Download Histogenesis

Histogenesis
149 DCT
Basic morphologic processes
Processes which are involved in development
Proliferation
Apoptosis
Association – cells express intercellular junctions
Migration – loss of intercellular contacts – cells
express adhesive molecules for attachment to the
intercellular matrix
Induction → determination and differenciation
Organogenesis: 3rd-8th week

Formation of all organ systems:
−
−
Cardiovascular and nervous - 3.week
External genitalia – later than 8.week

Changes in outer shape

Most critical period
Formation of 3D shape

Head fold

Tail fold

Lateral folds

Head fold - growth of brain and spinal cord – folding (septum
transversum and heart are pushed ventrally)

Changes in shape of intraembryonic coelomic cavity

Tail fold – cloacal membrane is also pushed ventrally

Lateral folds – gut closure, formation of umbilical cord
Notochord
Axial structure
Signalization – induction of changes in ectoderm –
neuroectoderm and ventral plate of neural tube,
in mesoderm – somites and in endoderm =
segmentation
It grows to the praechordal (oropharyngeal) plate
Prechordal plate – organizer in head regioninduction of prosencephalon development
Development of notochord
After notochord has reached oropharyngeal
membrane, it grows by proliferation and
migration of cells of primitive streak and node –
caudal morfogenetic system
After head and neck has formed, body grows by the
activity of caudal morfogenetic system
Primitive streak breaks down or
reduces gradually
Sacrococcygeal teratoma
Teratoma
Neurulation
Primitive node and notochord – signal molecules – interaction
between epithelial and mesenchymal cells
Regionalization – craniocaudal gradient -segmentation of CNS (hox
genes)
Neural plate – restriction, determination and differenciation of
ectoderm
Cell proliferation – neural groove, neural folds
Folds fuse – it starts in cervical region and continues
to the cranial and caudal end –
Cranial and caudal neuropores + Neural crest cells
Neural tube segmentation
Brain segmentation - 3 brain vesicules –
prosencephalon, mesencephalon and
rhombencephalon
Segments – neuromeres
Mechanism: segmental genes are expressed (hox)
Segmentation of neural tube – induction - signals
from notochord
Mesoderm development
Axial mesoderm – notochord and cranial organizer
(praechordal plate)
Intraembryonic mesoderm –
Paraaxial mesoderm– somites
Intermediate mesoderm
Lateral: somatopleura, splanchnopleura and
intraembryonic coelom
Cardiogenic field
Paraaxial mesoderm
Cranial region (head) –
somitomeres – swirls
or spirales of cells
th
From 8 somitomese –
somites are formed
Somites – gradual
development (42 – 44
pairs)
Derivatives of the three germ
layers




Ectoderm – CNS, PNS, retina, epidermis, mammary gland,
enamel
Cells of neural crest -– ganglia, Schwann´s cells,
melanocytes, medulla of suprarenal gland, meninx, muscle,
connective tissue and cartilages/ bones of pharyngeal arches
Mesoderm – connective tissue, cartilage, bone, muscle,
vessels, kidney, ovary, testes, spleen, cortex of suprarenal
gland, mesothelium
Endoderm – digestive and respiratory system (epithelium and
glands), thyroid gland, parathyroid glands, thymus, pancreas,
liver, urinary bladder
4 week
th

Closure of rostral and caudal neuroporus (24th and 26th
day)

Somites (4.-12.)

Pharyngeal arches are visible by 26th day

Heart prominence

Upper limb buds 26th- 27th day

Otic pits and lens placodes

Lower limb buds – by the end of week
Tubular embryo
5 week
th




Head growth – brain and pharyngeal arches
Pharyngeal arches – development of face and
neck
Ectodermal grooves and endodermal pouches,
pharyngeal membranes
Aortic arches – vessels in pharyngeal arches
6 week
th



Development of limbs – future fingers – digital
rays are visible
Development of ear: external acustic meatus (first
pharyngeal groove), swelling around it fuse to
form auricle
Head is longer than body
7 week
th


Development of limbs – digits of upper limbs
Umbilical herniation– intestine enters the
extraembryonic coelom in the proximal region of
umbilical cord.
8the week

Digits also in lower limbs

Tail disappears at the end of 8th week

Embryo has distinct human characteristics – head
constitutes almost ½ of embryo

Eyes – eye lids fuse by end of 8th week

External genitalia - indifferent
Somitogenesis
Segmentatio – stimulated from notochord (Shh) and
ectoderm
Various concentration of signal molecules
Other signals – Wnt, Pax, BMP-4
Dermatomyotome – dermatome and myotome
Sclerotome
Somites
Cell association
Development of vertebrae



Vertebrae develop from
sclerotome
Mesenchymal tissue from
sclerotome surrounds
notochord (nucleus
pulposus)
Vertebral body forms
from the cranial and
caudal halves of two
succesive sclerotomes
Chicken embryo
Sclerotome
Neural tube development
Signaling from
notochord and
superficial ectoderm –
histo-differentiation of
neuroectoderm
Various neuron types
Neural tube – proliferating cells
Neuroectoderm differentiation
Neuroectoderm differentiation
Germ layer – proliferating cell – future ependym
Cells migrating to mantel layer – neuroblasts –
neurons – enter G0 phase
Other cells – glioblast – radial glia (Müller cells in
retina) and glia – astrocytes and oligodendrocytes
Neural crest cells
Cranial neural crest cells
Development of head,
pharyngeal arches and
heart
Segmentation of brain
and neural crest
Mesenchyme
Blood cells
Endothelium
Connective tissue cells – fibroblast, mast cell,
adipocytes, chondrocyte, osteoblast and
osteocyte,odontoblast
Skeletal muscle development
Cells in somite
Myoblast – they can
migrate and proliferate
Myotubes – myoblast
fuse
Mature myofiber –
presence of actin and
myosin – fully
differentiated cells
Development of epidermis
Simple cuboidal
epithelium
Periderm – 2 layers
Squamous stratified
epithelium
Later – superficial cells
start to cornified
Fetal period



By 9th week till birth
Measurement: Biparietal distance, head
circumference, body circumference, femur length
Disorder – IUGR – intrauterinne growth
retardation – reduction of vascular supply,
placental insufficiency