The integumentary system (skin) has been called a membrane and an organ but, it is generally considered a system because it has organs that work together as a system. It is sometimes considered an organ because it contains several types of tissues and a membrane and it covers the body.
The skin is the largest organ of the body and includes associated organs and derivatives of the skin such as hair, nails, glands, and specialized nerve endings. One square centimeter of skin contains approximately 70 cm of blood vessels, over 100 glands, and well over 200 sensory receptors! For this reason, it is virtually impossible to find an area of the skin that is insensitive to sensations of touch, pressure, heat, cold, pain, or vibration.
Skin serves the primary function of protection. It also cushions internal organs and serves as the first line of defense from infection and injury. It is waterproof, stretchable, and capable of repairing itself.
Three main layers make up the skin:
1. Epidermis: the outer layer of skin. It is made up of 5-6 layers with no blood vessels. The layers (outer to innermost) are the stratum corneum, stratum granulosum, stratum spinosum, and the stratum germinativum which replaces the outer layers with new cells. The stratum lucidum is found primarily in the palms of the hands and the soles of the feet. It adds additional thickness to the skin where greater friction typically occurs.
2. Dermis: also called corium or "true skin". The dermis contains elastic connective tissue, blood vessels, involuntary muscle, sweat and oil glands, and hair follicles. The dermis consists of two principal portions. The more superficial portion consists of areolar connective tissue with many fine elastic fibers. Papillae cover the top of the dermis which fit into ridges on the stratum germinativum. These ridges form lines (fingerprints or footprints) on the skin which is unique to each individual. This region is called the papillary region. The deeper portion of the dermis is the region which consists of dense, irregular connective tissue intertwined with course elastic fibers.
3. Hypodermis: also called subcutaneous fascia. It is the innermost layer and is made up of loose, connective tissues like areolar and adipose (fatty) tissue. About half the body's supply of adipose tissue is found in the subcutaneous fat. It is an excellent insulator and shock absorber, and anchors the skin to the organs below.
The integumentary system has two main types of glands: sudoriferous (sweat) glands and sebaceous (oil) glands.
The principal types of sudoriferous glands are eccrine, apocrine, ceruminous, and mammary. Eccrine are the most common and function primarily in thermoregulation by the production of sweat. The sweat (perspiration) eliminated by these glands contain water, salts, and some body wastes. Apocrine are confined to the anogenital and axillary regions of the body and produce sweat that contains fatty substances and proteins and may be analogous to sexual scent glands of animals.
The sebaceous glands produce a lipid based secretion called sebum, an oil that keeps the skin and hair from becoming dry and brittle ans serves as a bactericide. When an oil gland becomes plugged, the accumulation of dirt and oil results in a blackhead or pimple.
Hair consists of a root, which grows in a hollow tube called a follicle, and a shaft. Hair helps protect the body.
Nails are made of tightly packed, keratinized cells. The nail body is the visible portion with a free edge which may extend past the distal end of the digit. The nail root extends into a fold of skin and is continuous with the stratum basale of the epidermis. The region of the nail body that overlies the nail matrix appears as a white crescent called the lanula. Nails protect the end of the digits and serve as "tools" for the manipulation of small objects.
SOURCE:
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