Information AboutFetal |
| CATEGORIES ABOUT FETUS | |
| developmental biology | |
| embryology | |
"Foetus" redirects here. For the musical group Foetus, see Foetus (band) . A fetus (or '''foetus''', See Below ) is a developing Mammal after the Embryonic stage and before Birth . The plural is '''fetuses''' or very rarely, ''foeti''. In humans, a fetus develops from the end of the 8th week of Pregnancy , when the major structures and Organ System s have formed, until birth. ''Fetus'', in Latin , literally means "filled with young, pregnant, breeding, with young" as well as "bringing forth, bearing, hatching, producing." When speaking in the most literal of terms, a fetus is an Organism , as yet undeveloped, in the process of becoming a functional individual of a species. FETAL GROWTH . The size is 27 cm. The dark spot in the middle is the heart.]] There is much natural variation in the growth of the fetus. Approximately 52% of the variation in Birth Weight can be accounted for by Genetic factors, whereas 48% can be accounted for by Environmental factors. Ultimately, the offspring should be able to live up to its term growth potential. Factors affecting fetal growth can be ''maternal'', '' Placenta l'', or ''fetal''. Maternal factors include maternal size, Weight , Weight For Height , Nutritional State , Anemia , High Environmental Noise Exposure , Cigarette Smoking , Substance Abuse , or Uterine Blood Flow . Placental factors include size, microstructure (densities and architecture), Umbilical Blood Flow , transporters and binding proteins, nutrient utilization and nutrient production. Fetal factors include the fetus genome, nutrient production, and Hormone output. Inappropriate growth can result in low birth weight. If the Newborn is '' Small For Gestational Age '', he or she will have an increased risk for perinatal mortality ( Death shortly after birth), Asphyxia , Hypothermia , Polycythemia , Hypocalcemia , Immune Dysfunction , Neurologic abnormalities, and other long-term health problems. This can be the result of Fetal Growth Restriction . CIRCULATORY SYSTEM in the womb. Drawing by Leonardo Da Vinci ]] The and nutrients from the mother through the Placenta and the Umbilical Cord . Blood from the placenta is carried by the Umbilical Vein . About half of this enters the '' Ductus Venosus '' and is carried to the Inferior Vena Cava , while the other half enters the Liver proper from the inferior border of the liver. The branch of the umbilical vein that supplies the right lobe of the liver first joins with the Portal Vein . The blood then moves to the right atrium of the Heart . In the fetus, there is an opening between the right and left atrium (the '' Foramen Ovale ''), and most of the blood flows from the right into the left atrium, then into the left ventricle from where it is pumped through the Aorta into the body. Some of the blood moves from the aorta through the internal iliac arteries to the umbilical arteries, and re-enters the placenta, where Carbon Dioxide and other waste products from the fetus are taken up and enter the mother's circulation. Some of the blood from the right atrium does not enter the left atrium, but enters the right ventricle and is pumped into the Pulmonary Artery . In the fetus, there is a special connection between the pulmonary artery and the aorta, called the '' Ductus Arteriosus '', which directs most of this blood away from the lungs (which aren't being used for respiration at this point as the fetus is suspended in Amniotic Fluid ). Postnatal development ''See'' Adaptation To Extrauterine Life ''for more details'' With the first breath after birth, the system changes suddenly. The pulmonary resistance is dramatically reduced. More blood moves from the right atrium to the right ventricle and into the pulmonary arteries, and less flows through the '' Foramen Ovale '' to the left atrium. The blood from the lungs travels through the pulmonary veins to the left atrium, increasing the pressure there. The decreased right atrial pressure and the increased left atrial pressure pushes the ''septum primum'' against the ''septum secundum'', closing the ''foramen ovale'', which now becomes the ''fosse ovalis''. This completes the separation of the circulatory system into two halves, the left and the right. The ''ductus arteriosus'' normally closes off within one or two days of birth, leaving behind the ligamentum arteriosum. The umbilical vein and the ductus venosus closes off within two to five days after birth, leaving behind the '' Ligamentum Teres '' and the '' Ligamentum Venosus '' of the liver respectively. Developmental problems Infants with certain congenital anomalies of the heart can survive only as long as the ductus remains open: in such cases the closure of the ductus can be delayed by the administration of Prostaglandin s to permit sufficient time for the surgical correction of the anomalies. Conversely, in cases of Patent Ductus Arteriosus , where the ductus does not properly close, drugs that inhibit prostaglandin synthesis can be used to encourage its closure, so that surgery can be avoided. Differences from the adult circulatory system Remnants of the fetal circulation can be found in adults:
In addition to differences in circulation, the developing fetus also employs a different type of oxygen Transport Molecule than adults (adults use Adult Hemoglobin ). Fetal Hemoglobin enhances the fetus' ability to draw oxygen from the placenta. Its association curve to oxygen is shifted to the left, meaning that it will take up oxygen at a lower concentration than adult hemoglobin will. This enables fetal hemoglobin to absorb oxygen from adult hemoglobin in the placenta, which has a lower pressure of oxygen than at the lungs. LEGAL ISSUES USA Since the 1970s in the United States , there has been continuing debate over the " Personhood " of the fetus before birth, generally in the context of the argument over Abortion , which is currently legal in the United States following the case of '' Roe V. Wade ''. According to legislation which passed the US Senate in March 2004, an unborn child is defined as "a member of the species '' Homo Sapiens '', at any stage of development, who is carried in the Womb ...". ( Unborn Victims of Violence Act, April 2004 ) ETYMOLOGY AND SPELLING VARIATIONS The word ''fetus'' originates from the Latin ''fetus'' meaning "offspring," "act of bearing young," or "is or was filled with young". ''Foetus'' is an English variation on this rather than a Latin or Greek word, but has been in use since at least 1594 according to the OED , which describes fetus as etymologically preferable but almost unknown in actual use. In general, the medical community only permits the spelling ''fetus'' (preferred by the British Medical Journal , for example), but the spelling ''foetus'' persists in general use, especially in Britain. SEE ALSO
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