Skin Derivatives

1. Hair
2. Nails
3. Sebaceous glands
4. Mammary glands
5. Sweat glands

Hair

Hair consists of three parts: 

• Hair shaft is the part that projects from the skin and may extend slightly below the surface of the epidermis, 
• Hair root is the part embedded within the dermis, 
• Hair bulb contains a projection of the dermis called the hair papilla, with a capillary of blood supply.

Nails

Nails are hardened keratinous plate-like structures which grow as dead cells from the nail root, which lies below the skin at the base. A nail has following parts –

• Root: It is the hard and outer part of the nail. It is made up of dead, keratinized cells.
• Plate: It is the visible external part of the nail.
• Free margin: is the area that protrudes out and is generally trimmed to maintain hygiene
• Nail Bed: part under nail plate which is pink in colour due to presence of capillaries in dermis.

Sebaceous Glands

These are microscopic glands found in hair follicle that secretes sebum. It is an oily secretion that makes the hair and the outer surface of the skin oily and waterproof to keep the epidermis supple and prevent loss of moisture by evaporation. In cold and dry weather, the skin may become rough and leave a powdery surface when scratched this is due to a reduced secretion of oil from the sebaceous glands. In hot and humid weather, the skin becomes extra oily due to increased secretion of sebum.

Also Read: Difference Between Sweat and Sebum

Mammary Glands

The mammary (or milk) glands are modified sweat glands. Each breast carries a central conical projection called a nipple. 15-20 milk ducts open on the nipple. Each milk duct is continued inward in a branching manner to join a cluster of 15 to 20 lobes of the mammary glands. These glands are present both in males and females. But in males, they persist only in a rudimentary state, whereas in females at puberty, they enlarge in the form of pair of breasts. The activity of the mammary glands is related to reproductive hormones and pregnancy. 

Sweat Glands

Each sweat gland consists of a deeper secretory part and an excretory part that runs upwards to open on the surface. The secretory part of a sweat gland absorbs fluid from the surrounding cells and blood capillaries of the dermis and passes it into the excretory sweat duct which pours it out on the surface. Their total number in the body is estimated at about two million. Sweat consists of about 99 percent water, and 0.2 to 0.5 per cents salts. The urea lost through sweat is about 1 percent of the total urea excreted by the body.

Skin is the largest organ of the body covering an area of 20 sq feet. Skin is the outer tissue covering of the body. It helps us to regulate body temperature and allows the sensation of heat, cold, and touch. The study of skin is known as dermatology.