when does placenta develop

Human Placenta Project: How Does the Placenta Form? | NICHD ...

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By

, MD, Saint Louis University School of Medicine

A baby through several stages of development, begins as a fertilized egg. Egg develops into a blastocyst, embryo, fetus.

During each normal, one egg (ovum) is usually released from one of her ovaries, about 14 days after the last menstrual period. The release of the egg is called ovulation. the egg is swept into the funnel-shaped end of one of the fallopian tubes.

At ovulation, the mucus in the cervix becomes thinner and more elastic, allowing the sperm to enter the uterus quickly. Within 5 minutes, the sperm may move from the vagina, through the cervix into the uterus, and to the ends of the tube-shaped funnel-tube fertilization regular site. The cells lining the fallopian tube facilitate fertilization.

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

If the sperm to penetrate the egg, fertilization results. Tiny hairlike cilia lining the fallopian tube propel the fertilized egg (zygote) through the tube towards the womb. Cells of the zygote gap repeatedly as a zygote moves down the fallopian tube to the uterus. zygote enters the uterus in 3 to 5 days.

In the womb, the cells continue to divide, becoming a hollow ball of cells called a blastocyst. Blastocyst implants in the uterine wall about 6 days after fertilization.

If more than one egg is released and fertilized, pregnancy involving more than one fetus, usually two (twins). Because the genetic material in each egg and each sperm a little different, each is different fertilized eggs. twin generated so fraternal twins. Identical twins occur when one fertilized egg separates into two embryos after it has begun to divide. Because the egg is fertilized by one sperm, genetic material in the same two embryos.

Once a month, an egg is released from the ovary into the fallopian tubes. After intercourse, the sperm move from the vagina through the cervix and uterus to the fallopian tubes, where the sperm fertilizes the egg. The fertilized egg (zygote) divides repeatedly as it moves down the fallopian tube to the uterus. First, the zygote into a solid ball of cells. Then it becomes a hollow ball of cells called a blastocyst.

In the womb, the blastocyst implants in the uterine wall, where it develops into an embryo that is attached to the placenta and is surrounded by the liquid membranes.

Approximately six days after fertilization, the blastocyst attaches to the lining of the uterus, usually near the top. This process, called implantation, finished the day 9 or 10.

Wall blastocyst is one cell thick except in one area, where it is three to four cells thick. The cells of the inner thickened area develop into an 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 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 also carries oxygen and nutrients from mother to fetus and waste material from the fetus to the mother.

Some of the cells of the placenta develops into the outer layer of the membrane (chorion) around the blastocyst develops. Other cells develop into the inner layer of the membrane (amnion), which form the amniotic sac. When the pouch is formed (around day 10 to 12), are considered embryonic blastocyst. The amniotic sac fills with fluid (amniotic) clear and inflate envelop the developing embryo, floating in it.

The next stage in development is the embryo, which develops in the amniotic sac, under the lining of the uterus on one side. This stage is characterized by the formation of most of the internal organs and external body structures. Most organs begin to form around three weeks after fertilization, which is equal to 5 weeks of pregnancy (due date pregnancy doctor from the first day of the last menstrual women, typically two weeks before conception). At this time, extending the embryo, the first showing the human form. Soon, the area will become braand spinal cord (neural tube) begins to develop. Heart and major blood vessels begin to develop earlier-around day 16. The heart begins to pump fluid through blood vessels by day 20, and the red blood cells first appeared on the next day. continues to grow blood vessels in the embryo and placenta.

Almost all organs are completely formed by about 10 weeks after conception (which is equal to 12 weeks gestation). The exception is the brain and spinal cord, which continue to shape and develop during pregnancy. Most malformations (birth defects) occurred during a period when organs are forming. During this period, the embryo is most vulnerable to the effects of drugs, radiation, and viruses. Therefore, a pregnant woman should not be given live virus vaccination or take drugs during this period unless they are considered essential in order to protect their health (see).

At 8 weeks of pregnancy, the placenta and the fetus has developed for 6 weeks. Placental form of small hairlike projections (villi) that extends to the uterine wall. blood vessels of the embryo, which passes through the umbilical cord to the placenta, developed in the villi.

A thin membrane separates the embryo's blood in the villi of the mother's blood that flows through the space surrounding the villi (intervillous space). This setting is not the following:

Allow the material to be exchanged between maternal blood and embryonic

Preventing mother's immune system from attacking the embryo because the maternal antibodies are too large to pass through the membrane (antibodies are proteins produced by the immune system to help defend the body against foreign substances)

float embryos in liquid (amniotic fluid), which is contained in the bag (amniotic, sac)

amniotic fluid do the following:

Provides a space in which the embryo can grow freely

to help protect the embryo from injury

the amniotic sac is strong and resilient.

at the end of the 8th week after fertilization (10 weeks gestation), the embryo is considered a fetus. During this phase, the structure has been formed to grow and thrive. Here is a marker during pregnancy:

With the 12th week of pregnancy: The fetus fills the entire uterus

With about 14 weeks. sex can be identified <. p> with about 16 to 20 weeks: Typically, a pregnant woman can feel the fetus moving. Women who have been pregnant previously used to feel the movement of about 2 weeks earlier than women who are pregnant for the first time

With about 24 weeks: .. fetus has a chance of survival outside the womb

lungs continue to mature until near the time of delivery. Brain accumulates new cells during pregnancy and the first year of life after birth.

As the placenta develops, it extends tiny hairlike projections (villi) into the uterine wall. Projections branched and unbranched back in a complicated treelike arrangement. This arrangement greatly increases the contact area between the wall of the uterus and placenta, so that more nutrients and waste material can be exchanged. the placenta is fully formed by 18 to 20 weeks, but continued to grow during pregnancy. On delivery, weighing about 1 pound

Although pregnancy involves a continuous process, it is divided into three three-month periods called trimesters :.

The first trimester: Week 0-12

The second trimester: Week 13 to 24

Third trimester: Week 25 for delivery

Events

Weeks of Pregnancy

1 Trimester

her last period before fertilization occurs.

0

Fertilization occurs.

The fertilized egg (zygote) begins to develop into a hollow ball of cells called a blastocyst.

2

Investment blastocyst in the uterine wall.

The amniotic sac is formed.

3

area that will become the brain and spinal cord (neural tube) begins to develop.

5

the heart and major blood vessels develop. The heartbeat can be seen during the ultrasound.

6

At the beginning of the arms and legs appear.

7

The bones and muscles form. Face and neck develop.

The brain waves can be detected.

The framework is formed. Fingers and toes are fully defined.

9

The kidneys start functioning.

Almost all organs are completely formed.

fetus can moveand respond to touch (when prodded through the woman's abdomen).

She had gained some weight, and her stomach may be slightly enlarged.

10

2 Trimester

sex of the fetus can be identified.

The fetus can hear.

14

fetal finger can understand. Fetus moves harder, so that the mother can feel.

The body of the fetus begins to fill as fat stored under the skin. Hair on the head and skin. Eyebrows and eyelashes are present.

16

The placenta is fully formed.

20

The fetus has a chance to survive outside the uterus.

she began to gain weight more quickly.

24

3 Trimester

The fetus is active, changing positions often.

The lungs continue to mature.

fetal head moves into position for delivery.

average, the fetus is about 20 inches long and weighs about 7 pounds. woman's enlarged abdomen causes the navel to bulge.

25

Shipping

37-42

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