Search results
Results from the WOW.Com Content Network
An ultrasound can show the embryo at this time, which is about the size of a grape. [5] Around day 28 is when the fetal period starts, and it lasts until day 63, when the puppy is born. The puppy's organs and systems continue to develop and refine during this period of growth and development.
In mammals, the term refers chiefly to the early stages of prenatal development, whereas the terms fetus and fetal development describe later stages. [2] [4] The main stages of animal embryonic development are as follows: The zygote undergoes a series of cell divisions (called cleavage) to form a structure called a morula.
Prenatal development (from Latin natalis 'relating to birth') involves the development of the embryo and of the fetus during a viviparous animal's gestation. Prenatal development starts with fertilization , in the germinal stage of embryonic development, and continues in fetal development until birth .
Human embryonic development covers the first eight weeks of development, which have 23 stages, called Carnegie stages. 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.
Embryonic age: 7 weeks and 0 days until 9 weeks and 6 days old. Fetus at 10 weeks. Embryo measures 30–80 mm (1.2–3.1 in) in length. Ventral and dorsal pancreatic buds fuse during the 8th week; Intestines rotate. Facial features continue to develop. The eyelids are more developed. The external features of the ear begin to take their final shape.
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.
[83] 14–16 days after ovulation, the embryo attaches to the uterus, and after seven to eight more days, a heartbeat is detectable. [84] [85] Dogs bear their litters roughly 58 to 68 days after fertilization, [82] [86] with an average of 63 days, although the length of gestation can vary. An average litter consists of about six puppies. [87]
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.