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Skin (Integumentary System)
considered an organ or an organ system
body’s largest organ ‡organ of greatest surface area:15-20 sq ft. (1.5-2 m^2 )
General Functions:
1. protection mechanical chemical bacterial UV desiccation 2. temperature homeostasis >temp ‡ sweat glands, flushing <temp ‡ arrector pili, pale 3. excretion affects fluid & electrolyte balance sweat glands release: water, salts, ammonia oil glands release: lipids, acids 4. sensation touch (light touch, wind, etc) pressure heat cold pain 5. synthesis vitamin D precursor passes through capillaries in skin and light converts it to vitamin D 6. nonverbal communication eg. humans and other primates have much more expressive faces than other animals
Layers of Skin:
epidermis dermis hypoderms
Epidermis stratified squamous epithelium upper layers dead, filled with keratin (waxy protein) lower layers living cells replaced every 35-45 days
subdivided into 5 identifiable layers: a. stratum basale lowermost layer of epidermis single cell layer thick only cells that get adequate nutrition and oxygen by diffusion from tissues below actively dividing cells bordered below by basement membrane
b. stratum spinosum several layers thick less mitosis flattened, irregular, spinelike projections
[basale + spinosum = stratum germinativum ‡ growing layers]
c. stratum granulosum very thin; 2-3 cell layers thick as cells move up from s. basale they die & get flatter and thinner keratinization begins here
d. stratum lucidum thin translucent band only found in thick areas of epidermis: soles of feet palms of hand
e. stratum corneum thickest of all layers; 3/4th^ ‘s the thickness of epidermis 20-30 cell layers thick dead cells completely filled with keratin water resistant main protection against biological and chemical assault
takes keratinocytes 30-40 days from their formation in s basale until they flake off of the s corneum
cells of epidermis:
= hypodermis or superficial fascia
below skin mainly adipose tissue (ie subcutaneous fat) insulation infants and elderly have less of this than adults and are therefore more sensitive to cold
Skin Color
due to combination of three different pigments:
melanin yellow, orange, brown or black pigments racial shades due mainly to kinds and amount of melanin pigments mainly in stratum basale also, amount varies with exposure to sun=suntan carotene esp in stratum corneum and subcutaneous layers hemoglobin in blood of skin capillaries
Skin Color & Texture in Diagnosis cyanosis = bluish cast ‡poor oxygenation erythema = redness ‡ emotional, hypertension, inflammation pallor = paleness ‡ emotion, anemia, low blood pressure jaundice = yellowing ‡ liver disorder, >bile pigments in blood bronzing = Addison’s disease, adrenal cortex bruising (hematoma)= escaped blood has clotted hematomas ‡ deficiency in Vit C or hemophilia leathery skin = overexposure clumping of elastin fibers depressed immune system can alter DNA to cause skin cancer photosensitivity = to antibiotics & antihistamines
“Skin Markings”
skin is marked by many lines, creases and ridges
friction ridges: ‡ markings on fingertips characteristic of primates allow us to manipulate objects more easily
flexion lines: on flexor surfaces of digits, palms, wirsts, elbows etc
skin is tightly bound to deep fascia at these points
freckles: flat melanized patches vary with heredity or exposure to sun
moles: elevated patch of melanized skin, of the with hair mostly harmless, beauty marks
“Derivitives of skin”
during embryonic development 1000’s of small groups of epidermal cells from stratum basale push down into dermis to form hair follicles and glands
1. Hair covers entire body except palms, soles, lips, nipples, parts of external genitals
hormones account for the development of “hairy” regions: eg. head, axillary and pubic areas
humans are born with as many follicles as they will ever have
hairs are among the fastest growing tissues in the body
formation similar to epidermis
heavily keratinized
consists of: shaft : visible part root: follicle : sheath surrounding root papillae : vascularized, growing part of hair Arrector Pili muscles attached to follicle causes hair to stand on end (cold, fright) oil glands : ≥2/follicle hair receptor: entwines each follicle, responds to hair movements
hair color depends on kinds (yellow, rust, brown, and black) and the amount of melanin cortex of shaft contains
hair texture related to differences in cross-sectional shape eg. straight hair is round
Sweat Glands (sudoriferous)(eccrine glands) ~3 Million total on skin ~3000 sweat glands/inch^2 most numerous on palms, soles, forehead, armpits essentially a tiny coiled tube that opens to skin surface helps maintain temperature and fluid/electrolyte balance ‡ heat ‡ sweat ‡ evaporative cooling
Scent Glands (apocrine glands) modified sweat glands ‡ scent, pheromones much less common confined to axillary and genital area their ducts empty into hair follicles secretions contain fatty acids and proteins in addition to “sweat” respond especially to stress and sexual stimulation
Mammary Glands modified sweat glands produce milk
Ceruminous Glands modified sweat glands in external ear canal secrete waxy pigmented cerumin protection ‡ traps dust and particles
Skin Imbalances & Aging
the skin can develop >1000 different ailments
the most common skin disorders result from allergies or infections
less common are burns and skin cancers
A. Allergies
1. Contact Dermatitis allergic response eg. poison ivy, metals, etc **B. Infections
- viral** eg. cold sores herpes simplex especially around lips and oral mucosa 2. Fungal eg. athletes foot 3. Bacterial
eg. boils and carbuncles inflammation of hair follicle and sebaceous glands esp on dorsal side of neck eg. impetigo Streptococcus infection C. Genetic Diseases
1. Psoriasis chronic, noninfectious skin disease skin becomes dry and scaly, often with pustules many varieties cycle of skin cell production increases by 3-4x’s normal stratum corneum gets thick as dead cells accumulate seems to be a genetic component often triggered by trauma, infection , hormonal changes or stress 2. Hypertrichosis (human werewolves) patients show dense hair growth on faces and upper bodies due to malfunction of gene on x chromosome ‡ a gene silenced during evolution has been reactivated D. Burns too much sunlight or heat categorized by degree of penetration of skin layer 1 st^ degree burns skin is inflamed, red surface layer of skin is shed 2 nd^ degree burns deeper injury blisters form as fluid builds up beneath outer layers of epidermis 3 rd^ degree burns full thickness of skin is destroyed sometimes even subcutaneous tissues results in ulcerating wounds typically results in catastrophic loss of fluids: dehydration electrolyte imbalances also highly susceptible to infections slow recovery (from cells of hair follicles if they survive; otherwise must heal from margins of wound) may require: autografts cadaver skin pig skin prognosis may depend on extent of damage
to recurring infections
thermoregulation is less efficient due to loss of blood vessels and glands ‡ more vulnerable to hypothermia and heatstroke
photoaging = an acceleration of skin aging due to overexposure to sun (UV) accounts for 90% of the changes that people find medically troubling or cosmetically disagreeable
G. Autoimmune Disease eg. alopecia areata causes hair to fall out in small round patches ~2% of population (4.7M in US) have some form of it hair loss is usually short term and limited to a few patches in rare cases causes permanent loss of all body hair www.naaf.org
Clinical Terms:
Necrosis – cellular or tissue death, gangrene
Biopsy – tissue analysis
