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Foundation Sciences · Embryology
Cleavage and Blastocyst Formation
Cleavage is a series of rapid mitotic divisions of the zygote without cell growth, culminating in formation of the morula and then the blastocyst.
📌 Learning Objectives
- Describe the underlying mechanism of Cleavage and Blastocyst Formation.
- Identify the key clinical features and complications of Cleavage and Blastocyst Formation.
- Outline the appropriate investigations and management of Cleavage and Blastocyst Formation.
- Discuss the implications for patients and families of Cleavage and Blastocyst Formation.
📋 Overview
After fertilisation the zygote undergoes cleavage during transit through the fallopian tube. At ~16 cells (day 3–4) it forms a morula; cavitation produces the blastocyst by day 5, comprising the inner cell mass (embryoblast) and trophoblast around the blastocoel.
🔬 Basic Science
After fertilisation the zygote undergoes cleavage during transit through the fallopian tube. At ~16 cells (day 3–4) it forms a morula; cavitation produces the blastocyst by day 5, comprising the inner cell mass (embryoblast) and trophoblast around the blastocoel.
🏥 Clinical Relevance
Failure of cleavage causes early pregnancy loss; blastocyst stage embryos are used in IVF transfer.
🧪 Investigations
Investigation depends on clinical context: relevant blood tests, imaging, and specific genetic or histopathological tests as appropriate. Refer to specialist services where indicated.
💊 Management
Management is condition-specific and typically multidisciplinary, combining medical therapy, surgical intervention where appropriate, supportive care, and family/genetic counselling.
Revision Resources – expand the sections below for high-yield notes, exam pearls, key facts and further reading.
MLA High-Yield Notes & Quick Revision ⌄
Common SBA themes: recognising the underlying mechanism, identifying classic clinical features, and choosing the first-line investigation or management step. Watch for inheritance pattern and characteristic associations.
cleavage
morula
blastocyst
inner cell mass
trophoblast
- The morula forms at ~day 3–4 with ~16 cells.
- The blastocyst forms at ~day 5 and has an inner cell mass and trophoblast.
- The inner cell mass becomes the embryo proper; the trophoblast becomes the placenta.
- Blastocyst hatching from the zona pellucida precedes implantation.
- Cleavage divisions occur without an increase in overall embryo size.
Exam Pearls ⌄
⭐ High Yield
The morula forms at ~day 3–4 with ~16 cells.
The blastocyst forms at ~day 5 and has an inner cell mass and trophoblast.
The inner cell mass becomes the embryo proper; the trophoblast becomes the placenta.
Blastocyst hatching from the zona pellucida precedes implantation.
Cleavage divisions occur without an increase in overall embryo size.
💡 Clinical Pearl
Cleavage: Failure of cleavage causes early pregnancy loss; blastocyst stage embryos are used in IVF transfer.
⚠️ Exam Tip — Common Mistakes
Confusing the mechanism of Cleavage and Blastocyst Formation with related conditions.
Missing classic clinical features of Cleavage and Blastocyst Formation in SBA stems.
Failing to consider Cleavage and Blastocyst Formation in the differential diagnosis.
Key Facts ⌄
The morula forms at ~day 3–4 with ~16 cells.
The blastocyst forms at ~day 5 and has an inner cell mass and trophoblast.
The inner cell mass becomes the embryo proper; the trophoblast becomes the placenta.
Blastocyst hatching from the zona pellucida precedes implantation.
Cleavage divisions occur without an increase in overall embryo size.
Related Topics ⌄
References ⌄
- GMC MLA Content Map
- NICE Clinical Knowledge Summaries
- BMJ Best Practice
Further Resources
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