Unit 3 Anat

Integumentary system consists of

skin, hair, nails, sweat glands, sebaceous (oil) glands

Epidermis

superficial region of the skin, consists of epithelial tissue and is avascular; consists mostly of keratinized stratified squamous epithelium, made up of 4 to 5 distinct layers; contains phagocytic cells

Dermis

underlies epidermis, mostly fibrous connective tissue, vascular; strong and flexible, cells include fibroblasts, macrophages, and mast cells and white blood cells; also contains nerves, blood vessels, and lymphatic vessels, hair follicles, oil glands, and sweat glands

Hypodermis (superficial fascia)

subcutaneous layer deep to skin, not part of skin but shares some functions, mostly adipose tissue that absorbs shock and insulates, anchors skin to underlying structures, are mostly muscles

Keratinocytes

found in epidermis, produce fibrous keratin (protein that gives skin properties), major cell of epidermis, tightly connected by desmosomes, millions slough off every day

Melanocytes

found in epidermis, spider-shaped cell, produce pigment melanin that is packaged into melanosomes (transferred to keratinocytes where they protect nucleus from UV damage)

Dendritic (Langerhans) cells

star-shaped macrophages that patrol deep epidermis (key activators of immune system)

Tactile (Merkel) cells

sensory receptors that sense touch

Four types of cells in epidermis

Keratinocytes, melanocytes, dendritic/langerhans, tactile/merkel

Thick skin

contains five layers and is found in high-abrasion areas (hands, feet)

Thin skin

contains only four strata

Five layers of skin (Bottom to Top)

stratum - basale, spinosum, granulosum, lucidum (only in thick skin), corneum

Stratum basale (basal layer)

deepest, firmly attached to dermis, consists of single row of stem cells (daughter cell division), also known as stratum germinativum due to mitosis, 10 to 25% of layer also composed of melanocytes

Stratum spinosum (prickly layer)

several cell layers thick, weblike system of intermediate prekeratin filaments attached to desmosomes, scattered among keratinocytes are abundant melanosomes and dendritic cells

Stratum granulosum (granular layer)

4 to 6 cells thick, flattened / thin, keratinization begins, accumulate keratohyaline granules and lamellar granules, cells above this layer die

Stratum lucidum (clear layer)

found only in thick skin, consists of dead keratinocytes, lies superficial to the stratum granulosum

Stratum corneum (horny layer)

20 to 30 rows of flat keratinized dead cells, accounts for three quarters of epidermal thickness, though dead cells still protect deeper cells, prevent water loss, protect from abrasion and penetration, act as a barrier to outside factors

Apoptosis

Controlled cell death, dead cells slough off as dandruff and dander, humans shed 50,000 cells a minute

Papillary Layer

superficial layer of areolar connective tissue consisting of loose collagen, elastic fibers, and blood vessels

Two layers of the dermis

Papillary (areolar connective tissue) and Reticular (dense irregular connective tissue)

Dermal papillae

superficial region of dermis that sends fingerlike projections up into epidermis, contains capillary loops, free nerve endings, and touch receptors

In thick skin, dermal papillae

lie on top of dermal ridges, giving rise to epidermal ridges

Friction ridges

enhance gripping ability, contribute to sense of touch, sweat pores in ridges leave unique fingerprint pattern

Reticular Layer

makes up 80% of dermal thickness, consists of coarse, dense fibrous connective tissue, elastic fibers (stretch) and collagen fibers (strength)

Cutaneous plexus

network of blood vessels between reticular layer and hypodermis

Extracellular matrix

contains pockets of adipose cells

Cleavage (tension) lines

in reticular layer, caused by many collagen fibers running parallel to skin surface, externally invisible

Flexure lines

dermal folds at or near joints in reticular layer; dermis is tightly secured, skin’s inability to slide easily causes deep creases, visible on hands, wrists, fingers, soles, and toes

Striae

also known as stretch marks, extreme stretching of skin can cause dermal tears leaving silvery white scars

Blisters

acute short-term traumas to skin, fluid-filled pockets that separate epidermal and dermal layers

Melanin

only pigment made in skin, made by melanocytes; made from amino acid tyrosine by tyrosinase, packaged into melanosomes that shield DNA of keratinocytes from UV sunlight; two forms, reddish yellow to brownish black, skin color differences are due to amount and form of melanin; freckles and pigmented moles are local accumulations of melanin

Excessive sun exposure damage

elastic fibers clump, causing skin to become leathery, can depress immune system and cause alterations in DNA (skin cancer), UV light destroys folic acid which is necessary for DNA synthesis

Photosensitivity

increased reaction to sun, some drugs cause this, leading to skin rashes

Carotene

yellow to orange pigment, most obvious in palms and soles, accumulates in stratum corneum and hypodermis, can be converted to vitamin A for vision and epidermal health

Hemoglobin

pinkish hue of fair skin is due to lower levels of melanin, skin of caucasians is more transparent, so color of hemoglobins shows through

Cyanosis

blue skin color (low oxygenation of hemoglobin)

Pallor

balancing or pale color (anemia, low blood pressure, fear, anger)

Erythema

redness (fever, hypertension, inflammation, allergy)

Jaundice

yellow cast (liver disorders)

Bruises

referred to as ecchymoses or hematomas, a result of clotted blood beneath skin

Necklace bruises

hyperpigmented dark areas in axillae may be a sign of insulin resistance and elevated blood glucose levels

Hair

consists of dead keratinized cells, functions include warn of insects on skin, hair on head guards against physical trauma, protect from heat loss, shield skin from sunlight; Also called as pili, produced by hair follicles, contains hard keratin (soft in skin), regions include shaft (above scalp, keratinization completed) and root (within scalp, keratinization not complete)

