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