Chapter 4.Fetal development

Vernix caseosa

A protective, cheeselike, whitish substance made up of sebum and desquamated epithelial cells that is present on the fetal skin.

A pregnant client is concerned about a blow to the abdomen if she continues to play basketball during her pregnancy. The nurse's response is based upon her knowledge of which of the following facts concerning amniotic fluid?

Amniotic fluid functions as a cushion to protect against mechanical injury. Rationale: During pregnancy, the amniotic fluid protects against injury. After 20 weeks of pregnancy, fluid volume ranges from 700 to 1000 mL. Some of the amniotic fluid is contributed by the fetus's excreting urine. Amniotic fluid is slightly alkaline.

fertilization-

An ovum is considered fertile for about 12 to 24 hours after ovulation, and the sperm is capable of fertilizing the ovum for only about 24 hours after it is deposited in the female reproductive tract.

XX and XY chromosomes-

Sex chromosomes are referred to as X and Y. Females have two X chromosomes, and males have an X and a Y chromosome. Y chromosomes are carried only by the sperm. To produce a female child, both the mother and the father contribute an X chromosome. To produce a male child, the mother contributes an X chromosome and the father contributes a Y chromosome.

Foramen ovale

Special opening between the atria of the fetal heart. Normally, the opening closes shortly after birth; if it remains open, it can be repaired surgically.

Placenta

Specialized disk-shaped organ that connects the fetus to the uterine wall for gas and nutrient exchange. Also called afterbirth.

Embryonic membranes

The amnion and chorion.

Fetus

The child in utero from about the seventh to ninth week of gestation until birth.

Chorion

The fetal membrane closest to the intrauterine wall that gives rise to the placenta and continues as the outer membrane surrounding the amnion.

Endoderm

The inner layer of cells in the developing embryo that give rise to internal organs such as the intestines.

Amnion

The inner of the two membranes that form the sac containing the fetus and the amniotic fluid.

Blastocyst

The inner solid mass of cells within the morula.

Amniotic fluid

The liquid surrounding the fetus in utero. It absorbs shocks, permits fetal movement, and prevents heat loss.

Bag of waters (BOW)

The membrane containing the amniotic fluid and the fetus.

Trophoblast

The outer layer of the blastoderm that will eventually establish the nutrient relationship with the uterine endometrium.

Decidua capsularis

The part of the decidua surrounding the chorionic sac.

Decidua basalis

The part of the decidua that unites with the chorion to form the placenta. It is shed in lochial dischargeafter childbirth.

Meiosis

The process of cell division that occurs in the maturation of sperm and ova that decreases their number of chromosomes by one half.

Umbilical cord

The structure connecting the placenta to the umbilicus of the fetus and through which nutrients from the woman are exchanged for wastes from the fetus.

Fertilization

Impregnation of an ovum by a spermatozoon; conception.

Significant events that occur during the embryonic stage include-

the fetal heart beginning to beat at 4 weeks and the establishment of fetal circulation at 6 weeks.

The embryo is particularly vulnerable to teratogenesis during-

the first 8 weeks of cell differentiation and organ system development.

Meiosis

-•Meiosis is the process by which gametes (ova and sperm) are formed. It occurs during gametogenesis (oogenesis and spermatogenesis) and consists of two successive cell divisions (reduction division), which produce a gamete with 23 chromosomes (22 autosomal chromosomes and 1 sex chromosome), the haploid number of chromosomes.

Mitosis

Mitosis is the process by which additional somatic (body) cells are formed. It provides growth and development of the organisms and replacement of body cells.

Mitosis

Process of cell division whereby both daughter cells have the same number and pattern of chromosomes as the original cell.

Mesoderm

The intermediate layer of germ cells in the embryo that gives rise to connective tissue, bone marrow, muscles, blood, lymphoid tissue, and epithelial tissue.

Gametogenesis

The process by which germ cells are produced.

What are the 3 circulatory shunts for fetal circulation?

-•Fetal circulation is a specially designed circulatory system that provides for oxygenation of the fetus while bypassing the fetal lungs. foramen ovale, ductus arteriosis and ductus venosis.

A nurse is teaching a couple about the process of fertilization. Which statement by the couple would indicate understanding of fertilization?

"Fertilization takes place in the ampulla (outer third) of the fallopian tube." Rationale: The ampulla is the outer third of the fallopian tube. The word comes from the Latin word ampullae, meaning "jug." Ampulla is a general term used in anatomy to designate a flasklike dilation of a tubular structure. The fimbria is a funnel-like enlargement with many fingerlike projections reaching out to the ovary at the end of the fallopian tube. The isthmus is the straight and narrow portion of the inner third of the fallopian tube, and it opens into the uterus; this is the site for tubal ligation.

The nurse is preparing an educational workshop on the time frames for fetal exposure to potential teratogens. Which defect is most likely to occur at seven weeks gestation?

