Fertilization Flashcards
What does seminal fluid consist of?
→ Prostatic and seminal vesicle secretions
What is the function of seminal fluid?
→ It coagulates to prevent loss and later liquefies
What is the function of the cervical mucus?
→ To remove seminal fluid
→ removing morphologically abnormal sperm and cellular debris
When is cervical mucus less viscous and why?
→ in the absence of progesterone
→ allows sperm to pass
What forms a reservoir of sperm in the female?
→ Cervical crypts
When does fertilisation occur within?
→ 24-48 hours
→ sperm have been found alive after 5 days
What attracts the sperm to the egg?
→ Chemoattractants released from the oocyte cumulus complex
→ Sperm become hyperactivated near the egg
How do sperm become hyperactivated near the egg?
→ Forceful tail beats with increased frequency and amplitude
→ mediated by Ca2+ influx via CatSper channels
How is capacitation achieved?
→ Removing the sperm from the seminal fluid
→ uterine or tubal fluid may contain factors which promote capacitation
What must occur to the sperm before the acrosome reaction?
→ Biochemical rearrangement of the surface glycoprotein
→ changes in membrane composition
What time does capacitation occur?
→ 4-16 hours
Where does the acrosome reaction occur?
→ within the zona-cumulus complex
How does the acrosome reaction occur?
→ Acrosomal membrane on the sperm fuses
→ releases enzymes that cut through the zona-cumulus complex
→ acrosin bound to the inner acrosomal membrane digests the zona pellucida so sperm can enter
What causes the oocyte to undergo meiosis?
→ LH spike
What does the LH spike make the oocyte change into?
→ Primary oocyte becomes seconday oocyte + 1st polar body
What does the corpus luteum produce?
→ Progesterone
What does progesterone do to the endometrium?
→ Makes it secretory and receptive to implantation
What does progesterone do to the cilia?
→ Suppresses cilia in uterine tubes once the oocyte has passed
What does progesterone do the the cervical mucus?
→ It makes it viscous to prevent further sperm penetration
What is the function of estrogen in the luteal phase?
→ Maintains the endometrium
What causes the LH spike?
→ sustained levels of estrogen produced by the dominant follicle
After ovulation what happens to the follicle?
→ it becomes the corpus luteum
What does progesterone do in the secretory phase?
→ Makes the stratum functionalis thicker
→ uterine glands become more secretory
What causes the proliferative phase?
→ Estrogen from the follicular phase
What is the life span of the CL?
→ 14 days
What causes the inter cycle rise of FSH?
→ the fall in CL derived steroids
What does the CL becomes when it dies?
→ Corpus albicans
What happens to the CL in pregnancy?
→ It is rescued by the HcG from the embryo binding to the LH receptors
→ it continues to produce progesterone and maintain the endometrium
What does the menstrual cycle achieve?
→ Selection of a single follicle and oocyte
→ Correct number of chromosomes in the oocyte
→ Changes in cervix and uterine tubes to enable egg transport and sperm access
→ Preparation of the endometrium
→ Support of the implanting embryo
What are cumulus cells?
→ Remnants of the granulosa cells
What is the corona radiata?
→ innermost granulosa cells
What is the zona pellucida made from?
→ Matrix of proteins which are secreted from the egg
What is a polar body?
→ The other half of cell division without the cytoplasm
What does the first polar body mean?
→ That meiosis I has occurred
When is meiosis triggered to finish?
→ By LH at ovulation
Where does the acrosome reaction occur?
→ In contact with the zona-cumulus complex
Describe sperm binding
1) Sperm penetrates the cumulus and bind to the ZP
2) Sperm enzymes cut through the ZP with ZP3 and the sperm fuses with the plasma membrane
3) Sperm are taken in by phagocytosis
4) Phospholipase Zeta is activated by basal Ca2+ inside the egg
PIP2 → DAG + IP3 which causes intracellular release of Ca2+ leading to a large Ca2+ spike
5) Cortical reaction as a wave of Ca2+ sweeps over the egg
What is the cortical reaction?
→ Releases proteases, peroxides and hyaline which prevents polyspermy
After meiosis I how many chromosomes does the oocyte have?
→ 23
→ 2 copies of each chromosomes are arranged as a sister chromatid
What does entry of the sperm into the egg cause?
→ increase in Ca2+
What does Ca2+ cause in the egg?
→ Completion of Meiosis II
Describe syngamy
1) entry of sperm causes an increase in Ca2+ which causes the completion of meiosis II expelling the second polar body
2) Sperm nuclear membrane breaks down and chromatin decondenses and chromosomes separate
3) 4-7 hours after fusion the two sets of haploid chromosomes become surrounded by distinct membranes forming pro nuclei
4) the haploid structures synthesize DNA in preparation for the first mitotic division
5) pro nuclei fuse and mitotic metaphase spindle forms
6) mitosis occurs and one cell zygote becomes a two cell embryo
