9.0 Placentation Flashcards
What does the inner cell mass differentiate into?
1) Epiblast (contacts trophoblast)<br></br>2) Hypoblast (faces blastocele)<br></br>3) Mesoderm (develops in between the other 2 layers)
What layer forms the extra-embryonic mesoderm?
Hypoblast
What are the two layers of extra-embryonic mesoderm?
1) Chorion (applied to inside of trophoblast)<br></br>2) Cell layers that covers outer surface of yolk sac and amnion<br></br><br></br>Extra-embryonic coelom is found in between the above two layers
When is the extra-embryonic coelom obliterated?
12 weeks<br></br>Amnion expansion → obliteration of extra-embryonic coelom
Features of the outer surface of yolk sac:
1) Acts like absorptive epithelium<br></br>2) Contains transports (GLUT1)<br></br>2) Secretes proteins (alpha-fetoprotein)
Functions of placenta:
1) Gas exchange<br></br>2) Excretion, water and pH balance<br></br>3) Reabsorptive features<br></br>4) Synthesis and secretory function<br></br>5) Metabolic and secretory function<br></br>6) Immunological/protective
What shape is the placenta?
Discoid
What is the diameter of the placenta?
20-25cm
What is the weight of the placenta?
400-600g
What are the two layers of the placenta?
<b>1) Choronic plate</b><br></br>- Facing fetus<br></br><br></br><b>2) Basal plate</b><br></br>- Facing decidua basalis
What are the two layers that the trophoblast differentiates into on contacting uterine epithelium?
1) Syncytiotrophoblast (SCT)<br></br>- Multinucleated<br></br>- Non-proliferative<br></br><br></br>2) Cytotrophoblast (CTB)<br></br>- Deeper
What do STB and CTB become? (brief overview of steps)
STB → invade decidua → spaces form lacunae where maternal secretions and blood enter<br></br><br></br>CTB + extraembryonic mesoderm infiltrate trabeculae (in between lacunae) → placental villi
Where do stem villi arise from?
Chorionic plate
Where do anchoring villi connect to?
Basal plate
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<br></br><br></br>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<br></br>- Organogenesis<br></br>- Susceptible to malformation
What are the features of the fetal period of pregnancy?
- Haemotrophic nutrition<br></br>- Growth and functional maturation
What is the surface area of the placental villous tree?
12-14m²
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:<br></br>1) Endovascular<br></br>2) Interstitial
What occurs in spiral artery conversion?
1) Loss of smooth muscle<br></br>2) Loss of endothelial lining<br></br><br></br>Causes ↑ dilation and loss of vasoactivity<br></br>This slows rate of inflow and ↓ pressure in intervillous space
What does the placenta need for effective exchange?
<b>1) Stable low-pressure/high volume maternal blood supply</b><br></br>- Occurs following conversion of spiral arteries<br></br><br></br><b>2) Large surface area for exchange</b><br></br>- Terminal villi provide this<br></br><br></br><b>3) Transporter mechanisms</b><br></br><br></br><b>4) High placental gradient</b>
- Paracellular
- Tanscellular
- 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
1) Systems A + ASC → neutral amino acid
2) Systems Xag → acidic amino acid
3) Systems L → neutral amino acid
