11.a.the skin and its appendagesPresentation Transcript
The Skin and its
The skin is derived from three diverse component:
1. Surface Ectoderm:
The epidermis is derives from the surface ectoderm.
From single layer ectodermal cells proliferate to give rise
to typical stratified squamouse epithelium.
The superficial layer sheds off and get mixed with
secretions of sebaceous glands to form a whitish sticky
substance called vernix caseosa, which acts as a
protective covering for newborn infant. Vernix caseosa is
protective in function.
Epidermal ridges develops between 3rd and 5th months
of fetal age, this led to formation of characteristics
pattern on the tips of fingers and toes. These patterns
are genetically determined and are different for each
Melanoblasts (dendritic cells)
These are the cells of epidermis derived from the
neural crest cell. The cells synthesize melanin
pigments responsible for skin and hair colour.
Cells of Merkel
Appears in epidermis between 8th and 12th weeks of
They are associated with the sense of light touch
discrimination of shapes and textures.
iii. Cells of Langerhans
They are developed in bone marrow.
In skin infection, the local Langerhans cells take up
and process microbial antigen to become fully
functional antigen presenting cells.
3. The dermis
The dermis is formed by condensation and
differentiation of mesenchyme underlying the surface
This mesenchyme is believed to be derived from the
dermatome of somite.
Recently it has been held as follows:
a.Only the dermis on the dorsal aspect of the head and the
trunk arises from dermatomes.
b.The dermis of the limbs and that on the lateral and
ventral aspect of the trunk arises from the lateral plate
c.The dermis over most of the head and over the anterior
aspect of neck is derived from neural crest.
Stages in development of
The line of junction between dermis and epidermis is
at first straight.
Subsequently, the epidermis shows regularly spaced
thickenings that project into the dermis.
The portion of dermis intervening between these
projections form the dermal papillae.
Still later, surface elevations (epidermal ridges) are
formed by further thickening of the epidermis in the
The nails develops from surface ectoderm.
The ectoderm at the tip of each digits becomes
thickened to form a primary nail field.
Subsequently this thickening migrates from the tip of the
digit onto its dorsal aspect.
The cells in the most proximal part of the nail field
proliferate to form the root of nail.
Here the cells of the germinal layer multiply to form a
thick layer of cells called the germinal matrix.
As the cells multiply they are transformed into the nail
substance which corresponds to the stratum lucidum of
are also derived from surface ectoderm.
At the site where a hair follicle is to form, the germinal
layer of the epidermis proliferates to form a cylindrical
mass that grows down into dermis.
The lower end of this downgrowth becomes expanded
and is invaginated by a condensation of mesoderm,
which forms a papilla.
The hair itself is formed by proliferation of germinal cells
overlying the papilla.
As the hair grows to the surface, the cells forming the
wall of the downgrowth surrounds it and form the
epithelial root sheath.
In addition dermal root sheath is formed from the
surrounding mesenchymal cells.
sebaceous gland is formed as a bud arising from
ectodermal cells forming the wall of hair follicle.
sweat gland develops as a outgrowth from the
The outgrowth is at first solid but is later canalized.
The lower end of the outgrowth becomes coiled and
forms the secretory part of gland.
Anomalies of Akin and its
Absence of pigment in skin, hair and eyes occurs
because melanocytes are unable to synthesize
The skin may fail to develop in certain regions.
The skin may be in abnormal structure.
maybe absent. Occasionally they may show over
Congenital alopecia- hairs may be absent over the
Atrichia- absence of hairs in any body part.
Hypertrichosis- overgrowth of hairs.