The Integumentary System

The skin, hair, nails and cutaneous glands (sweat glands and others).

• the skin
• body's largest and heaviest organ
• consists of 2 layers; epidermis and dermis
• hypothermis not part of skin but studied in conjunction with it.

branch of medicine for the treatment of the skin

• covers palms, soles, and corresponding surfaces of the fingers and toes
• epidermis classifies it on thick or thin
• has sweat glands but no hair follicles or sebaceous (oil) glands

• Found in epidermis of thick skin and thin.
• layer of dead skin cells
• in thick skin resists pressure and friction that palms and soles are subjected to.

• thin stratum corneaum
• has hair, sebaceous glands, and sweat glands.

• Resistance to trauma and infection
• Water retention
• Vitamin D synthesis
• Sensation
• Thermoregulation (through thermoreceptors)
• Nonverbal Communication

• a keratinized stratified squamous epithelium, meaning;
• its surface consists of dead cells packed with keratin
• it lacks blood vessels and depends on the diffustion of nutruients from the underlying connective tissue
• has sparse nerve endings for touch and pain, but most sensations of the skin are due to nerve endings in the dermis

• undifferentiated cells that divide and produce keratinocytes
• found only in the deepest layer of the epidermis called the stratum basale

• great majority of epidermal cells
• named for role in synthesiing keratin

• Occur only in the stratum basale amid teh stem cells and deepest keratinocytes
• synthesize the brown to black pigment melanin

• relatively few in number
• receptors for touch
• found in basal layer of the epidermis
• tactile cell and its nerve fiber are called a tactile (Merkel) disc

• are found in two layers of the epidermis called the stratum spinosum and strum granulosum
• macrophages that originate in the bone marrow and migrate to the epidermis and epithelia of the oral cavity, esophagus and vagina
• epidermis has as many as 800 per sq mm
• guard against toxins microbes and other pathogens that penetrate into the skin
• when they detect invaders, they carry fragments of the foreign matter ot the lymph nodes and alert the immune system so the body can defend itself

• 1. stratum basale- consists mainly of a single layer of cuboidal to low columnar stem cells and keratinocytes resting on the basement membrane
• 2.stratum spinosum- consists of several layers of keratinocytes; in most places is thickest stratum except on palms and soles, deepest cells are capable of mitosis, have spiny appearance
• 3. stratum granulosum- consists of 3-5 layers of flat keratinocytes and some dendritic cells
• 4. stratum lucidum- thin translucent zone seen only in theick skin, the cells have no nuclei or other organelles and therefore do not stain well, has a pale featureless appearance with indistinct cell boundaries
• 5. stratum conrneum- consists of up to 30 layers of dead scaly, keratinized cells that form a durable surface layer, especially resistant to abrasion, penetration and water loss.

• 1.Produced deep in the epidermis by mitosis fo stem cells in stratum basale
• 2.New ones form and push older ones up, 30-40 days to reach surface and flake off, injured epidermis regenerates more rapidly than any other tissue in body
• 2. in the stratum granulosum ther keratinocyte nuclei and o/ organelles die, keratohyalin granules release a proten that binds keratin filaments into coarse, tough bundles, membrane-coating vesicles release lipid mixture that spreads out over the cell surface and waterproofs it.
• 3. epidermal water barrier forms between stratum granulosum ande stratum spinosum
• 4. keratinocytes die and exfoliate (flake off)

• connective tissue layer under dermis
• composed mainly of collagen, but also contains elastic and reticular fibers fibroblasts and other cells typical of fibrous connective tissue
• well supplied with blood vessels, cutaneous glands, and nerve endings
• hair follicles and nail roots are embedded in dermis
• contains smooth muscles in association with hair follicles
• dermal and epidermal boundaries interlock like corrugated cardboard- resists slippage of epidermis across dermis

formed by keratinocytes as they are shoved upward by the dividing cells below, they flatten and produce more keratin filaments and lipid-filled

• forms between the stratum spinosum and the stratum granulosum
• consists of lipids secreted by keratinocytes, tight junctions between the keratinocytes and a thicck layer of insoluble protein on th einner surfaces of their plasma membranes
• crucial to retaining water in body and preventing dehydration

tiny specks of the epidermal surface that have flaked off

upward waves, fingerlike extensions of the dermis

downward waves exteding from dermis

• thin zone of areolar tissue in an dnear the dermal papillaie
• especially rich in small blood vessels
• loosely organized tissue of papillary layer allows for mobility of leukocytes and other defenses against organisms intro'd thru breaks in epidermis

• deeper and thicker than papillary layer
• consists of dense irregular connective tissue
• collagen forms thicker bundles with less room for ground substance
• often small clusters of adipocytes
• stratch marks occur here

