Unit 3 - Integumentary System

Functions of the skin

Protection, sensation, production, temperature regulation, excretion

Protection

Function of the skin involving abrasion/UV light, barrier against microorganisms, reduce water loss

Sensation

Function of the skin involving receptors for temperature, pressure, pain, and touch

Production

Function of the skin involving vitamin D, keratin, and melanin

Temperature Regulation

Function of the skin involving constriction and dilation of peripheral blood vessels and shunting of blood

Excretion

Function of the skin involving small amounts of water, salts, and urea

Epidermis, dermis, hypodermis/subcutaneous

Layers of the skin

Epidermis

Superficial layer of epithelial tissue; lacks blood vessels/nervse

Keratinocytes

Produce keratin, a protein that accumulates within cells of the epidermis as they age causing them to die, but forming hardened, waterproof layers. 90% of cells in epidermis. Produce lamellar granules

Lamellar Granules

Release waterproof lipid sealant for skin

Melanocytes

Produce melanin pigment; transferred to keratinocytes by dendritic extensions of the melanocytes. Melanin granules cluster together in keratinocytes to protect nucleus/DNA. 8% of epidermal cells

Melanin

Pigment that contributes to skin, hair and eye color. Absorbs UV radiation. Albinos lack enzyme needed to produce melanin. Produced in epidermis. Eumelanin and pheomelanin. Differences in skin color depend on amount

Langerhans Cells

Participate in immune response to microbes that invade the skin; act as phagocytic macrophages, most prevalent in stratum spinosum

Merkel Cells

Least numerous, found in deepest layers of the epidermis; form Merkel discs which act as touch receptors and are in contact with sensory neurons

Stratum Basale/germinatium

Deepest layer, highly mitotic, single row of columnar keratinocytes, some stem cells - develop into new keratinocytes, contains melanocytes, Merkel cells, Langerhans cells

Stratum Spinosum

Second deepest layer, 8-10 layers of many-sided keratinocytes that fit closely together, most prevalent location of Langerhans cells

Stratum Granulosum

Middle layer, 3-5 layers of flattened keratinocytes, undergoing apoptosis, cells lose nucleus and organelles as keratin accumulates, cells contain membrane bound granules which produce a lipid-rich secretion that enters extracellular space and waterproofs layers of cells

Stratum Lucidum

Second most superficial layer. Present only in thick skin. 3-5 layers of flat, clear, dead keratinocytes with large amounts of keratin. Soles of feet, palms of hand. Thick skin = 5 layers, thin skin = 4 layers (face, arms, legs)

Stratum Corneum

Superficial layer. 25-30 layers of dead/flat keratinocytes, continually shed/replaced. Completely filled with keratin and lipid secretion from lamellar granules.

Apoptosis

Cell death

Keratinization

The process by which epithelial cells are pushed towards the skin surface; lose cytoplasm, nucleus, and organelles, accumulate keratin until they are sloughed off

Sloughed

Process by which the outer layer of skin cells are brushed off

Desquamation

Shedding of the outer layer of skin, 40-55 days,

Dermis

Mainly connective tissue containing collagen and elastic fibers, cell types: fibroblasts/macrophages/adipocytes, contains blood vessels, nerves, glands, and hair follicles

Stria

Stretchmarks; small tears in the dermis due to extreme stress, often caused by obesity or pregnancy

Papillary region (superficial)

Upper 20% of dermis, increased surface area due to small, upward projections into the epidermis called dermal papillae

Meissner’s Corpuscles (Mechanoreceptor)

Touch receptors found in some dermal papillae which are sensitive to light touch, sense heavy pressure and respond to low-frequency vibration or flutters. Found in upper dermis, project into epidermis

Dermal Papillae

Form papillary ridges (fingerprints) on the surface of fingers/toes, contain sensory nerves (signals produce sensation of warmth, coolness, pain, tickling, and itching)

Papillary Ridges

Fingerprints

Reticular Region (deep)

