38 Questions
Where does fertilization typically occur?
In the ampullary region of the uterine tube
What percentage of sperm deposited in the vagina enter the cervix?
1%
How do sperm primarily move from the cervix to the oviduct?
By their own propulsion
What is the minimum time required for sperm to travel from the cervix to the oviduct?
2 to 7 hours
What occurs in the isthmus that affects sperm motility?
Sperm become more motile due to chemoattractants
What is the duration of capacitation in the human reproductive tract?
7 hours
What is the last phase of fertilization?
Fusion of the oocyte and sperm cell membranes
Approximately how many sperm reach the site of fertilization?
300 to 500
What is the main mechanism of action of the combination contraceptive pill?
It acts on the level of FSH and LH, preventing their release from the pituitary
What is a disadvantage of In Vitro Fertilization (IVF)?
It has a low success rate
What is the role of the drug RU-486 in contraception?
It causes abortion if administered within 8 weeks of the previous menses
Why are multiple ova collected and fertilized in IVF?
To increase the chances of a successful pregnancy
What is the primary mechanism of action of the intrauterine device (IUD)?
It directly affects sperm and oocytes or inhibits pre-implantation stages of development
What is the purpose of intracytoplasmic sperm injection (ICSI)?
To overcome severe male infertility
What is the approximate number of sperm per ml in a normal ejaculate?
100 million
What is the percentage of couples who experience infertility?
15-30%
In Zygote Intrafallopian Transfer (ZIFT), where are the fertilized oocytes placed?
In the ampullary region
What is the main mechanism of action of the male 'pill'?
It contains a synthetic androgen that prevents both LH and FSH secretion
What is a benefit of fertilization using IVF?
The risk of producing malformed offspring is low
Why is it necessary for the uterine tubes to be patent in IVF and ZIFT?
So that the fertilized ova can be transferred to the uterus
What is the primary cause of occluded oviducts in women?
Pelvic inflammatory disease
What is the definition of fertility in terms of sperm count in males?
50 million sperm per total ejaculate
What is the function of the zona pellucida?
To facilitate and maintain sperm binding and induce the acrosome reaction
What is released from cortical granules lining the plasma membrane of the oocyte?
Lysosomal enzymes
What is the role of ZP3 protein in the fertilization process?
To induce the acrosome reaction and facilitate sperm binding
What happens to the plasma membrane covering the acrosomal head cap during the acrosome reaction?
It disappears
What is the result of the cortical and zona reactions?
The oocyte membrane becomes impenetrable to other spermatozoa and the zona pellucida alters its structure and composition to prevent sperm binding and penetration
What is the main consequence of the second meiotic division?
Production of the second polar body
What is the function of integrins in the fertilization process?
To mediate the interaction of sperm and the oocyte membrane
What is the role of the spermatozoon in metabolic activation of the egg?
It carries the activating factor
What happens to the spermatozoon after it enters the oocyte?
The plasma membrane is left behind on the oocyte surface
What happens to the chromosomes in the male pronucleus during growth?
They replicate their DNA
What is the result of the release of acrosomal enzymes?
The sperm is able to penetrate the zona pellucida
What is the result of the failure of DNA replication in the pronuclei?
The production of haploid cells in the zygote
What is the significance of the diploid number of chromosomes in the zygote?
It allows for the combination of chromosomes from both parents
What determines the sex of the new individual?
The type of spermatozoon (X- or Y-carrying)
What is the consequence of fertilization failure?
The degeneration of the oocyte
What is the result of the movement of sister chromatids to opposite poles?
The appearance of a deep furrow on the cell surface
Study Notes
Fertilization
- Fertilization occurs in the ampullary region of the uterine tube, which is the widest part of the tube and is close to the ovary.
- Spermatozoa can remain viable in the female reproductive tract for several days, but only 1% of sperm deposited in the vagina enter the cervix, where they may survive for many hours.
- Sperm movement from the cervix to the oviduct is primarily accomplished by their own propulsion, although they may be assisted by movements of fluids created by uterine cilia.
Capacitation and Acrosome Reaction
- Capacitation is a period of conditioning in the female reproductive tract that lasts approximately 7 hours in humans, during which sperm undergo epithelial interactions with the mucosal surface of the tube.
- The acrosome reaction is induced by zona proteins and culminates in the release of enzymes needed to penetrate the zona pellucida.
Phases of Fertilization
- Phase 1: Penetration of the corona radiata, during which capacitated sperm pass freely through corona cells.
- Phase 2: Penetration of the zona pellucida, which facilitates and maintains sperm binding and induces the acrosome reaction.
- Phase 3: Fusion of the oocyte and sperm cell membranes, which is mediated in part by the interaction of integrins on the oocyte and sperm.
Post-Fertilization Events
- The fertilizing spermatozoon moves forward until it lies close to the female pronucleus, and its nucleus becomes swollen and forms the male pronucleus.
- The oocyte responds to fertilization in three ways: cortical and zona reactions, resumption of the second meiotic division, and metabolic activation of the egg.
Clinical Correlates
- Contraceptive methods include barrier techniques (male and female condoms, diaphragm, cervical cap, and contraceptive sponge), hormonal methods (the pill), and intrauterine devices.
- Infertility affects 15% to 30% of couples, and may be due to male or female factors, such as insufficient numbers of sperm, poor motility, occluded oviducts, hostile cervical mucus, immunity to spermatozoa, and absence of ovulation.
- Assisted reproductive technologies, such as in vitro fertilization (IVF) and zygote intrafallopian transfer (ZIFT), can overcome infertility.
Fertilization occurs in the ampullary region of the uterine tube, where male and female gametes fuse. Learn about the journey of sperm from the vagina to the oviduct.
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