Final answer:
The germinal stage is the initial phase of human development, lasting about eight to nine days from fertilization to implantation in the uterus. It starts with a fertilized egg (zygote), progresses to a morula, transitions to a blastocyst, and ends as the blastocyst implants in the uterine wall.
Step-by-step explanation:
Germinal Stage of Human Development
The germinal stage is the earliest and shortest stage in the human lifespan, typically lasting from fertilization until the new organism, known as a blastocyst at this stage, implants in the endometrium of the uterus, occurring roughly between eight to nine days after fertilization. This period begins in a Fallopian tube with the formation of a zygote, continues as it divides into a morula and then a blastocyst, and ends with implantation. After which the blastocyst is referred to as an embryo.
During the germinal stage, the cells undergo rapid division and development. Critical developments include the transition from a zygote to a morula and eventually into a blastocyst. The stage concludes with the blastocyst implanting itself in the uterine wall, marking the beginning of the embryonic stage of development.
The rest of prenatal development is divided into subsequent stages: the embryonic stage, which lasts until the eighth week, characterized by significant growth and the formation of the organ systems, and the fetal stage, which lasts from the ninth week until birth. The fetal stage includes the development of functioning organ systems and the fetus's growth to a stage ready for life outside the womb, including sexual differentiation.