Skin and the Integumentary System

Chapter Six

Membranes

1.) Serous Membrane – line the body cavities that lack openings to the outside.

Ex. Thorax and abdomen

2.) Mucous Membrane

• Line cavities and tubes that open to the outside of the body.

Ex. Oral and nasal cavity

3.) Synovial Membrane

• Forms the inner linings of the joint cavities between the ends of bones at freely movable joints.

Ex. Any movable joint

4.) Cutaneous membrane –

skin

Functions of Skin

• Helps Maintain Homeostasis• Provides Protective Covering• Regulates Body Temperature

• Houses Sensory Receptors

• Synthesizes Various Biochemicals

• Excretes Small Quantities of Waste

Two Tissue Layers

• 1.) Epidermis is the outer layer and is composed of stratified squamous epithelium.

• Four parts of the epidermis are distinguishable:– 1. Stratum basale– 2. Stratum spinosum– 3. Stratum granulosum– 4. Stratum coreum

Skin Growth

• The stratum basale is nourished by the dermis.

• New cells are formed in this area which pushes old cells to the surface.

• When these cells are closer to the surface they experience a large amount of keratin protein (Keratinization).

• This caused the old cells to die and eventually shed.

Melanin

• Melanocytes are specialized cells that absorb UV radiation. They are in the deepest portion of the epidermis.

Dermis

• Largely composed of dense connective tissue.

• It connects the epidermis to the underlying tissue it contains nerve cells, touch receptors, hair follicles, and glands.

Subcutaneous Layer

• Made of loose connective tissue and adipose tissue.

• Helps insulate the body and contains major blood vessels.

Accessory Organs

• Nails – protective coverings that cells divide in the white area then are keratinized.

Nails

• A nail bed lies over the area of the skin known as the nail bed.

• The white area of the nail (lunula) is the area of most rapid division. These moved upward, keratinize and die.

Hair Follicles

• Hair is formed by a group of epidermal cells at the base of a tubelike depression known as a hair follicle.

• Color is determined by the amount of melanin.

Sebaceous Glands

• These glands contain specialized epithelium and secrete an oily mixture (sebum) that helps keep the hair soft and water proof.

Sweat Glands

• Exocrine glands that are widespread through the skin.

• Sweat is made of mostly water, but contains small amounts of salt and waste.

Body Temperature Regulation

• When warm blood enters the brain it responds in two ways.– It stimulates dermal blood vessels to dilate so

more blood is near the surface releasing some heat.

– It also stimulates sweat glands. When the sweat reaches the surface and evaporates it also releases heat.

Cold Weather

• Dermal blood vessels can be contracted which keeps blood from flowing through the skin.

• Muscle fibers and muscles can be caused to contract rhythmically to produce heat.

Healing

• Blood vessels dilate flooding a damaged area with fluid to provide nutrients and oxygen.

• Cuts stimulate the epithelium cells to divide more rapidly than normal and new cells fill the gap.

• A deep cut provides clotting by escaping blood. Then fibroblast form new collagenous material to bind the edges of the wound.

• Blood vessels will then grow in this area and phagocytic cells will clear debris and new tissue will be formed as a scar.

Skin Trivia• About 2 million sweat glands are in the

hands.• If the skin of a 150-pound person were

spread out flat, it would cover approximately 20 square feet.

• Skin cells help produce vitamin D, which is necessary for normal bone and tooth development.

• Just above the base of the hair follicle are stem cells that can be used to grow hair or new epidermal cells for burn patients.

• Most of the body’s heat (80%) escapes through the head.

More Skin Trivia

• The average square inch of skin holds 650 sweat glands, 20 blood vessels, 60,000 melanocytes, and more than a thousand nerve endings.

• The thumbnail grows the slowest; the middle nail grows the fastest.

• When a person lies in one position for a prolonged period, the weight of the body pressing against the bed blocks the skin’s blood supply, causing cells to die, tissues to breakdown, and a pressure ulcer (bedsore) may form.