W1 Embryology - Prenatal Development

Question 1

Describe the key event s that occur during the period of the ovum

Answer 1

Fertilization

Clevage

Morula formation

Blastocyst formation

Implantation

Question 2

Describe the key events of fertilization

Answer 2

Germination- Day 0 ZYGOTE FORMATION

1. Fusion of haploid gametes (sex cells).
2. Forms a diploid zygote (2 sets of DNA)
3. Nuclear membrane breaks down, DNA replication commences (mitosis).
   * Fertilization occurs at the distal end of the fallopian tube (Ovi duct) The newly formed zygote then travels via motions generated by microscopic cillia and contracts towards the uterous*

Question 3

Describe the key events of clevage

Answer 3

Germinal period - day 0-3.

Rapid cell division without cell growth. Cell size rapidly decreases as number of cells increased

Question 4

Describe the key events of Morula formation

Answer 4

Germinal period. Day 4.

Now a ball of 16-20 cells flattened again the zona pellucida. The morula is now located at the proximal end of the oviduct

Question 5

Describe the key events of Blastocyst formation

Answer 5

DAY 5 A cavity forms within the morula, and the ball of cells is now termed blastocyst

Question 6

Describe the key events of implantation

Answer 6

Germinal Period. DAY 7

Motility slows, adhesion to uterine epithelium, as the cells of the blastocyst digest the uterine endometrium permitting deeper penetration and attachment

Question 7

Describe the key events that occur during embryonic development

Answer 7

1) Bilaminar disc: Epiblast, Hypoblast.
2) Gastrulation→ trilaminar embryonic layers develop ectoderm, mesalderm, endoderm and differentiate
3) Embryronic folding

Question 8

Define Bilaminar disc

Answer 8

On Day 8-7

Epiblast: gives rise to future germ cell layers.

Hypoblast: (transient), gives rise to some umbilical tissues!

Question 9

Identify 4 embryonic membranes

Answer 9

1. Amniotic sac/amnion
2. Yolk sac (nourishment for disc)
3. Chorion: this will eventually become the chorionic sac, which will, along with the uterine wall, become the placenta
4. Allantois (connecting stalk): contributes blood vessels from the embryo to the placenta; eventually becoming ambilical cord

Question 10

Briefly state the events of gastrulation

Answer 10

Gastrulation Begins:

Emergence of the Primitive Streak (caudal) & node formation. *Induction and migration of cells into 3 layers to become the trilaminar (3 layered) embryonic disc.

Question 11

List the 3 embryonic layers and what they give rise to

Answer 11

Ectoderm

Mesoderm

Endoderm

Question 12

Provide two examples of structures in the 3 embryonic layers that will develop from each

Answer 12

Ectoderm: CNS, PNS, oral mucosa, teeth enamel

Mesoderm: BLood, bone, muscles

Endoderm: Epithelial lining of stomach, lungs, bladder

Question 13

Describe embryonic folding

Answer 13

On the establishment of the trilaminar embryonic disc, the embryo then undergoes Embryonic FOlding to establish the bodies axis. This allows for the formation of body cavities as a series of tubes.

Question 14

What are the three periods of human development?

Answer 14

Germinal Period 0-14 days Embryonic period 3rd week 8th week Fetal Period 9th- 40th week

Question 15

What are the key event in formation of a bilaminar embryo

Answer 15

Epiblast: gives rise to future germ cell layers, Hypoblast: Transient - gives rise to some umbilical tissues