Cytology · MU Sofia

80. Placentation and placenta.

Covers how the placenta forms after the blastocyst implants and where it usually attaches, including placenta previa and accreta. It then describes the fetal and maternal parts, the decidual septa and cotyledons, and the discoid shape, size and villi of the full-term organ. Transport and barrier roles, hormone production, immune functions and the maternal and fetal blood flow are also set out, with the trophoblast layers explained separately.

Inside: 7 sections · 4 labelled pictures · 12 flashcards · 3 min

Topic 80 of 127 in the MU Sofia syllabus for Cytology (Dental Medicine, Year 1). The free AceMed note covers it in 7 sections, about 373 words (3 min of reading), with 12 flashcards.

In this note

  1. Introduction
  2. Formation and Location:
  3. Structure:
  4. Functions:
  5. Key Layers:
  6. Immune Functions:
  7. Blood Flow:

Introduction

The placenta is an essential organ that develops during pregnancy, serving as the vital link between the fetus and the maternal uterine wall. It facilitates the exchange of gases, nutrients, and waste products between mother and fetus, and performs multiple other functions crucial for fetal development and maternal health.

Formation and Location:

  • The placenta forms when the blastocyst implants into the uterine endometrium.
  • The trophoblast (outer layer of the blastocyst) differentiates into cytotrophoblast and syncytiotrophoblast layers, creating a barrier between maternal and fetal blood.
  • Typically attaches to the upper uterine wall, but can have abnormal placements like placenta previa (low placement) or placenta accreta (abnormal attachment).

Structure:

  • Two main parts:
  • Fetal portion: Comprised of the chorionic plate covered by the amnion.
  • Maternal portion: Bordered by the decidua basalis.
  • Decidual septa form between the 4th and 5th months, dividing the placenta into cotyledons (distinct lobes).
  • The junctional zone is rich in extracellular matrix, containing trophoblasts and decidual cells for nutrient exchange.
  • Full-Term Placenta:
  • Shape: Discoid.
  • Size: Typically 15-20 cm in diameter, 2-3 cm in thickness, weighing 500-600 grams.
  • Surface: Covered with villi (finger-like projections) to increase surface area for nutrient and gas exchange.
  • Fetal side is smooth; maternal side is rough due to cotyledons.

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