Ch 5.1: "Prenatal Development"

What are the 3 stages of prenatal development?

1. Germinal Stage: Prenatal stage that lasts about 2 weeks postconception 2. Embryonic Stage: Prenatal stage that lasts from 2 weeks to 2 months postconception 3. Fetal Stage (pg. 134, paragraph 4)

What is a blastocyst?

A hollow ball of cells that consists of the inner cell mass and an outer ring of cells. (pg. 134)

What is the critical period?

A period of time during which development is occurring rapidly and the organism is especially sensitive to damage, which often is severe and irreversible.

What is the inner cell mass?

A solid clump of cells in the blastocyst, which later develops into the embryo. (pg. 134)

What occurs in the germinal stage (p. 2)?

As the number of cells continues to proliferate, the solid ball of cells become a hallow ball called a blastocyst with a solid group of cells called the inner cell mass at one end and an outer ring of cells called the trophoblast. The inner cell mass will go on to become the embryo and part of the amnion that surrounds the embryo, and the outer ring of cells will become the support system for the pregnancy, which includes the placenta and the chorion. (pg. 134, paragraph 6)

What occur in the fetal stage? (p.4)

At about 10 weeks, fetal breathing movements begin, although there is no air in the amniotic sac to breathe. Instead, fetuses breathe in and then expel amniotic fluid. Between week 12 and week 16, most women will begin to feel the movement of the fetus. By a gestational age of 20 weeks, fetuses have been recorded moving more than 50 times in a single 50 minute session. Fetal movement continues to decline from this point until the baby is born. At 32 weeks, the fetus spends between 90%-95% of its time sleeping, but it still develops quite a repertoire of activities prior to birth. (pg. 139, paragraph 2)

What occurs in the embryonic stage?

At this point the conception is called an embryo. The support system that is developing for the pregnancy includes 2 fetal membranes as well as the placenta and umbilical cord. You can think of the membranes as 2 sacs, one inside the other. The chorion is the outer one, and the connection that it establishes with the uterus gives rise to the placenta. The inner one, called the amnion, surrounds the developing embryo and is filled with amniotic fluid to cushion and protect the embryo (later called a fetus) (pg. 136, paragraph 4)

What occurs in the embryonic stage? (p.3)

Because the concentration of oxygen and nutrients in the fetal blood is lower than in the maternal blood, these substances move from the maternal blood through the artery walls where they are picked up by the fetal blood in the placenta and carried back to the developing fetus. The waste products that are high in concentration in the fetal blood move through the artery wall into the spaces, where the maternal blood picks them up to transport back to the mother for disposal through her organ systems. This transport system can prevent some substances from moving from the mother to the fetus because their molecules are too large to pass through the walls of the arteries, but there are many substances that are potentially damaging to the developing embryo that unfortunately can move across the placenta and enter the fetal blood system. (pg. 136, paragraph 6)

Where does the prenatal journey begin?

Begins when a follicle in a women's ovary matures and releases an ovum during her monthly menstrual cycle in the process called ovulation. Ovum travels down the fallopian tube toward the uterus. This is where fertilization occurs when the egg is penetrated by one of the approximately 300 million sperm that are released into the woman's reproductive system during an act of intercourse. (pg. 134, paragraph 2)

When does the germinal stage begin?

Begins when the sperm penetrates the egg. (pg. 134, paragraph 5)

What occur in the fetal stage?

Characterized by the continued growth of the fetus and a remarkable increase in size and weight. All of the organ systems need to complete their development and become functional so that the newborn will be capable of surviving independently of the mother after birth. (pg. 138, paragraph 1)

What occurs in the embryonic stage? (p.5)

During the prenatal period, development starts from the head region and progresses down through the body, this is called cephalocaudal development. Throughout the pregnancy, especially in the early months, the upper half of the embryo is more advanced than the lower half. At 9 weeks of age, the head represents about half of the entire length of the fetus because the brain is developing so rapidly that it outpaces the rest of the body. (pg. 137, paragraph 2)

What occur in the fetal stage? (p.2)

During this period the transformation of the genitalia of the fetus into male or female genitalia. Although the biological sex of the embryo is determined at conception by the chromosomal information carried in the sperm, up until this point in the pregnancy, the internal and external appearance of male and female embryos has been the same. In a male fetus, at 9 weeks the testes begin to produce the male hormone androgen, and that hormone alters the development of the genitalia from that point on. In a female fetus, the genitalia continue along their developmental pathway, and a female reproductive system is laid down. (pg. 138, paragraph 2)

What occur in the fetal stage? (p.3)

