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AN78.1-5 | Introduction to Second week of development
Learning Objectives
- Describe the process of implantation — where, when, and how the blastocyst embeds itself in the uterine wall (AN78.3)
- Explain how the trophoblast differentiates into cytotrophoblast and syncytiotrophoblast and why this matters for placentation (AN78.2)
- Describe the formation of the bilaminar embryonic disc (epiblast and hypoblast) and how it sets the stage for gastrulation (AN78.4)
- Explain the origin and significance of extraembryonic mesoderm, the extraembryonic coelom (chorionic cavity), and the prochordal plate (AN78.4)
- Describe the decidual reaction, the basis of pregnancy tests (hCG), and the clinical significance of ectopic implantation (AN78.5)
- Trace the complete sequence of events from Day 7 to Day 14, identifying what happens each day (AN78.1–78.5)
INSTRUCTIONS
This guide covers the second week of development (Days 7–14), often called the "Week of Twos" because nearly everything forms in pairs or layers of two. Work through the material in order — each section builds on the previous one. Try the self-check questions before reading the answers. Estimated time: 35 minutes.
What you're studying in parallel: In Biochemistry, you're learning about cell signalling and membrane receptors — the same signalling cascades that control implantation. In Physiology, you're studying the menstrual cycle and endocrine regulation — the hormonal environment that makes implantation possible. These three subjects converge here: the embryo (Anatomy), the hormones that prepare the uterus (Physiology), and the molecular signals that allow attachment (Biochemistry).
References
- Langman's Medical Embryology, 14th ed., Chapter 3: Second Week of Development — Bilaminar Germ Disc (textbook)
- Moore's The Developing Human, 11th ed., Chapter 3: Second Week of Human Development (textbook)
- Sadler TW. Langman's Medical Embryology, 14th ed. Wolters Kluwer, 2019. (textbook)
- Inderbir Singh's Human Embryology, 11th ed., Chapters 4–5 (textbook)
- OpenStax Anatomy and Physiology 2e, Chapter 28: Development and Inheritance (CC BY 4.0) (textbook (CC BY 4.0))
Version 2.0 | Claude (AI-generated), NMC CBUC 2024, Adapted from Langman's Medical Embryology 14e & Moore's The Developing Human 11e