Podcast
Questions and Answers
How are sperm moved upwards into the fallopian tube?
How are sperm moved upwards into the fallopian tube?
Contractions by smooth muscle cells in the uterine wall.
What is capacitation?
What is capacitation?
A period of time that sperm must reside in the female reproductive tract before they acquire the ability to fertilise oocytes.
How is polyspermy prevented?
How is polyspermy prevented?
Zona pellucida becomes impermeable.
What are the two types of molar pregnancy?
What are the two types of molar pregnancy?
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A molar pregnancy gives a ____ test.
A molar pregnancy gives a ____ test.
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What is cleavage?
What is cleavage?
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At first, is there an increase in overall size as cells divide during cleavage?
At first, is there an increase in overall size as cells divide during cleavage?
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What process produces a morula?
What process produces a morula?
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What are blastomeres?
What are blastomeres?
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What structure surrounds the morula?
What structure surrounds the morula?
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In IVF, a ____ can be removed for genetic testing prior to transfer into the uterus.
In IVF, a ____ can be removed for genetic testing prior to transfer into the uterus.
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The inner cell mass (ICM) develops into the ____ .
The inner cell mass (ICM) develops into the ____ .
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The outer cells are the trophoblast and develop into the ____ .
The outer cells are the trophoblast and develop into the ____ .
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Cells in the ICM differentiate into the ____ and ____ .
Cells in the ICM differentiate into the ____ and ____ .
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What do the hypoblast and epiblast establish?
What do the hypoblast and epiblast establish?
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What occurs in the zygote or blastocyst that commonly results in spontaneous pregnancy loss (miscarriage) at an early stage?
What occurs in the zygote or blastocyst that commonly results in spontaneous pregnancy loss (miscarriage) at an early stage?
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What are the three main stages of implantation?
What are the three main stages of implantation?
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What is the endometrium?
What is the endometrium?
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What is apposition?
What is apposition?
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The blastocyst is a foreign body as it does not have the same proteins or make up as maternal tissue – why is it not rejected by the mother?
The blastocyst is a foreign body as it does not have the same proteins or make up as maternal tissue – why is it not rejected by the mother?
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Maternal vessels which form blood-filled spaces called ____ .
Maternal vessels which form blood-filled spaces called ____ .
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The ICM flattens into two layers, what is this called?
The ICM flattens into two layers, what is this called?
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What develops between the epiblast and the trophoblast?
What develops between the epiblast and the trophoblast?
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The blastocyst cavity forms the ____ .
The blastocyst cavity forms the ____ .
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Implantation may not be successful – this might be because the:
Implantation may not be successful – this might be because the:
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Where might an embryo implant instead of in the body of the uterus?
Where might an embryo implant instead of in the body of the uterus?
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Sub-optimal implantation can result in ____ problems later in pregnancy.
Sub-optimal implantation can result in ____ problems later in pregnancy.
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The bilaminar disc develops into a ____ .
The bilaminar disc develops into a ____ .
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Establishes the ____ germ layers from which all the embryo's tissues develop.
Establishes the ____ germ layers from which all the embryo's tissues develop.
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Appears as a groove at which end of the epiblast?
Appears as a groove at which end of the epiblast?
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Epiblast cells migrate towards it and ____ through it.
Epiblast cells migrate towards it and ____ through it.
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Settle between the epiblast and hypoblast to form a third layer, the ____ .
Settle between the epiblast and hypoblast to form a third layer, the ____ .
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Laterality anomalies may occur – these are conditions of ‘abnormal sidedness'.
Laterality anomalies may occur – these are conditions of ‘abnormal sidedness'.
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Thoracic and abdominal viscera are ‘flipped' (mirror image).
Thoracic and abdominal viscera are ‘flipped' (mirror image).
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The heart is ‘flipped’.
The heart is ‘flipped’.
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What happens first during neurulation?
What happens first during neurulation?
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Neural plate formation is inducted by what structure?
Neural plate formation is inducted by what structure?
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The two sides of the groove fuse to form the ____ .
The two sides of the groove fuse to form the ____ .
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The neural tube detaches from the ____ .
The neural tube detaches from the ____ .
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Cranial end expands = ____
Cranial end expands = ____
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Caudal end remains tubular = ____
Caudal end remains tubular = ____
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Study Notes
Learning Objectives
- Describe the stages of development from fertilization to week 4.
- Understand how a blastocyst differentiates into an embryoblast and trophoblast.
- Understand how an embryoblast develops into a bilaminar disc.
- Understand gastrulation and the formation of three germ layers.
- Understand neurulation.
- Appreciate that congenital anomalies result from disruptions in embryonic development.
Fertilization
- Millions of sperm enter the female reproductive tract; only a few reach the uterine tube.
- Sperm are "conditioned" (capacitated) in the uterine tube before they can fertilize an egg.
- Fertilization is the fusion of gametes.
How Sperm Move
- Sperm are moved upwards into the fallopian tube by contractions of smooth muscle in the uterine wall.
