Topic 14 of 29 in the MU Plovdiv syllabus for Cytology, General Histology and Human Embryology (Medicine, Year 1). The free AceMed note covers it in 16 sections, about 1,662 words (13 min of reading), with 37 flashcards.
In this note
Introduction
Amnion:
Chorion:
Yolk Sac:
Allantois:
Formation and Location:
Structure:
Functions:
Key Layers:
Immune Functions:
Blood Flow:
The Umbilical Cord and Embryonic Circulation
The Umbilical Cord: Structure and Function
Embryonic Circulation: The Early Blood Flow Pathways
How the Embryonic Circulatory System Functions
Changes at Birth: Transition to Postnatal Circulation
Amnion:
Structure: The amnion is a thin, transparent membrane that surrounds the fetus.
Location: It forms from the epiblast layer of the bilaminar embryonic disc and grows to encase the fetus.
Function:
Contains amniotic fluid, which cushions and protects the fetus.
Maintains a stable temperature and pressure around the fetus.
Allows for fetal movement, which is important for musculoskeletal development.
Prevents adhesions between the fetus and the membranes.
Chorion:
Structure: The chorion is the outermost membrane surrounding the fetus and the amnion. It is formed by the trophoblast layer (specifically the cytotrophoblast and syncytiotrophoblast) and the extra-embryonic mesoderm.
Location: The chorion is located outside the amnion and forms the outermost layer of the fetal membranes.
Function:
Contributes to the formation of the placenta.
In the early stages of pregnancy, the chorionic villi (finger-like projections) invade the maternal endometrium to establish maternal-fetal blood exchange.
Produces human chorionic gonadotropin (hCG), which helps maintain the pregnancy by supporting the corpus luteum and stimulating the production of progesterone.
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