Integumentary System

Epidermis

The superficial, avascular layer of skin composed of epithelial cells that serve as outermost protective layer of the body. (broken into 5 layers)

Dermis

The deeper layer of skin composed primarily of connective tissue; broken into 2 layers

Hypodermis

The subcutaneous layer deep to the dermis composed of adipose tissue that insulates the body, absorbs shock, and anchors skin to muscle.

Keratinocytes

Makes up 90% of epidermal cell; responsible for producing keratin in the stratum basale, but gets pushed upward when new cells grow beneath it, causing it to flatten and die; new epidermis every 25-45 days; friction stimulated keratinocyte production

Melanocytes

Spider-shaped cells found only in the stratum basale; produce melanin that covers keratinocytes to shield cell nuclei from UV radiation

Langerhans cells

Dendritic cells that form in the bone marrow and migrate to the stratum spinosum; ingest foreign substances and activate our immune system

Merkel cells

located at junction between the epidermis and dermis; sense light touch

Stratum basale

The deepest layer of the epidermis, right above and attached to the dermis; consists of a single row of stem cells rapidly undergoing mitosis and creating keratinocytes (living keratinocytes)

Stratum spinosum

Keratinocytes are living and connected by desmosomes, making them appear shiny

Stratum granulosum

keratinocytes are living, but begin to die; keratinocytes begin producing keratohyalin granules that help form keratin in the upper strata; releases lamellar bodies—release lipids that waterproof our skin

Stratum lucidum

A clear layer where cells begin to lose nuclei and die (along with dead keratinocytes); found exclusively in the thick skin of the palms and soles.

Stratum corneum

The superficial, outermost epidermal layer consists of 20 to 30 layers of squamous (3/4 thickness of epidermis); anucleated keratinocytes (dead); highly keratinized cells.

Dermal papillae

Skin “ni**les”; bumps that bind the epidermis and dermis; create fingerprints

Meissner's corpuscles

sense light touch

Pacinian corpuscles

sense heavy touch (pressure and vibrations)

Free nerve endings

sense pain, heat, cold, itching and tickling

Arrector pili muscle

contracts to raise hair on end

Rickets

A disease causing soft, weakened bones resulting from insufficient vitamin D.

Hair shaft

part of the hair above the skin’s surface, determines texture

Hair follicle

tunnel in the epidermis/dermis that the hair grows from

Vellus hair

Peach fuzz found on the face, arms, legs, and stomach; become terminal hair in males during puberty

Terminal hair

Thick & dark hair found on the scalp, eyebrows, eyelashes, and axillary/pubic regions during puberty.

Nail matrix

thickened procimal portion of the nail bed

Lunula

visible portion of the nail matrixl; the white crescent

Eponychium

Also known as the cuticle; layer of clear skin along the bottom of a fingernail or toenail

Sebaceous glands

• Oil glands that secrete sebum

• Found all over the body except on thick skin

• small on the body and limbs, but large on the face, neck, and upper chest

• Usually grow on hair follicle

Functions:

• Soften and lubricate hair and skin

• Prevent water loss

• Bactericidal action: kills bacteria

Eccrine glands

• more numerous sweat glands

• abundant on the palms, soles of the feet, and forehead

• seat that they secrete is 99% water + some salt + traces of waste

• eccrine sweat prevents the body from overheating

Apocrine sweat glands

• You have approximately 2000

• Only in the axillary and genital regions

• Larger than the eccrine glands

• Sweat that they secrete is water + some salt + traces of waste + fats

• Due to the fat, apocrine sweat is milky and viscous

• Odorless, but bacteria on the skin feed on it and create body odor 

• Begin functioning at puberty

• Plays very little role in maintaining body temperature 

• Two types of modified apocrine sweat glands

Ceruminous glands

produces ear wax

Nail plate

also known as the nail body, the acutal fingernail, made of keratin

Nail bed

Pinkish colored soft tissue underneath the nail plate

Free edge

the nail tip, distal free part of the nail plate

Nail root

Proximal part of the nail plate embedded in the skin

Nail fold

Skin folds over the proximal and lateral borders of the nail

Papillary layer

superficial, thin layer of the dermis; top ⅕ of the dermis

Reticular layer

deeper, thick layer of the dermis; bottom ⅘ of the dermis

Hair root

part of the hair embedded in the skin

Sudoriferous glands

• Sweat glands 

• Distributed over the entire skin surface except for the nipple and parts of the genitals

• Up to 3 million per person

• Contraction of the glands forces sweat out to the skin’s surface

• Two types: eccrine and apocrine

Mammary glands

produces milk

Capillary loops

• Where oxygen and nutrients are dropped off in the dermis (and shared with the epidermis)

• Where CO2 and waste are removed from the dermis

Acid mantle

secreted by the skin to slow down bacterial growth

Functions of the skin

1. protection (physical, chemical, and biological barrier)

2. body temperature regulation

3. sensing

4. vitamin D synthesis

5. excretion

Types of shafts and its texture

straight hair=round shaft

wavy hair=oval shaft

curly hair=flat shaft

Motor Nerve

Sends messages from the brain to the arrector pili muscles, sebaceous glands, and sudoriferous glands

Sensory nerve

Sends messages from the Merkel cells, Meissner’s corpuscles, free nerve endings, and Pacinian corpuscles to the brain

Adipose tissue

• Adheres skin to underlying muscle (anchored loosely enough to allow skin to slide)

• Insulates heat

• Absorbs shock