Final answer:
By the end of 7 weeks, the embryo has grown to 13 mm and exhibits defined facial structures, digits formation through apoptosis, and the beginnings of bone ossification. The gastrointestinal and other organ systems are developing, with major brain structures in place, and the external genitalia formed but not sex-distinguishable.
Step-by-step explanation:
By the end of 7 weeks gestation, significant developments in fetal development are evident. The embryo is approximately 13 mm in length and displays major advancements such as complex facial structures including nostrils, outer ears, and eye lenses. Additionally, paddle-shaped hands and feet continue to differentiate, forming distinct fingers and toes through apoptosis.
At this stage, the gastrointestinal system expands rapidly, necessitating the temporary extension of the intestines into the umbilical cord. Organogenesis is proceeding, with major brain structures in place and bone beginning to ossify, replacing cartilage in the embryonic skeleton. Although the external genitalia are formed, they are not yet distinguishable by sex.
Ossification and brain development continue into weeks 9-12, with the fetus starting to practice swallowing amniotic fluid and producing urine, marking the beginning of partially functioning organs. All of these developments are preliminary stages for the further growth and maturation that will take place in the subsequent weeks of fetal development.