Transcript 11-Dev. Integumentary system

The Integumentary System
The Integumentary System
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Consists of skin &
Its derivatives:
 Sweat glands
 Sebaceous glands
 Arrector pili
muscles
 Nails
 Hair
 Mammary glands
Development of Skin
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Skin consists of two layers that are derived
from two different germ layers
 Epidermis, superficial epithelial tissue
derived from surface ectoderm
 Dermis, deeper layer of connective
tissue derived from the mesoderm
Epidermis
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In the 4-5th week, the skin of the
embryo consists of simple
cuboidal epithelium….the surface
ectoderm
By the 7th week, the surface
ectodermal cells proliferate and
form a layer of squamous
epithelium, the periderm
(epitichium) and a basal
germinative layer.
During 1st & 2nd trimesters,
epidermal growth occurs in
stages, which result in an increase
in epidermal thickness
Periderm
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The peridermal cells continually
undergo keratinization and
desquamation and are replaced
by cells arising from the basal
layer
The exfoliated cells form part of
the white greasy substance, the
vernix caseosa, that covers the
body of the fetus
Replacement of peridermal
cells continue untill about the
21st week, thereafter the
periderm disappears and the
stratum corneum forms
Basal Germinative Layer
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This layer becomes the
stratum germinativum of
the epidermis
It proliferates and the
new cells are displaced
into the layers superficial
to it.
By 11th week, an
intermediate layer,
containing several cell
layers, is interposed
between the basal cells
and the periderm.
Basal Germinative Layer cont’d
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Proliferation of stratum
germinativum also forms
epidermal ridges which
extend into the developing
dermis.
These ridges begin to
appear in embryo of 10
weeks and are permenantly
established by the 17th week.
These ridges produce
grooves on the surface of
palms of the hand and soles
of the feet including digits
Melanoblasts & Melanocytes
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During the early fetal
period the epidermis is
invaded by melanoblasts,
cells of the neural crest
origin.
Melanoblasts move to
dermoepidermal junction
and differentiate into
melanocytes
The melanocytes have
several long processes.
Melanoblasts & Melanocytes cont’d
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The cell bodies of
melanocytes are
confined to the basal
layers of the epidermis,
and their processes
extend between the
epidermal cells
The melanocytes begin
producing melanin
before birth and
distribute it to the
epidermal cells
 At
birth all
layers of the
adult epidermis
are present
Dermis
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The dermis is derived from
the mesenchyme underlying
the surface ectoderm
This mesenchyme is derived
from the:
 Somatic layer of the lateral
mesoderm (most of it)
 Dermatomes of the
somites (some).
By 11th week, the
mesenchymal cells begin to
produce collagenous and
elastic connective tissue
fibers
Dermal Papillae
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As the epidermal
ridges are formed, the
dermis projects
upward into the
epidermis and forms
the dermal papillae
Capillary loops and
sensory nerve endings
develop in these
papillae
DP
DP
Hair
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Begin to develop during
the 3rd month, but they do
not become visible until the
20th week
Begins as an epidermal
proliferation, the hair bud,
into the underlying dermis.
The deepest part of the
hair bud becomes cupshaped, forming a hair bulb
The hair bulb gets
invaginated by
mesenchymal hair papilla
Hair cont’d
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The central epithelial cells of
the hair bulb give rise to the
shaft of the hair, that grows
through the epidermis and
protrudes above the surface
of the skin
The peripheral cells of the
hair bulb form the epithelial
root sheath.
The cells of the epithelial
root sheath proliferate to
form a sebaceous gland
bud.
Hair cont’d
Surrounding
mesenchymal cells
differentiate into
dermal root sheath.
 The arrector pili
muscle differentiates
from the surrounding
mesenchyme
 Melanoblasts
migrate into the hair
bulb and differentiate
into melanocytes
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Hair cont’d
Hairs are first recognizable in the
region of eyebrows, upper lip and
chin
 The first set of hairs that appear are
fine and colorless and are called
‘lanugo’ hair
 Lanugo hair are replaced during the
perinatal period by coarser hair
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Sweat Glands
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Develop at about 20 weeks
as solid growth of epidermal
cells into the underlying
dermis
Its terminal part coils and
forms the body of the gland
The central cells degenerate
to form the lumen of the
gland
The peripheral cells
differentiate into secretory
cells and contractile
myoepithelial cells
Vernix Caseosa
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Vernix caseosa, is the waxy
or cheesy white substance
found coating the skin of the
newborn.
The vernix is secreted by the
sebaceous glands around the
20th week of gestation
It is composed of:
 Sebum (the secretion of
the sebaceous glands)
 Desquamated epithelial
cells
 Fetal hair (lanugo hair)
It protects the baby's skin
from dehydation and from
constant exposure to the
amniotic fluid.
Nails
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Begin to develop at about
10th week of gestation, as
thickened areas of the
epidermis at the tips of the
digits.
Later, these nail fields
extend to the dorsal surface
and become surrounded by
the nail folds.
Cells from the proximal nail
fold grow over the nail field
and form keratinized nail
plate, the primordium of the
nail.
The Mammary Glands
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Begin to develop during
the 6th week as
thickened strips of the
ectoderm (mammary
ridges) that extend from
the axillary to the
inguinal regions.
They regress in most
locations except in the
area of the pectoral
muscle, where they
proliferate.
The Mammary Glands cont’d
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The downgrowth of
epithelial tissue
continues to proliferate
into 16 to 24 solid
outbuddings which give
rise to the lactiferous
ducts.
Fibrous connective
tissue and fat of the
mammary gland develop
from the surrounding
mesenchyme.
The lactiferous ducts at
first open into a small
mammary pit.
Postnatal Development
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F.
Newborn (nipple is
inverted)
Child (nipple elevates to
form the usual nipple)
Puberty (breast
enlarges due to
development of the
mammary glands) &
deposition of fat
Late puberty
Young adult
Pregnant female
Anomalies
Gynecomastia
 Polythelia
 Inverted nipples
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