Male sexual physiology US Medical PG Practice Questions and MCQs
Practice US Medical PG questions for Male sexual physiology. These multiple choice questions (MCQs) cover important concepts and help you prepare for your exams.
Male sexual physiology US Medical PG Question 1: Fertilization begins when sperm binds to the corona radiata of the egg. Once the sperm enters the cytoplasm, a cortical reaction occurs which prevents other sperm from entering the oocyte. The oocyte then undergoes an important reaction. What is the next reaction that is necessary for fertilization to continue?
- A. The second meiotic division (Correct Answer)
- B. Degeneration of the sperm tail
- C. Release of a polar body
- D. Formation of the spindle apparatus
- E. Acrosome reaction
Male sexual physiology Explanation: ***The second meiotic division***
- Upon **sperm penetration**, the secondary oocyte completes its **meiosis II**, forming a mature ovum and a second polar body.
- This completion of meiosis II is a critical step for the pronuclear fusion and subsequent **zygote formation**.
*Degeneration of the sperm tail*
- While the sperm tail does degenerate within the ooplasm, it occurs **after** the genetic material has been released and is not the immediate next critical reaction for continued fertilization.
- This is a process of degradation and assimilation, not an active cellular reaction of the oocyte vital for fertilization progression.
*Release of a polar body*
- The first polar body is released **before fertilization** (at the completion of meiosis I), and the second polar body is released **concomitantly with the completion of meiosis II**, which is the required reaction.
- Releasing a polar body is a consequence of meiotic division, not an independent reaction that drives fertilization forward.
*Formation of the spindle apparatus*
- The **spindle apparatus** is formed during both meiotic divisions to separate chromosomes, but its formation itself is not the immediate "next reaction" necessary for fertilization to continue after cortical reaction.
- The key event is the progression of meiosis, which the spindle facilitates, not the mere formation of the apparatus.
*Acrosome reaction*
- The **acrosome reaction** occurs **before** the sperm binds to the zona pellucida and penetrates the oocyte, enabling the release of enzymes to digest the egg's outer layers.
- This reaction has already taken place for the sperm to have entered the oocyte and initiated the cortical reaction.
Male sexual physiology US Medical PG Question 2: A 58-year-old man comes to the physician for a 2-month history of increased urinary frequency. Urodynamic testing shows a urinary flow rate of 11 mL/s (N>15) and a postvoid residual volume of 65 mL (N<50). Prostate-specific antigen level is 3.2 ng/mL (N<4). Treatment with a drug that also increases scalp hair regrowth is initiated. Which of the following is the most likely mechanism of action of this drug?
- A. Gonadotropin-releasing hormone receptor agonism
- B. Decreased conversion of hydroxyprogesterone to androstenedione
- C. Decreased conversion of testosterone to dihydrotestosterone (Correct Answer)
- D. Decreased conversion of testosterone to estradiol
- E. Selective alpha-1A/D receptor antagonism
Male sexual physiology Explanation: ***Decreased conversion of testosterone to dihydrotestosterone***
- The patient's symptoms (urinary frequency), urodynamic findings (low flow rate, elevated postvoid residual), and slightly elevated PSA are consistent with **benign prostatic hyperplasia (BPH)**.
- A drug that treats BPH and also increases **scalp hair regrowth** is a **5α-reductase inhibitor** (e.g., finasteride), which works by blocking the conversion of testosterone to dihydrotestosterone (DHT), the primary androgen responsible for prostate growth and androgenetic alopecia.
*Gonadotropin-releasing hormone receptor agonism*
- GnRH agonists (e.g., leuprolide) are used for advanced **prostate cancer** by initially stimulating and then desensitizing GnRH receptors, leading to decreased testosterone production.
- They do not promote scalp hair regrowth but can cause **testicular atrophy** and **hot flashes**.
*Decreased conversion of hydroxyprogesterone to androstenedione*
- This pathway is involved in the synthesis of androgens in the adrenal glands and gonads but is not the primary mechanism targeted by drugs used for BPH with hair regrowth benefits.
- Drugs acting at this step are not typically associated with BPH treatment or hair regrowth.
*Decreased conversion of testosterone to estradiol*
- This refers to the action of **aromatase inhibitors** (e.g., anastrozole), which block the conversion of androgens to estrogens.
- Aromatase inhibitors are used in the treatment of **hormone-sensitive breast cancer** and do not treat BPH or promote scalp hair regrowth.
*Selective alpha-1A/D receptor antagonism*
- **Alpha-1 blockers** (e.g., tamsulosin) relax the smooth muscle in the prostate and bladder neck, improving urinary flow in BPH.
