Chapter 26

Front 1

Define fertilization.

Back 1

Fertilization is the fusion of a secondary oocyte and a spermatozoon to form a zygote.

Front 2

How many chromosomes are contained within a human zygote?

Back 2

A normal human zygote contains 46 chromosomes.

Front 3

Why are numerous spermatozoa required to fertilize a secondary oocyte?

Back 3

Many spermatozoa are needed to achieve fertilization because one sperm does not contain enough acrosomal enzymes to erode the corona radiata surrounding the secondary oocyte.

Front 4

Identify the stage of development that results from cleavage.

Back 4

The morula is the stage of development that results from cleavage.

Front 5

What developmental stage begins once the zygote arrives in the uterine cavity?

Back 5

The blastocyst stage begins once the zygote arrives in the uterine cavity.

Front 6

Describe the blastocyst and its role in implantation.

Back 6

The blastocyst consists of an outer trophoblast and an inner cell mass. Implantation occurs when the blastocyst adheres to and then becomes enclosed within the uterine lining about 7 days after fertilization.

Front 7

Define gestation trophoblastic neoplasia.

Back 7

Gestation trophoblastic neoplasia is a tumor formed by undifferentiated, rapid growth of the syncytial trophoblast; if untreated, the neoplasm may become malignant.

Front 8

Describe gastrulation and the formation of the germ layers.

Back 8

Gastrulation is the formation of the primary germ layers- the endoderm, ectoderm, and mesoderm,- from the embryonci disc. It is from these germ layers that the body systems differentiate.

Front 9

What germ layer gives rise to nearly all body systems except the nervous and respiratory systems?

Back 9

The mesoderm gives rise to nearly all body systems except the nervous and respiratory systems.

Front 10

Name the four extra-embryonic membranes.

Back 10

The four extra-embryonic membranes are the yolk sac, amnion, allantois, and chorion.

Front 11

Which extra-embryonic membrane later gives rise to the urinary bladder?

Back 11

The base of the allantois gives rise to the urinary bladder.

Front 12

From which germ layers do the extra-embryonic membranes form, and what are each membrane's functions?

Back 12

The yolk sac forms from endoderm and mesoderm; it is an important site of blood cell formation. The amnion forms from the ectoderm and mesoderm; it encloses the fluid that surrounds and cushions the developing embryo and fetus. The allantois forms from endoderm and mesoderm; its base gives to the urinary bladder. The chorion forms from mesoderm and trophoblast; it surrounds the blastocoele.

Front 13

Describe the chorionic villi.

Back 13

The chorionic villi are structures that extend outward into the maternal tissues, forming an intricate, branching network through which maternal blood flows. Embryonic blood vessels extend into each chorionic villus.

Front 14

Compare the body stalk with the yolk stalk.

Back 14

The body stalk is the connection between the embryo and the chorion; it contains portions of the allantois and blood vessels that carry blood to and from the placenta. The yolk stalk is the connection between the endoderm of the embryo and the yolk sac.

Front 15

Identify the structure connecting the fetus to the placenta, and name the extra-embryonic membrane from which it is derived.

Back 15

The umbilical cord connects the fetus to the placenta, and it is derived from the allantois.

Front 16

Name the hormones synthesized by the syncytial trophoblast.

Back 16

The hormones synthesized by the syncytial trophoblast are human chorionic gonadotropin (hCG), human placental lactogen (hPL), relaxin, progesterone, and estrogens.

Front 17

The presence of which hormone in the urine provides a reliable indicator of pregnancy in home pregnancy tests?

Back 17

The presence of human chorionic gonadotropin (hCG) in the urine provides a reliable indicator of pregnancy.

Front 18

When does the placenta become sufficiently functional to continue the pregnancy?

Back 18

After the first trimester, the placenta is sufficiently functional to maintain the pregnancy.

Front 19

Define organogenesis.

Back 19

Organogenesis is the process of organ formation.

Front 20

Identify the main event in fetal development during the second trimester and third trimester.

Back 20

In the second trimester, the organ systems increase in complexity. During the third trimester, many of the organ systems become fully functional.

Front 21

During the trimester does the fetus undergo its largest absolute weight gain?

Back 21

During the third trimester, the fetus undergoes its largest weight gain.

Front 22

List the major changes that occur in maternal systems during pregnancy.

Back 22

The major changes that occur in maternal systems during pregnancy are increases in respiratory rate and tidal volume, blood volume, nutrient requirements, glomerular filtration rate (GFR), and the size of the uterus and mammary glands.

Front 23

Why does a mother's blood volume increase during pregnancy.

Back 23

A mother's blood volume increases during pregnancy to compensate for the reduction in maternal blood volume resulting from blood flow through the placenta.

Front 24

Based on the illustrations showing the locations of the internal organs in nonpregnant an pregnant women, explain why some women experience difficulty breathing while pregnant.

Back 24

Difficulty breathing in pregnant women results from the enlarged urerus pressing against the diaphragm and crowding the lungs.

