Essay 1

Do not memorise these answers! These are guidelines. Be creative, devise your own expression and organisation! You can elaborate on the points in your own language.
Remember that there is no 'perfect' answer - a little shortfall in content is easily compensated by presentation.
You should aim at writing an essay in this examination in approximately 20 minutes.

Describe the key features of blood circulation in the foetus and the changes that take place at birth.

Key feature - non-functional lungs! Blood from the right side must go to the left. At the same time, some blood must flow through the right ventricle. The arterial system sends a large volume of blood to the placenta. Blood returning from the placenta goes to the right side bypassing the liver.

Passage between right and left atria : foramen ovale and foramen secundum. Passage between pulmonary artery and aorta - ductus arteriosus.

Two umbilical arteries carry blood to the placenta for oxygenation, enrichment by nutrients and for waste disposal. Placental blood returns via a single umbilical vein which joins the portal vein. Ductus venosus is the bypass to the IVC.

At birth - the two septa between the atria are pressed together, obliterating the passage. Ductus arteriosus, ductus venosus and umbilical vein obliterated by contraction of smooth muscle, later replaced by fibrous tissue. These structures thus form ligaments - arteriosum, venosum and teres respectively. The umbilical arteries have a similar fate.

Discussion

First and foremost, decide how much you wish to write. The question does not ask for details of development of the interatrial septum. If you mention the interatrial passage correctly, it is understood that you are aware of the details!

There are finer anatomical details of the precise attachments of the ductus arteriosus, ductus venosus and the umbilical vein. You do NOT need to know them - the facts mentioned here (and in the lecture) are adequate. The umbilical arteries are seen as fibrous cords on the inner surface of the abdominal wall.

Physiological mechanisms of the changes at birth are not mentioned because they would constitute an overload. The interested student may check the recommended embryology text/s.