Anatomy & Physiology

Anatomy & Physiology Study Guide Individuals with Turner syndrome have only a single, female sex chromosome; their sex chromosome complement is abbreviated XO. This kind of chromosomal deletion is known as monosomy. The incidence of this condition at delivery has been estimated as 1 in 10,000 live births. The condition may not be recognized at birth because the phenotype is normal female. But maturational changes do not appear at puberty. The ovaries are nonfunctional, and estrogen production occurs at negligible levels. 26.4 Chapter Twenty-Six Review Development, marked by various stages, is a continuous process that occurs from fertilization to maturity: • Development is the gradual modification of anatomical structures and physiological characteristics from conception to maturity. The formation of different types of cells is differentiation. • Prenatal development occurs before birth; postnatal development begins at birth and continues tomaturity, when aging begins. Inheritance is the transfer of genetically determined characteristics from generation to generation. Genetics is the study of the mechanisms of inheritance. Fertilization—the fusion of a secondary oocyte and a spermatozoon—forms a zygote: • Fertilization, or conception, normally occurs in the uterine tube within a day of ovulation. Spermatozoa cannot fertilize a secondary oocyte until they have undergone capacitation. • The acrosomal caps of the spermatozoa release hyaluronidase and acrosin, enzymes required to penetrate the corona radiata and zona pellucida of the oocyte. When a single spermatozoon contacts the oocyte membrane, fertilization begins and oocyte activation follows. • During activation, the oocyte completes meiosis II and thus becomes a functionally mature ovum. Polyspermy is prevented by membrane depolarization and the cortical reaction. • After activation, the female pronucleus and the male pronucleus fuse in a process called amphimixis. Gestation consists of three stages of prenatal development: the first, second, and third trimesters: • The nine-month gestation period can be divided into three trimesters. • During prenatal development, differences in the cytoplasmic composition of individual cells trigger changes in genetic activity. The chemical interplay among developing cells is induction. Cleavage, implantation, placentation, and embryogenesis are critical events of the first trimester: • In the first trimester, cleavage subdivides the cytoplasm of the zygote in a series of mitotic divisions; the zygote becomes a pre-embryo and then a blastocyst. During implantation, the blastocyst burrows into the uterine endometrium. Placentation occurs as blood vessels form

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