Block 7 Fertilization & Pregnancy MCQ's

The hardening of the zona pellucida is responsible for polyspermy block during fertilization. The zona pellucida is a protective layer surrounding the oocyte. After the entry of the first sperm, the zona pellucida undergoes a process called cortical reaction, which involves the hardening of the zona pellucida. This hardening prevents any additional sperm from entering the oocyte, ensuring that only one sperm fertilizes the egg and avoids the formation of polyploid embryos.

Dynein and microtubules are the molecular machinery responsible for the motility of mature sperm. Dynein is a motor protein that moves along microtubules, causing them to slide past each other and generate the force needed for movement. Microtubules, on the other hand, are cylindrical structures made up of tubulin proteins that provide structural support and serve as tracks for dynein to move along. Together, dynein and microtubules play a crucial role in the flagellar movement of sperm, allowing them to swim and reach the egg for fertilization.

FSH (follicle-stimulating hormone) is the most suitable for the induction of superovulation in in-vitro fertilization. FSH stimulates the growth and development of multiple follicles in the ovaries, which increases the chances of successful fertilization and implantation. This hormone treatment helps to increase the number of eggs produced, improving the success rate of IVF procedures. An androgen antagonist, prednisone, progesterone, and a nonselective COX inhibitor are not typically used for superovulation induction in IVF.

The stratum basale is the deepest layer of the epidermis and is responsible for regenerating new skin cells. After menstruation, the surface epithelium of the uterus is shed and the cells in the stratum basale replace it by dividing and differentiating into new epithelial cells. Therefore, the statement "Contains cells that replace the surface epithelium after menstruation" is characteristic of the stratum basale.

High levels of progesterone suppress contractile activity of uterine smooth muscle. Progesterone is a hormone that is produced in large amounts during pregnancy. It acts as a muscle relaxant and inhibits the contraction of the uterine smooth muscle. This helps to maintain the quiescence of the uterus and prevent premature contractions. As progesterone levels decrease towards the end of pregnancy, the uterus becomes more sensitive to other hormones, such as oxytocin, which can then stimulate contractions.

The patient's history of severe bleeding postpartum, followed by large urine volumes and low plasma levels of estradiol, LH, and FSH, suggests a disruption in the hypothalamic-pituitary-gonadal axis. This axis is responsible for regulating the menstrual cycle and fertility. The most likely explanation for her infertility is loss of normal pituitary function, which can result in decreased secretion of LH and FSH, leading to anovulation and infertility. The other options (involution of the fallopian tubes, GnRH tumor, destruction of primordial follicles, hypersecretion of adrenal cortical hormones) do not explain the patient's symptoms and laboratory findings.

Kartagener's syndrome is a genetic disorder that affects the structure and function of cilia in the body. This syndrome is characterized by chronic respiratory problems, such as the inability to clear airways of mucus, which is seen in the patient's case. Kartagener's syndrome can also lead to infertility due to the impaired function of cilia in the reproductive organs, including the fallopian tubes and sperm cells. Therefore, it is likely that the patient's chronic respiratory problems and infertility are connected due to Kartagener's syndrome.

The lack of dynein may account for the apparent infertility problem in this patient. Dynein is a motor protein that is necessary for the movement of sperm. Without dynein, the sperm may have motility problems and be unable to swim properly, which can lead to infertility. This is supported by the fact that the patient's semen analysis showed that more than 50% of the sperm had motility problems. The other options, such as insufficient supply of FSH or inability of Leydig cells to respond to LH, do not directly explain the motility problems observed in the semen analysis.

The most likely reason for adding the low-dose oral contraceptive (OC) is to prevent bone loss. Leuprolide, a gonadotropin-releasing hormone agonist, can cause a decrease in estrogen levels, which can lead to bone loss. The low-dose OC contains estrogen and progestin, which can help maintain bone density and prevent osteoporosis. Additionally, the OC can also help regulate menstrual periods and prevent pregnancy during the treatment with leuprolide. However, the primary reason for adding the OC in this case is to prevent bone loss.

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Based on the information provided, the most likely option for this couple in terms of in vitro fertilization is intracytoplasmic sperm injection using Mr. K's sperm. This is because the semen analysis showed that more than 50% of the sperm had motility problems, indicating a potential issue with the sperm's ability to fertilize an egg naturally. Intracytoplasmic sperm injection involves directly injecting a single sperm into an egg to achieve fertilization. This method would bypass any potential motility issues and increase the chances of successful fertilization.

The most reasonable next step for this patient to continue to sustain reliable contraception with minimal adverse events would be to switch to a combined oral contraceptive (OC) with a higher dose of the estrogen (E) component. Breakthrough bleeding is a common side effect of low-dose combined OCs, and increasing the dose of estrogen can help to reduce this side effect. Switching to a progestin-only mini-pill or a depot progesterone method may not be as effective in preventing breakthrough bleeding. Switching to a combined OC with a different E component or a higher dose of the progestin (P) component may not address the issue of breakthrough bleeding.

Insulin is the least likely substance to cross the placenta from the mother's blood into the fetal circulation. Insulin is a large protein molecule that cannot easily pass through the placental barrier. The placenta selectively allows certain substances to pass through, such as glucose, carbon dioxide, and some hormones. However, larger molecules like insulin are generally unable to cross the placenta and reach the fetus.

Amniotic fluid is primarily derived from maternal blood, but it also includes contributions from the fetus. A reduced volume of amniotic fluid is indeed called Oligohydramnios. The fetus contributes urine to the amniotic fluid, and it swallows its own amniotic fluid to maintain the correct volume of fluid in the amnion. However, amniotic fluid does not contain nutrients and is not the main nutritional support for the fetus. The fetus receives its nutrients through the placenta.

Lateral folding is the correct answer because ectopia cordis or Pentalogy of Cantrell is a congenital malformation of the anterior body wall, which is formed during the process of lateral folding in embryonic development. Lateral folding involves the folding of the embryo's sides towards the midline, which results in the formation of the body wall and the positioning of organs within it. In the case of ectopia cordis, the defect in lateral folding leads to the heart being located outside the chest.

During the process of fertilization of an oocyte, oocyte cortical granules have the function of preventing polyspermy, which is the fertilization of an egg by multiple sperm. Their site of action is the zona pellucida, which is the protective layer surrounding the oocyte. The cortical granules release their contents into the zona pellucida, causing it to harden and form a barrier that prevents additional sperm from entering the oocyte.

The most likely explanation for the contraceptive action of the oral contraceptive pill containing a synthetic progestin is inadequate decidualization of the uterus. Progestins are synthetic hormones that mimic the actions of progesterone in the body. Progesterone is necessary for the development and maintenance of the uterine lining (endometrium) to support implantation of a fertilized egg. Inadequate decidualization of the uterus refers to the insufficient development of the endometrium, making it less receptive to implantation and reducing the chances of pregnancy. This is one of the mechanisms by which progestins prevent pregnancy.

After the twentieth week of gestation, the placental membrane is thinned and consists of three layers: syncytiotrophoblast, connective tissue of the villus, and fetal capillary endothelium. This arrangement allows for efficient exchange of nutrients and waste products between the maternal and fetal circulations. The syncytiotrophoblast layer is responsible for nutrient transfer, while the connective tissue of the villus provides structural support. The fetal capillary endothelium allows for the exchange of gases and other molecules. This arrangement ensures the proper development and nourishment of the fetus during pregnancy.