BRS Embryology - Week 1 Flashcards
A 20-year-old woman presents at the emer- gency department with severe abdominal pain on the right side with signs of internal bleeding. She indicated that she has been sex- ually active without contraception and missed her last menstrual period. Based on this infor- mation, which of the following disorders must be included as an option in the diagnosis?
(A) Ovarian cancer (B) Appendicitis (C) Normalpregnancy (D) Ectopic tubal pregnancy (E) Toxemiaofpregnancy
D.
Ectopic tubal pregnancy must always be an option in the diagnosis when a woman in her reproductive years presents with such symptoms. Ninety percent of ectopic implanta- tions occur in the uterine tube. Ectopic tubal pregnancies result in rupture of the uterine tube and internal hemorrhage, which presents a major threat to the woman’s life. The uterine tube and embryo must be surgically removed. The symptoms may sometimes be confused with appendicitis.
When does a secondary oocyte complete its second meiotic division to become a mature ovum?
(A) At ovulation (B) Before ovulation (C) Atfertilization (D) At puberty (E) Before birth
C.
At ovulation, a secondary oocyte begins meiosis II, but this division is arrested at metaphase. The secondary oocyte will remain arrested in metaphase until a sperm pene- trates it at fertilization. Therefore, the term “mature ovum’” is somewhat of a misnomer because it is a secondary oocyte that is fertilized, and, once fertilized, the new diploid cell is known as a zygote. If fertilization does not occur, the secondary oocyte degenerates.
How soon after fertilization occurs within the uterine tube does the blastocyst begin implantation?
(A) Within minutes (B) By 12 hours (C) By day 1 (D) By day 2 (E) By day 7
E.
The blastocyst begins implantation by day 7 after fertilization.
Where does the blastocyst normally implant?
(A) Functional layer of the cervix (B) Functional layer of the endometrium (C) Basallayeroftheendometrium (D) Myometrium (E) Perimetrium
B.
The blastocyst implants in the functional layer of the uterine endometrium. The uterus is composed of the perimetrium, myometrium, and endometrium. Two layers are identi- fied within the endometrium: (1) the functional layer, which is sloughed off at menstrua- tion, and (2) the basal layer, which is retained at menstruation and serves as the source of regeneration of the functional layer. During the progestational phase of the menstrual cycle, the functional layer undergoes dramatic changes; uterine glands enlarge and vascu- larity increases in preparation for blastocyst implantation.
Which of the following events is involved in cleavage of the zygote during week 1 of development?
(A) A series of meiotic divisions forming blastomeres
(B) Production of highly differentiated blastomeres
(C) An increased cytoplasmic content of blastomeres
(D) An increase in size of blastomeres
(E) A decrease in size of blastomeres
E.
Cleavage is a series of mitotic divisions by which the large amount of zygote cytoplasm is successively partitioned among the newly formed blastomeres. Although the number of blastomeres increases during cleavage, the size of individual blastomeres decreases until they resemble adult cells in size.
Which of the following structures must degenerate for blastocyst implantation to occur?
(A) Endometrium in progestational phase (B) Zona pellucida (C) Syncytiotrophoblast (D) Cytotrophoblast (E) Functional layer of the endometrium
B.
The zona pellucida must degenerate for implantation to occur. Early cleavage states of the blastula are surrounded by a zona pellucida, which prevents implantation in the uterine tube.
Which of the following is the origin of the mitochondrial DNA of all human adult cells?
(A) Paternal only (B) Maternal only (C) A combination of paternal and maternal (D) Either paternal or maternal (E) Unknown origin
B.
The mitochondrial DNA of all human adult cells is of maternal origin only. In human fertilization, the entire sperm enters the secondary oocyte cytoplasm. However, sperm mitochondria degenerate along with the sperm’s tail. Therefore, only mitochondria present within the secondary oocyte (maternal) remain in the fertilized zygote.
Individual blastomeres were isolated from a blastula at the 4-cell stage. Each blastomere was cultured in vitro to the blastocyst stage and individually implanted into four pseudo- pregnant foster mothers. Which of the follow- ing would you expect to observe 9 months later?
(A) Birth of one baby
(B) Birth of four genetically different babies
(C) Birth of four genetically identical babies
(D) Birth of four grotesquely deformed babies
(E) No births
C.
This scenario would result in four genetically identical children. Blastomeres at the 4- to 8-cell stage are totipotent, that is, capable of forming an entire embryo. Since blastomeres arise by mitosis of the same cell (zygote), they are genetically identical. This phenomenon is important in explaining monozygotic (identical) twins. About 30% of monozygotic twins arise by early separation of blastomeres. The remaining 70% originate at the end of week 1 of development by a splitting of the inner cell mass.
Embryonic carcinoma (EC) cells were isolated from a yellow-coated mouse with a teratocarcinoma. The EC cells were then microinjected into the inner cell mass of a blastocyst isolated from a black-coated mouse. The blastocyst was subsequently implanted into the uterus of a white-coated foster mouse. Which of the following would be observed after full-term pregnancy?
(A) A yellow-coated offspring (B) A black-coated offspring (C) A white-coated offspring (D) A yellow- and black-coated offspring (E) A yellow-and white-coated offspring
D.
This scenario would result in a yellow- and black-coated offspring. Because EC cells and inner cell mass cells have very similar biochemical characteristics, they readily mix with each other, and development proceeds unencumbered. Because the mixture contains cells with yellow-coat genotype and black-coat genotype, offspring with coats of two col- ors (yellow and black) will be produced. The offspring are known as mosaic mice.
In oogenesis, which of the following events occurs immediately following the completions of meiosis II?
(A) Degeneration of the zona pellucida (B) Sperm penetration of the corona radiata (C) Formation of a female pronucleus (D) Appearance of the blastocyst (E) Completion of cleavage
C.
The secondary oocyte is arrested in metaphase of meiosis II, and it will remain in this mei- otic stage until fertilization occurs. Following fertilization, the secondary oocyte completes meiosis II, forming a mature ovum and a polar body. The nucleus of the mature ovum is called the female pronucleus, which fuses with the male pronucleus to form a zygote.
