36 Questions
What is the cavity formed in the blastocyst stage?
Blastocele
What is the function of proteolytic enzymes secreted by syncytiotrophoblasts?
To implant the embryo in the uterus
During which phase of the menstrual cycle does the uterine endometrium prepare for implantation?
Secretory phase
What is the function of human chorionic gonadotropin (hCG) secreted by syncytiotrophoblasts?
To maintain the corpus luteum
What is the term for the outer cell mass that forms the epithelial wall of the blastocyst?
Trophoblast
During which day of pregnancy do the trophoblastic cells begin to penetrate the uterine mucosa?
Sixth day
During which stage of development does fertilization occur?
Zygotic Stage
Where does fertilization typically occur?
Uterine tube
What is the purpose of the acrosome reaction?
To release enzymes needed to penetrate the zona pellucida
What is the result of ovulation?
Mature oocyte is expelled from the ovary
What is the function of capacitation?
To allow only capacitated sperm to pass through the corona cells
During which day of a regular 28-day menstrual cycle does ovulation occur?
14th day
What is the correct order of the phases of fertilization?
Penetration of the corona radiata, penetration of the zona pellucida, fusion of the oocyte and sperm cell membranes
What is the term for the period from 0-2 weeks of development?
Zygotic Stage
What is the role of the enzymes in the acrosome?
To break down the zona pellucida of the oocyte
What happens to the oocyte if it is not fertilized within 24 hours of ovulation?
It degenerates
What is the result of the cortical and zona reactions?
The sperm is prevented from entering the oocyte
What is the significance of the diploid number of chromosomes being restored?
It restores the normal number of chromosomes in the zygote
What is the result of the resumption of the second meiotic division?
The oocyte finishes its second meiotic division
What is the term for the series of mitotic divisions that occur after fertilization?
Cleavage
What is the term for the cells that result from cleavage?
Blastomeres
What is the stage of development that occurs approximately 3 days after fertilization?
Morula
What is the process called when syncytiotrophoblasts erode the endometrium and the blastocyst burrows into the compact layer of endometrium?
Implantation
What is the structure that forms from the hypoblast?
Primary yolk sac
What is the most common type of ectopic pregnancy?
Tubal pregnancy
What is the layer of the endometrium that the blastocyst burrows into during implantation?
Compact layer
What is the membrane that forms from the epiblast?
Exocoelomic membrane
When does the completion of implantation occur?
Between the 5th and 10th day
What is the most common type of ectopic pregnancy?
Tubal pregnancy
What is the role of Early Pregnancy Factor (EPF)?
As an immunosuppressant protein
During In Vitro Fertilization, what is the purpose of hormonal stimulation?
To form several mature follicles
What is the result of dispermy?
Fertilization of a secondary oocyte by two sperms
What is the stage of development after fertilization?
Cleavage
What is the purpose of an assay of HCG and Progesterone?
To detect pregnancy by the end of the second week
What is the term for a pregnancy that attaches to the mesenteric blood vessels?
Abdominal pregnancy
What is the stage of development where the zygote is transferred to the uterine cavity?
4-8 cell stage
Study Notes
Stages of Prenatal Development
- Zygotic (or Germinal) Stage: 0-2 weeks
- Embryonic Stage: 2-8 weeks
- Fetal Stage: 9-40 weeks
Ovulation
- Event in which a mature oocyte is expelled from the ovary
- Occurs on the 14th day of a regular 28-day menstrual cycle
Fertilization
- Process by which male and female gametes fuse
- Occurs in the ampullary region of the uterine tube
- Phases of fertilization:
- Phase 1: Penetration of the corona radiata
- Phase 2: Penetration of the zona pellucida
- Phase 3: Fusion of the oocyte and sperm cell membranes
Capacitation
- Only capacitated sperm can pass through the corona cells and undergo the acrosome reaction
- Acrosome reaction: Release of enzymes needed to penetrate the zona pellucida, including acrosin and trypsin-like substances
Results of Fertilization
- Restoration of the diploid number of chromosomes
- Determination of the sex of the new individual
- Initiation of cleavage
Cleavage
- Series of mitotic divisions, increasing the number of cells
- Cells, known as blastomeres, become smaller with each cleavage division
- Approximately 3 days after fertilization, cells divide again to form a 16-cell morula
Blastocyst Formation
- Fluid penetrates the zona pellucida, forming a single cavity, the blastocele
- Embryoblast and outer cell mass, or trophoblast, flatten and form the epithelial wall of the blastocyst
- Zona pellucida disappears, allowing implantation to begin
Implantation
- Trophoblastic cells over the embryoblast pole begin to penetrate between the epithelial cells of the uterine mucosa
- Approximately 6th day after fertilization
Syncytiotrophoblasts
- Show villous projections and lacunar spaces
- Secrete:
- Proteolytic enzymes, which erode the endometrium to implant
- HCG, which sustains the corpus luteum
Uterus at Time of Implantation
- Uterine endometrium passes through three stages:
- Menstrual phase
- Proliferative phase (influenced by estrogen)
- Secretory phase (influenced by progesterone produced by the corpus luteum)
Ectopic Pregnancy
- Most common type: Tubal pregnancy
- May secondarily attach itself to mesenteric blood vessels and continue as abdominal pregnancy
- Rarely: Falls into the pouch of Douglas
Pregnancy Tests
- Early Pregnancy Factor (EPF): appears in maternal serum by 24 to 48 hours
- Assay of HCG and Progesterone by the end of the second week
- Confirmation of pregnancy: by ultrasonogram by the end of the 5th week
Learn about the stages of development from conception to birth, including ovulation, fertilization, cleavage, and implantation. Test your knowledge of prenatal development.
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