Functions and Anatomy of the Integumentary System

Integumentary system

The organ system consisting primarily of the skin and its appendages, including hair, nails, and cutaneous glands.

Protection — function of skin

The skin forms a physical barrier that protects underlying tissues from mechanical damage, chemicals, microorganisms, and water loss.

Immune protection — function of skin

The skin helps defend the body against pathogens; dendritic cells in the epidermis participate in immune defense.

Body temperature regulation — function of skin

altering blood flow through dermal blood vessels and by producing sweat.

How does sweating cool the body?

sweat evaporates from the skin, removing heat from the body.

How do dermal blood vessels help cool the body?

they dilate (widen) when the body is hot, bringing more blood near the skin surface so heat can escape.

How do dermal blood vessels conserve heat?

Blood vessels constrict, reducing blood flow near the surface and decreasing heat loss.

Cutaneous sensation

The skin contains sensory receptors that detect stimuli such as touch, pressure, pain, and temperature.

Examples of sensory structures shown in the skin slides

Free nerve endings, lamellar corpuscles, and hair follicle receptors/root hair plexuses.

Metabolic function of skin

The skin participates in metabolic processes, most importantly the production of vitamin D precursor molecules following exposure to UV radiation.

Blood reservoir — function of skin

skin contains lots of blood vessels, dermal vessels store some blood → blood can be redirected when needed

Excretion — function of skin

Sweat removes small amounts of substances such as water, salts, and nitrogen-containing wastes from the body.

Two major layers of the skin

Epidermis and dermis.

Epidermis

The superficial/outer layer of the skin.

Dermis

The connective tissue layer located deep to the epidermis.

Two layers of the dermis

Papillary layer and reticular layer.

Hypodermis (subcutaneous tissue)

Tissue located deep to the dermis; importantly, it is NOT technically part of the skin. Contains adipose tissue.

Skin proper

The epidermis + dermis.

Epidermis tissue type

Keratinized stratified squamous epithelium.

Does the epidermis contain blood vessels?

No. The epidermis is avascular.

How does the epidermis receive nutrients?

since avascular → nutrients diffuse up from dermis.

Four major types of cells in the epidermis

Keratinocytes, melanocytes, dendritic cells, and tactile (Merkel) cells.

Keratinocytes

The most abundant cells of the epidermis; they produce keratin.

Keratin

A tough, fibrous protein that helps make the epidermis strong and resistant to damage.

Main function of keratinocytes

Produce keratin and contribute to the skin's protective barrier.

What happens to keratinocytes as they move toward the skin surface?

They become increasingly keratinized, eventually die, and form the protective outer layers of the epidermis.

Melanocytes

Pigment-producing cells located primarily in the stratum basale.

Melanin

Pigment produced by melanocytes that contributes to skin color and helps protect cellular DNA from UV radiation.

Where does melanin go after being produced?

packaged into granules and transferred to surrounding keratinocytes.

Dendritic cells of the epidermis

Immune cells that help protect against pathogens.

Main function of epidermal dendritic cells

Participate in the body's immune response by detecting foreign material.

Tactile (Merkel) cells

Specialized epidermal cells associated with sensory nerve endings.

Function of tactile/Merkel cells

Detect light touch.

Where are tactile cells located?

Near the stratum basale, where they associate with sensory nerve endings.

Five epidermal layers from DEEPEST to SUPERFICIAL

Stratum basale → stratum spinosum → stratum granulosum → stratum lucidum → stratum corneum.

Mnemonic for deep → superficial epidermal layers

Before Signing Get Legal Counsel = Basale, Spinosum, Granulosum, Lucidum, Corneum.

Stratum basale

The deepest epidermal layer, directly adjacent to the dermis.

Major activity in the stratum basale

Cell division/mitosis continually produces new keratinocytes.

Important cells found in the stratum basale

keratinocytes, melanocytes, and Merkel (tactile) cells.

Why is the stratum basale important for epidermal replacement?

Its dividing cells produce new cells that are pushed toward the surface as older cells are lost.

Stratum spinosum

Epidermal layer immediately superficial to the stratum basale.

Why do cells in the stratum spinosum look "spiny"?

Cells are strongly connected by desmosomes, which can give them a spiny appearance during tissue preparation.

Desmosomes

Strong cell-to-cell junctions that help hold neighboring keratinocytes together.

Stratum granulosum

Epidermal layer located superficial to the stratum spinosum where keratinocytes become increasingly flattened and keratinized.

What happens to cells as they pass through the stratum granulosum?

