Tham khảo tài liệu 'saladin anatomy and physiology the unity of form and function 2 episode 7', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 29. Human Development I Text Saladin Anatomy Physiology The Unity of Form and Function Third Edition The McGraw-Hill Companies 2003 Chapter 29 Human Development 1117 Chapter Review Review of Key Concepts Fertilization and Preembryonic Development p. 1090 1. Sperm must travel to the distal one-third of the uterine tube if they are to encounter the egg before it dies. This traveling or sperm migration may be aided by the cervical mucus female orgasm and chemical attractants emitted by the egg. 2. Freshly ejaculated sperm cannot fertilize an egg. They undergo capacitation becoming capable of fertilization as they migrate. 3. When a sperm encounters an egg it releases enzymes from its acrosome the acrosomal reaction enabling it to penetrate the cumulus oophorus zone pellucida and egg membrane. Hundreds of sperm may be needed to clear a path for the one that fertilizes the egg. 4. The egg has a fast block and a slow block to prevent fertilization by more than one sperm polyspermy . The fast block employs a change in egg membrane voltage that inhibits the binding of additional sperm. The slow block involves exocytosis of the egg s cortical granules to produce an impenetrable fertilization membrane around the egg. 5. The fertilized egg completes meiosis II and casts off a second polar body. The sperm and egg nuclei swell and form pronuclei. When the pronuclei rupture and their chromosomes mingle the egg is a diploid zygote. 6. The first two weeks of development called the preembryonic stage consists of cleavage implantation and embryogenesis resulting in an embryo. 7. Cleavage is the mitotic division of the zygote into cells called blastomeres. The stage that arrives at the uterus is a morula of about 16 blastomeres. It develops into a hollow ball called the blastocyst with an outer cell mass called the trophoblast and inner cell mass called the embryoblast. 8. Implantation is the attachment of the blastocyst to the uterine wall. The trophoblast differentiates into a .
