Integumentary system

The integumentary system is the external covering of the chordate body, comprising the skin, hair, feathers, scales, teeth, baleen , nails, claws, horns, beaks , hooves , pigments and various exocrine glands that produce sweat ,tears ,sebum and other oils, mucous, waxes , scents, milk . The integumentary system serves multiple functions in promoting homeostasis of the body.

1. restrict the movement of fluids leaving and entering the body
2. cushion and protect vital organs
3. protects the body against abrupt changes in and helps to regulate temperature
4. helps excrete waste materials through perspiration
5. houses sensory receptors which inform the brain of external stimuli
6. provide a front line of defense against foreign invaders
7. provides for gaseous exchange (respiration)
8. provide coloration and protection from the sun with skin pigments
9. generates vitamin D through exposure to ultraviolet light
10. stores water, fat, and vitamin D

The word integument is derived from the [Latin]] word integumentum, which means ' a covering '.

Skin layers: epidermis, dermis, and subcutis, showing a hair follicle, sweat gland & sebaceous gland.

As an organ system

The integumentary system is often considered to be a single organ system and as such it has the largest surface area of all the organ systems. In human beings it amounts to about 16 % of the body weight. It is composed of many types of tissue,including epithelial,connective ,neural and muscular. This organ system ,composed of many diverse cells and tissues ,provides a wall of defense between the body and the environment. These integumentary cells are the most vulnerable of all the bodily cells to death and destruction. The epidermal epithelial cells are replaced every 10 to 30 days. The wound healing system of the human skin is a remarkable feat of intercellular cooperation that continues to mystify medical researchers.

Cutaneous layers and Glands

The cutaneous layer or skin is composed of two layers of tissue : (1) the Epidermis and (2) the Dermis . The epidermis is an epithelial tissue and the dermis that supports it from below is a connective tissue. Beneath the dermis is a loose connective tisssue called the hypodermis or subcutaneous layer.

There are several types of cutaneous glands including:

• Sweat glands (also known as sudoriferous glands) - excrete sweat to regulate temperature
• Sebaceous glands - oil-producing glands that keep skin and hair moist and soft
• Ceruminous glands - glands of the ear canal that produce earwax
• Mammary glands - milk-producing glands located in the breasts.
• uropygial or preening glands of birds repel water from feathers
• poison glands of frogs
• mucous glands of fish and amphibians help prevent infection
• lacrimal glands produce tears to moisten the eyes
• scent glands in the anal or genital area may attract mates or repel attackers

Epidermis

The epidermis is the outermost layer of skin that varies in thickness (in people) from 0.07 to 0.12 mm. The palms of the hands average about 0.8 mm and the soles of the feet have a thickness of about 1.4 mm (Bloom et al. 1975). It's microscopic appearance is that of a keratinized stratified squamous epithelium. It is derived from two different cell lineages . The first lineage is derived from ectoderm and forms the progressively keratinizing layers. The second lineage is from the neural crest which forms the melanocytes or pigmentary system of the skin. There are two other cell types , which are neither keratinizing nor pigmentary : (1) Langerhans cell and (2) Merkel cells.

When the epidermis of the soles or palms is viewed under a microscope one can see 5 different layers or strata. In descending order they are :

1. Stratum corneum
2. Stratum lucidum
3. Stratum granulosum
4. Stratum spinosum or Stratum Malpighii or prickle cell layer
5. Stratum germinativum (also called "stratum basale")

The cells in the deepest layer ,the stratum germinativum, begin as cuboidal cells engaged actively in mitosis. As more cells are produced the older cells move upward to another layer. When they reach the stratum spinosum layer the cells become flattened and polyhedral. They develop an elongated nucleus and each appears to have "spines". These spiny processes meet to form desmosomes. This layer is stained darkly with basic dyes.

Once they become part of the stratum granulosum , they form 3-5 layers of flattened cells ,which now contain many irregularly shaped granules of keratohyalin.

As they move upward into the stratum lucidum they become more flattened and develop an affinity for acidic dyes like eosin. At this stage they lose their nucleus. This layer is only evident in the soles and palms.

In the top layer,the stratum corneum,the cells have become heavily cornified and most of the cytoplasm has been replaced with keratin. These lifeless cells are very tightly packed and the outermost layer is sloughed off to the environment. This layer is sometimes referred to as the stratum disjunctum.

This entire life course of the skin cells from the stratum germinativum until they are exfoliated and leave the body in the stratum disjunctum takes about 15 to 30 days. As the cells age they become filled with keratin , they lose their nuclei and all organelles until they are shed as lifeless shells (Bloom et al. 1975).

Dermis

The dermis is just below the epidermis, and forms a layer of skin with an average thickness in human beings of 1-2 mm . The thickness ranges from 0.6 mm on the eyelids and prepuce to 3 mm on the soles and palms. It contains blood vessels, nerves, lymph vessels, sebaceous glands , sweat glands and hair shafts. It can be subdivided into two layers:

1. Upper Papillary layer: Contains touch,pain and receptors which communicate with the central nervous system and is responsible for the folds of the fingerprints. It is a loose connective tissue.
2. Lower Reticular layer: Made of dense elastic fibers that house the hair follicles, nerves, and glands. It is a dense connective tissue with many bundles of collagenous fibers running parallel to the skin surface. There are smooth muscle cells,the arrector pili,associated with hair shafts, and many voluntary muscle cells to control facial expressions.

Diseases and injuries

The specialized treatment of the integumentary system is performed by dermatologists. Some of the diseases and injuries to the human integumentary system include:

• Rash
• Blister
• Acne
• Keratosis pilaris
• Athlete's foot
• Calcinosis cutis
• Sunburn
• Keloid
• Scabies
• Warts

References

ISBN links support NWE through referral fees

• Bloom ,W. and D. W. Fawcett. 1975. A Textbook of Histology. 10th edition. Philadelphia, Pa. : W.B.Saunders Company.

• Kardong, Kenneth V. 1998. Vertebrates: Comparative Anatomy, Function, Evolution. second edition. New York, NY: McGraw-Hill. ISBN 0-07-115356-X.

External links

• http://www.zoology.ubc.ca/~biomania/tutorial/skin/outline.htm

  drawings of skin structure

• Aquatic Path Details of the integumentary system of the fathead minnow. Retrieved October 3, 2007.
• biology4kids. Retrieved October 3, 2007.

Integumentary system

Skin • Sweat glands • Sebaceous glands • Hair (Hair follicle) • Nails

Skin
Epidermis (Stratum corneum, Stratum lucidum, Stratum granulosum, Stratum spinosum, Stratum germinativum/basale)

Dermis • Subcutis

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