What is Dermatology?

Dermatology is the study of skin, but it also includes the prevention, diagnosis, and treatment of skin, nails, and diseases. Dermatologists are the doctors that practice in this area of medicine. They can prescribe medication for your skin, and can perform skin treatments.
http://www.medterms.com/script/main/art.asp?articlekey=32812

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http://careers.stateuniversity.com/pages/473/Dermatologist.html
What is the integumentary system?
The integumentary system an organ system that includes the skin, and structures derived from the skin. An example of a structure is hair. Nails, and glands are also part of the integumentary system. It protects us from the outside world. It prevents injuries, and germs from entering our body. It also plays a role in synthesizing vitamin D, regulating body temperature, regulating water loss, and sensation. The integumentary system is important because of the functions, and the above reasons.

http://www.biology-online.org/dictionary/Integumentary_system

Why is the Integumentary System Considered an Organ System?
The tissues in the system- hair, skin, nails, glands, receptors- all work together to perform a specialized function. They all work together to provide protection, regulate water loss, synthesize vitamin D, sense things, and regulate body temperature.
Source-Yellow paper of notes “Integumentary System”

Parts of the Integumentary System and Their functions:
The skin is a major part of the integumentary system. Its function is to provide a barrier between our organs and the outside world. Hair is another part of the system. The hair allows for sensation, and it also provides protection against the sun and its UV radiation. Nails provide protection, and grip. The nails allow us to grab things, and work with small items. Glands allow us to keep cool when we get hot by releasing sweat, which when it evaporates cools us. They also release oil, which prevents our hair and skin from drying out, and also waterproofs our skin and hair. Receptors protect us. There are five types of receptors in our skin. They include free nerve endings, Pacininan corpuscle, Ruffini endings, bulb of Krause, and Meissner’s corpuscle. Free nerve endings sense pain, and are located in the dermis. Pacinian corpuscle sense deep pressure, and are located in the subcutaneous layer. Ruffini endings sense heat, and are in the dermis. Bulb of Krause senses cold, and can be found in the dermis. Meissner’s corpuscle senses light touch, and is found in the dermis. All of these receptors prevent us from being injured, and they tell us something is happening to our skin.
Source: Notes

What are the layers of the skin?
The three main layers of the skin are the epidermis, dermis, and subcutaneous layer (hypodermis).

Epidermis:
The epidermis is the outermost layer of skin. It is made up mainly of stratified squamous epithelium. The cells in the epidermis include the keratinocytes, melanocytes, granstein cells, and langerhans cells. The keratinocytes are cells that are responsible for producing keratin, a protein that protects epithelial cells from mechanical and non-mechanical stresses that cause damage. The protein also waterproofs the skin, creating a semi-permeable barrier.
The epidermis is composed of five sublayers. From the surface of the skin down, the layers are the stratum corneum, stratum lucidum, stratum granulosm, stratum spinosum, and the stratum basale. Each layer has a specific function within the epidermis.


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Stratum Corneum:
The stratum corneum is the outermost layer, furthest from the dermis. The cells in this layer are tightly packed and shed continuously. Cells in this layer are dead, however they provide a strong barrier to the outside and are first line of defense in our immunity.

Stratum Lucidum:
The next layer is the stratum lucidum, which is only present in certain parts of the body that possess no hair, including the soles of feet and palms of hands, and is missing on a majority of the body surfaces. The function of the stratum lucidum is to provide extra protection.

Stratum Granulosum:
The third layer of the epidermis is the stratum granulosum, commonly referred to as the granular layer. In this layer, the cells move farther from their source and begin to die. The stratum granulosum is a transition layer between living cells produced in the deeper layers and the dead cells lying in the outer layers. These cells contain granules of keratin.

Stratum Spinosum:
Beneath the stratum granulosum is the stratum spinosum, which is 8-10 layers thick. Keratinization begins in the stratum spinosum and the layer contains thick bundles of keratinocytes. Melanocytes in this layer undergo cytocrine secretion, a process of transfer of melanin from melanocytes to epithelial cells. This allows the melanin to be absorbed into the cells.

Stratum Basale:
The stratum basale is the base layer of the epidermis, closest to the dermis. This layer has stem cells that divide constantly to produce keratinocytes. The cells in this layer are alive and are pushed closer to the surface of the skin, continually dying at they reach the top.
The epidermis determines the thickness of the skin, particularly the presence of the stratum lucidum. In areas such as the palms and soles of feet, the skin is the thickest because of the stratum lucidum. The extra layer of epidermis is important for these areas because it provides extra protection. The thinnest layer of skin is the on the eyelids. On the eyelids, the stratum lucidum is missing and the skin is very thin.


