36 Questions
What is the duration of the Zygotic Stage of prenatal development?
0-2 weeks
Where does fertilization occur?
In the ampullary region of the uterine tube
What is the term for the event in which a mature oocyte is expelled from the ovary?
Ovulation
What is the function of the acrosome reaction?
To release enzymes needed to penetrate the zona pellucida
How many stages of prenatal development are there?
3
What is the term for the process of fusion of the oocyte and sperm cell membranes?
Fusion of the oocyte and sperm cell membranes
What is the purpose of capacitation?
To allow sperm to pass through the corona radiata
At what day of a regular 28-day menstrual cycle does ovulation occur?
14th day
At which stage do cells become arranged in a hollow sphere?
Blastocyst stage
What is the outer layer of cells in a morula called?
Trophoblast
How many cells are present in a morula?
12-16 cells
At which stage do cells start to lose totipotency?
After 8-cell stage
What is the function of the zona pellucida?
Protects the blastocyst during implantation
When does implantation of the blastocyst begin?
By day 5-6
How many cells are present after 72 hours of fertilization?
32 cells
What happens to the zona pellucida by day 5-6?
It disappears
What happens to the zona pellucida during blastocyst formation?
It disappears allowing implantation to begin
What is the function of the proteolytic enzymes secreted by the syncytiotrophoblast?
To erode the endometrium for implantation
During which stage of the menstrual cycle does the uterine endometrium prepare for implantation?
The secretory phase
What is the main function of the HCG secreted by the syncytiotrophoblast?
To sustain the corpus luteum
What is the purpose of the lacunar spaces in the syncytiotrophoblast?
To facilitate the exchange of nutrients and waste
How many days after ovulation does the secretory phase of the menstrual cycle begin?
2-3 days
What is the primary function of syncytiotrophoblasts during implantation?
To erode the endometrium and allow the blastocyst to burrow into the compact layer
During which days does the process of implantation take place?
5th to 10th day
What is the most common type of ectopic pregnancy?
Tubal pregnancy
What is the name of the membrane that forms around the exocoelomic cavity?
Hueser's membrane
What is the name of the layer of endometrium that the blastocyst burrows into?
Compact layer
What is the structure that forms from the epiblast?
Hypoblast
What is the main function of the enzymes in the acrosome of a sperm?
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?
Prevention of polyspermy
What is the term for the process by which the zygote undergoes a series of mitotic divisions?
Cleavage
What is the term for the cells that result from cleavage?
Blastomeres
What is the result of the metabolic activation of the egg?
Initiation of cleavage
How many cells are present in a morula?
16
When does the oocyte finish its second meiotic division?
Immediately after entry of the spermatozoon
Study Notes
Prenatal Development
- The three stages of prenatal development from conception to birth are:
- Zygotic (or Germinal) Stage (0-2 weeks)
- Embryonic Stage (2-8 weeks)
- Fetal Stage (9-40 weeks)
Ovulation
- A mature oocyte is expelled from the ovary around the 14th day of a regular 28-day menstrual cycle.
Fertilization
- Fertilization occurs in the ampullary region of the uterine tube.
- The three phases of fertilization are:
- Penetration of the corona radiata
- Penetration of the zona pellucida
- Fusion of the oocyte and sperm cell membranes
- Capacitation is necessary for sperm to penetrate the corona radiata and undergo the acrosome reaction.
- The acrosome reaction releases enzymes needed to penetrate the zona pellucida, including acrosin and trypsin-like substances.
Results of Fertilization
- The main results of fertilization are:
- Restoration of the diploid number of chromosomes
- Determination of the sex of the new individual
- Initiation of cleavage
Cleavage
- Cleavage is a series of mitotic divisions that increase the number of cells, known as blastomeres.
- The cells divide every 12-24 hours, resulting in:
- 2-cell stage (36 hours)
- 4-cell stage (48 hours)
- 8-cell stage (72 hours)
- Morula (12-16 cells) or Blastula
- Until the 8-cell stage, the cells are totipotent.
Blastocyst Formation
- The blastocyst forms around the 5th day.
- Fluid penetrates the zona pellucida into the intercellular spaces of the inner cell mass, forming a single cavity, the blastocele.
- The embryoblast is at one pole, and the outer cell mass, or trophoblast, flattens and forms the epithelial wall of the blastocyst.
Implantation
- Implantation begins around the 6th day.
- The trophoblastic cells over the embryoblast pole penetrate between the epithelial cells of the uterine mucosa.
- Syncytiotrophoblasts secrete proteolytic enzymes to erode the endometrium and human chorionic gonadotropin (hCG) to sustain the corpus luteum.
Uterus at Time of Implantation
- The uterine endometrium passes through three stages during the menstrual cycle:
- Menstrual phase
- Proliferative phase (influenced by estrogen)
- Secretory phase (influenced by progesterone produced by the corpus luteum)
Learn about the stages of prenatal development from ovulation to implantation, including fertilization, cleavage, and implantation. Understand the normal site of fertilization and results.
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