Question

Prenatal development: Tell a story of prenatal development during the germinal, embryonic and fetal stages. Include timing of various structures developing (umbilical cord, neural tube, heart, etc.). Identify when a fetus is viable (able to live) outside the mother's uterus.

1. germinal stage:

2. zygote stage:

3. embryonic stage:

4. fetal stage:

Answer 1

1.Germinal stage: The baby began to develop at the moment of conception; this is when the mother's egg is fertilized by the father's sperm. Pregnancy is considered to begin on the first day of the mother's last menstrual period. Conception typically occurs at what is considered the 2nd week of pregnancy.

Conception is also the beginning of the germinal period of prenatal development. This stage occurs during the first 2 weeks of development (or the 2nd - 4th weeks of pregnancy).

2.Zygote stage: The union of the sperm and egg cell forms a single cell called a zygote. The zygote moves along the Fallopian tube toward the uterus. At the same time, the zygote is rapidly dividing in a process called cleavage.

Once it reaches the uterus, the zygote becomes what is called a blastocyst, and it begins to implant into the wall of the uterus. The germinal period ends when the blastocyst is fully implanted into uterine tissue.

3.Embryonic stage:

This is the embryonic period of prenatal development. This stage lasts from implantation until about 8 weeks from the time of conception (or the 10th week of pregnancy). This is the most important time of prenatal development because the embryo is developing the foundations for a healthy baby.

The blastocyst that implanted in the uterus continues to divide rapidly after implantation. Through a process called differentiation, cells begin to take on different functions. One of the first examples of this is a division between the cells that will make up the placenta and the cells that will make up the baby.

After this, a process called gastrulation forms three layers called germ layers. The outer layer is called the ectoderm, the middle layer is called the mesoderm, and the inner layer is called the endoderm.

Each germ layer will differentiate into different structures. The ectoderm will form many outer tissues such as skin and hair, as well as most of the nervous system tissues - including the brain. The mesoderm will form tissues inside the body such as the lungs, bones, and muscles - including the heart. The endoderm will form tissues such as the digestive tract and bladder, as well as other internal organs.

All of the essential structures have been formed (both inside and outside) by the time the embryonic period comes to an end. The new title of the fetus is now given to the embryo.

4.Fetal stage: The remainder of prenatal development occurs during the fetal stage, which lasts from week 9 until birth (usually between 38 and 40 weeks). When the organism is about nine weeks old, the embryo is called a fetus. At this stage, the fetus is about the size of a kidney bean and begins to take on the recognizable form of a human being. Between 9 and 12 weeks, reflexes begin to appear and the arm and legs start to move (those first movements won’t be felt for a few weeks, however). During this same time, the sex organs begin to differentiate. At about 16 weeks, the fetus is approximately 4.5 inches long. Fingers and toes are fully developed, and fingerprints are visible. By the time the fetus reaches the sixth month of development (24 weeks), it weighs up to 1.4 pounds. The hearing has developed, so the fetus can respond to sounds. The internal organs, including the lungs, heart, stomach, and intestines, have formed enough that a fetus born prematurely at this point has a chance to survive outside of the womb.

viability of a fetus means having reached such a stage of development as to be capable of living, under normal conditions, outside the uterus. The age of viability has been pegged at 24 to 28 weeks.So that's. the fetal stage.