Nokea
Why do infants born at 25 weeks' gestation have a poor survival rate?
- A. Cardiac development is incomplete.
- B. Fetal lung alveoli are not present in sufficient numbers.
- C. Gastrointestinal development is incomplete.
- D. Sucking reflex is not present.
Correct Answer: B
Rationale: The correct answer is B because infants born at 25 weeks' gestation have a poor survival rate due to insufficient numbers of fetal lung alveoli. This leads to respiratory distress and difficulty in oxygen exchange, impacting their chances of survival. Choice A is incorrect as cardiac development is not the primary factor affecting survival. Choice C is incorrect as gastrointestinal development does not directly impact survival at this stage. Choice D is incorrect as the sucking reflex is not a critical factor in survival compared to respiratory function.
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Match each term with its description. Trophoblast
- A. None
- B. None
- C. Fertilized ovum.
- D. None
Correct Answer: C
Rationale: Trophoblast develops into the placenta.
The time period immediately following fertilization results in which circumstance?
- A. Formation of a zygote that contains the haploid number of chromosomes
- B. Formation of an embryo that contains the haploid number of chromosomes
- C. Formation of a zygote that contains the diploid number of chromosomes
- D. Formation of a 16-cell morula
Correct Answer: C
Rationale: The correct answer is C: Formation of a zygote that contains the diploid number of chromosomes. After fertilization, the sperm and egg combine to form a zygote with a complete set of chromosomes (diploid). This is crucial for genetic diversity and proper development.
Choice A is incorrect because a zygote is diploid, not haploid. Choice B is incorrect as an embryo is formed later in development and contains diploid chromosomes. Choice D is incorrect because a morula is a stage where the zygote undergoes several rounds of cell division, but it does not yet contain a full diploid set of chromosomes.
A 37-year-old patient is being seen for her first OB appointment after having a positive pregnancy test at home. She thinks she is about 6 weeks pregnant. She and her husband have been trying to conceive for 7 years, and she has a history of three spontaneous abortions. What antepartum testing do you anticipate the provider ordering at today’s visit?
- A. a vaginal ultrasound to confirm gestation age, due date, and pregnancy viability
- B. maternal assay blood tests to screen for genetic and chromosomal disorders
- C. a nuchal translucency ultrasound
- D. an integrated screen blood test
Correct Answer: A
Rationale: The correct answer is A: a vaginal ultrasound to confirm gestation age, due date, and pregnancy viability. At the first OB appointment, confirming gestational age and viability is crucial, especially for a patient with a history of spontaneous abortions. This ultrasound will help determine the accurate due date and assess the viability of the pregnancy. Maternal assay blood tests for genetic and chromosomal disorders (choice B) are usually done later in the pregnancy, around 10-13 weeks. Nuchal translucency ultrasound (choice C) and integrated screen blood test (choice D) are typically done between 11-14 weeks and are not usually ordered at the first OB appointment.
What protects the blood vessels in a healthy umbilical cord?
- A. None
- B. Wharton's jelly.
- C. None
- D. None
Correct Answer: B
Rationale: Wharton's jelly provides structural support and protection.
What is the point after which an ovum is fertilized and becomes impenetrable to any other sperm?
- A. The zona reaction
- B. Gametogenesis
- C. The zona pellucida
- D. Cleavage
Correct Answer: A
Rationale: The correct answer is A: The zona reaction. After fertilization, the zona pellucida undergoes a biochemical change called the zona reaction, which makes the ovum impenetrable to any other sperm. This process prevents polyspermy and ensures that only one sperm can fertilize the egg. Gametogenesis refers to the production of gametes, not the post-fertilization event. The zona pellucida is the glycoprotein layer around the ovum, and cleavage is the rapid mitotic cell division that follows fertilization, but neither of these directly relate to the ovum becoming impenetrable to other sperm.