Gametogenesis and Fertilization — MCQs
Primordial germ cells are derived from:
A 23-year-old woman accompanied by her mother-in-law comes to the infertility clinic. She has been having regular intercourse for 6 months but is not able to conceive. What is the next best step?
After injecting testosterone in a hypoandrogenic male, which of the following occurs ?
Ovulation is influenced by
Which of the following inhibit gonadotropin-releasing hormone pulse secretion?
All are steps of GIFT, except:
Statement 1 - A 59-year-old patient presents with flaccid bullae. Histopathology shows a suprabasal acantholytic split. Statement 2 - The row of tombstones appearance is diagnostic of Pemphigus vulgaris.
After ovulation, the oocyte is:
What is the duration of embryogenesis in human development?
Regarding “conjoined twins”, which of the following statements is/are true? 1. These are always monozygotic 2. These result when division occurs before the embryonic disc is formed 3. Most common variety is thoracopagus Select the correct answer using the code given below:
Gametogenesis and Fertilization Indian Medical PG Practice Questions and MCQs
Question 1: Primordial germ cells are derived from:
- A. Neural crest
- B. Genital ridge
- C. Somatopleuritic mesoderm
- D. Yolk sac (Correct Answer)
Explanation: ***Yolk sac*** - **Primordial germ cells (PGCs)** arise from **epiblast** cells but are first identifiable in the wall of the **yolk sac** during the **3rd week** of development. - From the yolk sac, they migrate during the **4th-6th week** through the dorsal mesentery to reach the developing **genital ridges** (gonads) where they form **gametes** [2]. - The yolk sac is considered the site where PGCs are recognized and begin their journey to the gonads. *Neural crest* - Neural crest cells are multipotent cells that migrate to various locations and differentiate into structures like **neurons**, **glial cells**, **melanocytes**, and **facial cartilage**, not germ cells. - They arise from the dorsal part of the **neural tube** during neurulation. *Genital ridge* - The genital ridge is the embryonic structure that develops into the **gonads** (testes or ovaries) [1]. - Primordial germ cells migrate *to* the genital ridge, but they do not originate *from* it — it is their destination, not their source. *Somatopleuritic mesoderm* - **Somatopleuritic mesoderm** (somatic mesoderm) forms the **parietal layer** of serous membranes, the dermis of the body wall, and the skeletal elements of the limbs. - It does not give rise to **primordial germ cells**.
Question 2: A 23-year-old woman accompanied by her mother-in-law comes to the infertility clinic. She has been having regular intercourse for 6 months but is not able to conceive. What is the next best step?
- A. Hysterolaparoscopy
- B. Diagnostic hysteroscopy
- C. Reassure and review the couple after 6 months (Correct Answer)
- D. Semen analysis for husband
Explanation: ***Reassure and review the couple after 6 months*** - Infertility is defined as the inability to conceive after **12 months** of regular, unprotected intercourse in women under 35 years old. For women aged 35 or older, this period is 6 months. - Since the patient is 23 years old and has been trying for only 6 months, she does not yet meet the diagnostic criteria for infertility. The appropriate action is to advise them to continue trying and to return for evaluation if conception does not occur after a full year. *Semen analysis for husband* - While a semen analysis is a crucial initial step in an infertility workup, it is premature at this stage given the duration of attempted conception. - It would be appropriate to order this test after the couple has met the criteria for infertility (12 months for women under 35). *Hysterolaparoscopy* - This is an invasive procedure typically reserved for more advanced stages of an infertility workup, especially when suspected pathologies like endometriosis or tubal factor infertility are present. - It is not indicated as an initial step for a couple who has only been trying to conceive for 6 months and does not yet meet the definition of infertility. *Diagnostic hysteroscopy* - A diagnostic hysteroscopy is used to visualize the inside of the uterus to identify intrauterine pathologies that could contribute to infertility. - Like hysterolaparoscopy, it is an invasive diagnostic tool and should only be considered after initial, less invasive investigations have been performed and the couple meets the criteria for infertility.
