Parts of the Integumentary System

SkinThe skin is the most important organ of the body, as it protects the delicate organs of the body. The skin is divided into three separate layers as follows:

Epidermis: This is the outermost layer of the skin that contains four separate layers of epithelial tissue. The outer most layer is the stratum corneum that is about 2 to 30 cells thick. These are keratinized and dead cells that make the skin waterproof! The second and third layer consists of the stratum granulosum and stratum lucidum, which contain cells that are not keratinised as yet. As these skin grows, the cells are pushed outward and come towards the surface. The last and the deepest layer of the epidermis is the stratum germinativum. These cells are active mitotically and have the ability to reproduce, as these cells are living, thus, making them the manufacturing center for growing skin.Dermis: The dermis lies immediately after the epidermis. The dermis consists of its own blood supply and thus contains many complex structures. The sweat glands are present in this layer that collect waters and waste products from the blood stream. This waste is excreted from the pores in the epidermis along with the water in form of sweat. The hair roots are also present in this layer that help in the growth of hair. When the hair reaches outside the epidermis, the cells are

dead. The connective tissue made of collagen fibers are also found in the dermis that help give the skin elasticity and strength.Subcutaneous Layer: The last layer of the skin containing the adipose tissues, cushions the delicate organs beneath the skin. The body temperature is also maintained within this layer by insulating the body to the temperature fluctuations.

Functions of the Skin

Thermoregulation: The thermoregulation of the skin is carried out with the help of evaporation of the sweat and regulation of the blood flow to the dermis.Sensations: The cutaneous sensations like touch, pressure, vibration, pain, cold, hot, etc, are felt by the skin.Protection: The protective barrier of the skin helps prevent diseases, infections, dehydration, etc.Production of Vitamin D: The precursor present in the skin and UV rays, helps in the production of vitamin D, an important nutrient of the body.Healing: When the epidermis breaks away due to a minor cut or burn, the cells on the lower layers of the skin migrate upwards as a sheet. When two ends of the sheet meet, the cells stop growing due to a process called 'contact inhibition'. Thus, the epidermis is sealed and the skin returns to normal.

HairHair, feathers, scales, etc. are all derived from the skin. In case of humans, the hair extends to the surface from the hair roots or hair bulbs present in the dermis. The functions of the hair include protection and sensation to touch. Hair is made up of dead, keratinized cells that are bound together with the extracellular proteins. Each hair is divided into hair shaft that is the superficial layer and the root that is in the dermis. Hair follicle is the structure that surrounds the hair root. The oil glands present around the hair follicles help keep the hair and the surrounding skin moist. It also acts as a protective organ involved in temperature regulation.

Arrector Pili MusclesThese are smooth muscle cells that extend from the hair follicle till the papillary layer of the dermis. These arrector pili muscles cause the hair to become erect and give the feeling of 'goose bumps'. Hair can trap more warm air when they are erect. Hence, during extreme cold environment, these muscles contract leading to erect hair. Under conditions of high temperature, the arrector pili muscles relax so that the hair lie flat on the skin and thus aid in the escape of heat.

NailsNails, claws and horns are structures that are derived from the skin. The nail is a highly keratinized structure of modified epidermal cells. The nail bed gives rise to nails, that is thickened to form a lunula. The moon shaped structure that you observe at the base of your nails is called the lunula. The function of nails is to help in grasping and holding things. The nails act as counter force and help increase the sensitivity of the fingertip. They also protect the fingertips and underlying tissues from damage.

Sebaceous Glands and Nerves

Sebaceous glands secrete the oil coating for the hair shaft. When these sebaceous glands become clogged with dirt and microorganisms, they become infected and cause pimples or acne. The complex network of the nerves present all over the skin helps send and receive important impulses to and from the brain, thus playing a vital role in sense of touch.

Sweat GlandsSweat glands have an opening through the skin pores, and they help in excretion of water and electrolytes. Eccrine sweat glands are found all over the body whereas apocrine sweat glands are present in armpits and groin. Eccrine glands are involved in the cooling mechanism of thermoregulation whereas, apocrine glands are involved in the secretion of chemicals and pheromones.

AcneAcne is a skin disease marked by pimples on the face, chest, and back. The most common skin disease. Increased levels of androgens (male hormones) cause the sebaceous glands to secrete an excessive amount of sebum into hair follicles. The excess sebum combines with dead, sticky skin cells to form a hard plug that blocks the follicle. Bacteria that normally lives on the skin then

invades the blocked follicle. Weakened, the follicle bursts open, releasing the sebum, bacteria, skin cells, and white blood cells into the surrounding tissues. A pimple then forms.