They begin to deteriorate as the process of keratinization progresses.

Stratum lucidum

A thin, translucent epidermal layer present only in thick skin.

Where is the stratum lucidum found?

Between the stratum granulosum and stratum corneum.

ONLY IN THICK SKIN

Where do you find thick skin?

Palms of the hands and soles of the feet- startum lucidum

Stratum corneum

The most superficial epidermal layer, consisting primarily of many layers of flattened, dead, keratinized cells.

Main function of the stratum corneum

durable protective barrier against external environment, helps reduce water loss.

Thick skin

Skin containing all five epidermal strata, including the stratum lucidum.

Thin skin

Skin that lacks a distinct stratum lucidum and has a thinner epidermis.

Locations of thick skin

Palms and soles.

Most of the body is what type of skin?

Thin skin.

Dermis

Connective tissue layer located beneath the epidermis that provides the skin with strength and support.

Two layers of dermis

Papillary layer and reticular layer.

Papillary layer

The superficial, thinner portion of the dermis, located immediately underneath the epidermis.

AREOLAR TISSUE

Papillary layer tissue type

areolar connective tissue.

Dermal papillae

Fingerlike projections of the papillary dermis that extend toward the epidermis.

Function of dermal papillae

Increase the surface area of contact between the epidermis and dermis and contain structures involved in blood supply and sensation.

Reticular layer

The deeper and thicker portion of the dermis.

Reticular layer tissue type

dense irregular connective tissue.

Main fibers of the reticular layer

Collagen and elastic fibers.

Function of the reticular layer

Provides skin with strength and elasticity and houses many skin appendages, blood vessels, and nerves.

Three major contributors to skin color

Melanin, carotene, and hemoglobin.

Carotene

yellow-orange pigment → contributes to skin color → vitamin A precursor

Hemoglobin's contribution to skin color

Oxygenated blood in dermal blood vessels contributes a pinkish/reddish coloration, especially in lightly pigmented skin.

Does having darker skin necessarily mean having many more melanocytes?

Skin color differences are primarily related to the amount, type, and distribution of melanin, rather than simply the presence versus absence of melanocytes.

Skin appendages

Structures associated with the skin, including hair, nails, and cutaneous glands.

Hair shaft

Portion of the hair that projects above the surface of the skin.

Hair root

Portion of the hair located below the skin surface within the follicle.

Hair bulb

enlarged base of root → contains matrix → hair growth

Hair matrix

Region of actively dividing cells within the hair bulb that produces the hair.

Hair papilla

at the base of the hair follicle- contains blood vessels supplying nutrients to the growing hair.

Hair follicle

Tubelike structure surrounding the hair root.

Three layers of a hair from outside → inside

Cuticle → cortex → medulla.

Hair cuticle

Outermost layer of the hair.

Hair cortex

Thick middle layer of the hair.

Hair medulla

Innermost/core region of the hair.

Major components of the follicle wall

Peripheral connective tissue (fibrous) sheath, glassy membrane, and epithelial root sheath.

Epithelial root sheath

Portion of the follicle wall containing an external root sheath and internal root sheath.

External root sheath

Outer portion of the epithelial root sheath.

Internal root sheath

Inner portion of the epithelial root sheath surrounding the developing hair.

Arrector pili muscle

Small band of smooth muscle attached to a hair follicle.

What happens when the arrector pili contracts?

It pulls the hair upright, producing goose bumps.

Nail

A modification of the epidermis consisting primarily of hard keratin.

Nail body

Visible attached portion of the nail.

Free edge

Portion of the nail that extends past the fingertip.

Nail root

Proximal portion of the nail embedded beneath the skin.

Nail bed

Skin located underneath the nail body.

Nail matrix

Growth region that produces the nail through cell division.

Lunule

Pale, crescent-shaped region visible near the proximal end of the nail.

Eponychium (cuticle)

Fold of skin covering the proximal border of the nail.

Hyponychium

Thickened region of epidermis underneath the free edge of the nail- protects/seals nail

Proximal nail fold

Fold of skin covering the proximal part of the nail.

Lateral nail folds

Folds of skin bordering the sides of the nail.

Exocrine gland

A gland that releases its secretion through a duct onto an epithelial surface.- all glands

Three major cutaneous glands you need to know

Eccrine sweat glands, apocrine sweat glands, and sebaceous glands.

Eccrine sweat gland

A widely distributed sweat gland that releases a watery secretion onto the surface of the skin.

Where does an eccrine gland release its secretion?

Through a duct that opens at a sweat pore on the skin surface.