10 topics with brief reviews: definitions, key facts, and class questions.
In this section, we examine the histological structure of provisional organs that provide the connection between the maternal organism and the developing embryo. You will study the formation and structure of the decidua, chorion, and amnion, as well as the histology of the umbilical cord.
The central topic of this section is the placenta. We will look closely at its fetal and maternal parts, morphological classification, and the features of fetal circulation. Special emphasis is placed on physiology: substance transport and the powerful endocrine function that maintains pregnancy.
During colloquiums and exams, examiners traditionally demand a thorough knowledge of the placental barrier: you need to know its structural components precisely and how they change as the fetus develops. Understanding the microscopic structure of chorionic villi is the foundation without which it is impossible not only to pass histology, but also to understand pathology in obstetrics and gynecology in the future.
Where do the first foci of embryonic hematopoiesis appear?
The first foci of hematopoiesis, as well as primordial germ cells, are initially established in the yolk sac during the first weeks of development.
In which layer does placental separation occur during labor?
Detachment of the placenta and fetal membranes during labor occurs at the level of the spongy layer of the decidua.
Why is the chorion divided into the smooth and villous parts?
This depends on contact with the decidua. Where nutrition is sufficient (adjacent to the decidua basalis), the villi proliferate. Where nutrition is insufficient (at the decidua capsularis), they atrophy, forming the chorion laeve.
Does maternal and fetal blood mix?
No. Placental circulation is arranged so that gas exchange and metabolism occur through the placental barrier without direct contact and mixing of the two blood flows.
What is a cotyledon?
This is a structural lobule of the placenta that includes a single stem villus with all its ramifications (branches of the 2nd and 3rd order).
Do maternal tissues participate in the formation of the placental barrier in humans?
No. The key principle is that in humans, the barrier is formed exclusively by fetal structures. Maternal blood bathes these structures from the outside.
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