What Changes Happen Between Fertilization And Implantation

A baby goes through several stages of evolution, starting time equally a fertilized egg. The egg develops into a blastocyst, an embryo, so a fetus.

At ovulation, the mucus in the cervix becomes more fluid and more 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 end of a fallopian tube—the usual site of fertilization. The cells lining the fallopian tube facilitate fertilization.

If fertilization does non occur, the egg moves down the fallopian tube to the uterus, where information technology degenerates, and passes through the uterus with the adjacent menstrual catamenia.

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 dissever repeatedly every bit the zygote moves down the fallopian tube to the uterus. The zygote enters the uterus in 3 to 5 days.

In the uterus, the cells continue to divide, becoming a hollow ball of cells called a blastocyst. The blastocyst implants in the wall of the uterus about half-dozen days after fertilization.

If more than one egg is released and fertilized, the pregnancy involves more i fetus, usually two (twins). Because the genetic material in each egg and in each sperm is slightly different, each fertilized egg is different. The resulting twins are thus fraternal twins. Identical twins upshot when one fertilized egg separates into two embryos after it has begun to divide. Because one egg was fertilized by one sperm, the genetic material in the two embryos is the same.

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 down the fallopian tube to the uterus. First, the zygote becomes a solid ball of cells. Then it becomes a hollow ball of cells called a blastocyst.

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

About six days later fertilization, the blastocyst attaches to the lining of the uterus, usually near the top. This process, called implantation, is completed by twenty-four hours nine or 10.

The wall of the blastocyst is one jail cell thick except in one area, where it is three to four cells thick. The inner cells in the thickened expanse 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 assistance maintain the pregnancy. For example, 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 besides carries oxygen and nutrients from mother to fetus and waste product materials from fetus to female parent.

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 course 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 articulate liquid (amniotic fluid) and expands to envelop the developing embryo, which floats inside it.

The next stage in development is the embryo, which develops within the amniotic sac, nether the lining of the uterus on one side. This stage is characterized by the formation of most internal organs and external trunk structures. Well-nigh organs begin to course about three weeks afterward fertilization, which equals 5 weeks of pregnancy (considering doctors engagement pregnancy from the first twenty-four hour period of the woman's terminal menstrual period, which is typically 2 weeks before fertilization). At this time, the embryo elongates, first suggesting a human shape. Presently thereafter, the area that will go the brain and spinal string (neural tube) begins to develop. The heart and major claret vessels begin to develop earlier—by nigh day 16. The heart begins to pump fluid through blood vessels by mean solar day xx, and the first red blood cells appear the adjacent day. Blood vessels continue to develop in the embryo and placenta.

Placenta and Embryo at About 8 Weeks

At 8 weeks of pregnancy, the placenta and fetus accept been developing for six weeks. The placenta forms tiny hairlike projections (villi) that extend into the wall of the uterus. Blood vessels from the embryo, which pass through the umbilical cord to the placenta, develop in the villi. A thin membrane separates the embryo's claret in the villi from the mother's blood that flows through the infinite surrounding the villi (intervillous infinite). This arrangement does the following: Allows materials to be exchanged between the blood of the mother and that of the embryo Prevents the female parent's immune arrangement from attacking the embryo because the mother's antibodies are too large to pass through the membrane (antibodies are proteins produced by the immune organization to assistance defend the trunk against foreign substances) The embryo floats in fluid (amniotic fluid), which is contained in a sac (amniotic sac). The amniotic fluid does the following: Provides a space in which the embryo can grow freely Helps protect the embryo from injury The amniotic sac is strong and resilient.

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

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

• Past about 14 weeks: The sex activity tin be identified.

• By about xvi to xx weeks: Typically, the pregnant woman can feel the fetus moving. Women who have been pregnant before typically feel movements about 2 weeks before than women who are significant for the offset time.

• Past about 24 weeks: The fetus has a adventure of survival outside the uterus.

The lungs continue to mature until near the fourth dimension of delivery. The encephalon accumulates new cells throughout pregnancy and the first twelvemonth of life after nascence.

Every bit 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 organization greatly increases the expanse of contact between the wall of the uterus and the placenta, so that more nutrients and waste materials tin can exist exchanged. The placenta is fully formed by xviii to 20 weeks just continues to abound throughout pregnancy. At delivery, it weighs about i pound.

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

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