What Begins 18 to 21 Days After Conception

A baby goes through several stages of development, get-go equally a fertilized egg. The egg develops into a blastocyst, an embryo, then a fetus.

At ovulation, the mucus in the cervix becomes more fluid and more than elastic, allowing sperm to enter the uterus rapidly. Within 5 minutes, sperm may move from the vagina, through the cervix into the uterus, and to the funnel-shaped finish of a fallopian tube—the usual site of fertilization. The cells lining the fallopian tube facilitate fertilization.

If fertilization does not occur, the egg moves down the fallopian tube to the uterus, where it degenerates, and passes through the uterus with the next menstrual period.

If a sperm penetrates the egg, fertilization results. Tiny hairlike cilia lining the fallopian tube propel the fertilized egg (zygote) through the tube toward the uterus. The cells of the zygote divide repeatedly every bit the zygote moves downwardly the fallopian tube to the uterus. The zygote enters the uterus in three to 5 days.

In the uterus, the cells go along to divide, becoming a hollow ball of cells called a blastocyst. The blastocyst implants in the wall of the uterus near 6 days subsequently fertilization.

If more than one egg is released and fertilized, the pregnancy involves more than than ane fetus, usually two (twins). Because the genetic material in each egg and in each sperm is slightly dissimilar, each fertilized egg is unlike. The resulting twins are thus fraternal twins. Identical twins result when one fertilized egg separates into two embryos after it has begun to carve up. Because one egg was fertilized by one sperm, the genetic material in the two embryos is the aforementioned.

From Egg to Embryo

In one case a month, an egg is released from an ovary into a fallopian tube. After sexual intercourse, sperm move from the vagina through the cervix and uterus to the fallopian tubes, where one sperm fertilizes the egg. The fertilized egg (zygote) divides repeatedly as it moves downward the fallopian tube to the uterus. Kickoff, the zygote becomes a solid brawl of cells. And then it becomes a hollow brawl of cells called a blastocyst.

Inside the uterus, the blastocyst implants in the wall of the uterus, where it develops into an embryo attached to a placenta and surrounded by fluid-filled membranes.

About six days after fertilization, the blastocyst attaches to the lining of the uterus, unremarkably near the peak. This process, chosen implantation, is completed by day 9 or x.

The wall of the blastocyst is one prison cell thick except in one area, where information technology is three to four cells thick. The inner cells in the thickened area develop into the embryo, and the outer cells burrow into the wall of the uterus and develop into the placenta. The placenta produces several hormones that help maintain the pregnancy. For instance, the placenta produces human chorionic gonadotropin, which prevents the ovaries from releasing eggs and stimulates the ovaries to produce estrogen and progesterone continuously. The placenta also carries oxygen and nutrients from female parent to fetus and waste materials from fetus to mother.

Some of the cells from the placenta develop into an outer layer of membranes (chorion) around the developing blastocyst. Other cells develop into an inner layer of membranes (amnion), which form the amniotic sac. When the sac is formed (by about day 10 to 12), the blastocyst is considered an embryo. The amniotic sac fills with a clear liquid (amniotic fluid) and expands to envelop the developing embryo, which floats within it.

The next phase in development is the embryo, which develops inside the amniotic sac, under the lining of the uterus on i side. This stage is characterized by the formation of nearly internal organs and external trunk structures. Most organs begin to form about three weeks after fertilization, which equals 5 weeks of pregnancy (because doctors date pregnancy from the first 24-hour interval of the woman's last menstrual flow, which is typically 2 weeks before fertilization). At this time, the embryo elongates, first suggesting a human shape. Before long thereafter, the expanse that will go the brain and spinal cord (neural tube) begins to develop. The centre and major blood vessels begin to develop earlier—by near twenty-four hour period 16. The center begins to pump fluid through claret vessels by day twenty, and the beginning red claret cells appear the next day. Blood vessels keep to develop in the embryo and placenta.

Placenta and Embryo at About 8 Weeks

At 8 weeks of pregnancy, the placenta and fetus take been developing for 6 weeks. The placenta forms tiny hairlike projections (villi) that extend into the wall of the uterus. Claret vessels from the embryo, which pass through the umbilical string to the placenta, develop in the villi. A sparse membrane separates the embryo'due south blood in the villi from the mother'southward blood that flows through the infinite surrounding the villi (intervillous space). This organization does the post-obit: Allows materials to exist exchanged between the blood of the mother and that of the embryo Prevents the female parent'southward immune system from attacking the embryo because the mother's antibodies are besides big to pass through the membrane (antibodies are proteins produced by the allowed system to help defend the body against foreign substances) The embryo floats in fluid (amniotic fluid), which is independent in a sac (amniotic sac). The amniotic fluid does the following: Provides a space in which the embryo can abound freely Helps protect the embryo from injury The amniotic sac is strong and resilient.

At the end of the 8th week afterward fertilization (10 weeks of pregnancy), the embryo is considered a fetus. During this stage, the structures that accept already formed grow and develop. The following are markers during pregnancy:

• By 12 weeks of pregnancy: The fetus fills the unabridged uterus.

• By near xiv weeks: The sex tin can be identified.

• Past near 16 to xx weeks: Typically, the pregnant woman can experience the fetus moving. Women who have been pregnant earlier typically feel movements about 2 weeks earlier than women who are pregnant for the start time.

• By about 24 weeks: The fetus has a gamble of survival outside the uterus.

The lungs go on to mature until nigh the time of delivery. The brain accumulates new cells throughout pregnancy and the outset year of life after birth.

As the placenta develops, it extends tiny hairlike projections (villi) into the wall of the uterus. The projections branch and rebranch in a complicated treelike arrangement. This arrangement greatly increases the area of contact between the wall of the uterus and the placenta, so that more nutrients and waste materials can be exchanged. The placenta is fully formed by xviii to xx weeks but continues to grow throughout pregnancy. At commitment, information technology weighs almost ane pound.

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Source: https://www.msdmanuals.com/home/women-s-health-issues/normal-pregnancy/stages-of-development-of-the-fetus

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