SKIN

General comments

1. Integument - another name for the skin and its derivatives; translates into coat

2. Surface area - 1.5 to 2 square meters

3. Structure - made up of two main layers, dermis and the epidermis

Epidermis

1. Epidermis- upper layer consisting of keratinized stratified squamous epithelium

2. Cells - four major cell types

-a. Keratinocytes - chief; connected, desmosomes; produce protein keratin

-b. Melanocytes - in deepest layers; melanin to keratinocytes; UV protection

-c. Langerhans’ cells – macrophages immune system

-d. Merkel cells - half hemisphere found at the boundary; associated sensory nerve

3. Epidermal layers - 4 (thin skin) or 5 (thick skin of palms, finger tips, and soles

-a. Stratum basale (germinativum) - diving keratinocytes; melanocytes; Merkel cells

-b. Stratum spinosum - several cell layers; desmosomes hold tight; histological

-c. Stratum granulosum - 5 cells thick; granules; keratin, glycolipid; disintegrate

-d. Stratum lucidium - clear layer in thick skin; few rows of dead clear keratinocytes

-e. Stratum corneum – horny, 20 - 30 cells; all cells dead, keratinized, waterproof;

Dermis

1. Dermis - strong underlying connective tissue layer; leathery hide of animals

2. Papillary layer - smooth thin layer; areolar; vascularized; 20% of thickness

-a. Dermal papillae - superior surface; bumps; palms, soles lie on dermal ridges

3. Reticular layer - dense irregular connective tissue

4. Blood vessels – papillary layer feed dermis; thermoregulation

5. Nerve receptors – include several

-a. Free nerve endings - pain receptors

-b. Meissner’s corpuscles - fine touch receptors mostly in papillary layer

-c. Pacinian corpuscles - deep pressure receptors in reticular layer

Hypodermis

1. Hypodermis - not really part; share some of its protective functions

2. Superficial fascia – also called this

3. Adipose tissue - stored fat for food, insulation, and shock absorption

4. Areolar connective tissue - universal packaging material

Skin color

1. Melanin - only pigment produced skin; from yellow to reddish brown to black

-a. Melanocytes - produce melanin and export it to keratinocytes in stratum basale

-b. UV radiation - stimulates production of melanin; protect epidermal cells DNA

-c. Racial differences amount and kind of melanin produced

2. Carotene – yellow, orange, carrots; stratum corneum, adipose of hypodermis

3. Hemoglobin - melanin poor, transparent; pink color, blood in dermal capillaries

4. Variations - may be the sign of emotions or pathology

-a. Cyanosis – blue, result poorly oxygenated hemoglobin; heart attack

-b. Erythema (redness) - embarrassment, fever, hypertension, allergy, inflammation

-c. Pallor (blanching) - pale skin due to emotional stress, low blood pressure, anemia

-d. Jaundice – yellowing; accumulation of bile pigments indicating liver disease

APPENDAGES OF THE SKIN

General comments

1. Epidermal derivatives - originate in the epidermis and grow down into the dermis

Sweat (sudoriferous) glands

1. Number - about 2.5 million over body except nipples, parts of external genitalia

2. Eccrine sweat glands - most numerous

-a. Distribution - abundant on palms, soles, and forehead

-b. Exocytosis – means by which secretory cells release sweat

-c. Sweat - 99% water, some salt, antibodies, metabolic waste, and lactic acid

-d. Thermoregulation – function of eccrine sweat glands

3. Apocrine sweat glands - larger and empty into hair follicles

-a. Location - axillary (arm pit) and anogenital region

-b. Sweat – same as eccrine, also fatty materials and proteins

-c. Odor - due to the action of bacteria cause a musty odor

-d. Function - may be analogous to scent glands; enlarge under androgens

4. Ceruminous glands - modified apocrine glands which produce

-a. Cerumen - (ear wax); deter insects and foreign material

5. Mammary gland - modified sweat gland which produces milk

Sebaceous (oil) gland

1. Hair follicle - often empties into; sometimes into pore

2. Distribution - all over body except soles and palms

3. Sebum - oily secretion

4. Holocrine gland - secretory cells rupture; sebum contains oil and cell debris

5. Functions - softens hair and skin; prevents water loss; bactericidal mostly

Hairs and hair follicles

1. General – features

-a. Function – protection, filtration (nose hairs), sensory

-b. Pili (hair) – another name; flexible strands produced by hair follicle

-c. hard keratin - more durable than soft; individual cells do not flake off

2. Regions of the hair

-a. Shaft - projects from the skin

-b. Root - embedded in skin

3. Layers

-a. Medulla - central portion consist of large cells partially separated by air spaces

-b. Cortex - surrounds the medulla; several layers of flattened cells

-c. Cuticle - outer layer consisting of a single layer of overlapping cells, like shingles

4. Pigment - melanocytes in the hair follicle; the transferred to cortical cells

5. Hair follicle –epidermal surface into dermis; scalp into hypodermis

-a. Connective tissue root sheath - outer wall of hair follicle derived from dermis

-b. Epithelial root sheath - from epidermis; two layers; to single layer at hair bulb

-c. Hair bulb - deep expanded end of the hair

-d. Connective tissue papilla - dermal tissue; capillaries, nutrients, growth

-e. Hair matrix - actively dividing; new cells push up older cells; keratinized and die

