The main functions of the skin include: [1]. Expand all sections Register Log in. Trusted medical expertise in seconds. Find answers fast with the high-powered search feature and clinical tools.
Try free for 5 days Evidence-based content, created and peer-reviewed by physicians. Read the disclaimer. Skin and skin appendage. Summary The skin is the largest organ of the body, covering an area of approximately 2 m 2.
Structure of the skin The skin is composed of several layers, which are categorized as follows from superficial to deep : Cutis Epidermis Derived from ectoderm Primarily composed of keratinocytes , which constantly regenerate approximately every 30 days The outermost and nonvascularized layer of the skin that maintains the skin's barrier function There are 5 layers of the epidermis , which are categorized as follows from superficial to deep : Stratum corneum : outer layer of the epidermis Consists of dead anuclear ; , keratin -filled cells This layer is constantly being sloughed off.
Stratum lucidum : thin, translucent layer Located only on thick skin palms and soles Composed of a homogeneous layer of keratinocytes with no nuclei or organelles Stratum granulosum : also called the granular layer Contains keratohyalin This layer has waterproof properties.
Stratum spinosum Composed of actively dividing keratinocytes ; with spinous-like projections prickle cells This layer produces keratin and induces keratinization.
Langerhans cells are also located in this layer. Stratum basale also called the basal cell layer of the epidermis Stem cells of the epidermis their daughter cells migrate upwards and differentiate into other cells Melanocytes and Merkel cells are also located in this layer. The stratum basale is regenerative and it proliferates to fill skin defects. Dermal-epidermal junction Basement membrane Anchors the epidermis to the dermis Consists of two layers: Lamina lucida superficial Lamina densa deeper Hemidesmosomes : connect the epidermis to the basement membrane Collagen fibrils : connect stratum basale to the papillary layer Dermis Derived from mesoderm ; contains blood vessels and provides structural integrity to the skin Papillary dermis Consists of fine, loosely arranged collagen fibers Supplies the epidermis with nutrients Plays an important role in temperature regulation Forms dermal ridges , which connect dermal papillae extension of the papillary dermis into the epidermis to epidermal downgrowths known as epidermal ridges or rete ridges Contains Meissner corpuscles for fine-touch and two-point discrimination and free nerve endings Contains immune cells mast cells and macrophages Reticular dermis Consists of thick, densely packed fibers e.
Allows for the subcutaneous administration of medication Skin appendages Hair , nails , glands e. References: [1] [2] [3] Cells of the skin Cells of the epidermis [1] The epidermis is mainly composed of four different types of cells. Keratinocytes Definition : principal cells of the epidermis Location Throughout the whole epidermis Mitotically active in the basal layer basal cells Connected to the basement membrane via hemidesmosomes Function Primarily protect against environmental damage and form a barrier against pathogens Protect against ultraviolet UV radiation by storing melanin produced by melanocytes Produce proinflammatory mediators to activate the immune system when exposed to pathogens Aid in the process of wound healing Form tight junctions with nerve endings and hold lymphocytes and Langerhans cells in place.
Clinical significance Abnormal keratinocyte desquamation contributes to the development of acne. Sunburn : apoptosis of keratinocytes Blistering skin disorders e. Dendritic processes transfer melanosomes to adjacent and distant keratinocytes. Langerhans cells Definition : : macrophages of the skin ; a type of dendritic cell Location : : stratum spinosum Characteristics Langerhans cells act as antigen-presenting cells APCs.
These are noncancerous growths that are common and not harmful. Although if you notice a new growth, or changes in an existing one, you should have it looked at by a practitioner. There is a vast array of inflammatory conditions that can affect the skin. Some are temporary, while others are chronic. Some may require treatment while others will heal on their own. They often resemble one another, so it's always a good idea to get a diagnosis from a healthcare provider.
The skin is vulnerable to all sorts of injuries. In most cases, the skin is able to heal through it's remarkable, and complex, process. Serious injuries should always be treated by a healthcare professional. Common skin injuries include:. Infections can take hold whenever there is a break in the skin barrier that allows microbes to pass through. Infection can be caused by bacteria, viruses, or fungi.
They include:. Many conditions that don't originate in the skin can cause cutaneous symptoms. These are disorders that affect the way the skin produces melanin. Pigmentation conditions can either cause an increase in color hyperpigmentation or a loss of color hypopigmentation.
