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P & A Notes Integumentary System

February 07, 2011

The Integumentary System 

-when two or more kinds of tissues are grouped together and performing specialized functions-- it is then called and organ

- the thin sheet like membranes that cover body surfaces and line cavities are all organs
* one of these membranes, together with various accessory organs make up the integumentary system (skin).
(group of organs working together make up a system)

Major types of membranes:

1.) Serous Membrane- lines body cavities that lack openings to the outside. Lining the thorax it is called parietal pleura. Lining the abdomen it is called the parietal peritoneum. It also covers the organs of these cavities, (visceral pleura) and (visceral peritoneum). Serous membranes also make-up the mesentery and greater omentum. Mesentery is a doubled layered serous membrane that anchors the intestines to the dorsal wall. The greater ometum is connected to the ventral surface of the stomach and intestine where it drapes like an apron over those organs.
-Serous membranes are made up of a layer of loose connective tissue which is covered by simple squamous epithelium. These serous membranes secrete a watery serous fluid, which helps to lubricate the surfaces of the membrane,

2.) Mucous membranes- Line cavities and tubes that open to outside of the body.
-oral and nasal cavities, tubes to the digestive, respiratory, urinary, and reproductive systems.
-Made up of epithelium overlying a loose connective tissue. Specialized cells in this membrane secrete mucus (goblet cells, cell of salivary glands)

3.) Synovial membrane- forms the inner lining of joint cavities
-Is usually made of fibrous connective tissue covering loose connective tissue and adipose tissue.
*It secrete a colorless synovial fluid into the joint cavity which lubricates the ends of the bone at the joint.

4.) Cutaneous membrane- (skin) An organ of the integumentary system.
skin is the largest and probably the most versatile organ of the body.
Functions: -protective covering
-regulates body temp.
-houses sensory receptors
-synthesizes some chemical substances.
Is composed of 2 distinct layers.
Outer layer is called the epidermis
Inner layer is called the dermis
Epidermis- composed of stratified squamous epithelium.
The deepest cells of this tissue form a layer called stratum germinativium. These cells are nourished by dermal blood vessels and are able to reproduce. This pushed the older cells outward. The further out they get, the less nourishment they get. These older cells undergo a hardening process called keratinization--the cytoplasm develops a tough, fibrous, waterproofing protein called keratin. After this “waterproofing” the cells die and are easily rubbed off. This outer layer of stratified squamous E. is called stratium corneum.
*The production of epidermal cells is closely balanced with the loss of stratum corneum. If skin is being rubbed regularly it responds by growing a callus.
Functions of epidermis:
-prevents water loss to underlying tissue
-protects against mechanical injury
-protects against harmful chemicals
-protects against disease causing microbes.
Melanin- A pigment found in deeper layers of the epidermis, absorbs light and protects the deeper cells from damaging ultraviolet light. The cells that produce melanin are called melanocyes. (see skin cancer pg. 122)

The dermis: Binds epidermis to the underlying tissue.
-composed largely of loose fibrous connective tissue.
Networks of collagenous and elastic fibers give dermis strength and elasticity.
-Blood vessels in the dermis supply nutrients to all skin cells, including the epidermis.
-Dermal blood vessels also aid in regulating body temperature.
Why do doctors or nurses have their patients moved to different positions and have them massaged if they are unable to move?
(the answer has to do with what you have been writing on)
If a person lies in one position for a long time-- the weight of their body pressing against the bed interferes with the skins blood supply. As a result decubitus ulcers may develop. (bed sores)
-Nerve fibers are scattered throughout the dermis.
Some nerves are motor neurons that carry impulses from the C.N.S. to dermal muscles or glands, causing them to react.
Some nerves are sensory neurons that carry impulses from the receptor to the C.N.S.
-Skin also plays an important role in the production of vitamin D, which is necessary for the development of normal bones and teeth.
Skin cells produce dehydrocholesterol. When this is exposed to ultra violet rays it produces vitamin D. (milk has vitamin D added to it)
-A deficiency in Vit. D may lead to a diseases called rickets.
Bones of legs, ribs, sternum, and vertebrae may be deformed.
Accessory organs of the skin:
1.) Hair Follicles-
Hair is found on all skin surfaces except the palms, soles, nipples, and penis.
-In other places it may not be well developed, but is present.
-Each hair develops from a group of epidermal cells at the base of a tube- like depression, called a hair follicle. The cells near the hair follicle are alive and reproduce. The older cells push upward and become keratinized and die. Hair is composed of dead epidermal cells. A bundle of smooth muscle cells, forming the arrector pili muscle, is attached to each hair follicle.
If a person is emotionally upset or very cold, nerve impulses stimulate the arrector pili muscle to contract. This causes goose pimples. In dogs and wild animals the hair will bristle up.
2.) Sebaceous Glands: (holocrine gland)
-usually attached to the hair follicles.
-they produce an oily secretion called sebum. Sebum is a mixture of fatty material, disintegrating cells and cell wastes.
-Sebum helps to keep hair and skin soft, pliable and waterproof.
-It is these sebaceous glands that are responsible for acne.
During hormonal changes, there is an over reaction of the sebaceous glands to produce sebum. The follicles become dilated and plugged resulting in blackheads. If pus-forming bacteria is present then pimples, boils and carbuncle will form.
Nails- Protective coverings on the ends of the fingers.
They are produced by specialized epithelial cells that are continuous with epithelium of the skin. (Lunula) The white half-moon shaped area at the base is the growing area. the cells are produced and undergo keratinizaion. They contain more keratin and are harder than those of the skin.
Sweat glands:
Found in almost all regions of the skin - 2 types
1.) Apocrine glands- Responsible for perspiration when a person is upset or uneasy.
Are most numerous in the armpits and groin areas. Are usually attached to hair follicles.
2.) Eccrine glands- Respond to elevated body temperature due to exercise or environmental heat. common in forehead, neck, and back. Can produce large amounts of sweat.
Sweat is mostly H2O, but also contains small amount of salts, urea and uric acid. so, to a small degree, it serves as an excretory function.