Capacitation
- Sperm must reside in the female reproductive tract for a period of time to acquire the ability to fertilize oocytes.
Fertilization Process
- Sperm reach the ovum.
- Chemicals released from the cells surrounding the ovum trigger the acrosome reaction.
- The acrosome swells and fuses with the sperm cell surface membrane.
- Digestive enzymes are released from the acrosome, digesting through the follicle cells and zona pellucida surrounding the ovum.
- The sperm nucleus enters the ovum.
- Nuclei of the ovum and sperm fuse.
- Enzymes released from lysosomes in the ovum thicken the jelly-like layer, preventing entry of other sperm.
Polyspermy Prevention
- The zona pellucida becomes impermeable to prevent polyspermy (multiple sperm fertilizing one egg).
Molar Pregnancy
- Two types of molar pregnancy: complete and partial.
- Complete mole: sperm fertilizes an egg with no genetic material, resulting in an abnormal trophoblast, no embryo.
- Partial mole: normal egg fertilized by two sperm; embryo starts to develop, but cannot survive.
- Molar pregnancy results in a positive pregnancy test.
The Zygote
- Fertilization produces a zygote that is genetically unique.
Cleavage
- Zygote undergoes cell division immediately after fertilization.
- Initially, there is no overall increase in size as cells divide.
The Morula
- Cleavage produces a morula.
- Blastomeres are cells formed from cleavage of the fertilized ovum.
- Blastomeres are tightly compacted in the morula.
- The morula is surrounded by the zona pellucida (glycoprotein coat).
In Vitro Fertilization (IVF)
- In IVF, the zona pellucida can be removed for genetic testing prior to transfer into the uterus.
The Blastocyst
- Morula forms a fluid-filled cavity (blastocyst cavity).
- Cells separate into inner and outer groups.
- The inner cell mass (ICM) becomes the embryo.
- The outer cells (trophoblast) become the placenta.
- Cells in the ICM differentiate into hypoblast and epiblast.
Blastocyst Hatching
- Blastocyst sheds its outer membrane and attaches to the lining of the uterus to prepare for implantation.
Implantation
- Implantation begins around day 6.
- Three main stages: apposition, adhesion, and invasion.
- Endometrium (inner lining of the uterus) is essential for implantation.
Apposition
- First physical contact between the blastocyst and the endometrium.
Adhesion
- Blastocyst adheres to the endometrium.
Invasion
- Trophoblast invades the endometrium.
- Complex signalling between the endometrium and the trophoblast.
- The blastocyst must implant adequately, but not too deeply.
- Is a foreign body, so why is it not rejected by the mother?
Trophoblast Differentiation
- Cytotrophoblast at embryonic pole proliferates and invades the endometrium.
- Syncytiotrophoblast forms maternal vessels that will form blood filled spaces called lacunae.
- Trophoblast contacts maternal vessels.
- This will allow exchange of gases between maternal and fetal circulation
Implantation: Changes in the Inner Cell Mass
- The inner cell mass (ICM) flattens into two layers: epiblast and hypoblast.
- This structure is called a bilaminar disc.
- Amniotic cavity developes between epiblast and trophoblast.
- The blastocyst cavity forms the primitive yolk sac.
Clinical Relevance: Implantation Problems
- Implantation may not be successful.
- Blastocyst may be abnormal.
- Blastocyst does not reach the uterus.
- The endometrium may not be receptive.
- Implantation may be ectopic (outside the uterus).
- Ectopic implantation may occur in fallopian tubes, ovaries, abdomen, or cervix.
- Sub-optimal implantation can result in placental problems later in pregnancy.
Clinical Relevance: Ectopic Pregnancy
- Tubal pregnancies are ectopic, meaning implantation occurs outside the uterus.
Clinical Relevance: Invasive Placentation
- Placenta invades too far into the uterus.
- May invade the muscle wall (myometrium) or adjacent organs.
- Placenta does not separate easily after birth.
- Can result in haemorrhage.
Gastrulation (Week 3)
- A critical process forming a trilaminar disc.
- Establishes germ layers (ectoderm, endoderm, and mesoderm).
- Further specification of body axes (anterior-posterior, left-right, dorsal-ventral).
The Primitive Streak
- Appears as a groove on the caudal end of the epiblast.
Neurulation (Week 4)
- Process that forms the neural tube.
- Neural plate forms as thickening of the ectoderm.
- Notochord induces neural plate formation.
- Neural plate bends to form a groove.
- Cells at the top of folds are neural crest cells.
- Two sides of the groove fuse to form neural tube.
- Neural tube detaches from the ectoderm.
- Cranial end expands to form the brain.
- Caudal end remains as the spinal cord.
Clinical Relevance: Laterality Anomalies
- Sidedness abnormalities may occur, like situs inversus (mirror-image of thoracic and abdominal viscera).
- Dextrocardia: flipped heart position.
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Description
This quiz covers the critical stages of embryonic development from fertilization to week 4. Test your knowledge on key concepts including blastocyst formation, gastrulation, and the development of germ layers. Understand the factors that may lead to congenital anomalies during this crucial period.
