a resting (telogen) stage - about 85% of scalp hairs are in the growth stage

functions of hair

hair on the head guards the scalp from injury and the sun - decreases heat loss from the scalp - protect the eyes, nose, ear from foreign particles - sensing light touch

accessory structures of the skin

hair, sebaceous (oil) glands, sudoriferous (sweat) glands, ceruminous glands, nails

nails

hard plate, composed largely of keratin, that develops from the epidermis of the skin to form a protective covering on fingers and toes - protection, allow us to grab and manipulate things, scratch ourselves

terminal hairs

heavily pigmented hairs of the eyebrows, eyelashes and scalp that replace downy lanugo hair prior to birth - replace vellus hairs at puberty in hairy areas

thermoregulation

homeostatic regulation of body temperature - liberating sweat at its surface and by adjusting the flow of blood in the dermis

dermis

second, deeper part of the skin - composed of a strong connective tissue containing collagen and elastic fibers - has the ability to stretch and recoil easily - divided into a superficial papillary region and a deeper reticular region

cutaneous sensations

sensations that arise in the skin - tactile sensations (touch, pressure, vibration, and tickling) - thermal sensations - pain - wide variety of nerve endings and receptors distributed throughout the skin - the tactile discs of the epidermis, the corpuscles of touch in the dermis, and hair root plexuses

vellus hairs

short, fine, pale hairs that replace lanugo of the rest of the body - adulthood, about 95% of body hair on males is terminal hair and 5% is vellus hair; on females, about 35% of body hair is terminal hair and 65% is vellus hair

apocrine sweat gland

simple, coiled tubular glands - found in puberty hair areas - secretory portion of these sweat glands is located mostly in the subcutaneous layer, and the excretory duct opens into hair follicles - slightly viscous and appears milky or yellowish in color - sexual activities, not activated by thermoregulation

eccrine sweat gland - merocrine sweat gland

simple, coiled tubular glands that are much more common than apocrine - distributed throughout the skin of most regions of the body - secretory portion of eccrine sweat glands is located in the deep dermis (sometimes upper subcutaneous layer) - the excretory duct projects through the dermis and epidermis and ends as a pore at the surface of the epidermis - water, ions (mostly Na+ and Cl-), urea, uric acid, ammonia, amino acids, glucose, and lactic acid - thermoregulation

arrector pili muscle

smooth muscle, extends from the superficial dermis of the skin to the dermal root sheath around the side of the hair follicle - under physiological or emotional stress autonomic nerve endings stimulate the arrector pili muscles to contract, which pulls the hair shafts perpendicular to the skin surface - causes "goose bumps"

anatomy and major functions of skin

superficial, thinner epidermis (epithelial tissue) and a deep, thicker dermis (connective tissue) that is anchored to the subcutaneous layer - regulates body temperature, stores blood, protects body from external environment, detects cutaneous sensations, excretes and absorbs substances, synthesizes vitamin D.

epidermis

superficial, thinner layer of skin - composed of keratinized stratified squamous epithelium - contains four principal types of cells

ceruminous glands

sweat glands in the external ear that produce a waxy lubricating secretion - excretory ducts open either directly onto the surface of the ear canal or into ducts of sebaceous glands

synthesis of vitamin D

synthesis of vitamin D requires activation of a precursor molecule in the skin by UV rays in sunlight

burn

tissue damage caused by excessive heat, electricity, radioactivity, or corrosive chemicals that denature (break down) the proteins in the skin cells - destroy some of the skin's important contributions to homeostasis—protection against microbial invasion and desiccation, and thermoregulation.

granulation tissue

tissue filling the wound during migratory phase

nail body

visible portion of the nail - flattened, keratinized cells fill with a harder type of keratin and do not shed