Answers to Clinical Vignettes and Review Questions

Clinical Vignette

• 3.

  Although most tissues of the body are affected to some extent, the heart is not a primary target tissue of ovarian steroid hormones.

Review Questions

• 1.

  D

• 2.

  E

• 3.

  B

• 4.

  A mediastinal teratoma, which is likely to have arisen from an aberrant primordial germ cell that became lodged in the connective tissue near the heart.

• 5.

  In the female, meiosis begins during embryonic life; in the male, meiosis begins at puberty.

• 6.

  At prophase (diplotene stage) of the first meiotic division and at metaphase of the second meiotic division.

• 7.

  Chromosomal abnormalities, such as polyploidy or trisomies of individual chromosomes.

• 8.

  Spermatogenesis is the entire process of sperm formation from a spermatogonium. It includes the two meiotic divisions and the period of spermiogenesis. Spermiogenesis, or sperm metamorphosis, is the process of transformation of a postmeiotic spermatid, which looks like an ordinary cell, to a highly specialized spermatozoon.

• 9.

  Estrogens, secreted by the ovary, support the preovulatory proliferative phase. From the time of ovulation, progesterone is secreted in large amounts by the corpus luteum and is responsible for the secretory phase, which prepares the endometrium for implantation of an embryo.

• 10.

  Follicle-stimulating hormone (FSH) produced by the anterior lobe of the pituitary gland and testosterone produced by the Leydig cells of the testis.

Clinical Vignette

• 1.

  Before the plane crash, the issue is who is the “real” mother. After the crash, the issue is who gets the money—the surrogate mother who claims that she is the real mother or the aunt who claims a blood affinity. Although these present as legal issues that would likely be decided in a court, the concept of what is meant by surrogacy also involves psychological and religious issues.

• 2.

  This is a very important issue that has not been resolved. If the parents were of a religion that strongly supports the rights of embryos to life, should the remaining embryos also be implanted into someone, and, if so, into whom? In a case where a considerable inheritance is involved, the financial implications could cloud the issue. If there were no parental money, who would undergo the risk and the expense to prevent the frozen embryos from being simply thrown out? In many cases of in vitro fertilization and embryo transfer, the question of what to do with the “extra” frozen embryos when the first transfer is successful is a real one. Many frozen embryos are stored at various sites around the world.

Review Questions

• 1.

  E

• 2.

  D

• 3.

  The sharp surge of luteinizing hormone produced by the anterior lobe of the pituitary gland.

• 4.

  Capacitation is a poorly understood interaction between a spermatozoon and female reproductive tissues that increases the ability of the sperm to fertilize an egg. In some mammals, capacitation is obligatory, but in humans the importance of capacitation is less well established.

• 5.

  Fertilization usually occurs in the upper third of the uterine tube.

• 6.

  The ZP ₃ protein acts as a specific sperm receptor through its O-linked oligosaccharides; much of its polypeptide backbone must be exposed to stimulate the acrosomal reaction.

• 7.

  Polyspermy is the fertilization of an egg by more than one spermatozoon. It is prevented through the fast electrical block on the plasma membrane of the egg and by the later zona reaction, by which products released from the cortical granules act to inactivate the sperm receptors in the zona pellucida.

• 8.

  She had probably taken clomiphene for the stimulation of ovulation. Natural septuplets are almost never seen.

• 9.

  The introduction of more than one embryo into the tube of the woman is common because the chance that any single implanted embryo will survive to the time of birth is quite small. The reasons for this are poorly understood. Extra embryos are frozen because if a pregnancy does not result from the first implantation, the frozen embryos can be implanted without the inconvenience and expense of obtaining new eggs from the mother and fertilizing them in vitro.

• 10.

  In cases of incompatibility between the sperm and egg, poor sperm motility, or deficient sperm receptors in the zona, introducing the sperm directly into or near the egg can bypass a weak point in the reproductive sequence of events.

• 11.

  The sperm protein ligand IZUMO1 and its receptor JUNO on the oolemma of the egg.

Review Questions

• 1.

  A homeobox is a highly conserved region consisting of 180 nucleotides that is found in many morphogenetically active genes. Homeobox gene products act as transcription factors.

• 2.

  B

• 3.

  In contrast to many receptors, the receptors for retinoic acid (α, β, and γ) are located in the nucleus.

• 4.

  A

• 5.

  D

• 6.

  D

• 7.

  E

Clinical Vignette

She had an ectopic pregnancy in her right uterine tube. With the rapidly increasing size of the embryo and its extraembryonic structures, her right uterine tube had ruptured.

Review Questions

• 1.

  D

• 2.

  E

• 3.

  A

• 4.

  C

• 5.

  The embryonic body proper arises from the inner cell mass.

• 6.

  Trophoblastic tissue.

• 7.

  They allow the trophoblast of the embryo to adhere to the uterine epithelium.

• 8.

  Cells derived from the cytotrophoblast fuse to form the syncytiotrophoblast.

• 9.

  In addition to the standard causes of lower abdominal pain, such as appendicitis, the physician should consider ectopic pregnancy (tubal variety) as a result of stretching and possible rupture of the uterine tube containing the implanted embryo.

• 10.

  They maintain the cell in an undifferentiated state.

Clinical Vignette

• 3.

  Because of the respiratory problems associated with his situs inversus, this man probably has a mutation of a dynein gene. Commonly, such individuals also have immotile spermatozoa, a condition that would lead to infertility.

Review Questions

• 1.

  D

• 2.

  A

• 3.

  B

• 4.

  B

• 5.

  C

• 6.

  The epiblast.

• 7.

  The primitive node acts as the organizer of the embryo. Through it pass the cells that become the notochord. The notochord induces the formation of the nervous system. The primitive node is also the site of synthesis of morphogenetically active molecules, such as retinoic acid. If a primitive node is transplanted to another embryo, it stimulates the formation of another embryonic axis.

• 8.

  Hyaluronic acid and fibronectin.

• 9.

  Vg1 and activin.

• 10.

  Cell adhesion molecules are lost in a migratory phase. When the migratory cells settle down, they may reexpress cell adhesion molecules.

• 11.

  Nanog in the epiblast. Gata-6 in the hypoblast.

Review Questions

• 1.

  B

• 2.

  C

• 3.

  E

• 4.

  C

• 5.

  A

• 6.

  A change in cell shape at the median hinge point and pressures of the lateral ectoderm acting to push up the lateral walls of the neural plate.

• 7.

  Neuromeres provide the fundamental organization of parts of the brain in which they are present. Certain homeobox genes are expressed in a definite sequence along the neuromeres.

• 8.

  The somites. Axial muscles form from cells derived from the medial halves of the somites, and limb muscles arise from cellular precursors located in the lateral halves of the somites.

• 9.

  In blood islands that arise from mesoderm of the wall of the yolk sac.

• 10.

  A, B, D