Early Fetal Development Flashcards
What two ways can we measure embryo fetal development
Fertilization age
Gestational age
Fertilization age
Age measured from time of fertilization
Assumed to be 1 day after ovulation
Gestational age
Age calculated from start of last menstrual period
14 days longer than fertilization age
What are the Carnegie stages of embryo development?
23 stages of embryo development
Based knowledge embryo features
Allows comparison of different developmental rates between species
0-60 days in humans
Embryogenic stage
14-16 days post fertilization
Forms early embryo from fertilized oocyte
Forms pluripotent embryonic cells
Forms extraembryonic cells
Embryonic stage
16-50 days
Establish germ layers
Establishes body plan
Fetal stage
50-270 days post fertilization
Major organs present
Migration of some organ systems
Extensive growth
Trimesters
1st consists of embryogenic and embryonic
2nd and 3rd consists of fetal stage
Oocyte to blastocysts
- Ovulated oocyte fertilized → unicellular zygote → 2, 4, 8 cell embryos (cleavage stage embryos) → Morula (16 cell embryo) → blastocyst
- This development is happening as the oocyte and the early embryo is migrating along to fallopian tube and into the uterus where it can implant
Zonna pellucida
Protein shell of egg cell
Protects embryo
Inhibits polyspermy
Up until maternal to zygotes transition what is the development of the embryo dependent on
Maternal mRNAs and proteins
Occurs between the 4-8 cell stage
These are made pre ovulation
what happens at maternal to zygotic transition
Transcription of embryonic genes (zygomatic genome activation)
increased protein synthesis
organelle maturation
occurs at 4-8 cell stage
what is compaction
embryo forms spherical (inner) and wedge shaped (outer cell)
occurs at the 8 cell stage
outer cells become pressed against the zona pellucida causing wedge shaped compaction
outer cells connect via tight gap junctions and desmosomes to form a barrier to diffusion
what cell type do inner cells give rise to
extra embryonic cells
trophoectoderm
the outer cells of the embryo
what is the blastocoel
fluid filled cavity in the middle of the embryo
trophoblasts pump ssodium ions into the centre of the embryo so water moves in by osmosis
what is hatching and why is it needed
when blastocysts escape the zona pellucida
occurs via enzyme degredation and cellular contractions
What does the trophectoderm separate/differentiate into
-
Syncytiotrophoblast, what does it do (2 things)
- Invades the uterine endometrium, destroying local maternal cells
- Establishes maternal blood supply to embryo by breaking down capillaries
- Cytotrophoblast, what does it doContinue to divide to provide a source of syncytiotrophoblasts
What does the inner cell mass separate/differentiate into
epiblast which forms fetal tissue
hypoblast which forms yolk sac
what happens to the epiblast in bi laminar embryonic disc formation
some cells become separated by amniotic cavity
epiblast sits on top of hypoblast layer
What do the syncytiotrophoblasts secrete at this stage? (VSAQ no abbreviations)
hCG
detects beta subunit of pregnancy testing
Human chorionic gonadotrophin
gastrulation
the formation of 3 germ layers
1. Epiblasts of bilaminar embryonic disc form a primitive streak
2. Primitive streak elongates and forms a primitive node
3. Primitive node contains circular depression which eventually forms a primitive groove
4. Invagination occurs (cells separate from epiblast)
5. The first cells to invaginate through the primitive groove form the definitive endoderm, (the hypoblast is displaced by spreading endoderm)
6. The remaining cells of the epiblast form the ectoderm (the exterior layer)
7. The cells in the space between the endoderm and the ectoderm, form the mesoderm
Which organs does the endoderm give rise to? GILLT
- GI Tract
- Liver, Pancreas
- Lung
- Thyroid
Which organs does the ectoderm give rise to? CST
- CNS & neural crest
- Skin epithelia (epidermis)
- Tooth enamel
Which organs does the mesoderm give rise to? BMGB
- Blood (endothelial cells, RBCs and WBCs)
- Muscle (smooth, skeletal and cardiac)
- Gonads, Kidneys and adrenal cortex
- Bone, cartilage
notochord
a rod-like structure formed of cartilage-like cells which form along the embryo midline under the ectoderm
How does notochord organize neurulation
controls neural plate ectoderm
which germ layer is notochord derived from
mesoderm cells
neuralation
Trabsfornation of neural plate into neural tube
1. Signals from notochord cause invagination of neural plate ectoderm, forming neural groove
2. Forms two neural folds containing neural crest cells
3. Neural folds fuse together over neural groove, forming a hollow tube
4. Neural tube overlaid with epidermis (which is ectoderm derived)
5. Migration of the neural crest cells from folds
For CNS development what must happen at open ends of neural tubes
closure at head end and tail end
head end closure occurs first at 23 days then tail end at 27 days
which conditions can failure of neural tube development lead to
spina bifida- open neural tube
anencephaly-absence of skull and brain
Neural crest cells CCTVS
ectoderm
cranial
cardiac
trunk
vagral and sacral
defects of neural crest migration/specification lead
Somitogenesis
Forms somites-paired blocks of paraxial mesoderm with one on each side of neural tube
1 pair every 90 mins
44 pairs
what types of embryonic tissues do somites form
sclerotome gives rise to vertebrae and rib cartilage
dermamyotome which makes dermatome and myotome
dermatome-rise to dermis of skin
myotome-rise to muscle of embryo
Gut tube formation
ventral folding and lateral folding of embryo pinches of yolk sac to form primitive gut
ventral vs lateral folding
ventral is where head and tail end curl together
lateral is where two sides of embryo roll
3 derivative’s of primitive gut
foregut-esophagus, stomach, upper duodenum, liver, gallbladder, pancreas
Midgut-Lower duodenum & remainder of small intestine, ascending colon and 2/3 of transverse colon
hindgut-last third of the transverse colon, descending colon, rectum and upper anal canal
from which germ layer is heart derived
mesoderm
heart detected at 6 weeks
From which germ layer are the lungs derived?
endoderm
lungs arise from lung bud
From which germ layer are the gonads derived?
mesoderm
not commited to tested or ovaries
presence of SRY gene on Y chromosome causes gonodal cells to become sertolli cells triggering testes development
absence of SRY triggers granulosa cell fate and ovary development which requires reinforcement by FOXL2
From which germ layer is the epidermis derived?
ectoderm
From which germ layer is the dermis derived
mesoderm
