Block III: SKIN video 4 (embryology of skin) Flashcards
What cells are in the beggining of the embryo?
single layer of surface ectodermal cells sitting on a layer of mesoderm
explain the process of epidermis division Into what does the epithelium layer divide into?
- In the beginning of the 2nd month this epithelium
divides and a layer of flattened cells, the periderm or
epitrichium is laid down on the surface and the
original layer becomes the basal layer. The
periderm layer cells continually undergo
keratinization and are sloughed off and replaced by
cells from the basal layer - Following this, the basal layer of cells at ~11
weeks proliferates to form a third intermediate zone
which will give rise to the outer layers of the
epidermis apical to the basal layer. The basal layer is
now called the stratum germinativum. - By the end of the 4th - 5th month, the epidermis
has the definative 4 or 5 layers seen in the adult
skin. This process of differentiation of the layers
starts at the cranial end and moves caudally. The
cells at this point are called keratinocytes.
- The periderm is shed and lost at about this time.
Which cells invade suring the 6th-7th week?
Neural crest cells invade into the developing
epidermis as early as the 6th to 7th weeks to
become melanocytes
What cells enter from bone marrow?
langerhan cells (dendritic cells) 7th week
which cells differentiate by week 4th-6th?
merkel cells
Where does dermis derive from?
The dermis derives from the mesenchyme
underlying the surface ectoderm
explain development of dermis
This
mesenchyme is derived from the somatic layer
of the lateral plate mesoderm & the
dermatomes from somites. By the 11th week
this mesenchyme called the corium starts to
develop both collagenous fibers and elastic
fibers and be divided into the papillary and
reticular layers.
* During the 3rd & 4th months, this tissue the
corium also forms the dermal papillae
projecting up into the epidermis between the
developing downward epidermal ridges. Both
capillaries and nerve fibers invade or develop
with these dermal papillae
explain hair development?
- Hairs begin to develop during the 9th to 12th
weeks, but they do not become easily
recognizable until approximately the 20th week - A hair follicle begins as a proliferation of the
stratum germinativum of the epidermis and
extends into the underlying dermis as a hair bud. - The hair bud soon becomes a club-shaped hair
bulb which continues to invaginate into the
developing dermis. - At about the 12th week, the hair bulb is
invaginated by a small mesenchymal hair papilla
(hair dermal papillae) which induces the hair
follicle cells immediately above (germinal matrix
cells) to start formation of the hair, while the
peripheral cells of the developing hair follicle
form the epidermal root sheath, and the
surrounding mesenchymal cells differentiate into
the dermal root sheath. - Melanocytes invade the germinal matrix region of
the follicle to produce melanin for the hair color.
Explain development of sebaceous glands
Most sebaceous glands develop as buds
(~week 15) from the sides of the developing
epidermal root sheaths of the hair follicles.
The buds grow into the surrounding CT and
branch to form the primordia of the alveoli
and their associated ducts. The central cells
of the alveoli break down, forming an oily
secretion called sebum; this is released by
the short duct into the hair follicle and passes
to the surface of the skin.
explain development of eccrine sweat glands
develop as
epidermal down growths—cellular
buds—into the underlying mesenchyme
at about week 16- 17. As a bud
elongates, its end coils to form the
primordium of the secretory part of the
gland. The epithelial attachment of the
developing gland to the epidermis forms
the primordium of the sweat duct. The
central cells of the primordial ducts
degenerate, forming a lumen. The
peripheral cells of the secretory part of
the gland differentiate into myoepithelial
and secretory cells
explain develop of aprocine sweat glands?
Also develop
from the downgrowths of the stratum
germinativum of the epidermis that give
rise to the hair follicles. As a result, the
ducts of these glands open into the
upper part of the hair follicles, superficial
to the openings of the sebaceous glands.
They begin to secrete during puberty.
What is ichthyosis?
This is a general term for a
group of skin disorders resulting from
excessive keratinization (keratin
formation) and thickening of the fetal and
infant skin. The skin is characterized by
dryness and fish-skin–like scaling, which
may involve the entire body surface.
identify
child with ichthosis (epidermolytic
hyperkeratosis)
What is colloidon infant?
is covered at birth by a thick, taut membrane that
resembles collodion or parchment. This membrane cracks with the first
respiratory efforts and begins to fall off in large sheets. Complete shedding of
membranes may take several weeks, occasionally leaving normal-appearing
skin. However, more often find skin with either of 2 disorders:
1) Lamellar Ichthyosis
2) Harlequin fetus
What is lamellar ichthyosis?
Lamellar Ichthyosis: Inherited as an autosomal recessive trait. Once the outer
layer of the colloidin skin is shed, the skin is red and scaly. Lips may turn
outwards, palmar-plantar hyperkeratosis, nail abnormalities, dehydration and
respiratory problems.
90% of cases due to mutation/defects in transglutaminase-1 gene (TGM1)
involved in crosslinking of proteins on cytoplasmic surface of keratinocyte
membranes in stratum corneum to form cornified cell envelope necessary to
make the cells impermeable to water.
In addition, since the cornified cell envelope is also necessary as a scaffolding for
the lipids released from the membrane coating granules to form the waterproofing
barrier in the intercellular space, the water-proofing in this part of the
mechanism may also be affected.