-f. Root hair plexus - knot of sensory nerve endings; around hair bulb; stimulates

-g. Arrector pili - bundle of smooth muscle cells; pull hair straight; goose bumps

-h. Distribution - all over except lips, nipples, parts of genitalia, soles, and palms

6. Types – include

-a. Vellus hair - pale fine hair found on body hair of women and children

-b. Terminal hair - coarser hair of scalp, eyebrows; axillary, pubic; males

7. Growth cycle - resting phase; follicle matrix inactive; growth phase, old out, shed

Nails

1. Nails - scale like modification, epidermis; clear protective; hooves and claws

2. Function - good tools

3. Free edge - most distal unattached portion

4. Nail body - visible attached portion

5. Root - proximal portion embedded in skin

6. Nail bed - deeper epidermis beneath nail; nail corresponds, superficial epidermis

7. Nail matrix - thick proximal part of the nail bed; nail growth; cells keretinized

8. Lunula - crescent region at proximal end; caused by thickened nail matrix

9. Lateral nail folds - lateral skin folds which overlap the nail

10. Eponychium (cuticle) - proximal nail fold

FUNCTIONS

Protection

1. Chemical barriers – include

-a. Melanin - shields skin cells from UV damage to DNA

-b. Sebum - contains bactericidal chemicals

-c. Acid mantle - low pH of skin secretions retards the multiplication of bacteria

2. Physical (mechanical) barriers - prevent entry of water, soluble chemicals

3. Biological barrier - Langerhans’ cells, epidermis; dermal macrophages, dermis

Body temperature regulation

1. Sweating - cools the body by evaporation

2. Blood flow - dilating blood vessels, to cool off; constricting them, when cold heat

Cutaneous sensation

1. Receptors - Meissner’s, Pacinian corpuscles, hair plexuses, bare nerve endings

Metabolic functions

1. Vitamin D - sunlight on epidermal cells; chemical modification, precursor

2. Other functions - inactivate carcinogens; convert some drugs to active forms

Blood reservoir

1. Quantity - about 5% of blood found in dermal blood vessels

2. Rerouting - other organs need more blood, dermal blood vessels constricted

Excretion

1. Nitrogen containing waste - such as ammonia, urea, and uric acid are excretion

2. Salt loss - along with water

TISSUE REPAIR

Steps in tissue repair

1. Inflammation - blood vessels permeable to WBCs, fluid, and clotting proteins

-a. Clot - clotting proteins; holds edges of wound together; exposed, scab

2. Organization - restores blood supply

-a. Granulation tissue - replaces blood clot

-b. Capillaries - nub like buds of gives it a granular appearance

-c. Macrophages - phagocytic cells which eat up the clot

-d. Fibroblast – produce collagen fibers which bridge the gap

3. Permanent repair – regeneration and fibrosis

-a. Regeneration - replacement with the same kind of tissue

-b. Fibrosis - replacement of destroyed with fibrous connective tissue (scar)

Factors effecting tissue repair

1. Tissue type - ability to regenerate varies

-a. Very good – epithelium

-b. Good - bone and loose connective tissue

-c. Limited - smooth muscle and dense regular

-d. Poor - skeletal muscle and cartilage

-e. Never (almost) - cardiac and CNS tissue never regenerate

2. Type of injury - no kidding

3. Blood supply - greater the supply the greater ability to heal

4. Overall health - nutrition and age; the older the longer healing

DISORDERS

General comments

1. Indicator - homeostatic imbalances in other organ systems

2. Infections - bacteria (acne), viruses (warts), and fungi (dermatophytes)

Hair thinning and baldness

1. Alopecia - in the 40s hair follicles atrophy; replaced less quickly then it is shed

2. Male pattern baldness - sex linked gene; short follicular growth cycle

3. Other factors - high fever, emotional trauma, drugs such as chemotherapy

Burns

1. Effects – include

-a. Body fluid loss - the most immediate threat to life; circulatory shock

-b. Metabolic imbalances - loss of proteins, needs of tissue repair;

-c. Infection - the leading cause of death in burn patients

2. Depth of burns – for classification

-a. First degree burn - only the epidermis is damaged; sunburn

-b. Second degree burn - involves the epidermis and the upper dermis; blisters

-c. Third degree burns - full thickness burns; entire thickness; skin grafting

3. Rule of nine - 11 body regions with each making up 9% of the body area D.

Skin cancer

1. Basal cell carcinoma - most frequent; exposure to sun

-a. Stratum basale – cells proliferate to invade dermis and hypodermis

-b. Appearance - dome shaped nodule with central ulcer

-c. Treatment – surgery, does not readily metastasize

2. Squamous cell carcinoma – second most common

-a. Stratum spinosa – from cells in this layer

-b. Appearance - scaly red papule; will metastasize

-c. Treatment - surgery, radiation therapy

3. Malignant melanoma - most dangerous killing 50%

-a. Melanocyte cancer - proliferation of melanocyte; anywhere; 1/3 from moles

-b. Appearance - pigmented lesion, which spreads readily

-c. Treatment - usually surgery and immunotherapy

4. ABCD rule - asymmetry; border irregularity; color (several), diameter (< 6 mm)