Some pigmentation conditions are treatable while others are not. Skin cancer is most often linked to excessive sun exposure. Most forms of skin cancer are highly treatable, but early detection is key. There are three types of skin cancer:. If you have a sore that doesn't heal or keeps recurring, a new skin mole or lesion, or a change in size, shape, or color of an existing mole, you should have it evaluated by a healthcare provider. Certain genetic conditions can cause the skin to not function as it should.
Most are fairly rare. There are several tests that are performed on the skin to help diagnose various conditions that can affect this organ. A skin biopsy is a procedure in which cells or skin tissue is removed for examination under a microscope. A biopsy is used to check for skin cancer, infection, and to help identify certain rashes.
There are three main techniques used to do a skin biopsy: punch, shave, and excision. You will be given a local anesthetic prior to the biopsy. Stitches may be used to close the biopsy site in some cases.
Patch tests are common done to help identify possible causes of contact dermatitis. Adhesive patches with small pads impregnated with common allergens are placed on the back and left for a period of 48 hours. After the patches are removed, the skin is checked for signs of irritation, redness, or swelling.
This allows one to know the substances that trigger contact dermatitis. A Woods lamp is a type of black light that allows a medical professional to detect things that aren't easily seen with the naked eye. During an exam, you will sit in a dark room. The healthcare provider holds a Woods lamp close to your skin to look for color changes.
The presence of certain fungi or bacteria will appear in particular colors. The borders of hyperpigmentation or hypopigmentation are more easily seen under a Woods lamp as well.
The skin prick test is a test that is performed on the skin, but isn't used to diagnose a skin condition. Instead, skin prick tests are used to determine which substances a person may be allergic to. This includes things that cause allergic rhinitis and food allergies. Skin prick tests are typically done on the back or on the arm.
A device with small points, which have been dipped in allergen extracts, is used to prick or scratch the skin's surface. After 15 to 20 minutes, the skin is examined. Any inflamed bumps or wheals indicated a positive reaction. For an organ that is so visible and familiar, the skin is surprisingly complex. As the largest organ of the human body, the skin is responsible for many important functions.
There are hundreds of conditions that can affect the skin; many of them look incredibly similar and are difficult to distinguish one from another. If needed, see a healthcare provider for help in diagnosing and treating your skin condition. Sign up for our Health Tip of the Day newsletter, and receive daily tips that will help you live your healthiest life. Kanitakis J. Anatomy, histology and immunohistochemistry of normal human skin. Eur J Dermatol. Habif TP. Clinical Dermatology E-Book. Elsevier Health Sciences; Diagnostic Atlas of Common Eyelid Diseases.
Molecular Biology of the Cell, 4th ed. New York: Garland Science; Fingernails grow faster than toenails. Like hair, nails grow faster in summer than in winter. A nail that's torn off will regrow if the matrix isn't severely injured. Reviewed by: Larissa Hirsch, MD. Larger text size Large text size Regular text size. What Does Skin Do? Skin, our largest organ, has many jobs. It: protects the network of muscles, bones , nerves, blood vessels, and everything else inside our bodies forms a barrier that prevents harmful substances and germs from entering the body protects body tissues against injury helps control body temperature through sweating when we're hot and by helping keep heat in the body when we're cold Without the nerve cells in skin, people couldn't feel warmth, cold, or other sensations.
What Are the Parts of Skin? In these layers are three special types of cells: Melanocytes meh-LAH-nuh-sites make melanin , the pigment that gives skin its color. All people have roughly the same number of melanocytes; the more melanin made, the darker the skin.
Exposure to sunlight increases the production of melanin, which is why people get suntanned or freckled. Keratinocytes ker-uh-TIH-no-sites make keratin , a type of protein that's a basic component of hair, skin, and nails. Keratin in the skin's outer layer helps create a protective barrier. What Does Hair Do? The hair on our heads doesn't just look nice.
It keeps us warm by preserving heat. The fine hair that covers the body provides warmth and protects the skin. What Are the Parts of Hair? Human hair consists of: the hair shaft , the part that sticks out from the skin's surface the root , a soft thickened bulb at the base of the hair the follicle FAHL-ih-kul , a sac-like pit in the skin from which the hair grows At the bottom of the follicle is the papilla puh-PILL-uh , where the actual hair growth happens.
Each hair has three layers: the medulla meh-DULL-uh at the center, which is soft the cortex , which surrounds the medulla and is the main part of the hair the cuticle KYOO-tuh-kull , the hard outer layer that protects the shaft Hair grows by forming new cells at the base of the root.
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