Hormones produced prenatally not only shape the physical development of the fetus; they also influence the development of the brain. By the 26th week of the pregnancy, we can observe anatomical differences in brain structure of male and female fetuses. However, we should remember that there are many more similarities than differences between male and female brains, and many other factors, such as experiences later in life, also affect the formation and function of boys' and girls' brain. (pg. 139, paragraph 1)

What occurs in the embryonic stage? (p.4)

Inner cell mass differentiates into 3 layers, each of which goes on to develop into different organs and structures. All of the major organ systems of the body are laid down in a process called organogenesis. Because development occurs rapidly within a very short period of time, this is a critical period for development. Anything in the prenatal environment that disrupts the process at this point can cause damage that is both severe and irreversible. (pg. 137, paragraph 1)

What occurs during the germinal stage?

Once the zygote has been created, the outside thickens so that no other sperm will be able to enter the egg. The newly created zygote continues its journey through the fallopian tube, and the process of cell division begins. It takes about 15 hours for that single cell to become 2 cells, and then the process continues with 2 cells becoming 4, and so on, until there is a ball of 32 cells at 4 to 5 days following conception. Most pregnancies consist of a single conception, but about 3.3% of pregnancies result in the birth of twins. (pg. 134, paragraph 5)

How does an ultrasound work?

Some women have a prenatal ultrasound between 6-10 weeks of the pregnancy. During the test, high-frequency sound waves pass through the woman's uterus and bounce off of the baby. The returning sounds create a video image showing the embryo's size, shape, and position in the womb. The test is often repeated midpregnancy at about 20 weeks. At that point, the test can confirm that the baby is growing at the expected rate, and the physician can check for any physical abnormalities, can confirm if there is more than one fetus, determine whether other aspects of the pregnancy appear to be normal, and visually determine the sex of the baby, if the parents want that information. (pg. 137, paragraph 3)

Is stimulation that goes beyond what is normally provided better?

Stimulation that goes beyond what is normally provided to the developing fetus is not necessarily better and could even be harmful. The normal prenatal environment provides enough stimulation at this point in development. (pg. 139, paragraph 4)

What occur in the fetal stage? (p.5)

The cutaneous senses and the proprioceptive senses are the first to develop. The last to develop are the auditory and visual senses. The intrauterine environment provides at least some stimulation for all these senses are functional to some extent. What we see throughout the prenatal period is a great deal of continuity as systems develop and later become functional. This prepares the newborn to begin interacting with - and responding to - the environment almost immediately after birth. (pg. 139, paragraph 3)

What is an embryo?

The developing organism from conception to the end of the second month of a pregnancy. (pg. 136)

What is a fetus?

The developing organism from the end of the eighth week postconception until birth. (pg. 136)

What is infertility?

The inability to conceive within 1yr of frequent, unprotected sex. About 12% of married women in the U.S. have difficulty either getting pregnant or carrying a pregnancy to term. (pg. 136, paragraph 1)

What is the amnion?

The inner fetal membrane that surrounds the fetus and is filled with amniotic fluid. (pg. 136)

What is the placenta?

The organ that supports a pregnancy by bringing oxygen and nutrients to the embryo from the mother through the umbilical cord and carrying away fetal waste products. (pg. 136)

What is the trophoblast?

The outer ring of cells in the blastocyst that later develops into the support system for the pregnancy. (pg. 134)

What occurs in the embryonic stage? (p.2)

The placenta performs the essential functions of bringing oxygen and nutrients to the developing embryo from the mother through the umbilical cord and carrying away fetal waste products. This transfer between the mother and the embryo occurs without any intermingling of the blood of the mother and the embryo. When the fetal arteries enter the spaces in the placenta, they spiral around within the spaces and then return to the fetus as a closed loop. They do not directly connect to the maternal arteries or veins. This is why a mother and her child can have different blood types. The 2 blood systems remain separate throughout the pregnancy. (pg. 136, paragraph 5)

When does the fetal stage occur?

The prenatal stage that lasts from Week 9 postconception until birth. (pg. 138)

What is organogenesis?

The process in prenatal development by which all of the major organ systems of the body are laid down. (pg. 137)

What occurs in the germinal stage (p. 3)?

When the blastocyst reaches the uterus, it is ready to implant in the lining of the uterus. The cells in the trophoblast secrete an enzyme that digests some of the lining so that the blastocyst can securely embed itself there. If the ball of cells fails to implant for any reason, it passes out of the women's body without her even realizing there had been a conception. (not an uncommon occurrence) After implantation, fingerlike extensions from the outer layer of the trophoblast grow into the uterus, and a connection between the embryo and the mother is established. Once an outside source of nourishment is available, the blastocyst can really begin to grow in size. (pg. 135, paragraph 1)