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Dermis:
The dermis is the biggest layer of skin between the epidermis and the subcutaneous layer. The layer contains dense connective tissue made of collagen and elastic fibers. It is composed mostly of fibroblast, macrophages, and adipocyte cells. The fibroblasts provide structure for the tissues and assist in synthesizing dermal proteins. Macrophages play a role in clearing cellular debris through phagocytosis. In addition, adipocytes store energy as fat within the dermis.
The dermis is made up of two sublayers, the papillary and reticular. The papillary layer is the layer closest to the surface of the skin and serves as a boundary between the epidermis and the dermis. It is composed of loosely arranged collagen fibers. The papillary layer contains papillae, which are small projections that form into hills and valleys. These dermal papillae create the undulations of the skin at the palmer surface of the finger, providing grip and function. The reticular layer is the bottom layer of the dermis. It lies just beneath the papillary layer of the dermis and is made of dense connective tissue with densely packed collagen fibers. The functions of this layer include providing strength, extensibility, and elasticity to the skin.

Subcutaneous (Hypodermis):
The subcutaneous layer is the deepest layer of the skin, lying underneath both the dermis. It is made up of mainly adipose and areolar, or loose connective tissue. The collagen fibers within the layer provide strength, whereas the elastic fibers provide extensibility and elasticity. Macrophages and fibroblast are found in the subcutaneous layer. However, the layer’s most notable structure may be the large amounts of adipose tissue. The main functions of the subcutaneous layer is to provide cushion for organs lying beneath the skin and to insulate the body to help maintain homeostasis.


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What happens when a wound occurs?
When a wound occurs, the skin undergoes six different processes. The first of these processes is bleeding. During bleeding, the blood vessels dilate and white blood cells invade the wound. Clotting proteins in the blood migrate to the wound. The second stage is clotting, where the blood coagulates and a scab forms. Following the development of a scab, granulation tissue forms and capillaries supply blood. The granulation tissue is made up of fibrous connective tissue. The fourth stage includes fibroblasts, star-shaped cells, making new collagen fibers. Following the generation of fibers, cells called macrophages use phagocytosis to take in dead cell debris left from the wound. The final stage includes epithelial cells undergoing mitosis to regenerate the skin surface.

Stages of Deep Wound Repair:
The stages of deep wound repair include inflammatory, migratory, proliferative, and maturation. During the inflammatory stage, a blood clot forms and epithelial cells migrate across the wound. In the migratory stage, the blood clot formed becomes a scab and the epithelial cells migrate under the scab. Scar tissue begins to form and blood vessels in the area begin to regrow. Following this, granulation tissue fills the wound. In the proliferative stage, there is extensive growth of epithelial cells and the fibroblasts deposit collagen fibers. Also, the blood vessels continue to grow. The maturation stage includes the shedding of the scab when the epidermis returns to its original state and the disappearance of fibroblasts. Blood vessels return to normal and the collagen fibers in the area become more organized.

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After the steps of deep wound repair take place, scar tissue is usually seen. Scar tissue is different from normal tissue because it possesses more fibers, has no epidermis, and few blood vessels. Also, the area where scar tissue forms has no hair, glands, or receptors. There are two different types of scars, keloids and hypertrophic. A keloid is a scar that extends beyond the surface of the wound and a hypertrophic scar stays within the confines of the original wound.


Fun Facts
The average person has about 1.9 square meters of skin covering their body, this weighs around 5.6 pounds.

Most people shed close to 600,000 particles of skin per hour. This adds up to be around 1.5 pounds a year.

In most cases, a square inch of skin has 20 feet of blood vessels. It will also have 77 feet of nerves, and around 645 sweat gland, along with 65 hair follicles, and 97 sebaceous glands.

There are close to 32 million bacteria per square inch of skin. Most of the bacteria found on the body ( around 100 billion) are harmless.

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"Integumentary System." Biologyonline.org. N.p., n.d. Web. 22 Oct. 2012. < http://www.biology-online.org/dictionary/Integumentary_system >.

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Ferris. Adipose Tissue, Hypodermis 20x. N.d. N/A, N/A. My Home Page. Web. 19 Oct. 2012.

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Häggström, Mikael . Epidermis and Dermis. N.d. N/A, N/A. Wikimedia. Web. 19 Oct. 2012.

Häggström, Mikael . Epidermal Layers. N.d. N/A, N/A. Wikimedia. Web. 19 Oct. 2012.