Developmental biologyLesson 2 of 6 in the course Development and Inheritance

Human Prenatal Development: Implantation, Germ Layers, Placenta, and Organogenesis

5 flashcards · 4 quiz questions · 5 match pairs · 5 fill-in sentences · English

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Summary

The first two weeks after fertilization are called the pre-embryonic stage. During this time, the conceptus divides, changes structure, travels to the uterus, and may implant in the uterine lining. These early events establish the conditions needed for later development.

Gestation is the period of development in the uterus. Developmental ages in this unit are counted from fertilization. The first two weeks are the pre-embryonic stage; the developing human is called an embryo during weeks 3–8 and a fetus from week 9 until birth.

All flashcards

What is cleavage?
Cleavage is the series of rapid mitotic divisions after fertilization. It increases cell number without increasing the total volume of the conceptus.
How do a morula and a blastocyst differ?
A morula is a compact, solid ball of cells. A blastocyst has a fluid-filled blastocoel, an inner cell mass, and an outer trophoblast.
What is the role of the trophoblast?
The trophoblast is the outer cell layer of the blastocyst. It helps with implantation and contributes to the chorionic sac and fetal portion of the placenta.
What does hCG do during early pregnancy?
Trophoblast-derived hCG supports the corpus luteum, helping it continue producing progesterone and estrogen that maintain the uterine lining.
How do the umbilical arteries and vein differ in blood flow?
Two umbilical arteries carry blood away from the fetus toward the placenta; one umbilical vein returns oxygenated, nutrient-rich blood to the fetus.

Quiz questions

  1. Which structure develops into the central nervous system?Answer: The neural tube.
  2. When does organogenesis—the formation of rudimentary organ structures—occur?Answer: During the first eight weeks of gestation.
  3. Where do most ectopic pregnancies occur?Answer: In a uterine tube.
  4. Insufficient maternal folate during early pregnancy increases the risk of which developmental problem?Answer: Neural tube defects.

Based on Anatomy and Physiology 2e by J. Gordon Betts, Kelly A. Young, James A. Wise, Eddie Johnson, Brandon Poe, Dean H. Kruse, Oksana Korol, Jody E. Johnson, Mark Womble, Peter DeSaix (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.

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