fertilisation, cleavage, implantation

• What is the optimal time for sperm to arrive at an oocyte?

  1-2 days either side ovulation
• How many sperm are typically ejaculated?

  4-5 million sperm
• How many sperm reach the site of fertilization?

  300-500,000 sperm
• What changes occur in cervical mucus during ovulation?

  It increases and thins for easier sperm transport
• What happens to the fallopian tube during ovulation?

  It comes into close contact with the ovary
• What role do fimbria play during ovulation?

  They sweep the ovum into the tube
• How does the ovum move into the ampulla of the tube?

  Through peristaltic waves of tube musculature
• How long can sperm survive in the reproductive tract?

  Max 5 days
• What is capacitation in spermatozoa?

  A maturation step occurring in the female reproductive tract
• What happens to the sperm glycoprotein coat during capacitation?

  It undergoes extensive remodeling
• Why can't newly ejaculated sperm fertilize an oocyte?

  Membrane molecules are masked by plasma proteins
• Where does the plasma protein covering get removed?

  In the uterus
• How long does capacitation take?

  5-7 hours
• What are the stages of fertilization?

  1. Binding of sperm to zona pellucida
  2. Acrosome reaction
  3. Penetration through zona pellucida
  4. Fusion of plasma membranes
  5. Sperm nucleus enters oocyte cytoplasm
• What is the zona pellucida?

  A glycoprotein shell facilitating sperm binding
• What induces the acrosome reaction?

  Binding of sperm to zona pellucida
• What is required for sperm to penetrate the cumulus oophorus?

  Hyaluronidase released from sperm acrosome
• What triggers the acrosome reaction?

  Multiple adhesions to zona pellucida
• What happens during the acrosome reaction?

  Perforations develop in the acrosome
• What enzymes are released during the acrosome reaction?

  Acrosin, proteinases, collagenases
• What is the purpose of the acrosome reaction?

  To facilitate binding and penetration of zona pellucida
• What occurs during the penetration of zona pellucida?

  Exocytosis of cortical enzymes into zona pellucida
• What is the zona reaction?

  Hardening of the zona pellucida
• What is polyspermy?

  More than 1 sperm enters the ovum
• What is dispermy?

  Two sperm enter the ovum
• What is triploidy?

  Three sperm enter the ovum
• What happens to a fetus in case of triploidy?

  It nearly always aborts
• What triggers the completion of meiosis II in oocytes?

  Fusion of plasma membranes of oocyte and sperm
• What enters the cytoplasm of the oocyte during fertilization?

  Head and tail of spermatozoon
• How many chromosomes do the male and female pronuclei each have?

  23 chromosomes each
• What happens to the membranes of pronuclei during fertilization?

  They break down
• What is formed after the chromosomes are arranged for mitotic division?

  The first cleavage occurs
• What are the results of fertilization?

  Stimulates secondary oocyte to complete meiosis
• What is the diploid number of chromosomes restored after fertilization?

  46 chromosomes
• What initiates cleavage after fertilization?

  Restoration of diploid number of chromosomes
• What occurs during cleavage after fertilization?

  • Series of mitotic divisions
  • Blastomeres become smaller with each division
  • After 3 divisions, blastomeres undergo compaction
  • Compact blastomeres form a 16-cell morula
• What is a blastocyst?

  Embryo 5-7 days old after fertilization
• What are the two distinct cell types in a blastocyst?

  Outer cell mass (trophoblast) and inner cell mass (embryoblast)
• What is the central cavity of a blastocyst filled with?

  Blastocoel
• What happens to the blastocyst before implantation?

  It hatches from the zona pellucida