FoM:L2 - Embryology

Question 1

What steps are involved in fertilisation?

Answer 1

• attachment
• binding
• penetration
• fusion

Question 2

What are the results of fertilisation?

Answer 2

• restores diploid number of chromosomes
• determines sex
• initiates cleavage

Question 3

What happens between 1-4 days after fertilisation?

Answer 3

• cleavage and compaction
• zygote divides by mitosis
• blastomeres (cells) become smaller and compacted
• Morula reaches uterine cavity

Question 4

What happens on day 5 after fertilisation?

Answer 4

formation of blastocyst

Question 5

What happens on day 6 and 7 after fertilisation?

Answer 5

• start of implantation
• blastocyst attaches to endometrial epithelium (6)
• invasion of endometrial connective tissue (7)
• trophoblast (outer cells) become placenta

Question 6

What is an ectopic pregnancy?

Answer 6

• development of a blastocyst outside the uterus
• e.g. abdominal cavity; tubes; ampullary region; cervix; ovaries

Question 7

What happens in week 2 after fertilisation?

Answer 7

• complete implantation
• embryoblast develops into bilaminar disc: epiblast and hypoblast layers
• maternal blood fills lacunar within trophoblast
• cavities form: amniotic and yolk sac
• formation of connecting stalk

Question 8

What happens in the 3rd week after fertilisation?

Answer 8

Gastrulation
- primitive streak appears in epiblast: narrow groove with bulging regions on either side, elevated area around a pit
- epiblast at primitive streak is source of cells for all 3 germ layers

Question 9

What are the 3 germ layers in the trilaminar embryonic disc?

Answer 9

• ectoderm: brain, spinal cord, PNS, skin (hair and nails), sensory epithelium
• mesoderm: bone, cartilage, blood cells and vessels, muscle, heart, kidneys
• endoderm: respiratory tract, digestive tract, liver, pancreas, bladder

Question 10

What happens in the 3rd and 4th weeks after fertilisation?

Answer 10

• neurulation: neural plate forms neural tube
• foldings: lateral and cephalocaudal

Question 11

Outline what happens in the embryonic period

Answer 11

• 3 to 8 weeks after fertilisation
• gastrulation: ecto-, endo-, meso-derm layers
• neurulation
• foldings
• organogenesis: rudiments of major organs formed

Question 12

Outline the main events during the fetal period

Answer 12

• maturation of tissues and organs
• rapid growth of fetus
• growth in length in months 3-5
• growth in weight in last 2 months