Week 6 Embryology

Question 1

3 periods of prenatal development

Answer 1

1. Germinal period - first 2 weeks
2. Embryonic period - week 3 to 8
3. Fetal period - week 9 to birth

Question 2

2 processes of gametogenesis

Answer 2

1. spermatogenesis

2. oogenesis

Question 3

What do gametes derived from?

Answer 3

Primordial germ cells

Question 4

Steps in oogenesis

Answer 4

1. Primordial germ cells
2. Oogonium
3. Primary oocyte (3 months embryo)
4. Primordial follicle
5. Primary follicle
6. Vesicular follicle

Question 5

How many mature sperm cells do 1 primordial germ cell gives rise to?

Answer 5

4 mature sperm cells

Question 6

3 events that happen during spermiogenesis

What did mature sperm cell progress form?

Answer 6

Progress from spermatid cell

1. Loss of cytoplasm
2. Devleopment of tail
3. Formation of acrosome (on top of nucleus)

Question 7

3 phases of oocyte penetration

Answer 7

1. Penetration of corona radiata
2. Penetration of zona pellucida
3. Fusion of cell membrane

Question 8

2 reactions that prevent polyspermy

Answer 8

1. Zona reaction: zona pellucida alters its structure and composition to prevent penetration
2. Cortical reaction: oocyte releases cortical granules onto its surface -> impenetratable to other sperms

Question 9

2 parts of blastocyst

What is shedded during blastogenesis?

Answer 9

1. Trophoblast - give rise to placenta
2. Embryoblast - inner cell mass giving rise to embryo

Zona pellucida is shredded to allow blastocyst to grow in size

Question 10

2 phases of implantation

Answer 10

1. Attachment phase - increase in vascular permeability

2. Invasion phase - cytotrophoblast cells fuse and erode the adjacent endometrial tissues

Question 11

Location where fertilization occurs

Answer 11

ampulla region of oviduct

Question 12

2 cell types differentiated from trophoblast

Answer 12

1. Syncytiotrophoblast - invasion onto uterine wall

2. Cytotrophoblast - proliferative pool of cells that move into syncytiotrophoblast

Question 13

Bilaminar germ disc

Answer 13

1. Epiblast

2. Hypoblast

Question 14

Products of gastrulation

Answer 14

Trilaminar germ disc

1. Ectoderm
2. Mesoderm
3. Endoderm

Question 15

Features formed at cranial and caudal region during gastrulation

Answer 15

Caudal region:

1. primitive streak
2. primitive node

Cranial region:
Oropharyngeal membrane

Question 16

What are prechordal cells and notochordal cells for?

Answer 16

Prechordal cells: fore and mid brain formation

Notochordal cells: form notochord for formation of hind brain and spinal cord

Question 17

Which germ layer is the neural plate formed from? What process does this initiate?

Answer 17

Ectoderm

Initiation of neurulation

Question 18

3 parts mesoderm and future structures formed

Answer 18

1. Paraxial mesoderm - somite
2. Intermediate mesoderm - urogenital system
3. Lateral plate mesoderm - skin, limb, bone

Question 19

When are neural crest cells formed?

Answer 19

when neural tube fuses

Question 20

What are factors that cause birth defects called?

Answer 20

Teratogens

Question 21

What are the openings of neural fold called?

Answer 21

1. Anterior neuropore

2. Posterior neuropore

Question 22

What are the 2 portions of placenta?

Answer 22

Maternal portion: decidua basalis

Fetal portion: chorion

Question 23

2 types of twins

Answer 23

1. Monovular

2. Biovular

Question 24

3 types of monovular twins (monozygotic)

Answer 24

1. dichoridal, diamniotic twins
2. monochordial, diamniotic twins
3. monochordial, monoamniotic twins

Question 25

How many somites are there?

Answer 25

22 paired somites

Question 26

5 facial prominences

Answer 26

1. Frontonasal prominence
2. Maxillary prominenece X2
3. Mandibular prominenece X2

Question 27

Important stages of development during prenatal development

Answer 27

1. Fertilization
2. Implantation
3. Gastrulation
4. Neurulation
5. Segmentation

Question 28

3 Causes of cleft lip/palate

Answer 28

1. Chromosomal
2. Gene and environmental interaction
3. Drug: excessive retinoic acid (vitamin A)