Question 3: After injecting testosterone in a hypoandrogenic male, which of the following occurs ?
- A. Decreased LH secretion
- B. Decreased FSH secretion (Correct Answer)
- C. Increased spermatogenesis
- D. None of the options
Explanation: ***Decreased FSH secretion*** - Exogenous testosterone administration leads to **negative feedback** on the hypothalamic-pituitary-gonadal axis, suppressing **GnRH** release, which in turn decreases both **LH** and **FSH** secretion. - FSH suppression is particularly clinically significant because it results in **inhibition of spermatogenesis**, which is a key consideration when using testosterone replacement therapy. - The decrease in FSH, combined with reduced **intratesticular testosterone** (due to LH suppression), impairs Sertoli cell function and sperm production. *Decreased LH secretion* - **This also occurs** with exogenous testosterone administration due to negative feedback on the hypothalamus and pituitary. - Testosterone primarily suppresses **LH** through direct negative feedback at the hypothalamic-pituitary level. - However, in the context of this question focusing on the consequences in a hypoandrogenic male receiving testosterone, the **FSH suppression** and its impact on spermatogenesis is the more clinically emphasized outcome. - **Note:** Both LH and FSH decrease; this question likely emphasizes FSH due to its role in fertility concerns with testosterone therapy. *Increased spermatogenesis* - This is **incorrect**. Exogenous testosterone actually **suppresses spermatogenesis** through multiple mechanisms: - Decreased **FSH** (essential for Sertoli cell function) - Decreased **intratesticular testosterone** concentration (despite high systemic levels) - The high local testosterone concentration within the seminiferous tubules (30-100x serum levels) cannot be achieved by systemic testosterone alone. *None of the options* - This is incorrect because exogenous testosterone administration clearly causes **suppression of gonadotropins** (both LH and FSH) through well-established negative feedback mechanisms.
Question 4: Ovulation is influenced by
- A. LH+FSH
- B. LH (Correct Answer)
- C. FSH
- D. GnRH
Explanation: ***LH*** - A surge in **luteinizing hormone (LH)** is the primary trigger for ovulation, inducing the final maturation of the oocyte and rupture of the dominant follicle. - The **LH surge** leads to the release of the ovum from the ovary, typically occurring about 24-36 hours after its onset. *LH+FSH* - While both **LH** and **FSH** are essential for follicular development, the *final act of ovulation itself is primarily driven by the LH surge*, not a combined surge of both. - **FSH** mainly promotes the growth of ovarian follicles in the early to mid-follicular phase. *FSH* - **Follicle-stimulating hormone (FSH)** is crucial for the *development and maturation* of ovarian follicles but does not directly trigger the release of the egg. - High levels of **FSH** alone do not induce ovulation; its role is completed before the actual ovulatory event. *GnRH* - **Gonadotropin-releasing hormone (GnRH)** is released from the hypothalamus and stimulates the pituitary gland to release **LH** and **FSH**. - **GnRH** is a precursor to the release of LH and FSH, but it does not directly act on the ovary to cause ovulation.
Question 5: Which of the following inhibit gonadotropin-releasing hormone pulse secretion?
- A. Prolactin (Correct Answer)
- B. Oxytocin
- C. Thyroxine
- D. Insulin
Explanation: ***Prolactin*** - Elevated levels of **prolactin** inhibit the pulsatile secretion of **gonadotropin-releasing hormone (GnRH)** from the hypothalamus. - This inhibition leads to decreased production of **luteinizing hormone (LH)** and **follicle-stimulating hormone (FSH)** from the pituitary, ultimately affecting gonadal function. *Thyroxine* - **Thyroxine** (thyroid hormone) primarily regulates metabolism and growth, and while it interacts with the reproductive axis, its direct effect is not typically the **inhibition of GnRH pulse secretion**. - Extreme thyroid dysfunction can indirectly impact reproductive hormones, but it's not the primary mechanism of GnRH inhibition. *Oxytocin* - **Oxytocin** is largely involved in **uterine contractions** during labor and **milk ejection** during lactation, and has roles in social bonding. - It does not directly inhibit the pulsatile release of **GnRH**. *Insulin* - **Insulin** is a key hormone in **glucose metabolism** and energy regulation. - While insulin resistance and hyperinsulinemia can affect reproductive function (e.g., in polycystic ovary syndrome, PCOS), it does not **directly inhibit GnRH pulse secretion**.
