Chapter 11
Conception and Fetal Development
Resource Library
Prentice Hall Nursing Medialink DVD-ROM
Audio Glossary
NCLEX Review
Animations: Cell Division; Oogenesis;Spermatogenesis; Oogenesis and Spermatogenesis Compared; Conception; Development of Placenta; Fetal Circulation; Embryonic Heart Formation and Circulation
Activities: Oogenesis and Spermatogenesis matching exercise; Oogenesis and Spermatogenesis labeling exercise
Video: Through the Eyes of a Nurse—The First Trimester
Companion Website
Additional NCLEX Review
Case Study:Teaching about Pregnancy
Care Plan Activity: Client Fearful of Multiple Gestations
Applications: Fraternal or Identical Twins; Fetal Development
Critical Thinking
Learning Objective 1
Explain the differences between mitotic cellular division and meiotic cellular division.
Concepts for Lecture
1. Cell division that results in exact copies of the original cell is mitosis. The process of cell division that leads to the development of eggs and sperm that are essential to producing a new organism is meiosis.
2. Mitosis is divided into five stages: interphase, prophase, metaphase, anaphase, and telophase. The chromosomes condense during prophase. The chromosomes then line up at the equator of the spindles during metaphase. During anaphase, the two chromatids of each chromosome separate and move to opposite ends of the spindle, where they cluster at the two poles. During telephase, a nuclear membrane forms, which separates the newly formed nucleus from the cytoplasm. The spindle then disappears and the centrioles relocate outside of each new nucleus; within the nucleus, the chromosomes lengthen and become threadlike. A furrow then develops in the cell cytoplasm and divides it into two daughter cells.
3. In meiosis, there are two successive cell divisions. During the first division, the chromosomes replicate and pair up with similar chromosomes, becoming intertwined. There is a physical exchange of genetic material between the chromatids. The pairs then separate, with each member moving to an opposite side of the cell. The cell then divides, forming two daughter cells with 23 double-structure chromosomes. The chromatids separate and move to opposite poles of the daughter cells. The result is four cells, each containing 23 single chromosomes.
Review the cell division animation from the Prentice Hall Nursing MediaLink DVD-ROM.
Learning Objective 2
Compare the processes by which ova and sperm are produced.
Concepts for Lecture
1. Through the process of oogenesis, female gametes (ovum) are produced. Oogonial cells from the ovary develop into oocytes. Before the birth of a female child, meiosis begins in all oocytes but stops before the first division is complete and does not resume until puberty.At the time of puberty, the primary oocyte continues the first meiotic division in the graafian follicle.
2. At the time of puberty in the male, the germinal epithelium in the seminiferous tubules begin spermatogenesis, which produces the male gametes, sperm. Spermatogona are called the primary spermatocytes as they begin the first meiotic division. During this division, the spermatogonium replicates and forms two haploid cells called secondary spermatocytes. At the time of the second division, they divide to form four spermatids.
Suggestions for Classroom Activities
Have students review the animations for oogenesis and spermatogenesis from the Prentice Hall Nursing MediaLink DVD-ROM. Ask them to compare and contrast the processes.
Learning Objective 3
Describe the process of fertilization.
Concepts for Lecture
1. The creation of a zygote occurs when an ovum and sperm unite. Ova are available for fertilization for 12 to 24 hours after ovulation, whereas sperm remain viable in the female reproductive tract for 48 to 72 hours (sperm are believed to be healthy and fertile for only the first 24 hours). Fertilization takes place in the outer third or ampulla of the fallopian tube. The sperm move up the reproductive tract by using flagellar motion.
2. In order for fertilization to occur, the sperm must undergo two processes; capacitation and the acrosomal reaction. During capacitation, the plasma membrane and glycoprotein coat covering the spermatozoa’s acrosomal area is removed and seminal plasma proteins are lost. During the acrosomal reaction, the acrosome caps of the sperm surrounding the ovum release their enzymes, which break down the hyaluronic acid that hold the elongated cells of the corona radiata of the ovum.
3. When the ovum is penetrated by the sperm, the zona pellucida undergoes a reaction to prevent additional sperm from entering the ovum. After the sperm enters the ovum, the oocyte is signaled to complete the second meiotic division, which forms the nucleus of the ovum and ejects the second polar body. At this time, the nuclei of the ovum and the sperm swell and approach each other. True fertilization occurs as the nuclei unite, their individual nuclear membranes disappear, and their chromosomes pair up to produce the diploid zygote.
Review the conception animation from the Prentice Hall Nursing MediaLink DVD-ROM.
Learning Objective 4
Identify the differing processes by which fraternal (dizygotic) and identical (monozygotic) twins are formed.
Concepts for Lecture
1. Fraternal twins arise from two separate ova fertilized by two separate spermatozoa. Identical twins (monozygotic) develop from a single ovum and sperm. Monozygotic twins originate at different stages of early development. If it occurs within 3 days of fertilization, two embryos, two amnions, and two chorions develop. The placentas may be fused or distinct. If division occurs about 5 days after fertilization, the two embryos will have separate amniotic sacs, which will be covered by a common chorion. If division occurs 7 to 13 days after fertilization, the two embryos will have a common amniotic sac and chorion.
Learning Objective 5
Describe in order of increasing complexity the structures that form during the cellular multiplication and differentiation stages of intrauterine development.
