Integumentary system
The integumentary system is the external covering of the body, comprising the skin, hair, feathers, scales, nails, horns, hooves and various exocrine glands that produce sweat ,tears ,sebum and other oils, mucous, waxes , scents and milk . The integumentary system has a variety of functions; in animals, it may serve to waterproof, cushion and protect the deeper tissues, excrete wastes, regulate temperature and provide a site for the location of sensory receptors for pain, pressure and temperature. The name derives from the Latin integumentum, which means ' a covering '.
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 delineates, separates, protects and informs the animal with regard to its surroundings.
Small-bodied invertebrates of aquatic or continually moist habitats breathe by exchanging gases across the outer layer of the skin(integument). This gas exchange system, where gases simply diffuse into and out of the interstitial fluid, is called integumentary exchange.
Cutaneous layers and Glands
The cutaneous membrane (skin) and its accessory structures (hair, scales, feathers, nails, exocrine glands) make up the integumentary system.
Skin is composed of two layers of tissue : (1) Epidermis and (2) 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 :
- Stratum corneum
- Stratum lucidum
- Stratum granulosum
- Stratum spinosum or Stratum Malpighii or prickle cell layer
- Stratum germinativum (also called "stratum basale")
The most superficial layer of cells are constantly being lost to the environment through the process of exfoliation. The cells in the deepest layer ,the stratum germinativum, begin as cuboidal cells actively engaged 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 darkly stained with basophilic dyes.
- Langerhans cells are formed in the bone marrow and work to fight infection
Dermis
The dermis is the bottom-most, thick inner layer of skin, which comprises blood vessels, connective tissue, nerves, lymph vessels, sweat glands and hair shafts. It has two main layers:
- Upper Papillary: Contains touch receptors which communicate with the central nervous system and is responsible for the folds of the fingerprints
- Lower Reticular: Made of dense elastic fibers that house the hair follicles, nerves, and glands
Functions
The integumentary system has multiple roles in homeostasis. All body systems work in an interconnected manner to maintain the internal conditions essential to the function of the body. The skin has an important job of protecting the body and acts somewhat as the body’s first line of defense against infection, temperature change or other challenges to homeostasis. Functions include:
- Protects the body’s internal living tissues and organs
- Protects against invasion by infectious organisms
- Protects the body from dehydration
- Protects the body against abrupt changes in temperature
- Helps excrete waste materials through perspiration
- Acts as a receptor for touch, pressure, pain, heat, and cold (see Somatosensory system)
- Protects the body against sunburns
- Generates vitamin D through exposure to ultraviolet light
- Stores water, fat, and vitamin D
Diseases and injuries
The specialized treatment of the integumentary system is performed by dermatologists. Possible diseases and injuries to the human integumentary system include:
See also
- Exoskeleton and shell
- Major systems of the human body.
In botany
In botany, the integument refers to the envelope of an ovule.
ReferencesISBN 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
drawings of skin structure
- Aquatic Path Details of the integumentary system of the fathead minnow. Retrieved October 3, 2007.
- biology4kids. Retrieved October 3, 2007.
| Human organ systems |
|---|
| Cardiovascular system | Digestive system | Endocrine system | Immune system | Integumentary system | Lymphatic system | Muscular system | Nervous system | Skeletal system | Reproductive system | Respiratory system | Urinary system |
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