The body must protect its cells from harm. To do harm, chemicals
and other damaging substances have to get inside the body.
Thus, the first line of defense is skin,
which prevents many (but not all) harmful substances from entering
What is An Antibody?
How Does the Body Fight Invaders?
While Blood Cells
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
is the first line of defense against harmful substances.
= hair follicle 2 = oil gland 3 = connective tissue 4 = muscle
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.
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