fertilization - clark Flashcards
Where do ruminants and cats deposit semen?
Vagina
60% of semen is lost to retrograde transport 12 hours post insemination
Where do pigs and equines deposit semen?
Cervix
Where do dogs deposit semen?
Uterus
What structure is a major barrier to sperm transport? (all spp. but pigs & dogs)
Cervix
Utero-tubal junction
Where sperm accumulate & prior to fertilization– sperm “reservoir”. Get here via estrogen-induced peristaltic contractions
- located in the isthmus
- sperm bind to epithelium in folds of UTJ & are released slowly into the oviduct
Define Sperm Capacitation
the physiological changes sperm undergo in UTJ in order to undergo Acrosome Reaction & penetrate the ovum
- increased motility (head + tail modifications)
- metabolic changes (incr. cAMP, O2 consumption, Caltrin removal + Ca2+ influx)
- incr. plasma membrane fluidity
once it occurs, sperm lifespan drastically shortens
Caltrin and it’s significance
Protein present on sperm prior to AR exocytosis that blocks Ca2+ transport & prevent hyperactivated motility.
- Caltrin removal off sperm occurs in the uterus & oviduct prior to AR, allowing for Ca2+ influx which induces membrane fusion of sperm & oocyte.
Steps to Acrosome Reaction (AR)
Sperm binds to oocyte’s zona pellucida via ligand-receptor interaction:
1. Ca2+ influx induces interaction b/w outer acrosome & zona pellucida -> fusion + pore formation
2. Pores allow for exposure of acrosomal enzymatic contents, which help “digest” zona pellucida for sperm penetration into oocyte membrane (zona)
What happens once the sperm has penetrated into oocyte?
- Cortical granules are released from sperm and modify the zona, preventing other sperm from entering/polyspermy (a cortical reaction).
- Oocyte (2n) completes Meiosis II and becomes an ovum (1n).
- Sperm endocytosis into ovum.
- Sperm nucleus decondensation.
- Sperm & oocyte pronuclei fuse (syngamy) -> form the diploid (2n) zygote.
Recall: @ fertilization, oocyte has NOT complete meiosis; all 2º oocytes remain arrested in metaphase of meiosis II until fertilzation. At Fertilization, Meiosis II is completed, -> second polar body (containing unneeded complement of genetic material from meoisis) is ejected, and the oocyte becomes an ovum = haploid (1n) gamete.
Describe how the zygote develops into a blastocyst
- Zygote -> embryonic cleavage (several cell cycles of mitosis + cytokinesis) occurs, forming “blastomeres” with each completed cycle.
- Blastomeres cluster within zygote, forming compact Morula.
- Cleavage ends @ 8-16 cell stages (species-dependent), forming the Blastocyst.
- Blastocyst = mature stage -> hatches out through zona pellucida and implants into uterine wall