Regulation of body temperatures:
-Normal is 98.6 degrees F
-Skin is largely responsible for the maintenance of this temp.
A byproduct of cellular respiration. The more active the cells the more heat is produced.
-during exercise the muscle cells release heat
-blood picks up the excess heat and carries it away.
-the nervous system responds to the rise in temp. and stimulates the blood vessels in the dermis to dilate. This causes more blood to reach the surface of the skin and more heat will be lost.
-If the temp. is still above 98.6 degrees F, the eccrine sweat glands will be stimulated to release sweat.
-The sweat evaporates and takes heat with it.
If the body temp. drops below normal. The nervous system signals dermal blood vessels to constrict, reducing the amount of heat to the surface.
-Sweat glands are inactive.
-Errector pili muscles contract.
-If temp. is still low then skeletal muscles are signaled to contract involuntarily...you tighten up and shiver.
This creates heat, due to increased cell respiration, and body temperature will rise.

Problems with temp regulation:
-Hot humid days- sweat doesn’t evaporate and body temp. will stay too high- may cause heat stroke.
-Many wrestlers try to drop several pounds the night before a meet by “sweating it off”. The large amount of sweat loss can cause an electrolyte imbalance. this happens because sweat contains essential electrolytes and if lost in excess can cause heat exhaustion. Symptoms- dizziness, headache, muscle, cramps, nausea. Is treated by replacing electrolytes (Gatorade).
Who would be the most effective?
Wound healing:
- Inflammation is a normal response to injury. In damaged tissue the blood vessels become more permeable and excessive fluids will leak out. This causes the skin to redden and get swollen. But, these dilated blood vessels bring more oxygen and nutrients to the area, increasing the healing rate.
-If the break in the skin is shallow then epithelial cells around the wound will be stimulated to reproduce more rapidly and the new cells will just fill the gaps. (also happens in deep injury)
-If the injury extends into the dermis, then blood vessels will be broken. the escaping blood will form a clot. the outer dried portion of the clot forms a scab, protects the damaged tissue.
fibroblasts from connective tissue that are close to the wound will begin to form fibers. These fibers help to bind the edges of the wound together.
As healing continues, blood vessels send out new branches into the area.
Phagocytic cells will remove dead cells and other debris. Eventually the damaged tissue is replaced. The wound heals and the scab sloughs off. Why would stitches help heal a wound quicker?
Minor- (first degree) Could be a sunburn where the dermal blood vessels become dilated and appear red. the skin may become warm. This damage is mainly to the epidermis.
If damage is more severe and extends into the dermis, fluid may accumulate in spaces between dermal and epidermal layers....blisters. (second degree)
-If large areas of epidermis are destroyed by burning, then replacement may come from epithelial cells growing out of the hair follicles that survived in the deeper layers.
-In a third degree burn the epidermis, dermis, and accessory organs of the skin have been destroyed. If the area is large, then treatment would involve removal of a thin layer of skin from an unburned region and transplanting it to the burned area. This is a type of skin graft called an autograft.

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