Cleavage of zygote

Question 1

First step after zygote forms

Answer 1

Zygote begins to replicate inside zona pellucida

Question 2

<16 cells, each cell called

Answer 2

blastomeres

Question 3

cells totipotent until

Answer 3

totipotent until more than 8 cells

Question 4

> 16 cells, each cell called

Answer 4

morula

Question 5

transition from morula to blastocyst

Answer 5

trophoblast forms (outer layer of cells)
embryoblast forms (inner cell mass)
blastocyst cavity forms

Question 6

process of blastocyst leaving zona pellucida

Answer 6

blastocyst hatching

Question 7

importance of blastocyst hatching

Answer 7

allows embryo to embed within the posterior uterus wall

Question 8

changes during day of implantation

Answer 8

1) trophoblast splits in 2 forming syncytiotrophoblast + cytotrophoblast
2) embryoblast splits into 2 forming epiblast and hypoblast
3) blastocyst cavity surrounded by hypoblast - primitive yolk sac
4) amniotic cavity forms (surrounded by epiblast)

Question 9

features of syncytiotrophoblast

Answer 9

• unicellular, multinucleated outer most cell of embryo

- lacunae form - vacuole like nutrient stores

Question 10

features of cytotrophoblast

Answer 10

• Individual cells next most outer part of embryo

Question 11

features of epiblast

Answer 11

• larger columnar cells, surround the amniotic cavity

- dorsal side of embryo

Question 12

features of hypoblast

Answer 12

• less regular sized cells

- form lining of primitive yolk sac

Question 13

Day 9 changes

Answer 13

• fibrin coagulum forms to secure embryo to uterus wall

- secondary yolk sac forms surrounded by second layer of Heuser’s membrane (hypoblast cells)

Question 14

changes during day 12

Answer 14

• uteroplacental circulation is established (lacunae envelop capillaries allowing nutrients to diffuse through syncytiotrophoblast)
• exraembryonic mesoderm develops then degenerates leaving chorionic cavity
• connecting stalk forms (made from extraembryonic mesoderm)
• notochord forms in centre of mesoderm

Question 15

changes during week 3

Answer 15

• primitive streak forms
• epiblast cells move through primitive streak becoming mesoderm cells - forms trilaminar layer
• epiblast cells -> ectoderm
  - > mesoderm
• hypoblast cells -> endoderm

Question 16

3 parts of primitive streak

Answer 16

• primitive node, primitive pit + primitive groove

Question 17

ectoderm differentiates to become;

Answer 17

• nervous tissue + epidermis of skin

Question 18

endoderm differentiates to become;

Answer 18

• lining of gut, respiratory tract, bladder and urethra

Question 19

3 sections of mesoderm from medial to lateral

Answer 19

• paraxial mesoderm
• intermediate mesoderm
• lateral plate mesoderm

Question 20

2 types of lateral plate mesoderm

Answer 20

• somatic (superior)

- visceral (inferior)

Question 21

paraxial mesoderm differentiates to become;

Answer 21

• axial skeleton

Question 22

intermediate mesoderm differentiates to become;

Answer 22

• urogenital system, kidney, ureter + gonads

Question 23

somatic lateral plate mesoderm differentiates to become;

Answer 23

• dermis of skin + parts of limbs

Question 24

visceral lateral plate mesoderm differentiates to become;

Answer 24

• cardiovascular system, smooth muscle, mesothelial covering of organs