foetal adj : of or relating to a fetus; "fetal development" [syn: fetal]

English

Alternative spellings

• italbrac mainly US fetal
• italbrac Commonwealth fœtal
• italbrac archaic phoetal, phœtal

Adjective

1. In the context of "embryology}}

A fetus (or foetus or fœtus) is a developing mammal or other viviparous vertebrate, after the embryonic stage and before birth. The plural is fetuses, or sometimes feti. The fetal stage of prenatal development starts when the major structures have formed, and lasts until birth.

In humans, the fetal stage of prenatal development starts at approximately the beginning of the 9th week after fertilization, which is equivalent to the start of the eleventh week in "gestational age."

Etymology and spelling variations

The word fetus is from the Latin fetus, meaning offspring, bringing forth, hatching of young. It has Indo-European roots related to sucking or suckling.

Fœtus is an English variation on the Latin spelling, and has been in use since at least 1594, according to the Oxford English Dictionary, which describes "fœtus" as "incorrectly written". The variant fœtus may have originated with an error by Saint Isidore of Seville, in AD 620. The preferred spelling in the United States is fetus, but the variants foetus and fœtus persist in other English-speaking countries and in some medical contexts, as well as in some other languages (e.g., French).

Human fetus

The circulatory system of a human fetus works differently from that of born humans, mainly because the lungs are not in use: the fetus obtains oxygen and nutrients from the mother through the placenta and the umbilical cord.

Blood from the placenta is carried to the fetus by the umbilical vein. About half of this enters the fetal 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 through this hole directly into the left atrium from the right atrium, thus bypassing pulmonary circulation. The continuation of this blood flow is into the left ventricle, and from there 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 woman's circulation.

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.

Developmental problems

seealso Congenital disorder

Congenital anomalies are anomalies that are acquired before birth. 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 prostaglandins 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.

A developing fetus is highly susceptible to anomalies in its growth and metabolism, increasing the risk of birth defects. One area of concern is the pregnant woman's lifestyle choices made during pregnancy Diet is especially important in the early stages of development. Studies show that supplementation of the woman's diet with folic acid reduces the risk of spina bifida and other neural tube defects. Another dietary concern is whether the woman eats breakfast. Skipping breakfast could lead to extended periods of lower than normal nutrients in the woman's blood, leading to a higher risk of prematurity, or other birth defects in the fetus. During this time alcohol consumption may increase the risk of the development of Fetal alcohol syndrome, a condition leading to mental retardation in some infants. Smoking during pregnancy may also lead to reduced birth weight. Low birth weight is defined as 2500 grams (5.5 lb). Low birth weight is a concern for medical providers due to the tendency of these infants, described as premature by weight, to have a higher risk of secondary medical problems.

Legal issues

In the United States, some states have laws that impose strict punishments for those who inflict violence that results in damage to a fetus or the unwanted termination of a pregnancy. The severity of the punishment, and the stage of fetal development where laws start to apply vary from state to state.

Abortion of a fetus is legal in many countries such as Australia, Canada, Mexico, UK and USA. Many of those countries that allow abortion during the fetal stage have gestational time limits, so that late-term abortions are not normally allowed.

Non-human fetuses

The fetus of most mammals develops similarly to the Homo sapiens fetus. After the first stages of development, the human embryo reaches a stage very similar to all other vertebrates. The anatomy of the area surrounding a fetus is different in litter-bearing animals compared to humans: each fetus is surrounded by placental tissue and is lodged along one of two long uteri instead of the single uterus found in a human female. Development at birth is similar, with animals also having a poorly developed sense of vision and other senses.

See also

• Prenate
• Embryo
• Pregnancy
• Child
• Superfetation
• Neural development
• Fetoscopy
• Fetal position
• Fetal rights
• Womens rights

References

External links

• High Resolution Nissl-stained Rat Fetus