fertilization - clark

Question 1

Where do ruminants and cats deposit semen?

Answer 1

Vagina

60% of semen is lost to retrograde transport 12 hours post insemination

Question 2

Where do pigs and equines deposit semen?

Answer 2

Cervix

Question 3

Where do dogs deposit semen?

Answer 3

Uterus

Question 4

What structure is a major barrier to sperm transport? (all spp. but pigs & dogs)

Answer 4

Cervix

Question 5

Utero-tubal junction

Answer 5

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

4 parts of uterine tube: Infundibulum (proximal), Ampulla (wide part), Isthmus (narrow, tortuous), UTJ

Question 6

Define Sperm Capacitation

Answer 6

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

Question 7

Caltrin and it’s significance

Answer 7

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.

Question 8

Steps to Acrosome Reaction (AR)

Answer 8

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)

Question 9

What happens once the sperm has penetrated into oocyte?

Answer 9

1. Cortical granules are released from sperm and modify the zona, preventing other sperm from entering/polyspermy (a cortical reaction).
2. Oocyte (2n) completes Meiosis II and becomes an ovum (1n).
3. Sperm endocytosis into ovum.
4. Sperm nucleus decondensation.
5. 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.

Question 10

Describe how the zygote develops into a blastocyst

Answer 10

1. Zygote -> embryonic cleavage (several cell cycles of mitosis + cytokinesis) occurs, forming “blastomeres” with each completed cycle.
2. Blastomeres cluster within zygote, forming compact Morula.
3. Cleavage ends @ 8-16 cell stages (species-dependent), forming the Blastocyst.
4. Blastocyst = mature stage -> hatches out through zona pellucida and implants into uterine wall