Lower 80%, dense irregular Connective tissue, collagen and elastic fibers, contains adipose cells, hair follicles, and nerves. Capillaries, sebaceous (oil) glands, and sudoriferous (sweat) glands

Hypodermis (subcutaneous layer)

Loose connective tissue and adipose, not a layer of skin, attaches dermis to underlying tissues/organs, contains nerve endings called lamellated (Pacinian) corpuscles which are sensitive to pressure

Lamellated (Pacinian) corpuscles

Nerve endings found in hypodermis that are sensitive to presure

Hair

Formed by cells of the matrix that differentiate, are keratinized, and die. As new cells are added at the base the substance grows

Hair Pili

Composed of fused columnar of dead, keratinized cells

Hair Root

Part of hair below the surface, penetrates into the dermis

Hair Follicle

Surrounds the root, two layers of epidermal cells covered by connective tissue

Hair Root Plexus

Nerve endings that surround hair follicles and are sensitive to touch, sense if the hair moves

Hair Bulb

Enlarged base of the hair follicle, contains hair papillae, contains hair matrix

Hair Papillae

Found in hair bulb, indentation containing blood vessels that provide nutrients to growing hair

Hair Matrix

Found in hair bulb, region of cells that produces new cells by cell division to replace older, shed hairs

Arrector Pili

A bundle of smooth muscles attached to the side of the hair follicle.  Under stress, muscles contract causing hairs to “stand on end”

Sebaceous (oil) glands

Typically connected to hair follicles, secrete oily substance sebum

Sebum

Secreted by sebaceous glands, prevents hair from drying out, keeps skin soft, prevents excessive water loss

Sudoriferous (sweat) glands

Releases sweat that helps regulate body temperature and eliminate wastes

Apocrine Sweat Glands

Found in skin of the armpit and pubic region, open into hair follicles, become active at puberty, stimulated during emotional stress or sexual activity, secrete sticky viscous secretion

Eccrine Sweat Glands

Have ducts which terminate at a sweat pore on the surface of the skin, distributed throughout the skin, function throughout life and produce a more watery secretion than apocrine glands

Ceruminous Glands

Present in outer ear canal, cerumen and hairs in the outer ear provide a sticky barrier against foreign bodies

Cerumen

Combined secretion of ceruminous and sebaceous glands

Pacinian Corpuscles (Mechanoreceptors)

Feel deep pressure, painful squeezes. Deep in dermis (reticular)

Ruffini Endings

Detect skin stretch and heat, deep in dermis (reticular)

Merkel’s Disks (Mechanoreceptor)

Respond to light touch, receptive fields are small, well defined borders. Very sensitive to edges. Upper layers of skin near base of the epidermis.

Thermoreceptors

Broad term for Krause end bulbs (cold) and ruffini endings (heat)

Krause end bulbs

Sensitive to cold, found deeper in dermis

Nociceptors (free nerve endings)

Sensitive to pain, dermis

Signal Transduction

The process by which a cell receives a signal from its environment and converts it into electrical signals (or another type of response)

Nails

Tightly packed, hard, keratinized cells of the epidermis

Nail plate

Portion of the nail that is visible; dead cells filled with keratin

Nail bed

Skin below the nail plate

Distal Edge

Part of the nail plate that extends past the end of the toe/finger

Nail root

Portion of the nail that is not visible

Nail growth

Results from transformation of superficial cells in the nail matrix into nail cells (1mm/week)

Nail Matrix

Contains nerves, lymph and blood vessels. Produces cells that become the nail plate

Cuticle (eponychium)

Protective layer of stratum corneum around nail

Lunula

Whitish, semilunar area near the nail root; vascular tissue doesn’t show through due to thickened stratum corneum in the area

Eumelanin

Most common form of melanin, black and brown

Pheomelanin

Less common form of melanin, red color

Carotene

Accumulates in lipids produced in the stratum corneum and fat cells of the dermis/hypodermis. Gives skin a slight yellowish tint

