THE INTEGUMENTARY SYSTEM

The integumentary system protects the body against pathogenic organisms and injury. It consists of
the skin, lymph canals and lymph nodes.

The skin is a protective, elastic, waterproof and sensitive organ covering the entire body surface,
and has two layers:

a) Epidermis - or the outer skin, which consists of closely packed epithelial cells and is divided
into layers of the epithelial tissue. The top layer of cells is continuously shed from the body as
inner cells reproduce themselves; these new cells push the upper ones to the surface, where they
die and slough off - this process is called desquamation. The body makes and loses millions of
these cells every day. The epidermis contains no blood vessels but it contains melanin. This is a
pigment that determines the dark or light colour of the skin and is inherited genetically. Some
other factors, such as sunlight, can increase deposits of melanin in the epidermis. This is the
body’s method of protecting the skin from damage due to long exposure to sunlight.

b) Dermis - is the second layer, which is composed of connective tissue. It contains nerves,
capillaries and lymph vessels. Sensory nerve endings provide the sense of touch.

Hair, nails and oil glands are called the skin appendages. Hairs grow on all body surfaces except
the palms of the hands and the soles of the feet. The roots of hairs are located in the dermis;
each hair has a follicle, that surrounds the roots and capillaries around the follicle to provide
nourishment. Small muscles are attached to every hair follicle and are contracted when the body is
exposed to cold. This action causes the hair to stand up and increases the oil supply to the skin,
which prevents further loss of heat from the body surface. The reactions of the skin to cold are
small muscle contractions promoting shivering which produces heat when additional warmth is needed.
The oil also slows the evaporation of water from the skin.

Nails, which are hardened epidermal tissue, serve as tough protective plates for ends of fingers
and toes and also assist in picking up objects. The skin has several vital functions such as
protecting against microorganisms and toxic substances, sense of touch, regulation of body
temperature and elimination of body waste. As to elimination, the skin influences the loss of body
fluids through perspiration. It is also a means of elimination of certain salts, which helps to
maintain the mineral balance of the body. In addition, the skin protects the body against chemicals
in the air and ultraviolet rays from the sun. Body hair aids in protection of the skin against
burns from the sun’s gamma rays; hair in the nasal cavities acts as a barrier to harmful particles
in the air, etc. The sense of touch keeps the body aware of its surroundings and protects it by
transmitting messages to the brain and from the brain to the muscles.