The integumentary system consists of the skin and its accessory
structures, including the hair, nails, sebaceous glands, and sweat glands.
The skin is the exterior covering of the body.
It weighs more than 6 pounds in the average adult,
and covers more than 3,000 square inches.
It is the
largest organ of the body.
It is supplied with blood vessels and nerves.
Functions of skin
The skin provides protection. It protects against
invasion by bacteria and other harmful agents.
It protects delicate cells beneath the surface from
It inhibits excessive loss of water and
It produces a protective pigmentation to protect the
body against excessive exposure from the sun.
It helps produce the body’s supply of Vitamin D.
The skin regulates body temperature.
When the body is too cold, the skin’s blood vessels
This allows more heat-carrying blood to circulate to
the muscles and organs.
When the body is too hot, the blood vessels in the
That brings more blood to the surface for cooling by
At the same time, sweat glands secrete more sweat
that cools the body when it evaporates.
The skin provides sensations.
It contains millions of nerve endings that act as
sensory receptors for pain, heat, cold, and pressure.
When stimulation occurs, nerve impulses are sent to
the cerebral cortex of the brain… and the brain triggers any necessary
The skin has two layers… the epidermis and the
The epidermis actually has 4 străta…
The stratum corneum is the outermost strata
of the epidermis.
It is mostly dead cells, filled with a protein
substance called keratin.
It is thicker on the soles of the feet than on the
eyelids…where there is less pressure.
The stratum lucidum is a translucent layer
lying directly beneath the corneum.
It may not even exist in thinner skin.
Cells in this layer are also dead or are in the
process of dying.
The stratum granulosum is one or more layers
of cells starting to die and become hard.
They are in the process of keratinization…
Becoming fibrous protein similar to that in hair and
1. The stratum
germinativum is composed of several layers of living cells capable of cell
2. It is the
innermost layer of the epidermis, and contains melanin… the pigment that gives
color to the skin.
3. The more
abundant the melanin… the darker the skin color.
Damage to this layer, such as in severe burns,
requires skin grafts.
The dermis is beneath the epidermis and is composed
of connective tissue.