- While effective for BPH, they do not impact **hair regrowth** and may cause orthostatic hypotension or ejaculatory dysfunction.
Male sexual physiology US Medical PG Question 3: A 76-year-old male presents to his primary care physician because he is concerned about changes in urination. Over the last few months, he has noticed increased urinary frequency as well as difficulty with initiating and stopping urination. He denies having pain with urination. Physical exam reveals a uniformly enlarged and non-tender prostate. Lab tests showed that the prostate specific antigen (PSA) was within normal limits. The patient did not tolerate an alpha blocker due to episodes of syncope so another medication is prescribed that affects testosterone metabolism. Which of the following disorders can also be treated with the medication most likely prescribed in this case?
- A. Prostate adenocarcinoma
- B. Male pattern baldness (Correct Answer)
- C. Hypogonadism
- D. Erectile dysfunction
- E. Polycystic ovarian syndrome (PCOS)
Male sexual physiology Explanation: ***Male pattern baldness***
- The patient's symptoms (urinary frequency, difficulty initiating/stopping urination, uniformly enlarged prostate, normal PSA) are consistent with **benign prostatic hyperplasia (BPH)**. Since he couldn't tolerate alpha-blockers, a **5-alpha reductase inhibitor** like **finasteride** or **dutasteride** would likely be prescribed, which works by blocking the conversion of testosterone to dihydrotestosterone (DHT).
- **Male pattern baldness (androgenetic alopecia)** is also caused by DHT and can be treated with 5-alpha reductase inhibitors such as finasteride.
*Prostate adenocarcinoma*
- While 5-alpha reductase inhibitors can reduce the risk of prostate cancer, they are **not a primary treatment** for established prostate adenocarcinoma.
- Prostate adenocarcinoma is typically managed with surgery, radiation, or more aggressive hormonal therapies if advanced.
*Hypogonadism*
- Hypogonadism is characterized by **low testosterone levels**; 5-alpha reductase inhibitors actually decrease the conversion of testosterone to DHT, which could potentially worsen symptoms associated with low testosterone if used inappropriately.
- The primary treatment for hypogonadism is **testosterone replacement therapy**.
*Erectile dysfunction*
- Erectile dysfunction is often treated with **phosphodiesterase-5 inhibitors (PDE5i)** like sildenafil or tadalafil, which improve blood flow to the penis.
- While BPH can sometimes contribute to ED, 5-alpha reductase inhibitors are **not a first-line treatment** for primary ED and can even have ED as a side effect.
*Polycystic ovarian syndrome (PCOS)*
- PCOS is a hormonal disorder affecting women, characterized by **elevated androgen levels** and ovarian cysts.
- While anti-androgens can be used in PCOS to manage symptoms like hirsutism, **5-alpha reductase inhibitors are not a standard treatment** for the overall syndrome and this medication is prescribed for a male patient.
Male sexual physiology US Medical PG Question 4: A 70-year-old male presents to his primary care provider complaining of decreased sexual function. He reports that over the past several years, he has noted a gradual decline in his ability to sustain an erection. He used to wake up with erections but no longer does. His past medical history is notable for diabetes, hyperlipidemia, and a prior myocardial infarction. He takes metformin, glyburide, aspirin, and atorvastatin. He drinks 2-3 drinks per week and has a 25 pack-year smoking history. He has been happily married for 40 years. He retired from his job as a construction worker 5 years ago and has been enjoying retirement with his wife. His physician recommends starting a medication that is also used in the treatment of pulmonary hypertension. Which of the following is a downstream effect of this medication?
- A. Increase cGMP degradation
- B. Increase cAMP production
- C. Increase PDE5 activity
- D. Decrease nitric oxide production
- E. Decrease cGMP degradation (Correct Answer)
Male sexual physiology Explanation: ***Decrease cGMP degradation***
- The medication described is likely a **phosphodiesterase-5 (PDE5) inhibitor** (e.g., sildenafil, tadalafil), used for erectile dysfunction and pulmonary hypertension.
- These drugs work by inhibiting the enzyme PDE5, which is responsible for the breakdown of **cyclic GMP (cGMP)**, thereby increasing cGMP levels.
*Increase cGMP degradation*
- This is the **opposite** of the medication's intended effect, as it would lead to reduced cGMP levels and worsen erectile dysfunction.
- An increase in cGMP degradation would diminish the **vasodilatory** effects necessary for erection.
*Increase cAMP production*
- This medication primarily affects the **cGMP pathway**, not directly boosting cyclic AMP (cAMP) production.
- While cAMP also plays a role in vasodilation, it's regulated by different enzymes and pathways, such as **adenylyl cyclase**.
