SKIN
Description:
The skin is the largest organ of the human body, acting as the outer layer of the body to protect it from pathogens, physical and chemical damage, and ultraviolet light. There are three layers of the skin. The top layer, called the epidermis, is the part visible to the human. The cells composing the epidermis are keratinocytes, (which produce keratin to make the skin tough), melanocytes (which make melanin for UV protection and produce melanin, determining skin color), Langerhans cells (which take care of pathogens), and Merkel cells (involved in the touch sense). The middle layer, which is much thicker than the epidermis, is composed of a papillary layer and a reticular layer. Both layers contain connective tissue, nerves, sweat glands, hair follicles, and blood vessels. The papillary layer, however, has papillae that protrude through the top layer to increase its surface area, while the reticular layer is tougher. Finally, the hypodermis stores fat is made of connective tissue, and attaches to muscles.
Diseases and Conditions
Dermatitis
While less extreme inflammation of the skin only leads to red skin that may be itchy, more extreme versions may lead to rashes, cracks, and blisters. If it is caused by physical contact with something, it can be due to an allergy or irritants. Atopic dermatitis is a type of eczema that is usually genetic and causes blistering skin. Seborrheic dermatitis is a result of stress and leads to a greasy scaling. It also leads to dandruff. Stasis dermatitis is the darkening of the skin due to the lack of blood circulation to areas like the legs.
Squamous Cell Carcinoma
Cancer caused by UV light that can spread to other parts of the body, including tissues. It leads to warts, sores, and crusty patches of skin.
Psoriasis
The buildup of skin cells due to overactive multiplication leads to patches or red skin that may crack, build up plaque, and arthritis.
Scabies
A female mite Sarcoptes scabiei var. hominis may deposit its egg into the skin, causing a rash as the parasite begins to develop on the human.
Acne
When the sebaceous glands clog the pores of hair follicles, they can begin to form blackheads or whiteheads. As they grow larger, these nodules become acne. It is common among teenagers due to hormones during puberty signaling the production of sebum.
Ringworm
Mold such as fungi infects the skin, and is contagious, leading to a ring-shaped bump.
Basal Cell Carcinoma
A type of cancer caused by sun exposure that results in tumors around the nose or other parts, which creates a bump on the body that can bleed. It will not spread to other parts of the body.