• beneath the skin layer
• generally has more areolar and adipose tissue
• pads body and binds the skin to the underlying tissues
• drugs are introduced here by hypodermic injection because the subcutaneous tissue is highly vascular and absorbs quickly

• hypodermis composed predominantly of adipose tissue
• serves as energy reservoir and thermal insulation
• not uniformly distributed
• virtually absent from scalp
• varies with age, women have 8% more than men

• most significant factor in skin color
• produced by melanocytes but accumulates in keratinocytes of stratum basale and stratum spinosum
• has 2 forms; _{eumelanin- brownish black,} or _{pheomelanin- reddish yellow sulfur containing pigment}
• people have same number of melanocytes, but dark skinned people produce more melanin

• depends on amount of melanin, exposure to UV rays (stimulate melanin sythesis)
• hemoglobin
• carotin

• the red pigment of blood
• imparts reddish to pinkish hues to the skin
• color is lightened by collagen
• seen most in areas like lips where blood capillaries come closer to surface

• yellow pigment acquired from egg yolks, and yellow and oragne vegetables
• concentrates to various degrees in stratum corneum and subcutaneious fat, depending on diet
• most conspicuous in skin of the heel and in calluses of the feet because this is where the stratum corneum is thickets

• blueness of skin resulting from a deficiency of oxygen in the circulating blood
• oxygen deficiency turns hemoglobin a reddish violet color
• occurs from conditions that prevent blood from picking u a normal load of oxygen, cold weather, cardiac arrest and when blood flows so slowly thru the skin that the tissues consume most of its oxygen faster than freshly oxygenated blood arrives

• abnormal redness of the skin
• happens in exercise, hot weather, sunburns, anger, and embarrassment
• caused by increased blood flow in dilated cutaneous blood vessels or by dermal pooling of red blood cells that have escaped from abnormally permeable capillaries

• pale or ashen color that occurs when there is little blood flow through skin th@ white color of the dermal collagen shows through
• can result from emotional stress, low blood pressure, circulatory shock, cold temperatures or sever anemia

• genetic lack of melanin that usually results in milky white hair and skin, and blue-gray eyes,
• synthesized from the amino acid tyrosine by the enzyme tyrosinase
• people with it have inherited a recessive nonfunctional tyrosinase gene from both parents

• yellowing of skin and whites of eyes
• resulting from high levels of bilirubin (hemoglobin breakdown product in blood)
• can be a sign of failing liver function

• bruise
• mass of clotted blood showing through skin
• usually due to accidental trauma
• but may indicate hemophilia, o/ metabolic or nutritional disorders, or physical abouse

markins on fingertips that leave distinctive oily fingerprints on surfaces we touch

• lines on flexor surfaces of the digits, palms, wrists, elbows and other places
• mark sites where skin folds during flexion of the joints
• skin is tightly bound to the deeper connective tissue along these lines

flat, melanized patches that vary with heredity and exposrue to the sun

• elevated patch of melanized skin often with hair
• changes in color, diameter, or contour may suggest malignancy

• birthmarks
• patches of discolored skiin caused by benign tumors of the blood capillaries
• capillary hemanigiomas (strawberry birthmarks) usually develop about a month after birth

• A hair, plural is pili
• sledner filament of keratinized cells that grows from an oblique tube in the skin called a hair follicle.

Fine, downy, unpigmented hair of the fetus

• fine, pale hair
• constitutes about two thirds of the hair of women, one tenth of hair of men and all hair of children except for the eybrows, eyelashes, and hair of the scalp

• longer, corser, and usually more heavily pigmented
• forms eyebrows and eylashes, covers scalp; and after puberty, it forms axillary and pubic hair, male facial hair, and some hair on trunk and limbs

• serves to retain body heat in most mammals, humans have too little of it
• divisible into the bulb, root, and shaft
• only living cells of hair are in and near the bulb

• a bud of vascular connective tissue around the bulb
• provides hair with sole source of nutrition

• hair's growth center
• immediately above papilla
• all cells higher up are dead

• core of loosely arranged cells and air spaces
• most prominent in thick hairs

• constitutes most of the bulk of a hair
• consists of several layers of elongated keratinized cells that appear cuboidal to flattened in cross sections

• composed of multiple layers of very thin, scaly surface cells that overlap each other like roof shingles
• when a hair is pulled out, this layer of follicle cells comes with it

• two principle layers of a follicle
• 1. an extension of the epidermis, lies immediately adjacent to the hair root, toward deep end of the follicle it widens to form a bulge (source of stem cells for follicle growth)
• 2. deriveds from the dermis, surrounds the epithelial sheath and is somewhat denser than the adjacent dermal connective tissue

entwine each follicle and respond to hair movements

• bundle of smooth muscle cells extending from dermal collagen fibers to the connective tissue root sheath of the follicle
• makes hair stand on end (goosebumps)
• in other mammals makes the animal appear larger and less vulnerable to a potential enemy

