Early fetal development

Question 1

how is gestational age calculated

Answer 1

beginning of last menstrual period

Question 2

Carnegie stage:

Answer 2

23 stages of embryo development based on embryo features not time
Allows comparison of developmental rates between species
Covers the window of 0-60 days fertilization age in humans

Question 3

fertilization age

Answer 3

also known as conceptual age):
measured from the time of fertilization (assumed to be +1 day from last ovulation)
difficult to know time of fertilization exactly (unless IVF)

Question 4

how long does the embryonic stage last?

Answer 4

16-50 days
Establishment of the germ layers and differentiation of tissue types
Establishment of the body plan

Question 5

fetal stage

Answer 5

after 50 days
8-38 weeks
organ systems present
migartion of organ systems to final location

Question 6

embryogenic stage

Answer 6

14-16 days Determining two populations of cells: pluripotent embryonic cells (contribute to fetus)
Extraembryonic cells (contribute to the support structures eg placenta)

Question 7

first few days of life

Answer 7

-Ovulated oocyte
(1 cell)
- Zygote
- cleavage stage embryos (2-8 cells)
- Morula 16+cells
- blastocyst 200-300 cells

Question 8

when is zona pelucida formed?

Answer 8

surrounds the ovulated oocyte so from very beginning

Question 9

zygotic genome activation

happens when?

Answer 9

4-8 cell stage
transcription of embryonic genes so embryo is no longer dependant on maternal mRNAs and proteins
- now genes of embryo can be transcribed

Question 10

Compaction

Answer 10

stage when outer cells begin to press against zona pelucida

Question 11

how does ovulated oocyte become morula > blastocyst

Answer 11

1- compacted morula with outer cells pressed agaibst zona pelucida
2- inner and outer cells reorganize

= blastocoel cavity is formed

Question 12

outline what are the effects of outer cells becoming pressed against zona pelucida?

Answer 12

COMPACTION
Change from spherical to wedge-shaped.

Outer cells connect to each other through tight gap junctions and desmosomes
Forms barrier to diffusion between inner and outer embryo
Outer cells become polarised

Question 13

blastocoel

Answer 13

fluid filled cavity formed
osmotically by
trophoblast pumping
Na+ ions into cavity

Question 14

zona pellucida

Answer 14

Hard protein shell inhibiting polyspermy and protects early embryo

Question 15

Inner cell mass

Answer 15

Pluripotent embryonic cells that will contribute to the final organism

Question 16

which cell contribute to the extraembryonic structures

Answer 16

Trophoectoderm

Question 17

to implant what must the blastocyst do ?

how ?

Answer 17

escape zona pellucida

by contraction and digestion

Question 18

formation of syncitiotrophoblast

Answer 18

trophoblast cells fuse to form

Question 19

syncitiotrophoblast

function

Answer 19

destroys local uterine endometrium cells, syncitiotrophoblast cells invade
- interface between maternal blood and embryo formed

Question 20

what are cytotrophoblast cells

Answer 20

from trophoectoderm

cells remain individual to provide source of syncitiotrophoblast cells

Question 21

how do inner cells divide?

Answer 21

epiblast

hypoblast

Question 22

final stage before gastrulation?

Answer 22

bilaminar embryonic disc

amnionic cavity forms ; creating 2 cavities

This leaves a two-layer disc of epiblast and hypoblast, sandwiched between cavities.

Question 23

amnion, amniotic cavity, ___,hypoblast,____

Answer 23

amnion, amniotic cavity, epiblast, hypoblast, blastocoel, Cytotrophoblast

Question 24

amnion, _____ , _____, hypoblast, _____, Cytotrophoblast

Answer 24

amnion, amniotic cavity, epiblast, hypoblast, blastocoel, Cytotrophoblast

Question 25

draw out embryonic cell lineages complete

Answer 25

zona pelucida> inner cell mass and the outer cells > trophoblast
inner cell: epiblast and hypoblast

trophoblast > syncitiotrophoblast, cytotrophoblast

epiblast split into amnion and epiblast by formation of amniotic cavity

epiblast > ectoderm, mesoderm, endoderm

Question 26

endoderm - which organs

Answer 26

GI tract, liver, pancreas, lung, thyroid

Question 27

ectoderm- organs

Answer 27

CNS , neural crest
skin epithelia
tooth enamel

Question 28

mesoderm

Answer 28

blood 
muscle 
gonads
kidneys, adrenal cortex
bone , cartilage
heart

Question 29

notochord

Answer 29

is a rod-like tube structure formed of cartilage-like cells

Forms along the embryo midline, under the ectoderm

Acts as a key organizing centre for neurulation and mesoderm development

Question 30

neurulation

Answer 30

notochord signalling creates neural groove

= creates two ridges : neural folds
> move towards each other over neural groove
= forms hollow tube
neural tube overlaid with epidermis - ectoderm derived

Question 31

failure of neural tube closure causes which conditions?

Answer 31

spina bifida

anencephaly

Question 32

outline somitogenesis

Answer 32

either side of neural tube
paired blocks of paraxial mesoderm
symmetrical blocks bud off in pairs
= somites

commences at head end and progresses down the long axis of the embryo

Question 33

how many pairs of somites do humans have?

Answer 33

42-44

Question 34

somite initial two types of tissue?

Answer 34

dermomyotome

sclerotome

Question 35

what is the vertebrae and rib cartilage derived from?

Answer 35

sclerotome

Question 36

dermomyotome

Answer 36

dermatome

myotome

Question 37

dermatome

Answer 37

gives rise to dermis of the skin, some fat and connective tissues of neck and trunk

Question 38

mytome

Answer 38

forms the muscles of the embryo

Question 39

what arises from two types of folding in the embryo:

and what type of folding is this?

Answer 39

primitive gut

Ventral folding: where the head and tail ends curl together
Lateral folding: where the two sides of the embryo roll

this folding pinches of the yolk sac = forming primitive gut

Question 40

when is the fetal heartbeat detectable?

Answer 40

Fetal heartbeat detectable from ~6 weeks gestational age