L11- Early embryology 2 Flashcards
outline the broad stage of early embryology
- fertilisation and implantation
- gastrulation
- neurulation
- segmentation- somites
- folding
a zygote
single cell formed when egg and sperm cell fuse- fusion is known as fertilisation
cleavage- first cell division- occurs
within 24-30h after fertilisation
by late cleavage what is formed
morula (32 cells)
when does blastulation occur
day 4
blastulation
2 types of cell are produced
- outer cell- trophoblast cells
- inner cell mass
compaction
first cavity forms within blastocyst- blastocoel- pushes inner cell mass to one side
after blastulation
blastocyst hatches from zona pellucida
inner cell mass differentiates into
epiblast- aminiotic cavity
hypoblast- primitive yolk sac
implantation occurs
on day 6-7
summary of zygote to embryoblast
gastrulation starts on
day 16 (week 3)
during gastrulation what occurs
production of germ layers
name the germ layers
ectoderm
mesoderm
endoderm
ectoderm
epidermis, hair, nails, brain, spinal cord, peripheral NS
mesoderm
muscle, bone, connective tissue, notochord, kidney, gonads, circulatory system
endoderm
epithelial lining of the digestive tract
first step of gastrulation
formation of primitive streak
primitive streak determines the
midline of the body
- should have mobile cilia which mean the body structures are on the right side of the body
prior to gastrulation the embryonic disk is
bilaterally symmetrical
- but int he body clear differenc ebetween left and right side
situs invetus
- Complete mirror image viscera
- Commonly exults in immobile cilia
- Infertile
- No associated morbidity
- Problems arise if there is both normal and mirror image disposition
immotile cilia during gastrulation mean
waft organs into the right direction
during gastrulation the hyboblast is replaced and the epiblast differentitated into the trilaminar disk
ectoderm
mesoderm
endoderm
directly beneath the primitive the streak in the mesoderm what is formed
the notochord
when does the notochord form
week 4
the notochrod
notorchord helps define major axis of the body and are important in neurulation (triggers it)
neurulation occurs
in two stages
stage 1
formation of neural tube
second stage of neurulation
Notochord also causes the mesoderm to subdivide and differentiate
in the first stage the notochord causes the ectoderm above to
thicken
neural tube formation
- Triggered by signals from the notochord
- Just above the notochord the ectoderm thickens (neural plate) and forms a fold producing a neural groove
- On either side of the neural groove folds will form
- Neural folds come together until the two-fold touch each other
- Neural tube found in the mesoderm dissociates from the rest of the ectoderm and the rest of the ectoderm will seal itself back together
neural tube will become the
brain stem
second stage of neureulation
Notochord also causes the mesoderm to subdivide and differentiate
notochord comes from the
axial meosderm
somites will come from the
paraxial mesoderm
somites differentiate into
muscle, cartilage, bone, and dermis
myotomes and dermatomes
intermediate mesoderm si the
original of urogenital sysrtem- kidney, gonads, adrenal glands
lateral plate mesoderm
heart, blood vessels, muscle in our organs
after neurulation
segmentation and organisation of the mesoderm–> giving rise to somites
somites
organisation of oparaxial mesoderm into segements
how many somite pairs
31
first pair of somites appear
on day 20 in the occipital region
somites give rise to
repeating structures such as…
- vertebrae
- ribs
- intercostal muscle
- spinal cord segments
somites guide
innervation by myotomes
somite derivative
dermatome
myotome
sclerotome
dermatome
skin section
- dermis
myotome
- muscles
sclerotome
hard tissue section
- bone
31 somites and 31
spinal nerves
why is embryonic folding important
before embryonic folding, the mouth is at the same level as the heart
aim of folding
to present only ectoderm to the otuside world
what folding achieves
Draws together the margins of the disk
- Creating a ventral body wall
- Pilling amniotic membranes around the disc
- Embryo becomes suspended within the amniotic sac
- Pulling connecting stalk enthralling
- Also creates the primordium of the gut, put the heart and the primordium of the diaphragm in the right place and creates a new cavity within he embryo (GI tract)
explain folding brefiled
the cranial (head) and caudal (back) fold in towards eachother
- the endoderm (GI tract) folds into the middle, with the ectoderm covering around it
- when the tract is formed, the defintitve yolk sac will be coming out from it
- this yolk sac will be pinched off
diagram of folding con..
by the end of the 4th week
- Nervous system has started to form
- Segments have appeared
- Assigning tasks to specific cells
- Embryo has folded, putting everything in right place