Hemoglobin

A protein found in blood that flows through the dermis of the skin, giving it a pinkish tink

Erythema

Temporary change in skin color, blood flow increases to the skin, red color intensifies (blushing, anger, inflammation)

Cyanosis

Temporary change in skin color, bluish color due to lack of blood oxygen

Shock

Inadequate perfusion, temporary change in skin color due to lack of blood to surface, makes skin appear pale

Jaundice

Temporary change in skin color, yellowing of skin; result of liver disorder, too much bilirubin

Skin Cancer

Most common form of cancer, caused by excessive exposure to UV radiation. Most cancers develop on exposed parts of body (face, neck, hands, etc)

Asymmetry

Sign of cancer when half of mole doesn’t match other half

Border

Sign of cancer when the edges of the mole is ragged

Color

Sign of cancer when color of mole is not uniform

Diameter

Sign of cancer when mole is larger than 5mm across

Evolving

Sign of cancer when mole changes in appearance over time

Asymmetry, border, color, diameter, evolving

ABCDE method of skin cancer diagnosis

Basal cell carcinoma

Most common form of skin cancer, 78%, occurs in epidermis; rarely spreads to other organs

Squamous Cell Carcinoma

Less common form of skin cancer (20%), occur in epidermis, if left untreated can invade dermis, spread, and cause death

Malignant Melanoma

Rarest form of skin cancer, 2%, arise from melanocytes, usually in a pre-existing mole, spread is common and unless diagnosed/treated early is usually fatal

First degree (superficial partial thickness) burns

Mildest, limited to top layer of the epidermis, redness, pain, minor swelling, no blisters

Second degree (deep partial thickness) burns

Produces blisters (fluid escaping from damaged dermal capillaries), severe redness and pain, wet/weeping, very painful, affects all of the epidermis and into the upper dermis

Third degree (deep full thickness) burns

Involve both epidermis and dermis and underlying tissues, surface appears leathery, brown, charred. May be little to no pain at first - nerve damage. May require skin grafts to help heal the burn wound

Total body surface area

TBSA

TBSA, Depth, Cause, Location

Aspects used to determine severity of burns

Rules of Nine

A quick measurement of the total surface area of the burn. Severe burns over large areas of the body can cause the patient to be subject to infection and fluid loss; more than 10% of the body covered with burns requires hospitalization. Head covers more surface area in children. 

Shallow Wounds

Epithelial cells along the base of the epidermis are stimulated to divide more rapidly than normal, newly formed cells fill the gap

Deeper Wounds

Into dermis/hypodermis. Blood vessels break, escaping blood forms a clot in the wound, blood clot and dried tissue fluids form a scab that covers and protect underlying tissues. Specialized cells (fibroblasts) travel to injured region, form new collagen fibers to hold edges of wound together. Suturing speeds up process. Blood vessels extend to area below the scab as healing continues. WBCs remove dead tissue, eventually tissue replaced and scab sloughs off newly formed connective tissue/haphazardly laid down - scar

Granulation Tissue

New connective tissue formed at the site of a wound

Inflammatory, proliferative, maturation

Phases of wound healing

Inflammatory Phase

Begins when wound develops, 4-6 days, marked by edema, erythema, inflammation and pain. Healing process triggered. Immune system works to prevent microbial colonization

Proliferative Phase

4-24 days, granulation tissue fills wound, fibroblasts lay collagen in the wound bed, strengthening new granulated tissue. Wound edges begin to contract, epithelial cells migrate from wound margins

Maturation Phase

21 days - 2 years. Length of time depends on patient, wound-related complicating factors (duration of wound, patient comorbidities, infection status). Filled in wound is covered and strengthened. Scar tissue forms

Abrasion

Skin is rubbed off or scraped off (rope burn)

Laceration

Ragged skin tear

Amputation

Removal of a limb

Incision

Wound from a sharp object; a cut

Puncture

Wound caused by a penetration object