Skin Study Guide:

Skin:

• Consists of three major regions
• Epidermis-outermost superficial region
• Dermis-Middle Region
• Subcutaneous-Deepest region

Epidermis:

• Composed of keratinized stratified squamous epithelium, consisting of four distinct cell types and four or five layers.
• Cell types include: keratinocytes, melanocytes, Merkel Cells, and Langerhans’ Cells
• Outer portion of the skin is exposed to the external environment and functions in protection

Cells of the Epidermis:

• Keratinocytes-makes skin tough, produces the fibrous protein keratin
• Melanocytes-produce the brown pigment melanin, natural sunblock
• Langerhans’ Cells- epidermal macrophages that help activate the immune system
• Merkel Cells-function as tough receptors in association with sensory nerve endings, senses deeper touch

Layers of the Epidermis:

• Stratum Basale
• Deepest epidermal layer firmly attached to the dermis
• Consists of a single row of the youngest keratinocytes
• Cells undergo rapid division, hence its alternative name, stratum germinativum
• Takes 20-25 days from when cell is produced to when it is flaked off
• Stratum Spinosum (Prickly Layer)
• Cells contain a weblike system of intermediate filaments attached to desmosomes.
• Melanin granules and Langerhans’ cells are abundant in this layer
• Stratum Granulosum (granular layer)
• Thin; threet o five cell layers in which drastic changes in keratinocyte appearance occurs.
• Keratohyaline and lamellated granules accumulate in the cells of this layer.
• Stratum Lucidium (Clear Layer)
• Thin, transparent band superficial to the stratum granulosum.
• Consists of a few rows of flat, dead keratinocytes.
• Present only in thick skin.
• Stratum Corneum (Horny Layer)
• Outermost layer of keratinized cells
• Accounts for three quarters of the epidermal thickness.
• Functions:
• Waterproofing
• Protection from abrasion and penetration
• Renders the body relatively insenstitive to biological, chemical and physical assaults.

Dermis

• Second major skin region containing strong, flexible connective tissue
• Cell types include fibroblasts, macrophages, and occasionally mast cells and white blood cell.
• Composed of two layers—Papillary and reticular

Layers of Dermis:

• Papillary layer
• Areolar connective tissue with collagen and elastic fibers
• Its superior surface contains peg-like projections called dermal papillae
• Dermal papillae contains capillary loops, Meissner’s corpuscles, and free nerve endings.
• Reticular Layer
• Accounts for approximately 80% of the thickness of the skin.
• Collagen fibers in this layer add strength and resiliency to the skin
• Elastin fibers provide stretch-recoil properties.

Subcutaneous (Hypodermis)

• Layer deep to skin
• Composed of adipose and areolar connective tissue
• Layer of insulation and cushion

Skin Color

• Three Pigments Contribute to skin color
• Melanin-yellow to reddish-brown to black pigment, responsible for dark skin colors
• Freckles and pigmented moles-result from local accumulations of melanin
• Carotene-yellow to orange pigment, most obvious in the palms and soles of feet
• Hemoglobin-reddish pigment responsible for the pinkish hue of the skin

Sweat Glands

• Different types prevent overheating of the body; secrete cerumen and milk.
• Eccrine sweat glands- found in palms, soles of feet and forehead, (most wide spread)
• Apocrine sweat glands- found in axillary and anogenital areas (armpits, odor, thicker, attacked by bacteria)
• Ceruminous glands-modified apocrine glands in external ear canal and secrete cerumen (wax)
• Mammary glands-specialized sweat glands that secrete milk

Sebaceous Glands

• Soften skin when stimulated by hormones
• Simple alveolar glands found all over the body
• Secrete an oily secretion called sebum

Hair

• Helps maintain warmth, alerts the body to presence of insects on the skin, and guards the scalp against physical trauma, heat loss, and sunlight
• Filamentous strands of dead keratinized cells produced by hair follicles
• Contains hard keratin, which is tougher and more durable that the soft keratin of the skin
• Made up of the shaft projecting from the skin and the root embedded in the skin
• Consists of a core called medulla, a cortex and an outermost cuticle
• Pigmented by melanocytes at the base of the hair (surrounded by the dermal papilla)

Hair Follicle

• Root sheath extending from the epidermal surface into the dermis
• Deep end is expanded forming a hair bulb
• A knot of sensory nerve endings (a root hair plexus) wraps around each hair bulb (when a fly walks on your arm you feel it, if arm was shaved you wouldn’t be able to feel it)
• Bending a hair stimulates these endings, hence our hairs act as sensitive touch receptors

Types of Hair

• Vellus-pale, fine body hair found in children and the adult female
• Terminal-coarse, long hair of eyebrows, scalp, axillary (armpit), and pubic regions

Hair Thinning and Baldness

• Alopecia-hair thinning in both sexes
• True, or frank, baldness-genetically determined and sex influenced condition (male pattern baldness)
• Hormones in females don’t allow baldness

 

Structure of a Nail

• Scalelike modification of the epidermis on the distal, dorsal surfaces of fingers and toes.

 

Functions of the Integumentary System

• Protection-chemical, physical, and mechanical barrier
• Body temperature
• Regulated by dilation (cooling) and constriction (warming) of dermal vessels
• Sweat glands increase secretions to cool the body
• Cutaneous sensation-exoreceptors sense touch and pain
• Metabolic functions-synthesis of Vitamin D in dermal blood vessels
• Blood reservoir-skin blood vessels store up to 5% of the body’s blood volume
• Excretion-limited amounts of nitrogenous wastes are eliminated from the body in sweat

Skin Cancer

• Basal cell carcinoma
• Least malignant and most common skin cancer
• Stratum basale cells proliferate and invade the dermis and hypodermis
• Slow growing and do not often metastasize
• Can be cured by surgical excision in 99% of the cases
• Squamous Cell Carcinoma
• Arises from keratinocytes of stratum spinosum
• Arise most often on scalp, ears, and lower lip
• Grows rapidly and metastasizes if not removed
• Prognosis is good if treated by radiation therapy or removed surgically
• Melanoma
• Cancer of melanocytes is the most dangerous type of skin cancer
• Melanomas have the follwing characteristics (ABCD Rule)
• A: Asymmetry; the two sides of the pigmented area do not match
• B: Border is irregular and exhibits indentations
• C: Color (pigmented area) is black, brown, tan, or sometimes red or blue
• D: Diameter is larger than 6 mm (size of a pencil eraser)
• Treated by wide surgical excision accompanied by immunotherapy
• Survival is poor if the lesion is over 4 mm thick

 

 

 

Burns

• First-degree-only the epidermis is damaged
• Symptoms include localized redness, swelling, and pain
• Second-degree-the epidermis and upper regions of the dermis damaged
• Symptoms mimic first degree burns, but blister also appear
• Third-degree- involve entire thickness of the skin
• Burned area appears gray-white, cherry red, or black, and there is not initial edema (swelling) or pain (since nerve endings are destroyed)
• Rule of Nines
• Estimates the severity of burns
• Burns considered critical if:
• Over 25% of the body has second-degree burns
• Over 10% of the body has 3rd degree burns
• There are third-degree burns on face, hands or feet.