Sperm migration and capacitation- Within 12 to 72 hours of ovulation, it takes about 72 hours for an egg to reach the uterus. Since only one sperm will fertilize out of 300 millions many of them will not make it. Many are destroyed by vaginal acids or drain out the vagina, other fail to penetrate the mucus of cervical canal and many destroy by leukocytes of the uterus. About 200 spermatozaa reach the egg. (Saladin,2020,p.1076).
It takes about 30 minutes or less after ejaculation for sperm to to reach the uterine tube. While migrating they under go a process called capacitation. The capacitation makes the sperm capable of penetrating an egg. When a sperm is fresh, the plasma membrane is toughened by cholesterol. It’s job is to prevent the premature sperm to release acrosomal enzymes while sperm are still in the male. After ejaculation fluids of the woman productive tracts reach cholesterol from the plasma membrane and dilute other inhibitory factors in the semen. Because of calcuim ions the sperm head becomes more fragile and more permanent, After ejaculation the sperm remain viable up to 6 days.(Saladin,2020,p.1077).
Fertilization- When a sperm reach an egg it undergoes an acrosomal reaction. The sperm will penetrate the granulosa cells and zona pellucida that surround it. When a path has been cleared the zona pellucida, It releases enzymes digesting a pathway till it contacts the egg. Once the sperm head and middle pieces enter the egg the egg will destroys the sperm mitochondra and the mitochondra will pass through off springs. Diploid produces when fertilization combine the haploid and the sperm chromosome. Polyspermy is when 2 or more cells fertilized.( Saladin,2020.p.1078).
Before ovulation secondary oocyte begins. The fertilized egg discards one chromatid from each chromosome the egg and nucleic swells and becomes pronuclei. What pushes the sperm toward the egg is the sperm towards the egg is the sperm centrosome sprouts microbules. And once egg is fertilized it calls zygotes.(Saladin,2020,p.1078).
6 days after ovulation, after ovulation, blastocyst attached to the endometrium. This process is call implantation. The trophoblast cells separate into two layers. The trophoblast cells fuse into multinucleate mass called cytotrophoblast. The syncytiotrophoblast grows into the uterus. Endometrium reacts by growing over the blastocyst and cover it. It takes about 1 week for implantation process and completes around the time of the next menstrual period.(Saladin,2020,p.1080)
Embryo-blast undergoes embryo genesis during implantation , it arrange blastomeres into 3 primary germs layers and they are ectoderm. At the beginning of this process embryoblast slightly separate from trophoblast and creates a narrow space between them that calls amniotic cavity. The yolk sac form by some hypo-blast and close the blastocoel. The amniotic cavity on the side and the yolk sac. Around day 15 days primary streak a thick cell layered form along the midline of the epiblast with premature grove running down midline. Then gastrulation happen epiblast cells migrate medially toward the primitively groove and down it. It replaced hypoblast with endoderm (which will become the inner lining of digestive tract). A day later epiblast form a third layer. Once the three primary germs layers are form it complete the individual embryo. And that is day 16 and the embryo is about 2 mm long.(Saladin,2020,p1081).
A man ejuculate about 300 million sperm and about 200 soermatoza reach the uterus.First trimester is the most dangerous because miscariage can occur to stress, drugs and alcohol and fetus may die due to chromosomal defect factor. Although many pregnacies succeed,not every pregnancy is success during implantation ectopic pregnancy can occure it is 1 out 300 pregnancies.It is when the blastocyst implants some where other than the uterus (Saladin, 2020,p.1076-1077,1081)
Words count: 655Reference
Saladin, K. (2020). Anatomy & physiology: The unit of form and function (9th ed.). McGraw Hill Education
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