🧬 Fertilization, Cleavage & Gastrulation
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40 Terms
What is fertilization?
A complex sequence of coordinated molecular events that begins with contact between sperm and ovum and ends with intermingling of maternal and paternal chromosomes
What is the usual site of fertilization?
The ampulla of the uterine tube.
Why is the ampulla suitable for fertilization?
It is the longest and widest part of the uterine tube.
What happens if the oocyte is not fertilized in the uterine tube?
It slowly passes to the uterus, where it degenerates and is absorbed.
Does fertilization occur in the uterus?
No
How long does the fertilization process take?
About 24 hours.
What are the major phases of fertilization?
Passage through the corona radiata; penetration of the zona pellucida; fusion of the plasma membranes; completion of the second meiotic division and formation of the female pronucleus; and formation of the male pronucleus.
What is the corona radiata?
The layer of follicular cells surrounding the oocyte and zona pellucida.
What enzyme mainly helps sperm pass through the corona radiata?
Hyaluronidase released from the acrosome.
What else assists in dispersing the corona radiata?
Tubal mucosal enzymes.
What is the important phase in initiating fertilization?
Passage of a sperm through the zona pellucida.
Which enzymes appear to cause lysis of the zona pellucida?
Esterases, acrosin and neuraminidase.
What is the function of these enzymes on the zona pellucida?
They form a path for the sperm to follow to the oocyte
What is the zona reaction?
A reaction that occurs after sperm penetration and makes the zona pellucida impermeable to other sperm.
What happens when the sperm and oocyte plasma membranes fuse?
The membranes fuse and break down at the area of fusion.
Which parts of the sperm enter the oocyte cytoplasm?
The head and tail enter, while the sperm’s plasma membrane remains behind.
What activates the oocyte to complete its second meiotic division?
Penetration of the oocyte by a sperm.
What is formed after completion of the second meiotic division?
A mature oocyte and a second polar body.
What does the nucleus of the mature oocyte become?
The female pronucleus.
What happens to the sperm nucleus after entering the oocyte?
It enlarges to form the male pronucleus.
What happens to the sperm tail?
It degenerates.
How do the male and female pronuclei appear morphologically?
They are morphologically indistinguishable.
What is an ootid?
An oocyte containing two haploid pronuclei.
What is cleavage?
Rapid cell divisions following fertilization, with very little growth while the cells are dividing.
What is each cell produced during cleavage called?
A blastomere.
What is a morula?
A solid ball of cells resulting from cleavage.
After how many divisions does the morula result?
The first 5–7 divisions.
How many blastomeres are present in the morula?
About 12–32 blastomeres.
When does the spherical morula form?
About 3 days after fertilization.
What happens as cleavage continues after the morula?
A fluid-filled cavity called the blastocoel forms within the embryo.
What is the hollow ball of cells formed after the blastocoel develops called?
A blastula.
What are the two cell masses of the blastocyst?
The outer cell mass, called the trophoblast, and the inner cell mass, called the embryoblast.
What does the embryoblast divide to form?
The epiblast and hypoblast.
What is gastrulation?
The morphogenetic process that rearranges the cells of a blastula into a three-layered (triploblastic) embryo called a gastrula.
What is the blastopore?
The first opening in the embryo and the point of invagination during gastrulation.
What is the archenteron?
The primitive gut that forms during gastrulation.
What are the two layers of the bilaminar germ disc?
Epiblast and hypoblast.
What type of cells make up the epiblast and hypoblast?
The epiblast consists of columnar cells adjacent to the trophoblast, while the hypoblast consists of cuboidal cells adjacent to the blastocoele.
What are the three germ layers of the trilaminar germ disc?
Ectoderm, mesoderm and endoderm.
How are the three germ layers formed?
Endoderm forms when cells from the primitive groove replace the hypoblast; mesoderm forms between the epiblast and hypoblast; and the remaining epiblast forms ectoderm.