Integumentary system
In zootomy, the integumentary system is the external covering of the body, comprising the skin, hair, scales, nails, sweat glands and their products (sweat and mucus).  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 is 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 the largest organ system.  It distinguishes, separates, protects and informs the animal with regard to its surroundings. Small-bodied invertebrates of aquatic or continually moist habitats respire using the outer layer (integument). This gas exchange system, where gases simply diffuse into and out of the interstitial fluid, is called integumentary exchange.

# Anatomy
The cutaneous membrane (skin) and its accessory structures (hair, scales, feathers, nails, exocrine glands) make up the integumentary system.
There are three layers of skin:
- Epidermis
- Dermis
- Subcutaneous tissue
Below the dermis, the subcutis acts to protect underlying muscles, tissues, and other organs.  Hair on the surface of the skin helps maintain body temperature and filter out harmful particles.
Cutaneous glands include:
- 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.

# Layers

## Epidermis
The epidermis is the thin outer layer of skin that contains melanin which gives skin its color and allows for the skin to tan. Carotene, and oxygen-rich hemoglobin also contributes to the color of skin.  The epidermis also encompasses the protein keratin which stiffens epidermal tissue to form finger nails.  The outermost layer consists of 25-30 layers of dead cells.  Further levels include:
- Scaly Cells form the surface of the skin
- Melanocytes give the skin color
- Langerhans cells are formed in the bone marrow and work to fight infection
It is divided into the following sub-layers:

### Sublayers
Epidermis is divided into the following 5 sublayers or strata:
- Stratum corneum
- Stratum lucidum.....
- Stratum granulosum
- Stratum spinosum
- Stratum germinativum (also called "stratum basale")

## 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, gland, and that gives the skin most of its stretchiness and strength.
The dermis papillary or the upper part of the skin produces the fngerprints and its receptors communicate with central nervous system that includes, touch, pressure, hot, cold, and pain
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## Subcutaneous tissue
The subcutaneous tissue or subcutis is the layer of tissue directly underlying the cutis. It is mainly composed of adipose tissue. Its physiological function includes insulation and storage of nutrients. It also cushions the body for extra protection.

# 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 bodys first line of defense against infection, temperature change or other challenges to homeostasis.  Functions include:
- Protects the bodys 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
Possible diseases and injuries to the human integumentary system include:
- Rash
- Blister
- Athlete's foot
- Infection
- Sunburn
Australian Institute of Health and Welfare National Perinatal Statistics Unit, UNSW published congenital malformation rate 1981-92 / 10,000, shows that only a 0.5% of birth defects are in the integumentary system.