A cleft palate Rationale: Cleft palate is the defect most likely to occur at seven weeks gestation. Shortening of fingers and toes most likely occurs at eight weeks gestation. Cleft lip most likely occurs at six weeks gestation. Septal or aortic abnormalities are most likely to occur at six weeks gestation.

Ductus arteriosus

A communication channel between the main pulmonary artery and the aorta of the fetus. It is obliterated after birth by rising PO2 and changes in intravascular pressure in the presence of normal pulmonary functioning. It normally becomes a ligament after birth but sometimes remains patent (patent ductus arteriosus, a treatable condition).

Zygote

A fertilized egg.

Ductus venosus

A fetal blood vessel that carries oxygenated blood between the umbilical vein and the inferior vena cava, bypassing the liver; it becomes a ligament after birth.

Morula

Developmental stage of the fertilized ovum in which there is a solid mass of cells.

Diploid number of chromosomes

Containing a set of maternal and a set of paternal chromosomes; in humans, the diploid number of chromosomes is 46.

At 17 weeks pregnant, a mother asks the nurse questions about the development of her baby. The mother states that it may be too early to visualize any body structures via ultrasound. The nurse's best response in relation to fetal development at 17 weeks is:

Differentiation of hard and soft palate can be seen. Rationale: Differentiation of hard and soft palate are structures developed by 17 weeks gestation. Myelination of the spinal cord begins at 20 weeks gestation. Soft earlobes with little cartilage develop at 36 weeks gestation. Teeth form hard tissue (enamel) at 18 weeks gestation.

Gamete

Female or male germ cell; contains a haploid number of chromosomes.

Where does fertilization occur?-

Fertilization usually takes place in the ampulla (outer third) of the fallopian tube. Both capacitation and acrosomal reaction must occur for the sperm to fertilize the ovum. Capacitation is the removal of the plasma membrane, which exposes the acrosomal covering of the sperm head. Acrosomal reaction is the deposit of hyaluronidase in the corona radiata, which allows the sperm head to penetrate the ovum.

Lanugo

Fine, downy hair found on all body parts of the fetus, with the exception of the palms of the hands and the soles of the feet, after 20 weeks' gestation.

How many gamates does a fetus have?

Gametes must have a haploid number of chromosomes (23) so that when the female gamete (ovum) and the male gamete (spermatozoon) unite (fertilization) to form the zygote, the normal human diploid number of chromosomes (46) is reestablished.

A client in the prenatal clinic tells the nurse that her sister has twins and is concerned that she may also have twins. The nurse's response is based upon which fact?

Genetic factors in the mother may lead to elevated serum gonadotropin levels, causing double ovulation. Rationale: A genetic factor that results in elevated serum gonadotropin levels may cause double ovulation. The chance of dizygotic twins increases with maternal age up to about 35 years and then decreases abruptly. Monozygotic twins share a common amniotic sac only if division occurs 7-13 days after fertilization. The survival rate of dizygotic twins is about 10% lower than that of monozygotic twins.

Haploid number of chromosomes

Half the diploid number of chromosomes. In humans there are 23 chromosomes, the haploid number, in each germ cell.

When is the cell referred to as a blastocyst?-

Intrauterine development first proceeds via cellular multiplication in which the zygote undergoes rapid mitotic division called cleavage. As a result of cleavage, the zygote divides and multiplies into cell groupings called blastomeres, which are held together by the zona pellucida. The blastomeres eventually become a solid ball of cells called the morula. When a cavity forms in the morula cell mass, the inner solid cell mass is called the blastocyst.Implantation usually occurs in the upper part of the posterior uterine wall when the blastocyst burrows into the uterine lining.

A nurse is instructing her students where to listen for a uterine souffle. Each student has placed the fetoscope on the pregnant women's abdomen. Based on the following placements of the fetoscopes, the student most likely to hear a uterine souffle is the one who placed her fetoscope on which of the following areas?

Just above the symphysis pubis Rationale: A uterine souffle is best heard just above the mother's symphysis pubis. There are no specific placental circulatory sounds that can be heard under the area of the umbilical cord of the fetus. A funic souffle can be heard over the area of the umbilical cord of the fetus in late pregnancy. There are no specific placental circulatory sounds that can be heard in the area just below the symphysis pubis.

Teratogen

Nongenetic factors that can produce malformations of the fetus.

Decidua vera (parietalis)

Nonplacental decidua lining the uterus.

Cotyledons

One of the rounded portions into which the placenta's uterine surface is divided, consisting of a mass of villi, fetal vessels, and an intervillous space.

Ectoderm

Outer layer of cells in the developing embryo that gives rise to the skin, nails, and hair.

Postconception age periods

Period of time in embryonic fetal development calculated from the time of fertilization of the ovum.

Wharton's jelly

Yellow-white gelatinous material surrounding the vessels of the umbilical cord.

A nurse in the fertility clinic is teaching clients about the process of fertilization. Which statement by the client would not require further teaching by the nurse?

