Human Physiology

Lesson 08 : Integumentary System


Fingernails and toenails of the human body are protective keratinized appendages, closely related to the hooves and claws of animals that develop on the dorsal surface of the terminal phalanges of fingers and toes. Nails are formed in follicle like structures made up of the nail bed and fold. The nail bed consists of the skin lying beneath the nail, while the nail fold consists of a fold of skin surrounding the proximal surface and lateral borders of the nail. The visible portion of the nail is the body of the nail plate, and the hidden portion the root. The matrix is the portion of the nail follicle that gives rise to the nail root. As new cells are formed by the matrix, the nail plate moves forward over the nail bed and older cells become keratinized. Nail growth rate is dependent on the health and nutritional state of the individual. When a nail is injured, it will often die and drop off. If the nail matrix is still intact, a new nail will form under the dead one before it drops off.


Dermis is vascularized layer and also contains numerous nerve endings. This is why a slight cut on skin does not cause oozing of blood and pain, if restricted to epidermis only. When dermis is involved, both bleeding and pain is observed. Skin appendages like hair follicles, sweat glands and sebaceous glands are also situated in the dermis layer. Apart from these, dermis is also rich in several kinds of sensory receptors involved in touch, pressure, pain, heat, cold sensations. Density and distribution of these receptors differs in different areas of skin. Due to this, skin is also considered as a largest sensory organ and provides fruitful awareness about the surrounding environment. Skin appendages like horns, hooves nails/claws are the extension of keratin layer epidermis.

Last modified: Tuesday, 10 April 2012, 6:01 AM