Three parts of hair shaft

Medulla, Cortex, Cuticle

Medulla

central core of large cells and air spaces

Cortex

several layers of flattened cells surrounding medulla

Cuticle

outer layer consisting of overlapping layers of single cells

Hair pigments

made by melanocytes (yellow, rust, brown, black); red hair has additional pheomelanin, gray/white hair results from decrease in melanin production

Hair bulb

expanded area at deep end of follicle

Hair follicle receptor (or root hair plexus)

sensory nerve endings that wrap around bulb

Wall of hair follicle is composed of

peripheral connective tissue / fibrous sheath (dermis), glassy membrane, and epithelial root sheath (epidermis)

Hair matrix

actively dividing area of bulb that produces hair cells, older ones get pushed upward

Arrector pili

small band of smooth muscle attached to follicle, responsible for goose bumps

Hair papilla

dermal tissue containing a knot of capillaries that supplies nutrients to growing hair

Vellus hair

pale fine hair of children and adult females

Terminal hair

coarse, long hair found on scalp and eyebrows, at puberty

Follicle cycle

between active and regressive phases, average 2.25mm growth per week, lose 90 scalp hairs daily

Hirsutism

results in excessive hairiness, most cases no clinical problem is found

Alopecia

hair thinning both sexes after age 40

Baldness

genetically determined and sex-influenced condition, male pattern baldness is follicular response to DHT (dihydrotestosterone)

Telogen effluvium

abrupt hair thinning, can be due to stress induced factors such as hormonal changes, surgery, severe emotional trauma, or crash dieting; or drugs, hypothyroidism, protein-deficient diets

Nails

scale-like modifications of epidermis that contain hard keratin, act as a protective cover for distal, dorsal surface of fingers and toes; consists of free edge, nail plate, and root; nail bed is epidermis underneath keratinized nail plate

Nail matrix

thickened portion of bed responsible for nail growth

Nail folds

skin folds that overlap border of nail

Eponychium

nail fold that projects onto surface of nail body (cuticle)

Hyponychium

area under free edge of plate that accumulates dirt

Lunule

thickened nail matrix, appears white while nails normally appear pink due to underlying capillaries

Nail appearance can help indicate diseases such as

respiratory or thyroid gland disorder (yellow-tinged), (spoon nail) iron deficiency / koilonchya, beau’s lines (horizontal lines indicate uncontrolled diabetes, heart attack, or cancer chemotherapy)

Sweat glands

also called sudoriferous glands, 3 million per person, contain myoepithelial cells, which contract upon nervous system stimulation to force sweat into ducts

The two main types of sweat glands

eccrine (merocrine), apocrine

Eccrine (Merocrine) Sweat glands

Most numerous, abundant on palms, soles, and forehead; ducts connect to pores, function in thermoregulation, secretion is sweat

Sweat

99% water, salts, vitamin C, antibodies, dermicidin (microbe-killing peptide), metabolic wastes, causes salt and water loss

Apocrine Sweat Glands

confined to axillary and anogenital areas, secrete viscous milky or yellowish sweat that contains fatty substances and proteins, leads to body odor via bacteria breaking down sweat; larger than eccrine sweat glands, functional at puberty

Modified apocrine glands

ceruminous glands (lining of external ear canal / ear wax), mammary glands (secrete milk)

Sebaceous (oil) glands

widely distributed, except for thick skin; mostly develop from hair follicles and secrete, inactive until puberty, secrete sebum (oily secretion, softens hair and skin)

Acne

an infectious inflammation of the sebaceous glands, resulting pimples (pustules or cysts), associated with Propionibacterium acne

Whiteheads

blocked sebaceous glands, secretion is oxidized -> blackhead

Seborrhea

overactive sebaceous glands in infants, “cradle cap”

Function of skin

protection, body temperature regulation, cutaneous sensations, metabolic functions, blood reservoir, excretion of wastes

Acid mantle

low pH of skin prevents bacterial multiplication

If heavy metals pass through skin and enter blood

kidneys can shut down, brain can be damaged, absorption of lead can result in anemia and neurological defects

Insensible perspiration

unnoticeable sweat

Sensible perspiration

noticeable sweat, designed to cool body

Cutaneous sensations

exteroreceptors respond to stimuli outside body, such as temperature and touch; free nerve endings sense painful stimuli

Blood reservoir

Skin can hold up to 5% of body’s total blood volume, skin vessels can be constricted to shunt blood to other organs such as an exercising muscle

Effects of Aging

Epidermal thinning, decreased number of dendritic cells, decreased vitamin D production, decreased melanocyte activity, decreased glandular activity, reduced blood supply, decreased function of hair follicles, reduction of elastic fibers, decreased hormone levels, slower repair rate

Three major types of skin cancer

Basal cell carcinoma, squamous cell carcinoma, melanoma

First-degree burn

Epidermal damage only, localized redness, swelling, and pain

Second-degree burn

blisters appear due to epidermal and upper dermal damage

Third degree burn

entire thickness of skin involved, skin color turns gray-white, cherry red, or blackened; skin grafting usually necessary

Macule

flat, “spot”

Patches

flat, larger macules

Pimple

small, raised

Plaques

large, raised

Nodules

“small knot”, mid-deep dermis

Vesicles

fluid-filled papules, small blisters

Bulla

large vesicles

Pustule

pus liquid leukocytes

Erosion

loss part or all of epidermis, weep and become crusted, usually do not heal

Ulcer

sore, heal with scarring