Edited Invalid date
42.3 Human Embryonic and Fetal Development
The final development of anterior segments of the animal's body is determined by the first genes in the sequence.
We have already talked about the importance of cell death in the immune system and in preventing cancer.
Apoptosis is a part of morphogenesis.
In tadpoles, the disappearance of the tail is largely caused by apoptosis.
The webbing between fetal fingers and toes needs to be removed during human development.
When a cell-death signal is received, an apoptotic cascade ensues that ends in the destruction of the cell.
Define two mechanisms of cellular differentiation.
List the functions of the human embryo's membranes.
There are major events that occur during fetal development.
9 months is the length of time from conception to birth in humans.
Adding 280 days to the start of the last menstruation is usually used to calculate the time of birth.
Only a small percentage of babies arrive on the predicted date because the time of birth is influenced by so many variables.
Fetal development is divided into months 3 through 9.
During fetal development, the major organs are formed, and these structures are refined.
There are specific developmental accomplishments in each trimester.
The development of organs and organ systems is the second trimester.
The fetus appears to be human by the end of the second trimester.
The major organ systems become functional in the third trimester when the fetus grows rapidly.
The function of extraembryonic membranes in birds and reptiles is best understood.
The development of land first was possible in reptiles.
Oxygen is supplied to the embryo by the water and waste products are taken away.
The surrounding water provides a cushion and prevents desiccation.
The extraembryonic membranes are used to perform these functions for an embryo that develops on land.
Extensions of the germ layers spread over the yolk in the chick.
Next to the shell lies a gas exchange.
The amniotic fluid bathes the developing embryo.
The surrounding of the remaining yolk provides sustenance.
During the development of humans and chick, extraembryonic membranes are not part of the embryo.
Each has a function.
The function of the extraembryonic membranes in humans has been changed to suit internal development.
Their presence shows that we are related to the reptile.
There are blood vessels in the chorionic villi.
The allantois accumulates the small amount of urine produced by the fetal kidneys and later gives rise to the urinary bladder.
The first site of blood cell formation is the yolk sac.
Theamniotic fluid protects the embryo and protects the fetus.
It is interesting to note that all animals are born in Page 797 water, either in bodies of water or surrounded byamniotic fluid.
The first 2 months of embryo development are the most important.
The morula is when the embryo reaches the uterus on the third day.
In mammals, a blastocyst forms after the morula transforms into a blastula.
A single sperm nucleus enters the oocyte and fertilization of the egg occurs in the uterus.
A morula is produced when the zygote moves along the uterine tube.
There is a single layer of outer cells called the (Gk.
The early function of the trophoblast is to provide food for the embryo.
The trophoblast develops into a fetus.
The embryo begins its journey in the wall of the uterus at the end of the first week.
The trophoblast is able to digest some of the tissue and blood vessels of the uterus.
The embryo is about the size of a woman's period at a pregnancy test, and it keeps the corpus luteum past the time it normally dies.
menstruation does not occur because the endometrium is maintained.
The inner cell mass detaches from the trophoblast as the week progresses.
The first site of blood cell formation in chickens is the yolk sac, which has no nutritive function as it does in chickens.
The amnion is where the embryo and the fetus develop.
amniotic fluid absorbs shock and insulates against cold and heat in humans.
The embryo contains only tissues.
The embryo is above the amniotic sac.
The exchange between mother and child is important to the development of the chorion.
The allantois and yolk sac are positioned inside the body as it becomes the umbilical cord.
The embryo has two regions, the head and the tail.
The second week is when gastrulation occurs.
The embryo is composed of two layers of cells, one of which is the inner cell mass.
The third germ layer, the mesoderm, is formed when cells along the streak are invaginated.
The chorion is reinforced by the trophoblast.
The germ layers are related to the development of future organs.
During the third week, there are two important organ systems.
The first organ system to be visible is the nervous system.
The neural folds appear along the entire length of the embryo.
The neural tube is formed when the neural folds meet at the midline.
The nerve cord is called the spine after the notochord is replaced.
Page 798 continues into the fourth week as the development of the heart begins.
Even though the chambers of the heart are not fully formed, the right and left heart tubes start pumping blood.
All major blood vessels are located anteriorly when the arteries exit from this largely tubular heart.
The embryo is barely larger than the print.
The chorion has treelike projections that connect the caudal end of the embryo with the body stalk.
The allantois is contained within the stalks and becomes the umbilical blood vessels.
The developing embryo is connected to the placenta.
During the fifth week, the head enlarges and the developing eyes, ears, and nose are visible.
The human embryo is at the beginning of the fifth week.
There is a scanning electron micrograph.
The embryo is curled so that the head touches the heart, which is farther along than the rest of the body.
The limbs are growing from bulges called limb buds.
The tailbone is an evolutionary remnant that became the coccyx.
Humans and fishes have different pharyngeal arches and first pair of pharyngeal pouches.
The second pair becomes the pharyngitis, while the third and fourth become the parathyroid glands.
The embryo becomes recognizable as a human during the sixth to eighth weeks of development.
As a neck region develops, the head reaches its normal relationship with the body.
A startle response to touch is possible thanks to the development of the nervous system.
