Embryology Weeks 1-4

Question 1

Pre-implantation

Answer 1

when zygote moves through uterine tube and divides, but does not increase in size

Question 1

Fertilization

Answer 1

sperm passes through zona pellucida and invades the ovum (Day 1)

Question 2

Zona Pellucida

Answer 2

outer coating of the ovum

Question 3

Cleavage

Answer 3

zygote travels toward the uterus and divides without growing in size (Day 2-4)

Question 4

Zygote

Answer 4

fertilized cell

Question 5

Morula

Answer 5

day 4 16-celled, consistes of the blastomere (divided cells) and the zona pellucida

Question 6

Blastocyst

Answer 6

Day 5, morula has entered the uterine cavity and become a blastocyst, zona pelliucida degrades and trophoblast and embryoblast and blastocyst cavity form

Question 7

Trophoblast

Answer 7

cells in the blastocyst that form the outer ring and a larger cell mass at the embryonic pole with the embryoblast

Question 8

Embryoblast

Answer 8

cells in the blastocyst near the embryonic pole that reside between the trophoblast and the blastocyst cavity

Question 9

Two poles of the Blastocyst

Answer 9

embryonic pole (near differentiated layers), abembryonic pole (away from differentiated layers)

Question 10

Implantation

Answer 10

Week 2, embryoblast differentiates into 2 layers (epiblast and hypoblast) to form the bilaminar disc

Question 11

Bilaminar disc

Answer 11

in implantation, the embryoblast differentiates into the epiblast and and hypoblast (Day 6)

Question 12

Epiblast

Answer 12

cells between the trophoblast and the hypoblast that start to differentiate to form the amnioblasts and the amniotic cavity

Question 13

Hypoblast

Answer 13

differentiated from the embryoblasts, these cells send out a layer of cells within the blastocyst cavity to form the primary yolk sac (called the exocoelomic membrane), “hypoblast cells” are within the bilaminar disc

Question 14

Primary Yolk Sac

Answer 14

formed at Day 7 by the hypoblast cells creating the exocoelomic membrane, this provides nutrition for the fetus before the placenta forms

Question 15

Exocoelomic Membrane

Answer 15

membrane formed from hypoblast cells to create the primary yolk sac at Day 7 (also called heuser’s membrane)

Question 16

What does the trophoblast differentiate into during implantation?

Answer 16

the syncytiotrophoblast (outer most layer of cells when implanted) and the cytotrophoblast (second most outer layer of cells

Question 17

Choronic Cavity

Answer 17

the exocoelomic membrane spilts into 2 layers and to surround embryo and secondary yolk sac and to create this new cavity (Day 12)

Question 18

Connecting Stalk

Answer 18

the link between the exocoelomic membrane creating the outer choronic cavity and the exocoelmic membrane that covers the amniotic cavity, embryo (epiblast/hypoblst), and the 2 yolk sac (will become the umbilical cord)

Question 19

Gastrulation

Answer 19

formation of 3 embrionic germ layers (mesoderm, ectoderm, endoderm)

Question 20

Primitive Streak

Answer 20

forms at the caudal end of the epiblast (Day 15) and dorsal

Question 21

Primitive Pit

Answer 21

at cranial (toward head) end of primitive streak

Question 22

Mesoderm formation

Answer 22

epiblast cells migrate inbetween the epiblast and hypoblast to form the mesoderm (do not get between the epiblast in two places though - what will eventually be the mouth and the anus)

Question 23

Endoderm formation

Answer 23

migrating epiblast cells replace the hypoblast cells to form the endoderm (ventral)

Question 24

Ectoderm Formation

Answer 24

the ectoderm is formed from the epiblast cells (dorsal)

Question 25

Notochord

Answer 25

formed by mesodermal cells and will induce neurulation

Question 26

Neurulation

Answer 26

(Day 19-23) notochord induces ectoderm to differentiate into neural crest and neural tube and surface ectoderm

Question 27

Neural Crest

Answer 27

will become peripheral nervous system

Question 28

Neural Tube

Answer 28

will become central nervous system

Question 29

Surface Ectoderm

Answer 29

will become epidermis of the skin, glands, hair nails, tooth enamel, lens and cornea of eye, and induce limb bud formation

Question 30

Mesoderm differentiation

Answer 30

forms 3 domains: paraxial mesoderm (most medial, next to notochord), intermediate mesoderm(middle), and lateral plate mesoderm

Question 31

Paraxial Mesoderm

Answer 31

1. somites –> skeletal muscles of back, trunk and limbs 2. forms the vertebrae, dermis and hypodermis

Question 32

Intermediate Mesoderm

Answer 32

forms urogential system

Question 33

Lateral Plate Mesoderm

Answer 33

forms bones of limbs, heart and blood vessels, smooth muscle, serous linings of body cavity

Question 34

Endoderm differentiation

Answer 34

gut tube, epithelial linings of the GI and respiratory tract, parenchyma cells of liver, pancreas and bladder

Question 35

Longitudinal Folding

Answer 35

craniocaudally folding - mostly contributes to fetal body position and it forms the gut tube from endoderm

Question 36

Lateral Folding

Answer 36

growing and folding from dorsal to ventral to create body cavity between the visceral layer of lateral plate mesoderm (around organs) and parietal layer of lateral plate mesoderm (lining the cavity)