Development
The chorion undergoes rapid proliferation and forms numerous processes, the chorionic villi, which invade and destroy the uterine decidua and at the same time absorb from it nutritive materials for the growth of the embryo.
They undergo several stages, depending on their composition.
| Stage | Description | Period of gestation | Contents |
| Primary | The chorionic villi are at first small and non-vascular. | End of 4th week | trophoblast only |
| Secondary | The villi increase in size and ramify, while the mesoderm grows into them. | 5th week | trophoblast and mesoderm |
| Tertiary | Branches of the umbilical vessels grow into the mesoderm, and in this way the chorionic villi are vascularized. | 5th - 6th week | trophoblast, mesoderm, and blood vessels |
Until about the end of the second month of pregnancy the villi cover the entire chorion, and are almost uniform in size, but after this they develop unequally.
Read more about this topic: Chorionic Villi
Famous quotes containing the word development:
“John B. Watson, the most influential child-rearing expert [of the 1920s], warned that doting mothers could retard the development of children,... Demonstrations of affection were therefore limited. “If you must, kiss them once on the forehead when they say goodnight. Shake hands with them in the morning.””
—Sylvia Ann Hewitt (20th century)
“The proper aim of education is to promote significant learning. Significant learning entails development. Development means successively asking broader and deeper questions of the relationship between oneself and the world. This is as true for first graders as graduate students, for fledging artists as graying accountants.”
—Laurent A. Daloz (20th century)
“I could not undertake to form a nucleus of an institution for the development of infant minds, where none already existed. It would be too cruel.”
—Henry David Thoreau (1817–1862)