Chapter 5 Lecture

Cutaneous membrane (skin) =

Epidermis + Dermis

Subcutaneous layer (Hypodermis / Superficial Fascia)

Superficial fascia made of areolar/adipose tissue; not part of the cutaneous membrane (skin), anchors skin to underlying structures, cushioning, thermal insulator, energy storage

Integumentary system

Body’s outer protective boundary, comprised of the cutaneous membrane, accessory structures (hair, nails, glands..), subscanteous layer/ hypodermis (not technically part of skin - superficial fascia)

Primary functions of integumentary system

Protection, excretion, thermoregulation, vitamin D3 synthesis, lipid energy storage, general sensation

Epidermal layers (strata)

The tissue = keratinized stratified squamous epithelium

*the stratum lucidum is found in thick skin only

Thin skin (Epidermis)

Has 4 strata; covers most of the body, s. corneum is relatively thin, subtle epidermal ridges

Thick skin (Epidermis)

Has 5 strata (includes stratum lucidum); s. corneum significantly thicker, found only on palms and soles; lacks hair and sebaceous glands, epidermal ridges are pronounced

Epidermal Strata Order (Deep to Superficial)

Stratum basale/germinativum → Stratum spinosum → Stratum granulosum → Stratum lucidum (thick skin only) → Stratum corneum

Keratinocytes

Make up vast majority of epidermal cells, produce keratin and keratohyalin, have desmosomes that hold cells together, basal cells have hemidesmosomes that anchor cells to basement membrane

Melanocytes

Found near s. basale, convert into tyrosine (amino acid) into melanin (pigment)

Carotene

Organe-yellow pigment accumulating in the s. corneum and hypodermis

Heloglobin

Oxygen-bound red pigment in dermal blood vessels

Cyanosis

Bluish skin from sustained low oxygen levels

Pallor

Pale skin from temporarily reduced blood flow

Jaundice

Yellowing caused by bule pigment accumulation

Albinism

Genetic absence of tyrosinase

Vitiligo

Loss or death of melanocytes

Hormonal influence

Abnormal levels of Melanocyte-Stimulating Hormone (MSH) or Adrenocorticotropic Hormone (ACTH) cause hyperpigmentation

Sebaceous (oil) glands

Connected to hair follicles, they are a holocrine secretion of lipid based sebum into hair follicles

“Apocrine” sweat glands

Method of secretion is actually merocrine (yet name persists), produces odorous secretion that bacteria feeds, begins secreting at puberty, located at axillae (armpits), myoepithelial cells contract to discharge secretion into hair follicles

Eccrine (merocrine) sweat glands

Merocrine secretion of watery sweat (sensible perspiation) directly onto skin for thermoregulation, protects by flushing chemicals and bacteria from skins surface

Specialized glands

Mammary glands (modified apocrine glands for milk), Ceruminous glands (modified eccrine glands producing earwax/cerumen)

Nails

Functions: protects ends of the digits, facilitate manipulation with the fingers

Response to skin injury

Skin repair is possible because skin contains many stem cells, s. basale (germinativum) cells in epidermis and mesenchyme cells in the dermis

Skin injury phases

1. Inflammation phase

2. Migration phase

3. Proliferation phase

4. Scarring phase

Hairs

Nonliving keratin structures produced by hair follicles

Functions: Shield scalp of UV radiation, cushion impacts to head, insulates skull, senses touch, blocks particle entry

Hair follicles

Tiny organs that are internal extensions of the epidermis

Lanugo hairs

Fine, unpigmented embryonic hair shed before birth

Vellus hairs

Translucent “peach fuzz” covering most of the body

Vellus hairs

Translucent “peach fuzz” covering most of the body

Club hairs

When follicle becomes inactive at end of growth cycle, vellus or terminal hairs are also called club hairs

Melanin

Primary pigment influencing skin color and hair color

Synthesis pathway

Melanocytes use the enzyme tyrosinase to convert the amino acid tyrosine into melanin. Melanin is packaged into melanosomes, transferred along processes, & engulfed by neighboring keratinocytes

UV Protection

Melanin concentrates around keratinocyte nuclei, absorbing UV radiation to protect basal cell DNA. UV exposure stimulates increased melanocyte activity

Melanocyte Density vs. Pigmentation Differences

• All human skin shades contain the same # of melanocytes per unit area

• Color variations depend on:

• Melanin type (ration of black/brown melanin to red/yellow melanin)

• Melanin amount (total quantity of pigment produced)

• Melanosome Dispersal & Lysosomal Destruction:

• Lighter skin: Melanosomes are dispersed only in the s. basale and s. spinosum before being destroyed by lysosomes

• Darker skin: Melanosomes are larger, more numerous, & remain intact into the s. granulosum

The dermis

Contains blood vessels, lymphatics, nerves etc.

Made up of 2 layers: Papillary and Reticular

Papillary layer

Superficial and thinner, made up or areolar tissue, contains dermal papillae

Reticular layer

Deeper and thicker, made up of dense irregular CT, fibers arranged in parallel bundles to form tension (cleavage) lines

Accessory structures of the skin

Originated embryonically from epidermis (epidermal derivatives), even if no longer located in epidermis

Includes hair, sebaceous glands, sweat glands, nails