Question 6: All are steps of GIFT, except:
- A. Transfer of unfertilized egg into the fallopian tube
- B. Fertilization of oocyte in lab (Correct Answer)
- C. Ovulation stimulation
- D. Oocyte retrieval
Explanation: ***Fertilization of oocyte in lab*** - **Gamete intrafallopian transfer (GIFT)** involves the transfer of both sperm and eggs directly into the fallopian tube, where **fertilization occurs naturally** within the body. - The step of **fertilization in the lab** (in vitro fertilization) is characteristic of **IVF**, not GIFT. *Transfer of unfertilized egg into the fallopian tube* - In GIFT, **harvested eggs** (oocytes) are mixed with sperm and then immediately **transferred into the fallopian tube**. - This allows natural fertilization to occur within the woman's body, which is a key distinction of GIFT from IVF. *Ovulation stimulation* - Before GIFT, women undergo **controlled ovarian hyperstimulation** to produce multiple mature follicles and increase the chances of successful egg retrieval. - This process is essential for obtaining a sufficient number of **oocytes** for transfer. *Oocyte retrieval* - Once the follicles are mature, **oocytes are retrieved** from the ovaries, typically through transvaginal ultrasound-guided aspiration. - These retrieved oocytes are then prepared for transfer along with sperm into the fallopian tubes.
Question 7: Statement 1 - A 59-year-old patient presents with flaccid bullae. Histopathology shows a suprabasal acantholytic split. Statement 2 - The row of tombstones appearance is diagnostic of Pemphigus vulgaris.
- A. Statements 1 & 2 are correct, 2 is not explaining 1 (Correct Answer)
- B. Statements 1 and 2 are correct and 2 is the correct explanation for 1
- C. Statements 1 and 2 are incorrect
- D. Statement 1 is incorrect
Explanation: ***Correct: Statements 1 & 2 are correct, 2 is not explaining 1*** **Analysis of Statement 1:** - A 59-year-old patient with **flaccid bullae** and **suprabasal acantholytic split** on histopathology is the classic presentation of **Pemphigus vulgaris** - The flaccid (easily ruptured) nature of bullae distinguishes it from tense bullae seen in bullous pemphigoid - The suprabasal location of the split (just above the basal layer) with acantholysis (loss of cell-to-cell adhesion) is pathognomonic - **Statement 1 is CORRECT** ✓ **Analysis of Statement 2:** - The **"row of tombstones" or "tombstone appearance"** is indeed a diagnostic histopathological feature of Pemphigus vulgaris - This appearance results from basal keratinocytes remaining attached to the basement membrane while suprabasal cells separate due to acantholysis - The intact basal cells standing upright resemble a row of tombstones - **Statement 2 is CORRECT** ✓ **Does Statement 2 explain Statement 1?** - Statement 2 describes a **histopathological appearance** (tombstone pattern) that is a **consequence** of the suprabasal split - However, it does NOT explain the **underlying cause** of the flaccid bullae or the suprabasal split - The true explanation involves **IgG autoantibodies against desmoglein 3 (and desmoglein 1)**, which attack intercellular adhesion structures (desmosomes), causing **acantholysis** - Therefore, **Statement 2 does NOT explain Statement 1** ✗ *Incorrect: Statement 2 is the correct explanation for Statement 1* - While both statements describe features of Pemphigus vulgaris, the tombstone appearance is a descriptive finding, not an explanatory mechanism *Incorrect: Statements 1 and 2 are incorrect* - Both statements are medically accurate descriptions of Pemphigus vulgaris features *Incorrect: Statement 1 is incorrect* - Statement 1 correctly describes the cardinal clinical and histopathological features of Pemphigus vulgaris
Question 8: After ovulation, the oocyte is:
- A. Primary oocyte arrested in prophase II
- B. Secondary oocyte arrested in prophase II
- C. Secondary oocyte arrested in metaphase II (Correct Answer)
- D. Primary oocyte arrested in prophase I
