Lecture 4 - Fetal Nourishment and Development

Question 1

What are the three time periods of pregnancy?

Answer 1

1. Fertilization (day 1)
2. Embryonic period (week 1 to 8)
3. Fetal period (week 9 to 38)

Counted 40 weeks from your last period (accounts for ovulation)

Question 2

What are the 3 critical periods of fetal development?

Answer 2

1. Hyperplasia - increased cell multiplication
2. Hyperplasia and hypertrophy
3. Hypertrophy - increased cell size

Question 3

What are the stages in embryonic period - Week 1?

Answer 3

1. Stage 1: Fertilization→zygote
2. Stage 2: Zygote divides → 2 cell → 4 cell → 8 cell →Morula (~16-32 cells)
3. Stage 3: Early bastocyst → late bastocyst
   - blastocystic cavity, embryoblast (inner cell mass), trophoblasts (outer layer)
   - enters uterus, zona pellucida degenerates
4. Stage 4: Implantation begins (~day 6)

Question 4

Where does stage 1 and 2 of week 1 occur?

Answer 4

Both stage 1 and 2 within fallopian tube

Zona pellucida intact

Question 5

During week one, how are nutrients supplied?

Answer 5

Nutrients supplied by secretions from uterine glands (glycogen main nutrient)

Question 6

Explain the process of fertilization

Answer 6

Question 7

After sperm enters the egg what happens?

Answer 7

• Breaking of zona pellucida prevents other sperm from penetrating
• Fertilization prevents further sperm from entering and triggers meiosis
• Intermingling of chromosomes
• First mitotic cell division
• Sperm releases chromosomes which form with maternal chromosomes to form a zygote

Question 8

How does the zygote move into the uterus?

Answer 8

• Upon ovulation the egg is released and goes to the fimbrae
• It is then fertilized in the the widest part of the fallopian tube to become zygote
• The zygote then goes through the fallopian tube and divides until it is a morula
• Morula enters uterus and becomes a blastocyst
• Implantation then occurs

Question 9

When is a blastocyst formed? What does it look like?

Answer 9

• Blastocyst forms at the end of week 1
• ## It becomes the functional part of the body

Question 10

What 2 main things occurs in week 2 of the embryonic period?

Answer 10

1. Implantation - blastocyst will completely imbed in endometrium and inner cell mass forms the embryonic disc
2. Lacunar networks - development of lacunae - the spaces within trophoblast

Question 11

What occurs in early week 2 and later week 2?

Answer 11

• Early week 2: trophoblasts (outer layer)
  → invade endometrium
  → Secrete proteolytic enzymes: degrade the endometrium for nutrients and then can imbed there
• ** Later week 2**: inner cell mass becomes flattened disk (2 layers - epiblast, and hypoblast layer) and amniotic cavity develops

Question 12

Identify the structures of the endometrium and blastocyst

Answer 12

Question 13

Where is the epiblast layer and what does it give rise to?

Answer 13

• Formed in later week 2
• Adjacent to amniotic cavity
• Gives rise to ectoderm and mesoderm

Question 14

Where is the hypoblast layer? What does it give rise to?

Answer 14

• Adjacent to blastocyst cavity
• Gives rise to endoderm
• Localized thickening of hypoblast - will develop into cranial region