Skin and the Skin and the Integumentary SystemIntegumentary System

Chapter SixChapter Six

The skin maintains a barrier between us and our

surroundings. It is actually a system – The Integumentary

System

The skin:

• Provides a protective covering.

• Helps to maintain body temperature.

• Retards water loss.

• Houses sensory receptors.

• Synthesizes various biochemicals.

• Excretes small quanities of wastes.

The skin consists of two distinct layers:• The epidermis is the outer layer

consisting of stratified squamous epithelium.

• A basement membrane anchors the epidermis to the dermis.

• The dermis is a thicker inner layer consisting of collagenous and elastic fibers, smooth muscle, nerves, and blood vessels.

• The subcutaneous layer lies beneath the skin and consists of loose connective and adipose tissue. This is not a true layer of the skin.

Although the epidermis lacks blood vessels, the bottom layer,

the stratum germativium or stratum basale, lie close enough

to the blood vessels in the dermis to derive nutrients.

With a nutrient supply, the cells of the stratum basale divide. This pushes the outer cells

farther from the blood supply and they flatten, keratinize, and

die. The form a tough, compact layer called the

stratum corneum.

In most areas, four layers of the epidermis can be distinguished.

• Stratum germativium

• Stratum spinosum

• Stratum granulosum

• Stratum corneum

• In areas where there is a lot of frictional pressure, a stratum lucidum may form and cause the epidermis to be thicker.

If the growth of the epidermis is rapid in areas of high pressure, calluses may form on the palms and soles and corns may form

on the toes.

Specialized cells in the lower epidermis called melanocytes

produce dark granules of melanin that absorb UV rays to protect the

skin tissues. Although they lie deep in the epidermis, melanocytes

can pass melanin to all the cells from a number of long extensions. Sometimes the skin cells contain

more melanin that the melanocytes.

Skin color is largely due to melanin. All people have about

the same number of melanocytes but it is genetically determined how much melanin that they will produce and the

size of the granules.

Other physiological and environmental Other physiological and environmental factors may affect skin color.factors may affect skin color.

UV light stimulates the production of UV light stimulates the production of melinin.melinin.

Blood flow can cause the skin to be pink Blood flow can cause the skin to be pink or blueish (cyanotic)or blueish (cyanotic)

ββ-carotene in the diet can tint the skin -carotene in the diet can tint the skin toward orange.toward orange.

Jaundice conditions can cause the skin Jaundice conditions can cause the skin to be yellow.to be yellow.

Networks of connective fibers in the dermis bind the epidermis to

the underlying tissues. Epidermal ridges and dermal cones help to do this. They cause the fingerprints, palm

prints, and sole prints to form.

Dermal blood vessels supply blood to all of the skin cells and

help to regulate body temperature.

The dermis also contains the nerve endings and other accessory organs to be

discussed later.

There is no distinct boundary between the dermis and the

subcutaneous layer. The collagen and elastic fibers of the

dermis extend into the subcutaneous layer. Adipose

tissue is found in the subcutaneous layer as well as

larger blood vessels.

The nails are protective coverings over the ends of the

fingers and toes. Tiny keratinized cells are formed in the lunula at the base of the nail. The cells move forward

constantly to form a growing nail plate that is attached to a nail

bed.

The thumbnail grows slowest. The middle nail grows fastest.

Hair is present on all parts of the body except the lips, palms, soles, nipples, and parts of the external reproductive organs. Each hair grows as a shaft of

cells that form at a blood capillary in the hair follicle which

is contained in the dermis.

The hair consists of three regions

• A scaley cuticle

• A keratinized cortex

• A hollow medulla if present

Hair loss may be due to:Hair loss may be due to:

Loss of circulationLoss of circulation IllnessIllness Fungal diseasesFungal diseases HeredityHeredity

Melanocytes in the follicle add pigment to the hair. As melanin is added, hair is brown to black. If lesser amounts of melanin is present the

hair is blond. If no pigment is present the hair is white. A mixture of pigmented and unpigmented

hair is gray. Another pigment, trichosiderin, is found in

red hair.

The arrector pili muscle causes the hair follicle to stand up when a person is emotional or cold.

This causes goose bumps.

Sebacious glands contain groups of holocrine cells that secrete sebum or oil into the

hair follicle to keep the hair soft and pliable.

Sweat glands or sudoriferous glands open onto the surface of the skin through a pore from a tiny coil

that lies in the deep dermis or subcutaneous layer. They are

eccrine glands that exude perspiration onto the skin during physical activity or hot weather. They are most numerous on the

forehead, neck, and back.

Other sweat glands known as appocrine glands develop at puberty and exude when the

person is emotional, frightened, or in pain. They are found in the axillary regions and in the

groin.

Modified sweat glands include the ceruminous glands of the

ears and the mammary glands.

It is important that the body temperature of the organs stay at 37o C or 98.6o F to maintain normal metabolic reactions.

If active muscles produce excess heat, they warm the blood. The hypothalmus of the brain interprets the warmer blood

and signals the blood vessels of the dermis to dilate and the eccrine sweat glands to become active. As the blood

temperature approaches normal, the blood vessels are allowed to constrict to normal size and the sweat glands remain

inactive.

A wound and the area around it will become swollen and red. This is due to a body reaction

called inflammation. The blood vessels of the area become

dialated and more permeable to release fluids, nutrients, and oxygen into the area of the

wound.

If the wound is shallow, the epithelial cells in the area are

stimulated to divide more rapidly and repair the skin.

If it is a deep wound:

• A clot forms in the broken blood vessels and soon becomes a scab which protects the area.

• Fibroblasts invade the region and begin to bind the wound together with fibers.

• As the wound heals, phagocytes remove the dead and damaged cells and the new connective tissue forms a scar and the collagen fibers contract slightly pulling the wound together.

• With larger wounds, healing may be accompanied by granulations which consist of a blood vessel and a cluster of fibroblasts. As the wound heals, the blood vessels retreats from the scar.

Clinical Terms:Acne- Bacterial infection of the sebacious glands that produces blackheads and pimples.Alopecia- Sudden hair lossAthlete's Foot- Fungal infection of the feetBirthmark- Congenital imperfection of the skin that is present at birth.Boil- Bacterial infection of a hair follicle.Carbuncle- Boil that has spread into the subcutaneous tissues.Cyst- liquid filled capsuleDermatitis- Inflammation of the skin.Eczema- Noncontagious, itching, skin rashHerpes- Viral skin inflection causing reoccurence of skin vesicles

Mole- Fleshy, pigmented skin tumorPediculosis- Lice infestationPsoriasis- Chronic skin disease causing scaley red patches on the skinPostule- Pus filled area on the skinScabies- Infestation of mitesSeborrhea- Hyperactivity of scalp sebacious glands causing dandruffUlcer- Open soreWart- Raised viral infection of the skin.