Front 25

List and describe the factors involved in initiating labor contractions.

Back 25

Relaxin, produced by the placenta, softens the public symphysis and dilates the cervix, and the weight of the fetus deforms the exernal os of the uterus. Deformation of the cervix and rising estrogen levels promote the release of oxytocin, and the already stretching smooth muscles of the myometrium become even more excitable.

Front 26

What chemical are primarily responsible for initiating contractions of true labor?

Back 26

Estrogens and oxytocin stimulate the production of prostaglandins, which are then primarily responsible for the initiation of true labor.

Front 27

Name the three stages of labor, and describe the events that characterize each stage.

Back 27

The dilation stage begins with the onset of true labor, as the cervix dilates and the fetus begins to move toward the cervical canal; late in this stage, the amnion ruptures. The expulsion stage begins as the cervix dilates completely and continues until the fetus has completely emerged from the vagina (delivery). In the placental stage, the uterus gradually contracts, tearing the connections between the endometrium and the placenta and ejecting the placenta.

Front 28

What hormone causes the milk let-down reflex?

Back 28

oxytocin causes the milk let-down reflex.

Front 29

Explain the difference between colostrum and breast milk.

Back 29

Colostrum is produced by the mammary glands form the end of the sixth month of pregnancy until a few days after birth and contains antibodies. After that, the glands begin producing breast milk, which contains antibodies and lysozyme but has a higher fat content than colostrum.

Front 30

Name the stages of postnatal development, and describe the time frame involved for each of the stages.

Back 30

The postnatal stages development are the neonatal period, from birth to one month; infancy, form one month to age 2; childhood, form two until sexual maturation begins; adolescence, which begins with the onset of sexual maturation (puberty) between ages 9-14 and ends when growth in body size ends (around 18 years); and maturity, which includes the rest of the individual's life. A final stage called senescence, or aging, overlaps with maturity.

Front 31

Name the three major interacting hormonal events associated with the onset of puberty.

Back 31

The three interacting hormonal events associated with the onset of puberty are (1) increased GnRH production by the hypothalamus; (2) increased sensitivity to GnRH by the anterior lobe of the pituitary gland, and a rapid increase in circulating levels of FSH and LH; and (3) increased sensitivity to FSH and LH by ovarian and testicular cells.

Front 32

Why do males have deeper voices and larger larynxes than females?

Back 32

Males have deeper voices and larger larynxes than do females because testosterone stimulates laryngeal development in males to a greater extent than estrogen stimulates laryngeal development in females.

Front 33

Why are premenopausal women at lesser risk of atherosclerosis than men?

Back 33

The higher estrogen levels in premenopausal women (compared to adult men) cause reductions in plasma cholesterol levels, thereby slowing cholesterol levels, thereby slowing plaque formation and lowering the risk of atherosclerosis.

Front 34

Describe homozygous and heterozygous.

Back 34

Homozygous means that homologous chromosomes carry the same allele of a given gene; heterozygous means that homologous chromosomes carry different alleles of a given gene.

Front 35

Differentiate between simple inheritance an polygenic inheritance.

Back 35

In simple inheritance, phenotypic characteristics are determined by interactions between a single pair of alleles; polygenic inheritance involves interactions among alleles of several genes.

Front 36

The trait "curly hair" operates through strict dominance. What would be the phenotype of a person who is heterozygous for this trait?

Back 36

The phenotype of a person who is heterozygous for curly hair- that is, a person with one dominant allele and one recessive allele for that trait- would be "curly hair."

Front 37

Compare strict dominance with codominance.

Back 37

In strict dominance, one allele dominates the other, so an individual who is heterozygous for a given trait exhibits the dominant phenotype; in codominance, an individual who is heterozygous for a given trait exhibits both of the phenotypes for that trait.

Front 38

Why are X-linked traits expressed more frequently in males than females?

Back 38

X-linked traits are expressed more frequently in males because males have a Y chromosome that has no corresponding allele.

Front 39

Indicate the type of inheritance involved in each of the following situations: (1) children who exhibit the trait have at least one percent who also exhibits it; (2) children exhibit the trait even though parent exhibits it; and (3) the trait is expressed equally in daughters and sons.

Back 39

(1) simple inheritance (dominant); (2) simple inheritance (recessive); (3) autosomal inheritance

Front 40

Define single nucleotide polymorphism.

Back 40

A single nucleotide polymorphism is a variation in a single base pair in a DNA sequence.

Front 41

Name the disorder characterized by each of the following chromosome patterns: (1) XO and (2) XXY.

Back 41

(1) XO: Turner syndrome;
(2) XXY: Klinefelter syndrome

Front 42

Identify the chromosome involved in each of the following disorders: (1) ovarian cancer, (2) Tay-Sachs disease, and (3) spinocerebellar ataxia.

Back 42

(1) ovarian cancer: chromosome 9; (2) Tay-Sachs disease: chromosome 15; (3) spinocerebellar ataxia: chromosome 6