[APK2100C] Chapter 5

Skin (Integument)

Largest organ of the body

Accessory Organs

Hair, nails, oil/sweat glands, etc..

3 Regions of the Skin

(1) Epidermis

(2) Dermis

(3) Hypodermis

5 Functions of the Skin

(1) Thermoregulation

(2) Protection

(3) Sensory Reception

(4) Excretion

(5) Vitamin D Production

Epidermis

- Most superficial layer of the skin

- Keratinized stratified squamous epithelium

- Avascular

4 Principle Cells of the Epidermis

(1) Keratinocytes (> 90%)

(2) Melanocytes

(3) Langerhans cells (dendritic cells)

(4) Merkel cells (tactile epithelial cells)

Thin Skin

- Areas of skin where little friction develops

- Most of the body

- 4 epidermal layers

Thick Skin

- Area of skin with common friction

- Palms, feet, fingertips

- 5 epidermal layers

Layers of Thin Epidermis (Deep to Superficial)

(1) Stratum Basale

(2) Stratum Spinosum

(3) Stratum Granulosum

(4) Stratum Corneum

Layers of Thick Epidermis (Deep to Superficial)

(1) Stratum Basale

(2) Stratum Spinosum

(3) Stratum Granulosum

(4) Stratum Lucidum

(5) Stratum Corneum

Stratum Basale

- Deepest layer

- One row of active mitotic activity (new cells being pushed up to the superficial layer)

- Site of melanocytes (production of melanin)

Stratum Spinosum

- Several layers of keratinocytes unified by desmosomes (anchoring junction)

- Contain thick bundles of intermediate filaments made of pre-keratin (tonofilaments)

Stratum Granulosum

- 1-5 layers of flattened cells

- Organelles start to deteriorate

- Cytoplasm full of lamellar granules (releasing lipids), providing a waterproof layer

Stratum Lucidum

- Specific to the thick skin ONLY

- Slightly translucent layer

Stratum Corneum

- Most superficial layer

- 20-30 layers of dead cells

- Flat sacs filled with keratin

- Glycolipids in extracellular space

Melanin

A pigment that gives the skin its color

Carotene

Yellow-orange pigment

Hemoglobin Pigment

Pinkish hue of fair skin is due to lower levels of melanin

Pheomelanin

Produces yellow to red pigments in the hair

Eumelanin

Produces brown to black pigments in the hair

Difference in Skin Color

- Due to the amount of melanin produced and transferred to keratinocytes

- Number of melanocytes is the same for everyone

Light Skin

- Melanin clumped near nucleus

- Breaks down quickly

Dark Skin

- Melanin spread throughout keratinocytes

- Breaks down slowly

Melanocytes

- Cells that produce a protein called melanin

- Places itself between the Sun and a cell's nucleus

- Melanin acts as a shield to protect skin's nucleus from UV lights

Albinism

- Genetic disorder where melanocytes cannot produce any melanin

- Due to inability to produce tyrosinase enzyme

- Results in translucent hair, skin, and pink-reddish eyes

Dermis

- Middle layer of skin

- Made of mostly CT (very tough)

- Vascular and also contains lymphatic cells/nerves

Layers of the Dermis (Superficial to Deep)

(1) Papillary Layer

(2) Reticular Layer

Papillary Layer

- Outer layer of the dermis, directly beneath the epidermis

- Areolar loose CT proper

Reticular Layer

- Deeper layer of the dermis that supplies the skin with oxygen and nutrients

- Dense irregular CT proper

- Dermal ridges form FINGERPRINTS

Dermal Papillae

- Small projections of papillary dermis (nipple-like) into overlying epithelium

- Enhances surface area for nutrient/gas exchange

- Strengthens dermal-epidermal junction

- Does NOT make fingerprints

Cleavage Lines

- Separation or less dense regions of collagen bundles in the reticular dermis

- Creates invisible cleavage lines in skin

- Incisions ALONG lines gape less/heal faster than those cut ACROSS lines

Hypodermis

- Subcutaneous (sub-Q) layer of CT

- Located below the dermis

- NOT part of the skin

- Adipose loose CT proper

- Protects underlying structures, insulates, stores energy

- Large blood vessels, lymphatic vessels, and nerves extending into dermis

Appendages of the Skin

- Derived from the epidermis, but located in the dermis

- Hair, nails, sweat glands, and oil glands

Nails

- Scale-like modification of the epidermis containing dead keratinocytes full of HARD keratin

- Evolution "tool" of function

Hair

- Flexible columns of dead keratinocytes full of HARD keratin

Shaft (Hair)

Part of hair projecting from the skin

Root (Hair)

Hair that is within the skin; in contrast with the shaft

Medulla (Hair)

Inner most layer of hair

Cortex (Hair)

Middle layer of the hair

Cuticle (Hair)

Outermost layer consisting of a single thin layer of cells

Hair Follicle

Small tubular cavity containing the root of a hair

External Root Sheath (Hair Follicle)

- Superficial to the internal root sheath and resembles the layer of the epidermis

- Spans the entire length of the follicle

- Stratum Basale turns into this

Internal Root Sheath (Hair Follicle)

- Innermost layer of keratinocytes in the hair follicle that surround the hair root up to the hair shaft

- Stratum Corneum turns into this

Hair Bulb

- Rounded, club-shaped part of hair located at the end of the hair root

CT Papilla (Hair Bulb)

- Origin for blood vessels

- Mitotic for hair growth

Arrector Pili Muscle

- Small, involuntary muscle in the base of the hair follicle

- Causes hair to stand on end (goosebumps)

3 Types of Hair

(1) Straight

(2) Wavy

(3) Curly

Sebaceous Glands

- Located everywhere except plantar/palmar regions

- Duct dumps into hair follicle

- Secretes sebum

Sebum

- Oily substance secreted by sebaceous glands

- Keeps hair/skin soft

- Protects against brittle hair/skin

- Protects epidermis from cracking

- Collects dirt

Sweat Glands (Sudoriferous)

- Glands that produce a saline solution called sweat

- Two types: (1) Eccrine and (2) Apocrine

Eccrine Sweat Glands

- Palms, soles, forehead

- Produce true sweat (watery)

- Thermoregulation

- Duct opens directly onto skin surface

Apocrine Sweat Glands

- Axillary, anal, genital areas only

- Produce milky sweat

- Body odor and NO thermoregulation

- Duct opens to hair follicle

- Acts like sebaceous glands and releases sebum