Explain the Integumentary System in human biology?
The skin, its glands, and outgrowths form the Integumentary system. This system provides protection, sensory perception, temperature regulation and excretion of wastes for the human body.
The skin provides protection against physical injury, loss of fluids, chemicals and bacteria. It varies in thickness from 0.5 mm on the eyelids to over 4 mm on the soles of the feet. The skin is composed of two basic layers: 1.) the outer surface epidermis (derived from the Greek meaning skin, and for the outer skin, the prefix epi, meaning over), also called the corneum or cuticle, and 2.) the dermis . The outer layer, the epidermis, is 12 to 15 cells thick, beginning with packed columnar (taller than wide) cells at the base with successive layers becoming progressively more squat, flat, and dry. The exterior surface layer consists of horny (hard and callous) dead cells consisting mostly of the protein keratin, which serves to keep the skin waterproof. They are continuously shed and replaced from underneath.
Sensory cells in the skin respond to touch, pressure, vibration, pain, and temperature. Some nerve endings are located in the lower layer of epidermis, which is not supplied with blood vessels. Between the epidermis and the dermis are projections called papillae, which contain blood capillaries and nerve endings specialized for touch. Papillae join the two layers of skin and produce ridges unique to the individual. These ridges form the swirled patterns on fingers that are used in fingerprint identification.
The dermis is the inner layer of the skin, beneath the epidermis. The dermis contains arterioles and a meshwork of capillaries that supplies oxygen and nutrients to both dermal and living epidermal tissue. Lymph vessels opening into the dermis provide protection against infection.
The Integumentary system also helps to maintain a constant body temperature. Fat cells stored beneath the skin provide insulation. Capillary expansion and contraction in the skin helps to regulate body temperature - increased blood flow to the skin releases excess body heat, while blood flow to the skin is decreased to conserve body heat. Perspiration through sweat glands cools the body through evaporation. The sweat glands also excrete salts and urea.
Hair and nails are outgrowths consisting mostly of keratin. Nails are useful in the manipulation of objects. Hair is formed at the base of hair follicles in the dermis. Sebaceous glands in the skin secrete a substance called sebum that lubricates the hair shaft and helps keep the skin waterproof.
The color of skin varies with the amount of a pigment substance called melanin, produced by special cells called melanocytes. The concentration of melanin changes according to the exposure to sunlight or to heredity.