Sperm Transport in the Female Genital Tract of Different Animals Deposition of semen by male: Sperm deposited in the cranial part of the vagina of cow, sheep, bitch, queen, and primates. In the pig and horse the sperm is directly deposited in the cervix or uterus. Volume of semen in animals: In ruminants: Amount of semen is small in volume, from 3-5 ml with high proportion of spermatozoa. But majority of the spermatozoa destroyed by retrograde transport. Sperm Transport in the Female Genital Tract of Different Animals Volume of semen in animals: In boars: The volume of ejaculate is large (200-400 ml) with low concentration of spermatozoa. The boar ejaculate in 3 fraction. The first fraction contains few spermatozoa with secretion from accessory glands. The second fraction is rich in spermatozoa. The third fraction is consists of the secretion of bulbourethral gland which form coagulum that reduces retrograde sperm loss. Sperm Transport in the Female Genital Tract of Different Animals In Stallion: The stallion ejaculates in a series of “jets”. In the first jets the proportion of spermatozoa is maximum. The later Jets contains highly viscous mucous to block the retrograte spermatozoa loss. In dog: First ejaculate is clear fluid from prostate and ranges from 0.5 to 5 ml. Second one is rich in spermatozoa and the volume ranges from 1-4ml and contains 300 million to few billion spermatozoa. The third fraction is from the prostate also and contains high volume of fluid ranges from 1 to 80 ml. Sperm Transport in the Female Genital Tract of Different Animals In birds: The spermatozoa of the ejaculates of the cock reserves in the “sperm-host-gland” at the uterovaginal junction or at the infundibulum of the oviduct of hens. Here, the spermatozoa nourished by the enriched nutrient secreted by the tubular gland of sperm-host-gland. In these gland spermatozoa can survive up to three month and can fertilize the ova of hen. Transport of spermatozoa to the ampulla of the mammalian Oviduct: Due to tone and motility of the tunica muscularis of the female genital tract. Steps of Fertilization 1. Capacitation Changes of the spermatozoa in the female reproductive tract occurred after ejaculation by male constitute capacitation. Without this changes spermatozoa cannot fertilize the egg. Capacitation begins in the uterus and end in the isthmus of the oviduct. Steps of Fertilization 1. Capacitation Capacitation process includes: (1) Removal of the glycoprotein coat and seminal plasma proteins from its surface. (2) Alteration in the flagellar motility that are necessary to penetrate the zona pellucida. (3) Development of the capacity to fuse with the plasma membrane of the oocyte. Steps of Fertilization 2. Interaction Between Spermatozoa and the Zona Pellucida The zona pellucida (ZP) is an extracellular matrix surrounding the oocyte and the early embryo. Following steps are needed for perfect fertilization: 1. Capacited spermatozoa bind with the ZP. 2. Acrosome reaction and penetration of the ZP. 3. Modification of the ZP that prevent polyspermy (prevent to enter more than one spermatozoa). Steps of Fertilization 3. Acrosomal Reaction Acrosomal reaction performed by following steps: 1. The spermatozoa adhere with the zona pellucida. 2. Acrosomal cap secretes hydrolytic enzyme acrosin & hyaluronidase 3. Above two enzymes digest the Jelly coat and vitelline layer of ZP. 4. By the propulsive action of the tail and actin filament, spermatozoa Enters into the oocyte. Stage of Fertilization 4. Syngamy After penetration of ZP, sperm adhere to and fuse with the plasma membrane of the oocyte. The membrane of oocyte fuse with the membrane of spermstozoon. In the later stages the oocyte engulf fertilizing spermatozoon including its tail. This mechanism is called syngamy. The molecular protein fertilin α, fertilin β, and cyritestin causes fusion. Stage of Fertilization 5. Oocyte activation This step include: i. Establishment of a block to prevent polyspermy. It is accompanied by releasing of cortical granules which prevent other spermatozoa to enter into the oocyte. ii. Resumes of meiosis and pronucleus formation: It includes a) resumes of meiosis II, formation of ovum with enough yolk (at this stage is called Zygote) and 2nd polar body. b) Several changes of the nucleus of the spermatozoa which leads to the formation of male pronucleus. c) Changes in the nucleus of the zygote to form female pronucleus. d) Fusion of the male and female pronuclei, union of male and female haploid genomes in the centre of the zygote, a process known as synkaryosis. This leads to the mitosis and start to form new individuals.