Athlete’s footAthlete’s foot is a common fungus infection in which the skin between the toes becomes itchy and sore, cracking and peeling away. Properly known as tinea pedis, the infection received its common name because the infection causing fungi grow well in warm, damp areas such as in and around swimming pools, showers, and locker rooms (areas commonly used by athletes).

BurnsThere are few threats more serious to the skin than burns. Burns are injuries to tissues caused by intense heat, electricity, UV radiation (sunburn), or certain chemicals (such as acids).

DermatitisDermatitis is any inflammation of the skin. There are many types of dermatitis and most are characterized by a pink or red rash that itches. Two common types are contact dermatitis and seborrheic dermatitis.

PsoriasisPsoriasis is a chronic (long-term) skin disease characterized by inflamed lesions with silvery-white scabs of dead skin. Normal skin cells mature and replace dead skin cells every twenty-eight to thirty days.Psoriasis causes skin cells to mature in less than a week.

Skin cancerSkin cancer is the growth of abnormal skin cells capable of invading and destroying other cells. Skin cancer is the single most common type of cancer in humans. The cause of most skin cancers or carcinomas is unknown, but overexposure to ultraviolet radiation in sunlight is a risk factor.Basal cell carcinoma is the most common form of skin cancer, accounting for about 75 percent of cases. It is also the least malignant or cancerous (tending to grow and spread throughout the body). In this form of skin cancer, basal cells in the epidermis are altered so they no longer produce keratin. They also spread,

invading the dermis and subcutaneous layer. Shiny, dome-shaped lesions develop most often on sunexposed areas of the face. The next most common areas affected are the ears, the backs of the hands, the shoulders, and the arms.Squamous cell carcinoma affects the cells of the second deepest layer of the epidermis. Like basal cell carcinoma, this type of skin cancer also involves skin exposed to the sun: face, ears,

hands, and arms. The cancer presents itself as a small, scaling, raised bump on the skin with a crusting center. It grows rapidly and spreads to adjacent lymph nodes if not removed. If the lesion is caught early and removed surgically or through radiation, the patient has a good chance of recovering completely.Malignant melanoma accounts for about 5 percent of all skin cancers, but it is the most serious type. It is a cancer of the melanocytes, cells in the lower epidermis that produce melanin. In their early stages, melanomas resemble moles. Soon, they

appear as an expanding brown to black patch. In addition to invading surrounding tissues, the cancer spreads aggressively to other parts of the body, especially the lungs and liver. Overexposure to the Sun may be a cause of melanomas, but the greatest risk factor seems to be genetic.

VitiligoVitiligo is a skin disorder in which the loss of melanocytes (cells that produce the color pigment melanin) results in patches of smooth, milky white skin.

WartsWarts are small growths caused by a viral infection of the skin or mucous membrane. The virus infects the surface layer. Warts are contagious. They can easily pass from person to person. They can also pass from one area of the body to another on the same person.Hand warts grow around the nails, on the fingers, and on the backs of the hands. They appear mostly in areas where the skin is broken.Foot warts (also called plantar warts) usually appear on the ball of the foot, the heel, or the flat part of the toes. Foot warts do not stick up above the surface like hand warts. If left untreated, they can grow in size and spread into clusters of several warts. If located on a pressure point of the foot, these warts can be painful.

Alopecia Areata Is an autoimmune skin disease that causes the body’s immune system to attack the hair follicles, causing baldness in patches.

Seborrheic DermatitisAn advanced form of seborrhea, is a non-contagious skin disease that causes excessive oiliness of the skin, most commonly in the scalp, caused by overproduction of sebum, the substance produced by the body to lubricate the skin where hair follicles are present. Seborrhea is the form of the disease where oiliness only occurs without redness and scaling. The disease commonly occurs in infants, middle-aged people, and the elderly, and is commonly known in infants as cradle cap

Paronychia Is an often tender infection of inflammation around the base of the nail fold. It can start suddenly (acute paronychia) or gradually (chronic paronychia).

Accute ParonychiaAcute paronychia develops over a few hours when a nail fold becomes painful, red and swollen. Yellow pus may appear under the cuticle. In some cases fever and painful glands under the arms accompany a particularly severe case of acute paronychia. It is usually due to “Staph” bacteria germs.

Chronic ParonychiaChronic paronychia is a gradual process and much more difficult to get rid of. It may start in one nail fold but often spreads to several others. Each affected nail fold (the skin that lies next to the nail) becomes swollen and lifted above the nail. It may be red and tender from time to time, and sometimes a little thick pus (white, yellow or green) can be expressed from under the cuticle.