Integumentary System

The Integumentary System

The skin and its accessory structures. The largest organ system. Protects the body, provides immune defense, synthesizes hormones, maintains fluid content, modulates body temperature.

Epidermis

Keratinized, stratified squamous epithelium. Four (sometimes five) layers. Avascular.

Keratinocytes

Manufacture and store keratin. Outer layers of keratinocytes are dead and slough off.

Keratin

A fibrous structural protein. Makes hair, nails, and skin hard/tough

Layers of the Epidermis

Stratum Basale, Stratum Spinosum, Stratum Granulosum, Stratum Lucidum, Stratum Corneum.

Stratum Basale

Bottom layer; more cuboidal in shape. New daughter cells push older cells upward toward the apical surface. All keratinocytes come from this cell. Melanocyte and Merkel Cell (tactile cell)

Melanocyte

Covers the basal cells with its armlike extensions, like an umbrella. It’s melanin protein protects the basal cells from UV damage and determines the skin tone. 

Merkel Cell (tactile cell)

Detects “light touch”. Most abundant in hands and feet.

Stratum Spinosum

Appears spiny when stained due to the desmosomes connecting the cells. 8-10 cell rows thick. Some cell division. These cells begin synthesizing keratin protein. Contains langerhan cells. 

Glycolipids

Biomolecules consisting of a carbohydrate portion covalently bonded to a lipid protein, found on the outer surface of cell membranes.

Langerhans (aka Dentritic) Cells

Immune system cells that capture pathogens and debris similar to macrophages.

Stratum Granulosum

Cells are tightly interlocked, no longer divide, and become flatter and thicker as they near end of life cycle. Strictly producing: Keratin protein and keratohyalin. 

Keratohyalin

Connects keratins together making this layer appear “grainy”

Stratum Lucidum

Only found in thick skin: Palms and Soles. “Cells” are dead; sacs of protein wrapped in membrane is all that is left. Cells contain high amounts of eleidin protein which doesn’t stain, making it “translucent”

Eleidin

Fatty protein

Stratum Corneum

“Cells” are dead; sacs of protein wrapped in membrane is all that is left. 15-30 rows of squamous (flat) cells. Prevents mechanical damage and resists abrasion; outer cells slough off.

Dermis

Papillary Dermis (top) Reticular Dermis (bottom)

Papillary Dermis

Loose Areolar connective tissue. Free nerve endings and Meissner’s corpuscles. Very vascular and has lots of macrophages. Dermal papillae= Fingerlike projections.

Reticular Dermis

Dense irregular connective tissue. Collagens extend up into papillary layer and down into hypodermic. Rich nerve supply, both sensory and sympathetic. Very vascular. Hair follicles and sweat glands found here.

Free Nerve Endings

Pain and temperature

Meissner’s/tactile corpuscles

Discriminative Touch

Ruffini’s/bulbous

Stretch, grip, and slippage

Pacinian/lamellar corpuscles

Deep pressure and vibration

Root Hair Plexus

Senses movement of the hair

Hypodermis

The “subcutaneous layer”, underneath the skin. Primarily made of adipose tissue and loose areolar connective tissue. Considered the “superficial fascia.” Thermal insulation, cushioning, and lipid storage. 

Freckles

Accumulations of melanin

Nevus/Nevi

Moles; concentrated areas of melanocytes. Should be monitored for any changes indicating cancerous overgrowth.

Poliosis

A white patch of hair that lacks melanin

Albinism

A lack of melanin production due to double recessive gene.

Vitiligo

Autoimmune damage to melanocytes causing them to cease producing melanin. This condition tends to progress over time.

Melanoma

Skin cancer of the melanocytes

Carotene

Contributes yellowish tint

Pheomelanin

Responsible for red hair and “ruddy” skin color

Flushing/Blushing

Occurs with the vessels of skin dilate and bring a surge of blood flow

Cyanosis

Skin takes on a blueish tint when the body is oxygen deprived. Most easily noticed around lips and finger tips.

Jaundice

A toxic buildup of unconjugated bile salts from the liver will cause skin and eye scleras to take on a yellowish tint. Eyes and anterior wrists are early indicators.

Palor

Cold, extreme fright, anemia, and other situations where there is lower blood flow or less oxygenation of the skin resulting in pale tone.

Addison’s disease

adrenal insufficiency (low cortisol/aldosterone) leads to “bronzing” hyperpigmentation

Hair Follicles

Originate in the epidermis and have many different paths.

Hair Shaft

Unanchored portion; mostly visible

Hair root bulb

Anchored in the dermis

Hair matrix

Mitotically active basal cells

Medulla

Middle

Cortex

Compressed keratinized cells

Cuticle

VERY hard keratinized cells

Dermal hair papilla

Vessels and nerves

Arrector pili muscle

Moves the hair (ex: chill bumps)

Eccrine sweat glands

Use merocrine secretion. Regular sweat: water, salts, antibodies, urea and other wastes.

Apocrine sweat glands

Axilla and groin. Swear plus other organic compounds that bacteria consume. Under nervous system (sympathetic) and hormonal control.

Sebaceous glands

Use holocrine secretion. Sebum is a mixture of lipids that keep hair healthy inactive until puberty.

Thermoregulation

The skin releases or conserves heat as the body needs.

Heat Release Methods

Radiation, Evaporation, Convection, and Conduction.

Heat Conservation Methods

Vasoconstriction

Radiation

Heat leaves the skin as infrared waves

Evaporation

When skin becomes dry, sweat glands are triggered to release sweat (water) to the surface. As the water evaporates, heat leaves with it.

Convection

Heat is transferred by air that passes by

Conduction

Heat is transferred to items we touch (clothing, chairs, etc.)

Vasoconstriction

When we are cold, our skin vessels constrict so that less blood flows past the surface and less heat is lost.

Osteomalacia

Soft bones due to lack of calcium.

Rickets

The childhood form of osteomalacia, soft bones, due to a clack of vitamin D and/or a lack of dietary calcium. 

Acne

A result of over-productive sebaceous glands, which leads to formation of blackheads and inflammation of the skin.

Basal Cell Carcinoma

Stratum Basale (Cancer of skin)

Squamous Cell Carcinoma

Stratum Spinosum (Cancer of skin)

Melanoma

Melanocytes (Cancer of skin)

Contusion

“Bruise”: damages blood vessels in the dermis bleed. The lost blood changes colors as it breaks down and must be removed by macrophages. 

Petechiae

Superficial capillaries are broken leaving small red dots. (ex: ripping off medical tape or bandaid, suction injuries, etc.)

Laceration

“cut”: Even though the dermis is dense irregular tissue, there are still discernible patterns in the arrangement of the collagen called “lines of cleavage”

Burns

Measured in degrees

First Degree

Epidermis only (ex: Sunburn)

Second Degree

Involves the dermis (ex: blister)

Third Degree

Extends completely through the whole dermis (destroys the skin)

Fourth Degree

Invovles muscle and/or bone. “Full thickness burns,” cannot heal on their own because all of the origin tissues and cells for healing are destroyed.