Concepts for Lecture
1. As the zygote moves through the fallopian tube toward the uterus, cellular multiplication begins. This rapid period of mitotic divisions is called cleavage and the cells are called blastomeres. Eventually, the blastomeres form a morula, a solid ball of 12 to 16 cells. When the morula reaches the uterus, the intracellular fluid in themorula increases and a central cavity forms within the morula. Within this cavity, an inner solid mass of cells exists, which is called the blastocyst. Cells surrounding the cavity are called the trophoblast. The trophoblast will develop into the chorion and the blastocyst will develop into the embryonic disc. This disc will develop into the embryo and the amnion.
2. Implantation will occur between days 7 and 10 when the blastocyst implants itself by burrowing into the uterine lining until it is completely covered. Once implantation occurs, the endometrium is called the decidua.
3. Ten to 14 days after conception, the blastocyst differentiates into the primary germ layers: the ectoderm, the mesoderm, and the endoderm. The tissues, organs, and organ systems develop from these germ layers.
Learning Objective 6
Describe the development, structure, and functions of the placenta during intrauterine life.
Concepts for Lecture
1. The function of the placenta is metabolic and nutrient exchange between the fetus and the mother. There are two parts of the placenta: the decidua basalis, which is the maternal portion, and the chorionic villi, which is the fetal portion. The amnion covers the placenta.
2. The chorionic villi form spaces in the tissue of the decidua basalis, which will be filled with maternal blood and chorionic villi. The chorionic villi then differentiate, forming two trophoblastic layers: the synctium or outer layer, and the cytotrophoblast or inner layer. An inner layer of connective mesoderm develops in the chorionic villi, which form the anchoring villi. They will form the septa of the placenta. The septa divide the placenta into 15 to 20 segments called cotyledons. Within each of these, branching villi form a highly complex vascular system that provides compartmentalization for the uteroplacental circulation through which exchange of gases and nutrients takes place.
3. Attaching the embryo to the yolk sac is the body stalk, which contains blood vessels that extend into the chorionic villi. This fuses with the embryonic portion of the placenta to provide a circulatory pathway. In a fully developed placental umbilical cord, fetal blood will flow through two umbilical arteries to the capillaries of the villi and oxygen-rich blood flows from the umbilical vein to the fetus.
4. Placental functions include fetal respiration, nutrition, and excretion, and placental production of glycogen, cholesterol, and fatty acid for fetal use. The placenta also secretes the following hormones: human chorionic gonadotropin (hCG), human placental lactogen (hPL), estrogen, and progesterone. Transfer of nutrients occurs through simple diffusion, facilitated transport, active transport, and hydrostatic and osmotic pressures.
Review the formation of placenta animation from the Prentice Hall Nursing MediaLink DVD-ROM.
Learning Objective 7
Summarize the significant changes in growth and development of the fetus at 4, 6, 12, 16, 20, 24, 28, 32, 36, and 38 weeks postconception.
Concepts for Lecture
1. Fetal Development: Week 4
• Beginning development of GI tract
• Heart is developing
• Somites develop—beginning vertebrae
• Heart is beating and circulating blood
• Eyes and nose begin to form
• Arm and leg buds present
2. Fetal Development: Week 6
• Trachea is developed
• Liver produces blood cells
• Trunk is straighter
• Digits develop
• Tail begins to recede
3. Fetal Development: Week 12
• Eyelids are closed
• Tooth buds appear
• Fetal heart tones can be heard
• Genitals are well-differentiated
• Urine is produced
• Spontaneous movement occurs
4. Fetal Development: Week 16
• Lanugo begins to develop
• Blood vessels are clearly developed
• Active movements are present
• Fetus makes sucking motions
• Swallows amniotic fluid
• Produces meconium
5. Fetal Development: Week 20
• Subcutaneous brown fat appears
• Quickening is felt by mother
• Nipples appear over mammary glands
• Fetal heartbeat is heard by fetoscope
6. Fetal Development: Week 24
• Eyes are structurally complete
• Vernix caseosa covers skin
• Alveoli are beginning to form
7. Fetal Development: Week 28
• Testes begin to descend
• Lungs are structurally mature
8. Fetal Development: Week 32
• Rhythmic breathing movements
• Ability to partially control temperature
• Bones are fully developed but soft and flexible
9. Fetal Development: Week 36
• Increase in subcutaneous fat
• Lanugo begins to disappear
10. Fetal Development: Week 38
• Skin appears polished
• Lanugo has disappeared except in upper arms and shoulders
• Hair is now coarse and approximately 1 inch in length
• Fetus is flexed
Review the embryonic heart formation and circulation and fetal circulation animations from the Prentice Hall Nursing MediaLink DVD-ROM.
Learning Objective 8
Identify the vulnerable periods during which malformations of the various organ systems may occur, and describe the resulting congenital malformations.
Concepts for Lecture
1. If the intrauterine environment is not favorable before cellular differentiation, all cells will be affected, resulting in slowed growth and spontaneous abortion. When differentiation is complete, the effect is on the cells undergoing the most rapid growth. The embryonic period is the most vulnerable period during which congenital malformations can occur because the organs are primarily formed during this period. Teratogens can be drugs, viruses, or chemicals. The maternal environment can also play a role in congenital malformations. Nutritional deficiencies can affect brain growth. Maternal hyperthermia in the first trimester can cause spontaneous abortion, CNS defects, and failure to close the neural tube.
Factors Influencing Development
• Quality of sperm or ovum
• Genetic code
• Adequacy of intrauterine environment
• Teratogens