Defensive Structures

Skin
The distinct properties of skin include:
• creates a mechanical barrier
• has several layers of cells, packed together 
• has an outer layer of dead and dying cells
• has an inner layer of regenerating cells
• contains nerve endings that register pain and modified neuronal cells that register cold, heat, and pressure
• contains blood vessels, especially in the innermost parts

Skin Diagram

Skin is the first line of defense against harmful substances.
1 = hair follicle 2 = oil gland 3 = connective tissue 4 = muscle
The outermost layer at the top of the picture is what we usually think of as skin. Its surface is made up of dead cells, whereas new ones are continually being made and moving toward the surface.  In other words, you are continually "shedding your skin," but it happens so slowly that it is not obvious.

Skin consists mostly of an outer zone of flat, dead cells and inner layers of dividing and growing cells.  Like overlapping shingles on a roof, these cells  form an effective barrier to protect the cells of other tissues beneath the skin. The barrier also helps to keep the body from losing water. 

Skin also has blood vessels in its deeper parts (to nourish the dividing and growing cells) and various nerve fibers to register outside temperatures, touch and pressure stimulation of skin, and pain fibers that make you feel hurt when you are injured.

Introduction | Why It Matters | How We Find Out | What We Know | Story Time
Common Hazards | Activities | Self-Study Game | Teachers Pages | Standards (TEKS)