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At the beginning of the ninth week, the embryo is termed a fetus (spelled "foetus" in British English). In comparison to the embryo, the fetus has more recognizable external features and a more complete set of developing organs. Human embryology is the study of this development during the first eight weeks after fertilization.
The embryo and subsequent early fetus appear to be sexually indifferent, looking neither like a male or a female. Over the next several weeks, hormones are produced that cause undifferentiated tissue to transform into either male or female reproductive organs. This process is called sexual differentiation.
Sexual differentiation is the process of development of the sex differences between males and females from an undifferentiated zygote. [1] [2] Sex determination is often distinct from sex differentiation; sex determination is the designation for the development stage towards either male or female, while sex differentiation is the pathway towards the development of the phenotype.
An embryo is the initial stage of development for a multicellular organism.In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male sperm cell.
A fetus or foetus (/ ˈ f iː t ə s /; pl.: fetuses, foetuses, rarely feti or foeti) is the unborn mammalian offspring that develops from an embryo. [1] Following the embryonic stage, the fetal stage of development takes place. Prenatal development is a continuum, with no clear
The embryo, meanwhile, proliferates and develops both into embryonic and extra-embryonic tissue, the latter forming the fetal membranes and the placenta. In humans, the embryo is referred to as a fetus in the later stages of prenatal development. The transition from embryo to fetus is arbitrarily defined as occurring 8 weeks after fertilization.
Diagrams to show the development of male and female generative organs from a common type. A.—Diagram of the primitive urogenital organs in the embryo previous to sexual distinction. 3. Ureter. 4. Urinary bladder. 5. Urachus. cl. Cloaca. cp. Elevation which becomes clitoris or penis. i. Lower part of the intestine. ls.
The ova, which are the female sex cells, are much larger than the spermatozoon and are normally formed within the ovaries of the female fetus before birth. They are mostly fixed in location within the ovary until their transit to the uterus, and contain nutrients for the later zygote and embryo.