• has three stages; anagen, catagen, and telogen
• Club hairs can fall out during catagen, telogen or pushed out by new hair in next anagen phase
• we lose about 50-100 scalp hairs daily

• 90% if time scalp follicles are in anagen phase
• stem cells from the bulge in the follicle multiply and travel downward, push dermal papilla deeper into the skin and forming epithelial root sheath
• sheath cells transform into hair cells which synthesize keratin and then die as they are pushed upward away from papilla

• mitosis in the hair matrix ceases and sheath cells below the bulge die
• follicle shrinks and dermal papilla draws up toward bulge
• base of the hair keratinizes into a hard club (aka club hair) and loses its anchorage-are easily pulled out

• When papilla reaches the bulge, the hair goes into a resting period
• eventually anagen begins again and cycle repeats itself

• thinning of the hair, or baldness
• occurs to some degree in both sexes and may be worsened by disease, poor nutrition, feber, emotional stress, radiation or chemotherapy
• mostly simply matter of aging

• condition in which hair is lost from select regions of the scalp rather than thinning uniformly across the entire scalp
• results from combo of genes and hormonal influences

• clear, hard derivatives of the stratum corneum
• composed of very thin, dead, scaly cells, densely packed together and filled with parallel fibers of hard keratin

• hard part of nail
• includes _{free edge (overhanging tip), nail body (visible attached part of the nail), and nail root (extends proximally under the overlying skin)}

surrounds nail and rises a bit above nail

• seperates the nail fold from the margin of the nail plate
• groove and space under free edge accumulate dirt and bacteria

skin underlying the nail plate

epidermis of the nail bed

• thickened part of stratum basale thickens and creates a growth zone for nail matrix
• mitosis here accounts for the growth of the nail (bout 1mm per week- slightly slower in toe nails)

• opaque white crescent that appears at the proximal end of a nail
• happens because matrix hides underlying blood vessels

• sweat glands that occur in the groin, anal region, axilla, areola and beard area
• absent from axillary region of Koreans and sparse in Japanese
• ducts lead into nearby hair follicles rather than directly to the skin surface
• produce secretion by excocytosis
• larger lumen than that of a merocrine gland
• sweat is thicker and more milky because it hads more fatty acids in it
• scent glands that respond especially to stress and sexual stimulation
• not activated until puberty
• enlarge and shrink in women during menstrual cycles (possibly secrete pheromones?)
• bromhidrosis- stinky body odor

• widely distributed over entire body, especially abundant on palms, soles, and forehead
• found in dermis or hypodermis

• contract in response to sympathetic nervous system and squeeze perspiration up the duct
• exist and function similarly in apocrine sweat glands as well

• sweat glands
• two kinds; apocrine and merocrine

• found only in auditory canal
• secretion combines with sebum and dead epidermal cells to form earwax or cerumen
• keeps eardrum pliable, waterproofs canal, kills bacteria, and cots guard hairs of the ear, making them sticky and more effective in blocking foreign particles from entering the canal

• milk-producing glands that develop within the breasts (mammae) under conditions of pregnancy and lactation
• only women have them and usually in only small amounts
• are modified apocrine sweat glands

• most common tympe of skin cancer
• least deadly because it seldom metastasizes
• if neglected can cause sever facial disfigurement
• arises from cells of stratum basale and eventually invades the dermis
• lesion appears as a small shiny bump, as it enlarges often develops a central depresstion and a bearded "pearly" edge

• arises from keratinocytes of the stratum spinosum
• lesion has a raised, reddened, scaly appearance and later forms a concave ulcer with raised edges
• goood chance of recovery with early dection and surgical removal
• unnoticed tends to metastasize to the lymph nodes and can be lethal

• skin cancer arises from melanocytes, often in preezisting mole
• most deadly
• if it metastasizes (does so quickly) is unresponsive to chemo and usually fatal

• a leading cause of accidental death
• deaths result primarily from fluid loss, infection and toxic effects of eschar (burned, dead tissue)

• involve only epidermis and heal in a few days, seldom leaving scars
• mostly sunburns
• aka partial-thickness burns

• involve epidermis and part of the dermis but leave at least some of dermis intact
• aka partial-thickness burn
• may take 2 weeks to several months to heal and may leave scars
• severe sunburns and many scalds

• aka full-thickness burns
• epidermis and dermis completely destroyed- sometimes even deeper tissue damaged
• skin can only regenerate from edges of wound
• often require skin grafts
• if left byself to heal contracture (abnormal connective tissue fibrosis) and severe disfigurement may result