Answer
By the end of the eighth week of embryonic life, the development status of the of the fetus is as follows:
All organs are present:
Bone calcification begins; muscles begin to twitch(contract) spontaneously, and the heart begins to pump blood. However, the fetal circulation is different from postnatal circulation because of the presence of three prenataal shunts. The function of these shunts is to keep most of the blood away from immature lungs and liver.
1. The foramen ovale shunt. This is an opening in the interatrial septum that allows blood to flow
from right atrium directly into the left atrium, bypassing the lungs.
2. Ductus arteriosus shunt: This shunts allows blood to flow from the right ventricle through the
pulmonary artery directly to the aorta --also bypassing the lungs
3. The ductus venosus shunt takes blood "through " the immature liver. It carries blood from the
umbilical vein directly to the caudal vena cava, bypassing the liver.
Work Step by Step
Digital rays are limb buds seen in week eight. At this time ridges also develop on the paddle-like feet of the fetus. These ridges will develop into fingers and toes.
Other events and changes become apparent as fetal development proceeds. These include the following:
By week 16. Meconium ( fetal feces) has accumulated in the fetal intestine.
By week 20. Laguno, a fine, soft hair grows over the body and appendages f the fetus.
Vernix caseosa, a white cheesy secretion of sebaceous gland spreads over the fetus to
protect its skin from amniotic fluid. About this time also the quickening of the fetus
occurs, and the mother is able to feel the movements of the fetus in the uterus.
In week 28 ( in a normal pregnancy) the fetus assumes the vertex position, with its head closest to
the internal os of the cervix.
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