INTEGUMENTARY SYSTEM:THE EPIDERMIS AND ITS LAYERS

INTEGUMENTARY SYSTEM

Includes your entire outer layer of skin (16% of your total body weight), accessory organs like hair, nails, and glands.

Consists of two major parts: (1) Cutaneous membrane (2) Accessory structures

CUTANEOUS MEMBRANE (SKIN)

Made up of two layers: (1) Epidermis (superficial epithelium), and

Dermis (underlying connective tissue) (2) Accessory structures – Including hair,

nail , exocrine glands. Located mostly in the dermis and protrude into the epidermal layer

(3) Subcutaneous layer deep to the dermis is known as the hypodermis; often not considered part of the integumentary system, but because its fibers extend into the dermis, we will include it here

STRUCTURE OF THE SKIN

FUNCTION OF THE SKIN

(1) Protection of underlying tissues and organs against shocks, abrasion, and chemicals

(2) Excretion of salts, water, and organic wastes (3) Maintenance of normal body temperature via

insulation or evaporative cooling (sweating) (4) Synthesis of vitamin D3 (5) Storage of nutrients – including lipids/adipose (6) Detection of touch, pressure pain, and

temperature stimuli and relaying information to the control center (brain)

EPIDERMIS Recall epidermis composed of

stratified squamous cells for the purpose of protection

Most abundant epithelial cells are called keratinocytes

EPIDERMIS

Keratinocytes make up five layers of thick skin, and four layers in thin skin

Thick skin is found in the palms of your hands and soles of your feet

Thin skin is found everywhere else in your body

Thick and thin refer to the thickness of the epidermal layer

EPIDERMAL LAYERS OF THICK SKIN

Top layer of skin

Bottom layer of skin

STRATUM GERMINATIVUM/STRATUM BASALE

Stratum germinativum, also known as stratum basale, is the bottom most layer of skin

Epidermal ridges are found here, and they extend into the dermis.

Projections called dermal papillae creates an interlocking arrangement that increases the strength of the bond between the dermal and epidermal layers

STRATUM GERMINATIVUM/STRATUM BASALE

The contours of the skin surface follow the ridge patterns

Ridges on the palms and soles of feet increase the skin’s surface area and friction, helping to maintain grip

Ridge shapes are genetically determined, unique to you, and do not change throughout your life

Ridge prints located on your fingers are called fingerprints

STRATUM GERMINATIVUM/STRATUM BASALE

Basal cells dominate this layer. Basal cells are stem cells whose divisions replace skin cells lost to shedding at the skin’s surface

Merkel cells are also found in this layer. Merkel cells are sensitive to touch.

STRATUM GERMINATIVUM/STRATUM BASALE

Basal Cell

Melanocytes are pigment cells that give skin its color; they are also found in this layer

STRATUM GERMINATIVUM/STRATUM BASALE

STRATUM SPINOSUM Means “spiny layer” Contains Langerhans

cells, which are part of the immune system

Langerhans cells are responsible for stimulating a defense against:

(1) microorganisms that penetrate the epidermis

(2) superficial cancer cells

STRATUM GRANULOSUM

Known as the “grainy layer”

By the time the cells reach this layer, they have stopped dividing and now begin to make lots of the protein keratin

Keratin makes up our hair and nails

STRATUM LUCIDUM Present only in thick skin “Clear layer” filled with keratin

STRATUM CORNEUM Top layer of epidermis;

consists of 15-30 layers of cells

Keratinization or cornification, is the formation of protective, superficial layers of cells made of keratin

Dead layers of cells so tightly connected that when they slough off they separate as sheets of cells

EPITHELIAL CELL LIFE CYCLE

Takes 15-30 days for epithelial cells to move from stratum basale/germinativum to the stratum corneum

They stay in the stratum corneum for about two weeks before being washed/shed

STRATUM CORNEUM

A dry layer, so few microorganisms can survive here

Layer is water resistant, but not waterproof. Water from inside the body slowly penetrates to the surface where it is evaporated. We lose ~500mL (1 pint) of water/day

This process is called insensible perspiration If this layer is damaged or lost (as in burns),

the rate of water loss dramatically increases and you are at risk of dehydration

OSMOTIC PRESSURE Recall from biology that

freshwater will move into cells, causing them to SWELL

This is why when you take a bath your hands swell and look like raisins

Likewise, water will leave cells if placed in highly concentrated solutions, like oceanwater

Although the process occurs slowly, it will accelerate the dehydration process in shipwreck survivors

After 51 hoursof exposure to seawater andwearing gloves