Flashcards in 9.0 Placentation Deck (28)
What does the inner cell mass differentiate into?
1) Epiblast (contacts trophoblast)
2) Hypoblast (faces blastocele)
3) Mesoderm (develops in between the other 2 layers)
What layer forms the extra-embryonic mesoderm?
What are the two layers of extra-embryonic mesoderm?
1) Chorion (applied to inside of trophoblast)
2) Cell layers that covers outer surface of yolk sac and amnion
Extra-embryonic coelom is found in between the above two layers
When is the extra-embryonic coelom obliterated?
Amnion expansion → obliteration of extra-embryonic coelom
Features of the outer surface of yolk sac:
1) Acts like absorptive epithelium
2) Contains transports (GLUT1)
2) Secretes proteins (alpha-fetoprotein)
Functions of placenta:
1) Gas exchange
2) Excretion, water and pH balance
3) Reabsorptive features
4) Synthesis and secretory function
5) Metabolic and secretory function
What shape is the placenta?
What is the diameter of the placenta?
What is the weight of the placenta?
What are the two layers of the placenta?
1) Choronic plate
- Facing fetus
2) Basal plate
- Facing decidua basalis
What are the two layers that the trophoblast differentiates into on contacting uterine epithelium?
1) Syncytiotrophoblast (SCT)
2) Cytotrophoblast (CTB)
What do STB and CTB become? (brief overview of steps)
STB → invade decidua → spaces form lacunae where maternal secretions and blood enter
CTB + extraembryonic mesoderm infiltrate trabeculae (in between lacunae) → placental villi
Where do stem villi arise from?
Where do anchoring villi connect to?
When do terminal villi form?
2nd 1/2 of gestation
What is the main nutrient source in histiotrophic nutrition?
Carbohydrate and lipid secretions from the endometrial glands
Glands are stimulated by progesterone from the corpus luteum
When does haemotrophic nutrition start?
Week 12 of pregnancy
What are the features of the embryonic period of pregnancy?
- Histiotrophic nutrition
- Susceptible to malformation
What are the features of the fetal period of pregnancy?
- Haemotrophic nutrition
- Growth and functional maturation
What is the surface area of the placental villous tree?
What cells need to be present for conversion of spiral arteries?
Extravillous trophoblast cells
How to EVT cells migrate to spiral arteries?
From tips of anchoring villi. Via 2 methods:
What occurs in spiral artery conversion?
1) Loss of smooth muscle
2) Loss of endothelial lining
Causes ↑ dilation and loss of vasoactivity
This slows rate of inflow and ↓ pressure in intervillous space
What does the placenta need for effective exchange?
1) Stable low-pressure/high volume maternal blood supply
- Occurs following conversion of spiral arteries
2) Large surface area for exchange
- Terminal villi provide this
3) Transporter mechanisms
4) High placental gradient
What are the types of transplacental transport mechanisms
- Gasses, FFAs and urea
2) Facilitated diffusion
- Requires carrier proteins example = GLUT
- No ATP
- Glucose, FFAs
3) Active transport
- ATP dependent
- Needed for amino acids (because fetal:maternal amino acids >1)
4) Receptor mediated endocytosis
- Only transports IgG
- Mainly occurs in last month of pregnancy → passive immunity
What are the 3 active transport systems for transporting amino acids?
All Na⁺ dependent
1) Systems A + ASC → neutral amino acid
2) Systems Xag → acidic amino acid
3) Systems L → neutral amino acid
What peptide hormones does the placenta synthesise?