Even though all organ systems are established, the embryo is 38mm long and weighs less than 1 g at the end of this period.
Maternal and fetal cardiovascular systems are involved in exchange of gas, nitrogen, and waste.
Once the embryo is fully implanted, the placenta begins to form.
The entire chorion has chorionic villi.
In the areas where the placenta develops, these disappear.
The placenta is fully formed by the tenth week.
Fetal and maternal tissues make up the placenta.
Maternal blood surrounds chorionic villi in the uterus.
Fetal and maternal blood is exchanged across the walls of the chorionic villi.
Negative feedback control of the hypothalamus and anterior pituitary prevents new follicles from maturing.
The lining of the uterus is maintained by them.
During pregnancy, there is no menstruation.
Maternal and fetal blood don't mix under normal conditions because exchange always takes place across the blood vessels.
The fetus depends on the umbilical cord for its survival because it contains the arteries and vein that carry waste from the uterus to the mother's blood.
The lives of the fetus and the mother are at risk if the placenta tears from the wall.
Maternal antibodies are sent across the placenta to the fetal circulation just before birth.
This helps ensure that the newborn is protected against common pathogens until the baby's immune system matures.
Fetal development is marked by an increase in size.
The weight went from less than 28 g to 3 kg.
The fetus grows to 50 cm in length during this time.
It is possible to tell if the fetus is male or female by the appearance of the genitalia in the third month.
Hair, eyebrows, and eyelashes are added to the face and head.
The hands and feet are the same as fingernails and toenails.
The limbs and trunk are covered by a fine, downy hair.
The fetus is old because it is growing so fast.
"Cheese" protects the skin fromamniotic fluid.
The fetal heartbeat can be heard through a stethoscope.
The fetus is able to hear and respond to sounds by 18 weeks of age.
A fetus born at 24 weeks has a chance of survival because the lungs are still immature and can't capture enough oxygen.
The chances of a fetus surviving being born a month or two premature increase dramatically as it rapidly grows during the third trimester.
When the fetal brain is sufficiently mature, the fetal hypothalamus stimulates the pituitary to release androgens into the bloodstream.
The androgens are used in the uterus to make prostaglandins and oxytocin, hormones that increase the production of sex hormones.
The uterus contracts and the fetus is ejected.
The process of birth includes three stages.
The baby's head and body can be passed through the cervix during the first stage.
The mother's water breaking is an event when the amnion bursts.
The baby is born and the cord is cut during the second stage.
During the third stage, the baby is born.
Congenital disorders are abnormal conditions that are present at birth.
One in 33 babies in the United States have a birth defect, according to the CDC.
Not all birth defects can be prevented.
There are steps that women can take to increase their chances of delivering a baby.
There are certain birth defects that occur because the developing embryo doesn't get enough nutrition.
Women of childbearing age are urged to make sure they consume adequate amounts of the vitamins in order to prevent neural tube defects, such as spina bifida and anencephaly.
Part of the vertebral column can't adequately protect the spine in spina bifida.
Most of the fetal brain fails to develop with anencephaly.
In leafy green vegetables, nuts, and citrus fruits, there is a lot of folic acid.
Many breads and cereals are fortified with it.
The CDC recommends that all women of childbearing age get at least 400 micrograms of folic acid every day through supplements and a healthy diet.
Neural tube birth defects can occur just a few weeks after conception, when many women are still unaware that they are pregnant.
Fetal alcohol consumption is a leading cause of birth defects.
Fetal alcohol syndrome can occur in 0.2 to 1.5 of every 1,000 live births in the United States.
Children with FAS often have a small head, are overweight, and have intellectual disabilities.
Children with FAS often exhibit short attention span, impulsiveness, and poor judgement, as well as serious difficulties with learning and memory.
The risk of neural tube defects is increased by heavy alcohol use.
Smoking causes birth defects.
Smoking mothers are more likely to give birth to babies with low birth weight and defects of the face, heart, and brain.
Drugs that are illegal should also be avoided.
cocaine causes blood pressure fluctuations that affect the fetus.
Babies exposed to cocaine may have problems with vision and coordination.
Some medications may pose a risk to a developing fetus.
If pregnant women need to be immunized, they are usually given killed or inactivated forms of the vaccine, because live forms often present a danger to the fetus.
Because the rapidly dividing cells of a developing embryo or fetus are very susceptible to damage from radiation, pregnant women should avoid unnecessary X-rays.
If a medical X-ray is unavoidable, the woman should inform the X-ray technician so that her fetus can be protected as much as possible by covering her abdomen with a lead apron.
There are certain pathogens that can cause birth defects.
Intellectual disability, deafness, blindness, and heart defects were caused by this virus in the past.
In developed countries, Rubella is less of a problem because most women have been immunized as children.
There are infections that can cause birth defects.
20% of birth defects are due to genetic or chromosomal abnormality, which can be detected before birth.
Amniocentesis can be done from the fifteenth to the 17th weeks of pregnancy.
Chorionic villi sampling can be done from the eighth to the twelfth weeks of pregnancy.
Preimplantation genetic diagnosis can be done on oocytes that have been collected from the woman or on the early embryo.
View flashcards and assignments made for the note
Getting your flashcards
Privacy & Terms