Download Microscopic Level – Cells of the Epidermis

Microscopic Level – Cells of the Epidermis
The epidermis (or epithelial layer) is stratified squamous epithelia,
composed of four to five layers (depending on body region) of epithelial
cells. The top layers of the epidermis are made up ofkeratinocytes,
which are cells containing the protein keratin. The keratinocytes on the
most superficial layer of the epidermis are dead, and periodically slough
away, being replaced by cells from the deeper layers. As keratinocytes move
superficially from the deeper layers, they lose cytoplasm and become
flattened, allowing for many layers in a relatively small space.
Basal cells are an example of tissue-specific stem cells, meaning they
can turn into a variety of cell types found in that tissue. Under normal
conditions, daughter basal cells most commonly replace lost keratinocytes.
The deepest layer of the epidermis and the most superficial layer of the
dermis give out projections that interlock with each other (like Velcro) and
strengthen the bond between the epidermis and the dermis. The
projections originating in epithelial cells of the bottom layer of the
epidermis are called desmosomes, and the ones originating in the dermis
are called dermal papillae. Think of the projections as a formation of
folds of cellular matter. The greater the fold, the stronger the connections
made.
Merkel cells are sensory receptors that detect light touch. They form
synaptic connections with sensory nerves that carry touch information to
the brain. These cells are abundant on the surface of the hands and feet.
Melanocytes are cells in the bottom layer of epidermis that produce the
pigment melanin, which gives hair and skin its color. Individuals whose
melanocytes produce more melanin have darker skin color. Cellular
extensions of the melanocytes reach up in between the keratinocytes.
Dendritic or Langerhans cells are tissue macrophages that contribute
to the immune function of the skin. They engulf foreign organisms and
signal to the immune system. Since the skin is in constant contact with the
environment, it is important to have immune cells to help destroy any
pathogens that might get past the cell barrier of the epidermis.
EXAMPLE
Eczema
Eczema is an allergic reaction that manifests as dry, itchy patches of skin
that resemble rashes. Normally it is useful to have immune cells in the
skin, but they can also lead to dysfunction if they become overactive. In
eczema, this excess activity may be accompanied by swelling of the skin,
flaking, and in severe cases, bleeding. Other allergic (immune-mediated)
reactions include hives. Symptoms of these conditions are usually
managed with moisturizers and topically with corticosteroid or
antihistamine creams that reduce the inflammatory immune response.