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.