"If the sperm plasma membrane is not removed (capacitation), the sperm will not be able to fertilize the ovum." Rationale: If the sperm plasma membrane is not removed (capacitation), the sperm will not be able to fertilize the ovum. Transportation of the sperm to the fallopian tube takes an average of 4-6 hours after ejaculation. Prostaglandins in the semen help to transport the sperm. High estrogen levels increase peristalsis in the fallopian tubes during ovulation, moving the ovum toward the uterus.

A nurse is teaching a group of student nurses about amniotic fluid. Which statement by the student nurse reflects an understanding of the fetus's contribution to the quantity of amniotic fluid?

"The fetus contributes to the volume of amniotic fluid by excreting urine." Rationale: "The fetus contributes to the volume of amniotic fluid by excreting urine." Approximately 400 mL of amniotic fluid flows out of the fetal lungs each day. The fetus swallows about 600 mL of the fluid in 24 hours. A normal volume of amniotic fluid is necessary for good fetal movement. Normal movement is necessary for good musculoskeletal development.

The nurse is preparing an educational workshop on fetal development. Which statement by the student would require the nurse to explain further?

"The umbilical cord is made of two veins and one artery." Rationale: A nuchal cord exists when the umbilical cord encircles the fetal neck. Fetal movement causes the umbilical cord to knot. The umbilical cord is made of two arteries and one vein. The high blood volume and Wharton's jelly content of the umbilical cord prevents compression of the cord.

After implantation -

After implantation, the endometrium is called the decidua. Decidua capsularis is the portion that covers the blastocyst. Decidua basalis is the portion that is directly under the blastocyst. Decidua vera is the portion that lines the rest of the uterine cavity.

Acrosomal reaction

Breakdown of the hyaluronic acid in the corona radiata by enzymes from the heads of sperm; allows one spermatozoon to penetrate the ovum zona pellucida.

How many chromosomes does a fetus have?

Humans have 46 chromosomes, which are divided into 23 pairs—22 pairs of autosomes and 1 pair of sex chromosomes

A client states that she had a spontaneous abortion 12 months ago and asks if her hormones may have contributed to the loss of the pregnancy. The nurse's response is based upon which fact?

Progesterone decreases the contractility of the uterus. Rationale: Progesterone decreases the contractility of the uterus, thus preventing uterine contractions that might cause spontaneous abortion. Progesterone must be present in high levels for implantation to occur. After 10 weeks, the placenta takes over the production of progesterone. hCG reaches its maximum level at 50-70 days gestation.

Cleavage

Rapid mitotic division of the zygote; cells produced are called blastomeres.

Capacitation

Removal of the plasma membrane overlying the spermatozoa's acrosomal area with the loss of seminal plasma proteins and the glycoprotein coat. If the glycoprotein coat is not removed, the sperm will not be able to penetrate the ovum.

Embryo

The early stage of development of the young of any organism. In humans the embryonic period is from about 2 to 8 weeks' gestation and is characterized by cellular differentiation and predominantly hyperplastic growth.

Stages of fetal development include-

the preembryonic stage (the first 14 days of human development starting at the time of fertilization), the embryonic stage (from day 15 after fertilization, or the beginning of the third week, until approximately 8 weeks), and the fetal stage (from 8 weeks until birth, at approximately 38+ weeks after the last normal menstrual period).

What is the purpose of amniotic fluid?-

•Amniotic fluid cushions the fetus against mechanical injury, controls the embryo's temperature, allows symmetrical external growth, prevents adherence to the amnion, and permits freedom of movement.

What are the 2 embryonic membranes called?-

•Embryonic membranes are called the amnion and the chorion. The amnion is formed from the ectoderm and is a thin protective membrane that contains the amniotic fluid and the embryo. The chorion is a thick membrane that develops from the trophoblast and encloses the amnion, embryo, and yolk sac.

What are the 3 germ layers called?

•Primary germ layers will give rise to all tissues, organs, and organ systems. The three primary germ cell layers are ectoderm, endoderm, and mesoderm.

Placenta-

•The placenta develops from the chorionic villi and decidua basalis and has two parts: The maternal portion, consisting of the decidua basalis, is red and fresh looking; the fetal portion, consisting of chorionic villi, is covered by the amnion and appears shiny and gray. The placenta is made up of 15 to 20 segments called cotyledons.

What are the hormones related to the placenta?-

•The placenta serves endocrine (production of hPL, hCG, estrogen, and progesterone), metabolic, and immunologic functions. It acts as the fetus's respiratory organ, is an organ of excretion, and aids in the exchange of nutrients.

What is the anatomy of the umbilical cord?-

•The umbilical cord contains two umbilical arteries, which carry deoxygenated blood from the fetus to the placenta, and one umbilical vein, which carries oxygenated blood from the placenta to the fetus. The umbilical cord normally has a central insertion into the placenta. Wharton's jelly, a specialized connective tissue, helps prevent compression of the umbilical cord in utero.

What are the two types of twins?-

•Twins are either monozygotic (identical) or dizygotic (fraternal). Dizygotic twins arise from two separate ova fertilized by two separate spermatozoa. Monozygotic twins develop from a single ovum fertilized by a single spermatozoon.