Chapter 5 - The Integumentary System

Epidermis

• superficial region

• consists of avascular epithelial tissue

Dermis

• underlies epidermis

• mostly fibrous connective tissue, vascular

Hypodermis (superficial fascia)

• subcutaneous layer of deep skin

  • not part of skin

• mostly adipose tissue (shock and insulation)

• anchors skin to underlying structure (mostly muscles)

Keratinocytes

• major cells of epidermis

• produce fibrous keratin

• tightly connected by desmosomes

Melanocytes

• located in deepest epidermis

• produces melanin

• transferred to keratinocytes (more melanin than melanocytes)

Dendritic (Langerhans) cells

• star-shaped macrophages that patrol deep epidermis

• key activators of immune system

Tactile (Merkel) cells

• sensory receptors that sense light touch

• abundant in highly sensitive skin areas (fingertips)

• interacts with nerve endings

Keratinization

the process in which the outermost cells of the epidermis are replaced by dead cells containing keratin

Melanin

• pigment made by the skin

• amino acid tyrosine

• reddish yellow to brownish black

Carotene

• yellow to orange pigment

• can be converted to vitamin A for vision and epidermal health

Hemoglobin

• pinkish hue of fair skin due to lower levels of melanin

• more transparent skin, hemoglobin shows through

Stratum basale

• deepest layer

• single row of stem cells

  • one daughter cell moves up

  • other cell remains as a stem cell

• melanocytes and tactile cells

Stratum spinosum

• several cells thick

• “spikey”

  • cells shrink and spikes are due to the desmosomes

• dendritic cells and melanosomes from melanocyte

Stratum granulosum

• cells flatten

• nuclei and organelles being to disintegrate

• contains keratohyaline granules and lamellar granules

Keratohyaline granules

plays role in keratinization

Lamellar granules

plays role in formation of hydrophobic layer (water resistant barrier)

Stratum lucidum

• only in thick skin

• thin, translucent band of 2/3 rows of dead keratinocytes

Stratum corneum

• 20-30 rows of flat dead keratinized cells

• protects deeper cells

• prevents water loss

• protects from abrasion and penetration

• chemical, biological, and physical barrier

Papillary layer of dermis

• superficial

• areolar connective tissue

• dermal papillae (fingerlike progections up into epidermis)

Tactile/Meissner’s corpuscles

• light touch

• associated with dermis of skin

Reticular layer of dermis

• dense irregular connective tissue

• cutaneous plexus: network of blood vessels between reticular layer and hypodermis

Cleavage (tension) lines

• caused by fibers orienting themselves in same directions more than others

• typically externally invisible

Striae

• extreme stretching of skin

• dermal tears

Blisters

• acute, short-term trauma to skin

• fluid-filled pockets that separate epidermal and dermal layers

Cyanosis

• blue skin color

• low oxygenation of hemoglobin

Pallor

• pale skin

• reduction of blood flow to skin

• amenia, low blood pressure, fear, anger

Erythema

• redness

• dilatation of capillaries

• fever, hypertension, inflammation, allergy

Jaundice

• yellow cast

• build of bilirubin in blood, formed by breakdown of hemoglobin

• liver disorders

Ecchymoses/hematomas

• bruises, black and blue marks

• result of clotted blood beneath skin

Hairs (pili)

flexible strands of dead keratinized cells

• produced by hair follicles

• contains hard keratin

  • tougher and more durable

  • does not flake off

Shaft of hair

area that extends above scalp, keratinization is complete

Root of hair

area within scalp, where keratinization is still going on

Medulla

central core of large cells and air spaces

Cortex

layers of flattened cells

• surrounds medulla

• hair strength and flexibility

• melanin pigment and moisture

Cuticle (hair)

outer layer consisting of overlapping layers of single cells

Peripheral connective tissue sheath

• derived from dermis

• external layer of follicle wall

Epithelial root sheath

• epidermis

• external root sheath - continuation of epidermis

Hair bulb

expanded area at deep end of follicle

• location of hair growth

Hair matrix

• actively dividing cells area of bulb that produces hair cells

Hair papilla

• contains capillaries - supplies nutrients to grow hair

Hair follicle receptor (root hair plexus)

sensory nerve endings that wrap around bulb

Arrector pili

small band of smooth muscle attached to follicle

• goosebumps

Alopecia

hair thinning

Nail matrix

responsible for nail growth

Defensin

secretes antimicrobics

Acid mantle

low pH of skin retards bacterial multiplication

Vasoconstriction (dermis)

when temperature drops

• narrowing blood vessels

• increased blood flow near dermis of skin

Vasodilation

when temperature increases

• stimulation of eccrine sweat glands

• helps cool off

• increased blood flow near epidermis of skin (heat loss)

Basal cell carcinoma

• stratum basale cells proliferate and slowly invade dermis and hypodermis

• least malignant and most common

Squamous cell carcinoma

• involves keratinocytes of stratum spinosum

• second most common

• can metastasize

Melanoma

• cancer of melanocytes

• highly metastatic

• resistant to chemotherapy

First-degree

epidermal damage only

• localized redness, edema (swelling), and pain

• partial-thickness burns (only epidermis)

Second-degree

epidermal and upper dermal damage

• blisters appear

• partial-thickness burns (epidermis and upper dermis involved)

Third-degree

entire thickness of skin (full-thickness)

• skin turns gray-white

• not painful - nerve endings destroyed

• skin grafting

myoepithelial cells

contract upon nervous system stimulation to force sweat into ducts