Details about Human Embryology Developmental Biology 6th edition by Bruce, M. Carlson
Human Embryology Developmental Biology 6th ed PDF free download – Human pregnancy begins with the fusion of an egg and a sperm within the female reproductive tract, but extensive preparation precedes this event. First, both male and female sex cells must pass through a long series of changes (gametogenesis) that convert them genetically and phenotypically into mature gametes, which are capable of participating in the process of fertilization. Next, the gametes must be released from the gonads and make their way to the upper part of the uterine tube, where fertilization normally takes place. Finally, the fertilized egg, now properly called an embryo, must enter the uterus, where it sinks into the uterine lining (implantation) to be nourished by the mother. All these events involve interactions between the gametes or embryo and the adult body in which they are housed, and most are mediated or influenced by parental hormones. This chapter focuses on gametogenesis and the hormonal modifications of the body that enable reproduction to occur.
Gametogenesis is typically divided into four phases: the extraembryonic origin of the germ cells and their migration into the gonads, an increase in the number of germ cells by mitosis, a reduction in chromosomal number by meiosis, and structural and functional maturation of the eggs and spermatozoa. The first phase of gametogenesis is identical in males and females, whereas distinct differences exist between the male and female patterns in the last three phases.