<< Chapter < Page Chapter >> Page >

Although the fetal liver is semifunctional, the fetal lungs are nonfunctional. The fetal circulation therefore bypasses the lungs by shifting some of the blood through the foramen ovale    , a shunt that directly connects the right and left atria and avoids the pulmonary trunk altogether. Most of the rest of the blood is pumped to the right ventricle, and from there, into the pulmonary trunk, which splits into pulmonary arteries. However, a shunt within the pulmonary artery, the ductus arteriosus    , diverts a portion of this blood into the aorta. This ensures that only a small volume of oxygenated blood passes through the immature pulmonary circuit, which has only minor metabolic requirements. Blood vessels of uninflated lungs have high resistance to flow, a condition that encourages blood to flow to the aorta, which presents much lower resistance. The oxygenated blood moves through the foramen ovale into the left atrium, where it mixes with the now deoxygenated blood returning from the pulmonary circuit. This blood then moves into the left ventricle, where it is pumped into the aorta. Some of this blood moves through the coronary arteries into the myocardium, and some moves through the carotid arteries to the brain.

The descending aorta carries partially oxygenated and partially deoxygenated blood into the lower regions of the body. It eventually passes into the umbilical arteries through branches of the internal iliac arteries. The deoxygenated blood collects waste as it circulates through the fetal body and returns to the umbilical cord. Thus, the two umbilical arteries carry blood low in oxygen and high in carbon dioxide and fetal wastes. This blood is filtered through the placenta, where wastes diffuse into the maternal circulation. Oxygen and nutrients from the mother diffuse into the placenta and from there into the fetal blood, and the process repeats.

Fetal circulatory system

This figure shows a baby in the center of the image. To the left, is a panel showing the umbilical cord and how blood is supplied to the baby in the womb. Two panels on the right show the circulation of blood inside the baby’s body.
The fetal circulatory system includes three shunts to divert blood from undeveloped and partially functioning organs, as well as blood supply to and from the placenta.

Other organ systems

During weeks 9–12 of fetal development, the brain continues to expand, the body elongates, and ossification continues. Fetal movements are frequent during this period, but are jerky and not well-controlled. The bone marrow begins to take over the process of erythrocyte production—a task that the liver performed during the embryonic period. The liver now secretes bile. The fetus circulates amniotic fluid by swallowing it and producing urine. The eyes are well-developed by this stage, but the eyelids are fused shut. The fingers and toes begin to develop nails. By the end of week 12, the fetus measures approximately 9 cm (3.5 in) from crown to rump.

Weeks 13–16 are marked by sensory organ development. The eyes move closer together; blinking motions begin, although the eyes remain sealed shut. The lips exhibit sucking motions. The ears move upward and lie flatter against the head. The scalp begins to grow hair. The excretory system is also developing: the kidneys are well-formed, and meconium    , or fetal feces, begins to accumulate in the intestines. Meconium consists of ingested amniotic fluid, cellular debris, mucus, and bile.

Questions & Answers

drowning and level female reproductive system
Anas Reply
what are the types of homeostasis
Odey Reply
diagram of the digestive system
Zainab Reply
drown and level female reproductive system
Anas
anatomy
Anas
What is the best way to indicate the sperm
ADAM Reply
Definition of pathology
Promise Reply
what are the body organs and their functions
Comforter Reply
what are the body organs and their functions
Ruth
musculoskeletal
Ruth
what is cell
Oppicial Reply
a cell is the smallest structural and functional unit of life.
Patrick
To know how bones are functions
DAUDA Reply
diagram of the heart
Victoria Reply
what are the layers of the muscles
Tongdock Reply
What is Amebae
Najibu Reply
the collection of fluids in the throat is cause by what
Emmanuel Reply
what is difference between meiosis and mitosis
Aishetu Reply
what is difference between mitosis and meiosis
Aishetu
What is Anatomy
Najibu Reply
What the difference between the Anatomy and physiology
Najibu
What is the meaning of chromoprotein
Aisha Reply

Get Jobilize Job Search Mobile App in your pocket Now!

Get it on Google Play Download on the App Store Now




Source:  OpenStax, Anatomy & Physiology. OpenStax CNX. Feb 04, 2016 Download for free at http://legacy.cnx.org/content/col11496/1.8
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Anatomy & Physiology' conversation and receive update notifications?

Ask