Structure of Skin
The skin has three main functions: protection,
regulation
and sensation.
Layers
of the skin (from superficial to deep) are:
Epidermis
– it is made up of stratified squamous epithelium keratinized
Dermis
– it is made up of connective tissue.
Epidermis
It consists
of following layers (deep to superficial):
Stratum
basale or basal layer – It is made up of single layer of columnar cells that rest on
a basal lamina. The cells in this layer undergo mitosis to give off
keratinocytes.
Stratum
spinosum (Malpighian layer) – It consists of several layers of polygonal cells
(keratinocytes)
Stratum
granulosum – 1-5 layers of flattened cells with deeply stained granules in
their cytoplasm.
Stratum
lucidum – The layer appears homogenous with indistinct cell boundaries.
Flattened nuclei are seen.
Stratum
corneum – This layer is acellular and is made up of flattened scale like elements
containing keratin filaments. The thickness of this layer depends on the
exposure to friction like the layer is thicker on the palm and soles.
The
dermis
The
dermis is made up of connective tissue. Immediately below the epidermis the
connective tissue is dense and constitutes the papillary layer. Deep to this,
lies reticular layer of dermis which consists mainly of collagen fibers along
with elastic fibers and adipose tissue.
Functions of Skin
Protection: The
primary function of the skin is to act as a barrier. The skin provides
protection from: mechanical impacts and pressure, variations in temperature,
micro-organisms, radiation, chemicals and is water resistant.
Regulation: Skin is
also important for regulating several aspects of physiology, including: body
temperature via sweat and hair, and changes in peripheral circulation and fluid
balance via sweat.
Sensation: Skin
provides a sensory interface between the body and the external environment.
It also acts as a
reservoir for the synthesis of Vitamin D and helps in absorption of medicine
that is administrated through the skin.
REFERENCES:
Following resources are used while preparing this post (readers are strongly recommended to go through them for more details):
Wheater's Functional Histology: A Text and Color Atlas
Junqueira's Basic Histology: Text and Atlas