Final answer:
At 5/6 weeks, a fetus develops basic body structures, and significant growth occurs. Uncontrolled limb movements begin, and elements like fingers and toes form. By the eighth week, the head is nearly as large as the rest of the body, and all major brain structures are in place.
Step-by-step explanation:
Fetal Development at 5/6 Weeks
At 5/6 weeks, a fetus exhibits significant developmental milestones. By the fifth week, the embryo is about 4 mm in length and has various basic structures like limb buds, eyes, heart, and liver. As we progress to week six, there's an onset of uncontrolled fetal limb movements indicative of muscular and neurodevelopment. Paddle-shaped hands and feet are formed which later develop fingers and toes through apoptosis, leading to the disintegration of tissue between them. Notably, the gastrointestinal system develops so rapidly that the intestines temporarily extend into the umbilical cord due to the limited space within the embryonic abdomen.
By the end of the embryonic period, which is around the eighth week, significant growth and development are evident. The head is nearly the size of the rest of the body, and the facial structure includes complex features such as nostrils, outer ears, and eye lenses. Major brain structures are in place, and ossification begins as bones start to replace cartilage. Although external genitalia become apparent, male and female embryos cannot yet be distinguished. The fetus measures approximately 3 cm from crown to rump and weighs about 8 grams.