Stages of Development of a Human Fetus
The stages of development of a human fetus begin when sperm enters the vagina, travels through the cervix, enters the fallopian tube, and fertilizes an egg. These stages are divided into three trimesters. Human fetuses develop physical and neurological functions necessary for life outside their mother's womb.
Other People Are Reading
-
Zygote
-
The first stage of develop of a human fetus occurs when sperm penetrates the egg cell, resulting in a zygote. The zygote is the combination of the genetic material from the mother's eggs and the father's sperm. According to the U.S. National Library of Medicine website, this genetic material contains the entire DNA that will make a child. This genetic material determines what children will look like, from eye color to hair color, and personality. The zygote spends a few days going through the fallopian tube, dividing to form balls of cells that will become organs and body parts.
Blastocyst
-
Zygotes form a group of inner cells with outer shells during the blastocyst stage of fetal development. The inner cells become an embryo and the outer cells become a membrane that nourishes and protects the embryo. The U.S. National Library of Medicine website says the blastocyst reaches the womb around the fifth day and implants in the uterine wall around the sixth day. The blastocyst sticks to the lining and gets nourished through the woman's bloodstream.
-
Embryo
-
The human fetus cells begin differentiating and forming specific cells like blood cells, kidney cells, nerve cells and heart cells. External features also begin developing during this stage. The U.S. National Library of Medicine says this critical stage in the early part of the first trimester is when fetuses are more susceptible to damage from alcohol and drugs, infection, radiation and nutritional deficiencies.
First Trimester
-
Basic growth occurs during the first trimester, beginning with the brain, spinal cord, heart and gastrointestinal tract. Buds that will become arms and legs develop, and you can hear the heartbeat. The American Pregnancy Association website says other major developments include the placenta, hormones, structures that become eyes and ears, the beginning of lungs, jaws, noses and palates, and bones. Human fetuses are about three inches long and weigh about an ounce.
Second Trimester
-
Major organs have formed by the beginning of the second trimester, and human fetuses spend most of their time growing. Fetuses begin kicking and moving and recognize the sound of their mother's voice and respond to stimuli. The University of Virginia Health System website says fetuses develop reflexes like swallowing and sucking, nails grow on fingers and toes, fat forms on the fetus, fine hairs appear on the skin, and fetuses begin establishing a sleep cycle. Human fetuses weigh about two or three pounds and are 13 to 16 inches long. Fetuses born at the end of the second trimester can survive in a neonatal intensive care unit.
Third Trimester
-
Human fetuses get ready for birth at this stage of development. The American Pregnancy Association website says fetuses begin storing fat, calcium, iron and phosphorus. Lungs develop and rhythmic breathing movements begin. Bones fully develop and eyelids open and close. The fetus' head turns downward in preparation for birth and fine hairs on the skin disappear. By the end of the third trimester, fetal movement decreases as babies run out of room. Human fetuses are between 19 and 21 inches long. Healthy fetuses weigh between five and 10 pounds by the time they are born.
-
