Nokea
Within minutes following a normal delivery, flow through the foramen ovale decreases dramatically. What is the cause of this change?
- A. Increased formation of prostaglandin E2 in the endocardium
- B. Increased rate of flow through the pulmonary artery
- C. Increased left atrial pressure
- D. Increased right atrial pressure
Correct Answer: C
Rationale: Step-by-step rationale for the correct answer (C):
1. After delivery, the baby takes its first breath, increasing oxygen levels.
2. This leads to the closure of the foramen ovale to shift blood flow from the right to the left side.
3. Increased left atrial pressure occurs due to increased blood returning from the lungs.
4. This pressure change causes the foramen ovale to close.
Summary of incorrect choices:
A: Increased prostaglandin E2 does not directly affect flow through the foramen ovale.
B: Increased flow through the pulmonary artery is expected after birth, but it does not directly impact the foramen ovale.
D: Increased right atrial pressure would not cause a decrease in flow through the foramen ovale.
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With respect to Sertoli cells which of the following statements is incorrect
- A. Nourish developing sperm
- B. receive stimulation by testosterone
- C. phagocytose defective sperm
- D. secrete the hormone inhibin which inhibits luteinizing hormone secretion
Correct Answer: D
Rationale: The correct answer is D because Sertoli cells do secrete inhibin, but it does not inhibit luteinizing hormone secretion. Inhibin actually inhibits follicle-stimulating hormone (FSH) secretion. Sertoli cells support spermatogenesis by nourishing developing sperm (A), they are stimulated by testosterone (B), and they also phagocytose defective sperm (C). Therefore, option D is incorrect as it misrepresents the role of inhibin in the endocrine regulation of the male reproductive system.
The spermatozoon is made up of:
- A. head;
- B. mid piece or neck;
- C. flagellum;
- D. body;
Correct Answer: A
Rationale: The correct answer is A: head. The spermatozoon is composed of three main parts: head, mid piece or neck, and flagellum. The head contains the nucleus which carries genetic material. The mid piece or neck contains mitochondria for energy production. The flagellum is responsible for sperm motility. In this question, the head is the most essential part of the spermatozoon as it contains the genetic material required for fertilization. The other choices (B: mid piece or neck, C: flagellum, D: body) are incorrect as they are important for sperm function but do not carry the genetic material necessary for fertilization.
Which of the following statements is incorrect?
- A. both luteinising hormone and follicle stimulating hormone are secreted by the hypothalamus
- B. testosterone stimulates sertoli cells
- C. luteinising hormone stimulates Leydig cells to make testosterone
- D. sertoli cells secrete inhibin
Correct Answer: A
Rationale: The correct answer is A because luteinising hormone (LH) and follicle stimulating hormone (FSH) are not secreted by the hypothalamus, but by the anterior pituitary gland. LH stimulates Leydig cells to produce testosterone, not the hypothalamus. Testosterone stimulates sertoli cells, not the other way around. Inhibin is indeed secreted by sertoli cells, but it does not relate to the incorrect statement regarding the origin of LH and FSH.
The tiny female sex cell that unites with male sperm to form a zygote or fertilized egg.
- A. Ovary
- B. Ovum
- C. Gonad
- D. Gamets
Correct Answer: B
Rationale: The correct answer is B: Ovum. The ovum is the mature female sex cell that unites with a male sperm during fertilization to form a zygote. Ovary (A) is the organ that produces eggs but is not the actual female sex cell. Gonad (C) is a general term for reproductive organs, not the specific female sex cell. Gametes (D) refer to both male and female sex cells, so it is a broad term and not the specific female sex cell. The ovum is the only choice that accurately represents the tiny female sex cell involved in fertilization.
How many seminiferous tubules are found in each lobule?
- A. 1-3
- B. 50-100
- C. 200-300
- D. 500 or more
Correct Answer: B
Rationale: The correct answer is B (50-100) because each lobule in the testis contains multiple seminiferous tubules where sperm production occurs. The average number of seminiferous tubules per lobule ranges from 50 to 100. This is supported by anatomical studies and research on testicular structure.
Explanation:
A: 1-3 - This is too low as each lobule contains more seminiferous tubules for efficient sperm production.
C: 200-300 - This is too high as it overestimates the number of seminiferous tubules per lobule.
D: 500 or more - This is excessive and not accurate based on scientific findings.
In summary, choice B is correct because it accurately reflects the typical range of seminiferous tubules per lobule, while the other choices either underestimate or overestimate this number.