Anatomy/Integumentary System

The integumentary system or Integument is a focus topic of the event Anatomy. It comes into rotation for the 2014 season. The integumentary system is composed of skin, hair, nails, and glands.


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Functions
The major functions of the integumentary system are:


 * 1) Protection. Includes protecton from outside harm and also protecton from the loss of bodily fluids
 * 2) Temperature maintenance. Regulates heat exchange with environment. Keeps body at an average of 98.6 degrees F or 36.0 degrees C
 * 3) Synthesis and storage of nutrients. Synthesizes Vitamin D3 and stores lipids in adipose tissue
 * 4) Sensory reception. There are touch, pressure, pain, and temperature receptors in the skin which interact with the nervous system
 * 5) Excretion and secretion. Excretes salt water and organic wastes. In postpubescent females, specialized glands called mammary glands secrete milk

Epidermis


Made up of stratified squamous epithelium

Thick skin has five layers and is found in the palms of hands and the soles of feet (.5mm-thickness of a paper towel

Thin skin is found everywhere else and covers the rest of the body(.08mm-thickness of one side of a plastic sandwich bag

The epidermis is organized into strata (singular stratum) or layers. From the basement membrane to the surface they are:

The stratum germinativum, the stratum spinosum, the stratum granulosum, the stratum lucidum, and the strata corneum.

Stratum Germinativum
Stratum Germinativum is the deepest epidermal layer. It can also be called Stratum Basale

It is attached by hemidesmosomes, which are special disc shaped proteins, to the basement membrane, which is a network of protein fibers separating the epidermis from the dermis below.

The Stratum Germinativum, as pictured above, descends into the dermis in what are called Epidermal ridges. The areas where the dermis projects upward are called "'dermal papillae'". These are required because there are no blood vessels in the epidermis, so all nutrients must be obtained through diffusion from the dermis.

These ridges are what cause the elaborate patters in the epidermis of areas with thick skin, such as fingertips

In this layer, there are
 * germinative cells which are large stem cells that replace shed cells in the surface
 * melanocytes which are the cells that produce melanin, a brownish yellow pigment. These melanocytes have processes which extend throughout this layer in order to distribute the melanin
 * nervous receptors which provide information of the outside world to the brain.

Stratum Spinosum
After the germinative cells divide, the daughter cells progress to the Stratum Spinosum. here the cells divide rapidly.

Stratum Granulosum
After the cells cease mitosis, the progress to the Stratum Granlosum where they begin to produce large amounts of the protein "'Keratin'" which is both flexible and durable. This protein also makes up our hair and nails.

Stratum Lucidum
This layer is found only in thick skin. It consists of flattened densely packed cells that are filled with keratin.

Stratum Corneum
After the cells of Stratum Granulosum of Stratum Lucidum die, which is a total of around 2-4 weeks after they were born in the Stratum Germinativum, they are pushed up to the last layer, the Stratum Corneum. This consists of 15-30 layers of densely packed flattened dead cells that have accrued large amounts of keratin. They are considered keratinized or cornified cells. This is useful because keratin is very strong and it protects the deeper and more vulnerable dermis. They are very tightly attached to each other by desmosomes which are special proteins which join two cells and are very difficult to break. These desmosomes are why your skin peels off in sheets after a bad sunburn instead of just one by one.

Cells usually spend an extra 2 weeks in the Stratum Corneum before finally sloughing off to be replaced by the layer beneath it.



Pigmentation
Pigmentation is one of the two major methods of skin coloration

There are two major pigments which can influence skin color, carotene which is orangey yellow and found in carrots and squashes, and melanin which is brown, yellow brown, or black and produced by melanocytes.

Carotene can be synthesized into Vitamin A which is needed for the maintenance of epithelial cells. Eating large amounts if carotene can also cause the skin of light skinned individuals to turn orange.

Melanin is transferred into the Stratum Germinativum and Stratum Spinosum by intracellular vesicles arising from melanocytes, melanocytes are typically in a 1:4 - 1:20 ratio with basal stem cells depending in the area. Because cells rise through the strata, this colors the entire epidermis. When exposed to sunlight, melanocytes will gradually increase their production of melanin with the maximum about 10 days after the initial exposure. Freckles appear due to increased melanocyte activity in an area. They occur mostly on surfaces exposed it the sun, such as the face.

UV radiation, while beneficial in small amounts to the synthesis of Vitamin D3, can cause serious damage in large doses, melanin protects the body by absorbing the UV rays, and it clusters around the nuclei of epidermal cells to protect the DNA. Unfortunately, melanin cannot protect us from 100% of the UV light and some is bound to get through. Long periods if exposure can cause premature wrinkling and skin cancer even in dark skinned individuals. A minimum of SPF15 is recommended in sunscreen, and for fair skinned individuals it is better to have a 20-30 SPF sunscreen.

Dermal Circulation
The other major method of skin coloration is dermal circulation.

In times of vasoconstriction, such as fright, the skin will pale and in some cases turn blue. If the skin turns blue, it is called cyanosis.

In times of vasodilation, such as embarrassment, the skin will turn red.

Vitamin D3 Synthesis
One of the main functions of the integumentary system is the synthesis of Vitamin D3 from a cholesterol based steroid, which is required for the uptake of calcium into our bones. This function is carried out by the two deepest layers, the Stratum Germinativum and the Stratum Spinosum. A low amount of UV radiation is required for this process.

The Dermis
The dermis, which is beneath the Epidermis, consists of two layers. From most superficial to deepest, they are the Pappilary Layer and the Reticular Layer

Pappilary Layer
The Pappilary Layer is named after the dermal pappilae. It is a very loose connective tissue whose purpose is to supply the epidermis with nutrients. It is filled with cappilaries and nerves to reach this end.

Reticular Layer
The Reticular Layer is made up of very dense irregular connective tissue. It is filled with densely packed elastin fibers, which give the skin its elasticity. This layer is also filled with collagen fibers, which resist that elasticity, in order to keep the skin rigid. One of the major causes of wrinkles is the degradation of collagen fibers due to UV light.