Anatomy_1_of_2

Anatomy_1_of_2 - Anatomy 1 of 2 The structures shown in the...

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Unformatted text preview: Anatomy 1 of 2 The structures shown in the accompanying photomicrograph are derived from which of the following? A. A combination of fetal and maternal tissues B. Endometrial glands C. Endometrial stroma D. Fetal tissues E. Maternal blood vessels The answer is: D The placental structures shown in the photomicrograph are chorionic villi that are fetal tissues. The mother's contribution to the placenta is the blood that flows past the chorionic villi. A fertilized ovum reaches the uterus about four days after fertilization. At that time, it has developed into a multicellular, hollow sphere referred to as a blastocyst. The blastocyst soon adheres to the secretory endometrium and differentiates into an inner cell mass that will develop into the embryo and a layer of primitive trophoblast. The expanding trophoblast penetrates the surface endometrium and erodes into maternal blood vessels. Eventually, it develops two layers, an inner cytotrophoblast and an outer syncytiotrophoblast. Solid cords of trophoblast form the chorionic villi, which then are invaded by fetal blood vessels. 2. The secondary oocyte enters the second meiotic division and proceeds as far as metaphase. Which of the following is the stimulus required for continuation of the second meiotic division to produce the haploid ovum? A. Elevation of progesterone titers B. The environment of the oviduct and uterus C. Expulsion from the mature follicle D. Fertilization by a spermatozoon E. The presence of human chorionic gonadotropin (hCG) The answer is: D The secondary oocyte enters the second meiotic division just before ovulation and arrests at metaphase. Fertilization by a spermatozoon provides the stimulation for the division of chromatin to the haploid number. By the time the fertilized ovum reaches the uterus, the progesterone produced by the corpus luteum has initiated the secretory phase in the endometrium. Once implantation occurs and the chorion develops, human chorionic gonadotropin (hCG) is synthesized and the corpus luteum is maintained. 3. Which of the following is responsible for the prevention of polyspermy, the fertilization of an oocyte by more than one sperm? A. Resumption of the first meiotic division B. Resumption of the second meiotic division C. Capacitation D. The zona reaction E. The release of enzymes from the sperm acrosome The answer is: D On fusion of the first sperm with the oocyte cell membrane, the contents of secretory granules stored just beneath the oocyte membrane (cortical granules) are released (the zona reaction). Enzymes stored in these granules cause biochemical and electrical changes in the zona pellucida and the oocyte membrane that prevent the binding of additional sperm. Primitive female germ cells (oogonia) enter the first meiotic division during fetal development. This process becomes arrested in the metaphase stage until individual primary oocytes are hormonally induced to resume the first meiotic division during puberty and early adulthood (menarche to menopause). Fusion of the sperm and during puberty and early adulthood (menarche to menopause)....
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Anatomy_1_of_2 - Anatomy 1 of 2 The structures shown in the...

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