Explanation: ***Secondary oocyte arrested in metaphase II*** - After ovulation, the **oocyte** has completed **meiosis I** and extruded the **first polar body**, becoming a secondary oocyte. - It then arrests in **metaphase II** and will only complete meiosis II upon fertilization by a sperm. *Primary oocyte arrested in prophase II* - A **primary oocyte** is the stage before meiosis I is completed, and it is arrested in **prophase I** at birth, not prophase II. - Oocytes do not arrest in **prophase II** during normal meiotic development. *Secondary oocyte arrested in prophase II* - While it is a **secondary oocyte** that is ovulated, it is arrested in **metaphase II**, not prophase II. - **Prophase II** is a transient stage that occurs just before metaphase II, and arrest at this stage is not typical for the ovulated oocyte. *Primary oocyte arrested in prophase I* - This describes the state of the oocyte from **fetal development** until just before ovulation. - A **primary oocyte** completes meiosis I only in response to the **LH surge** before ovulation.
Question 9: What is the duration of embryogenesis in human development?
- A. From fertilization to the twelfth week
- B. From the second week to the eighth week
- C. From fertilization to the tenth week
- D. From fertilization to the eighth week (Correct Answer)
Explanation: ***From fertilization to the eighth week*** - **Embryogenesis** is the period during which the major **organ systems develop** [1]. - This critical phase begins at **fertilization** and extends through approximately the **eighth week of gestation** [1]. - The eighth week marks the end of the embryonic period, after which the **fetal period** begins [2]. *From the second week to the eighth week* - This period correctly identifies the **end of embryogenesis** but incorrectly states the **beginning**. - The first week post-fertilization involves **cleavage, morula, and blastocyst formation**, which are essential initial steps of embryonic development. - Excluding the first week misses critical early embryonic events. *From fertilization to the tenth week* - This duration is **too long** for embryogenesis, as the **ninth week marks the beginning of the fetal period** [1], [2]. - The fetal period is characterized by **growth and maturation** of already formed organ systems rather than organogenesis [2]. *From fertilization to the twelfth week* - This period is also **too long** for embryogenesis, encompassing a significant portion of the **fetal period**. - By the twelfth week, most major structures are already established and are undergoing further **development and growth**, not organogenesis.
Question 10: Regarding “conjoined twins”, which of the following statements is/are true? 1. These are always monozygotic 2. These result when division occurs before the embryonic disc is formed 3. Most common variety is thoracopagus Select the correct answer using the code given below:
- A. 1 and 2 only
- B. 2 and 3 only
- C. 1, 2 and 3
- D. 1 and 3 only (Correct Answer)
Explanation: ***1 and 3 only*** - **Identical (monozygotic)** twins are always conjoined because they develop from a single fertilized egg that imperfectly separates. - **Incomplete division** of the embryonic disc after 13 days from fertilization causes conjoined twins [1]. **Thoracopagus** is the most common type, where twins are joined at the chest [1, 2]. *1 and 2 only* - Conjoined twins are indeed **monozygotic**, but the timing of division is typically *after* the embryonic disc is formed, not before [1]. - Division *before* the embryonic disc forms would usually lead to separate monozygotic twins [1]. *2 and 3 only* - While **thoracopagus** is the most common variety [2], statement 2 regarding the timing of division is incorrect. - Conjoined twins are a result of incomplete separation *after* the formation of the embryonic disc, typically around 13-15 days post-fertilization [1]. *1, 2 and 3* - This option incorrectly states that division occurs *before* the embryonic disc is formed. - The formation of conjoined twins results from an *incomplete* splitting of the **monozygotic embryo** *after* the embryonic disc has already begun to differentiate [1].
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