Early Fetal Development

Question 1

What two ways can we measure embryo fetal development

Answer 1

Fertilization age
Gestational age

Question 2

Fertilization age

Answer 2

Age measured from time of fertilization
Assumed to be 1 day after ovulation

Question 3

Gestational age

Answer 3

Age calculated from start of last menstrual period
14 days longer than fertilization age

Question 4

What are the Carnegie stages of embryo development?

Answer 4

23 stages of embryo development
Based knowledge embryo features
Allows comparison of different developmental rates between species
0-60 days in humans

Question 5

Embryogenic stage

Answer 5

14-16 days post fertilization
Forms early embryo from fertilized oocyte
Forms pluripotent embryonic cells
Forms extraembryonic cells

Question 6

Embryonic stage

Answer 6

16-50 days
Establish germ layers
Establishes body plan

Question 7

Fetal stage

Answer 7

50-270 days post fertilization
Major organs present
Migration of some organ systems
Extensive growth

Question 8

Trimesters

Answer 8

1st consists of embryogenic and embryonic
2nd and 3rd consists of fetal stage

Question 9

Oocyte to blastocysts

Answer 9

• 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

Question 10

Zonna pellucida

Answer 10

Protein shell of egg cell
Protects embryo
Inhibits polyspermy

Question 11

Up until maternal to zygotes transition what is the development of the embryo dependent on

Answer 11

Maternal mRNAs and proteins
Occurs between the 4-8 cell stage
These are made pre ovulation

Question 12

what happens at maternal to zygotic transition

Answer 12

Transcription of embryonic genes (zygomatic genome activation)
increased protein synthesis
organelle maturation
occurs at 4-8 cell stage

Question 13

what is compaction

Answer 13

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

Question 14

what cell type do inner cells give rise to

Answer 14

extra embryonic cells

Question 15

trophoectoderm

Answer 15

the outer cells of the embryo

Question 16

what is the blastocoel

Answer 16

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

Question 17

what is hatching and why is it needed

Answer 17

when blastocysts escape the zona pellucida
occurs via enzyme degredation and cellular contractions

Question 18

What does the trophectoderm separate/differentiate into

Answer 18

• 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

Question 19

What does the inner cell mass separate/differentiate into

Answer 19

epiblast which forms fetal tissue
hypoblast which forms yolk sac

Question 20

what happens to the epiblast in bi laminar embryonic disc formation

Answer 20

some cells become separated by amniotic cavity
epiblast sits on top of hypoblast layer

Question 21

What do the syncytiotrophoblasts secrete at this stage? (VSAQ no abbreviations)

Answer 21

hCG
detects beta subunit of pregnancy testing
Human chorionic gonadotrophin

Question 22

gastrulation

Answer 22

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

Question 23

Which organs does the endoderm give rise to? GILLT

Answer 23

• GI Tract
• Liver, Pancreas
• Lung
• Thyroid

Question 24

Which organs does the ectoderm give rise to? CST

Answer 24

• CNS & neural crest
• Skin epithelia (epidermis)
• Tooth enamel

Question 25

Which organs does the mesoderm give rise to? BMGB

Answer 25

- Blood (endothelial cells, RBCs and WBCs) - Muscle (smooth, skeletal and cardiac) - Gonads, Kidneys and adrenal cortex - Bone, cartilage

Question 26

notochord

Answer 26

a rod-like structure formed of cartilage-like cells which form along the embryo midline under the ectoderm

Question 27

How does notochord organize neurulation

Answer 27

controls neural plate ectoderm

Question 28

which germ layer is notochord derived from

Answer 28

mesoderm cells

Question 29

neuralation

Answer 29

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

Question 30

For CNS development what must happen at open ends of neural tubes

Answer 30

closure at head end and tail end head end closure occurs first at 23 days then tail end at 27 days

Question 31

which conditions can failure of neural tube development lead to

Answer 31

spina bifida- open neural tube anencephaly-absence of skull and brain

Question 32

Neural crest cells CCTVS

Answer 32

ectoderm cranial cardiac trunk vagral and sacral defects of neural crest migration/specification lead

Question 33

Somitogenesis

Answer 33

Forms somites-paired blocks of paraxial mesoderm with one on each side of neural tube 1 pair every 90 mins 44 pairs

Question 34

what types of embryonic tissues do somites form

Answer 34

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

Question 35

Gut tube formation

Answer 35

ventral folding and lateral folding of embryo pinches of yolk sac to form primitive gut

Question 36

ventral vs lateral folding

Answer 36

ventral is where head and tail end curl together lateral is where two sides of embryo roll

Question 37

3 derivative's of primitive gut

Answer 37

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

Question 38

from which germ layer is heart derived

Answer 38

mesoderm heart detected at 6 weeks

Question 39

From which germ layer are the lungs derived?

Answer 39

endoderm lungs arise from lung bud

Question 40

From which germ layer are the gonads derived?

Answer 40

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

Question 41

From which germ layer is the epidermis derived?

Answer 41

ectoderm

Question 42

From which germ layer is the dermis derived

Answer 42

mesoderm