Embryology

Question 1

Zygote

Answer 1

Fertilised ovum

Question 2

Embryo

Answer 2

2-8 weeks

Question 3

Fetus

Answer 3

9 weeks - term

Question 4

Day 2

Answer 4

Zygote (2 cell)

Question 5

Day 3

Answer 5

Morula (16 cell) - reaches uterine cornu

Question 6

Day 4

Answer 6

Blastocyst - enters uterine cavity

Question 7

Day 6

Answer 7

Implantation

Question 8

Blastocyst

Answer 8

inner cell mass (embryoblast) - forms embryonic tissues

outer cell mass (trophoblast) - forms extra-embryonic tissues

70-100 cells

Fluid-filled cavity called blastocoele

Question 9

Gastrulation

Answer 9

Gastrulation is a phase early in the embryonic development of most animals, during which the single-layered blastula is reorganized into a trilaminar (“three-layered”) structure known as the gastrula

Question 10

Prior to gastrulation, the trophoblast differentiates in to

Answer 10

1. Syncitiotrophoblast - outer

2. Cytotrophoblast - inner

Question 11

Week 2: Day 8

Answer 11

Decidual reaction
Bilaminar disc - epiblast and hypoblast
Amniotic cavity forms

Question 12

Week 2: Day 9

Answer 12

Lacunar stage

Hypoblast forms Exocoelomic membrane

Question 13

Week 2: Day 12

Answer 13

Lacunae formation - communicate with endometrial sinusoids
Extra-embryonic mesoderm appears from yolk sac
Extra-embryonic coelum forms - chorionic cavity

Question 14

Week 2: Day 13

Answer 14

Implantation is complete
Cytotrophoblast forms primary chorionic villi
Yolk sac to secondary yolk sac
Syncitiotrophoblast excretes hCG
Uteroplacental circulation begins

Question 15

Week 3: Day 15

Answer 15

Primitive streak appears caudal end
Primitive node appears at cephalic end
Ectodermal cells migrate towards the streak and detach from it - intra-embryonic mesoderm
Mesoderm is between endoderm and ectoderm except at prochordal plate and cloacal plate

Question 16

Week 3: Day 16

Answer 16

Allantois appears - diverticular that forms from the posterior wall of the yolk sac and extends in to the connecting stalk

Question 17

Week 3: Day 18

Answer 17

Neurulation - neural plate formed at day 18

Question 18

Week 3: Day 20

Answer 18

Primitive heart tube

Question 19

Week 3: Day 21

Answer 19

First heart beat

Question 20

Gastrulation

Answer 20

formation of three germ layers
3rd week
ectoderm to intra-embryonic mesoderm

Question 21

Embryo folding

Answer 21

Occur in two planes
- longitudinal (enlarged cranial end)
- transverse (enlarged somites)
day 21-24

Question 22

Components of ectoderm

Answer 22

Epidermis

Nervous system

Question 23

Components of mesoderm

Answer 23

Muscles
Skeletal system
Connective tissues

Question 24

Components of endoderm

Answer 24

GIT
Resp
Endocrine
Auditory
Urinary

Question 25

Week 4

Answer 25

``` Septum premium appears Branchial arches Neural tube closes Optic pits appear Pulmonary primordium appear Hepatic plate appears Cystic diverticulum appear Dorsal pancreatic bud forms Spleen forms Urorectal septum appears Ureteric buds form ```

Question 26

Week 5

Answer 26

Lens pit and optic cups Nasal pits Leg buds Rudimentary blood starts moving

Question 27

Week 6

Answer 27

Lungs start to form Lymphatic system begins to form Gonadal ridges begin to be perceptible

Question 28

Week 7

Answer 28

Fetal heart tone audible Nipples form Hair follicles Spontaneous limb movements

Question 29

Week 8-10

Answer 29

eyelids close Tooth buds RBCs produced in liver

Question 30

Week 11-14

Answer 30

Lanugo hair Fetal skin transparent Men forms in GIT

Question 31

Week 17

Answer 31

Eyebrow and eyelashes | Nails

Question 32

Week 21

Answer 32

Alveoli

Question 33

Mesoderm - 3 parts

Answer 33

Paraxial mesoderm - segmental, forms somites Intermediate - forms urogenital system Lateral plate - forms the somatic and splanchnic mesoderm

Question 34

Somites

Answer 34

``` Either side of neural tube First pair at D20 Max 42-44 pairs 1. Dermomyotomes - form connective tissue and muscles 2. Sclerotomes - form bones ```

Question 35

Lateral plate mesoderm

Answer 35

- continuous with extra-embryonic mesoderm - somatic mesoderm (lines the amnion) - Splanchnic mesoderm (lines the yolk sac)

Question 36

Intra-embryonic coelom

Answer 36

D19 merging of the clefts within the lateral plate forerunner of serous cavities