Germ layers and Differentiation

Question 1

What is the trilaminar disc?

Answer 1

Flat, thin circular layers form at the stage of early development

Question 2

What are the three layers of the trilaminar disc?

Answer 2

• Ectoderm
• Mesoderm
• Endoderm

Question 3

What are the derivatives of the ectoderm?

Answer 3

• Nervous system
• Face
• Skin
• Teeth

Question 4

What are the derivatives of the mesoderm?

Answer 4

• Skeletal
• Muscular, vascular
• CT
• Epithelia of genital/urinary systems

Question 5

What are the derivatives of the endoderm?

Answer 5

• Gut epithelia
• Digestive organs
• Respiratory tract epithelium

Question 6

Describe female ovulation

Answer 6

• Follicles developed in the ovary that are released

- Only 500 ovulated

Question 7

Describe the timeline of pregnancy

Answer 7

• 0-2 weeks- fertilisation
• 3-8 weeks- embryogenesis
• 8-term- foetal development

Question 8

Describe fertilisation

Answer 8

• 180 million sperm ejaculated
• Enzyme releases enable sperm to cross zone pellicuda (only 1 or 2)
• Activation of egg

Question 9

Describe egg activation in fertilisation

Answer 9

• Restoration of diploid chromosomes
• Sex determination
• Initiation of cleavage

Question 10

Describe the hydatidiform mole

Answer 10

• Mostly made of trophoblasts
• Abnormal growth
• Empty egg may be fertilised (no chromosome)
• Division could lead to a malignant cystic structure

Question 11

Describe assisted reproductive technology

Answer 11

• ‘Test tube baby’= captured ovum + hormonal stimulated
• oocytes laparoscopically removed
• IVF or ICSI- grown in culture 2-6 days then transferred to uterus

Question 12

Describe cleavage and compaction

Answer 12

• Zygote divides by mitosis
• Blastomeres get smaller- loose clump becomes compacted
• 3 days- 16-cell morula has embryoblast (inner) and trophoblast (outer)
• Blastocyst (fluid-filled cavity) forms by 5 days (trophoblasts and embryoblasts)

Question 13

Describe embryonic stem cells

Answer 13

• Pluripotent cells derived from inner cell mass
• Potential use for Alzheimer’s, Parkinson’s, diabetes, anaemias and spinal cord injuries
• Differentiated in vitro and transferred in vivo

Question 14

Describe abnormal implantation

Answer 14

• Eptotic pregnancy- implantation in uterine tube so it ruptures and bleeds
• Embryo not usually viable- requires surgery

Question 15

Describe the folding of trilaminar disc

Answer 15

• Lateral and longitudinal foldings- head and tail curl

- Organogenesis by wk 8, yolk sac for nutrition (endoderm gut tube)