*Increase PDE5 activity*
- This would lead to a more **rapid breakdown of cGMP**, counteracting the goal of the medication and exacerbating erectile dysfunction.
- The medication's mechanism is specifically designed to **inhibit PDE5 activity**.
*Decrease nitric oxide production*
- **Nitric oxide (NO)** production is a **precursor** to cGMP synthesis, as NO activates guanylate cyclase to produce cGMP.
- Decreasing NO production would **reduce cGMP levels**, which is contrary to the action of PDE5 inhibitors.
Male sexual physiology US Medical PG Question 5: A 47-year-old man presents to the physician’s office with an inability to maintain an erection. He can achieve an erection, but it is brief and decreases soon after the penetration. His erectile dysfunction developed gradually over the past 2 years. He denies decreased libido, depressed mood, or anhedonia. He does not report any chronic conditions. He has a 20-pack-year history of smoking and drinks alcohol occasionally. He weighs 120 kg (264.5 lb), his height is 181 cm (5 ft 11 in), and his waist circumference is 110 cm (43 in). The blood pressure is 145/90 mm Hg and the heart rate is 86/min. Physical examination is performed including a genitourinary and rectal examination. It reveals no abnormalities besides central obesity. Which of the following laboratory tests is indicated to investigate for the cause of the patient’s condition?
- A. Total serum bilirubin
- B. 24-hour urine cortisol
- C. Plasma calcium
- D. Fasting serum glucose (Correct Answer)
- E. Follicle-stimulating hormone
Male sexual physiology Explanation: ***Fasting serum glucose***
- The patient has **risk factors for insulin resistance and type 2 diabetes**, including obesity, central obesity (waist circumference 110 cm), hypertension, and a sedentary lifestyle.
- **Type 2 diabetes mellitus is a common cause of erectile dysfunction** due to vascular and neurological complications, making fasting serum glucose an essential diagnostic step.
*Total serum bilirubin*
- **Elevated bilirubin** is typically associated with **liver or hemolytic disorders**, neither of which are suggested by the patient's presentation.
- While chronic illness can impact sexual function, bilirubin is not a primary screening tool for erectile dysfunction.
*24-hour urine cortisol*
- A 24-hour urine cortisol test is used to diagnose **Cushing's syndrome**, which can cause obesity and hypertension, but the patient's symptoms are more consistent with metabolic syndrome.
- There are no other features suggestive of Cushing's, such as **proximal muscle weakness, striae, or buffalo hump**, making this test less relevant initially.
*Plasma calcium*
- **Abnormal calcium levels** can indicate conditions like hyperparathyroidism or certain malignancies, which are not typically linked as direct causes of erectile dysfunction.
- There are no symptoms such as **nephrolithiasis, bone pain, or neuropsychiatric changes** to suggest calcium dysregulation.
*Follicle-stimulating hormone*
- While **gonadotropin levels** (FSH and LH) are relevant in evaluating **hypogonadism**, this patient denies decreased libido or symptoms suggestive of primary hypogonadism.
- A **total testosterone level is a more appropriate initial screening test for hypogonadism** if indicated, as FSH primarily reflects testicular function.
Male sexual physiology US Medical PG Question 6: A 27-year-old woman comes to the physician for the evaluation of infertility. She has been unable to conceive for the past 2 years. Menses occur at 45 to 80-day intervals. She is 168 cm (5 ft 6 in) tall and weighs 77 kg (170 lb); BMI is 27.4 kg/m2. Physical examination shows facial acne and pigmented hair on the upper lip. Serum studies show elevated levels of testosterone and an LH:FSH ratio of 4:1. Treatment with the appropriate drug for this patient's infertility is begun. Which of the following is the primary mechanism of action of this drug?
- A. Activation of pituitary dopamine receptors
- B. Activation of granulosa cell aromatase
- C. Activation of ovarian luteinizing hormone receptors
- D. Inhibition of hypothalamic estrogen receptors (Correct Answer)
- E. Inhibition of endometrial progesterone receptors
Male sexual physiology Explanation: ***Inhibition of hypothalamic estrogen receptors***
- The patient presents with classic symptoms of **polycystic ovarian syndrome (PCOS)**, including **oligomenorrhea** (menses every 45-80 days), **hirsutism**, **acne**, **elevated BMI**, **elevated testosterone**, and an **elevated LH:FSH ratio (4:1)**.
- **Clomiphene citrate** is the first-line drug for ovulation induction in PCOS patients with infertility.
- Clomiphene is a **selective estrogen receptor modulator (SERM)** that acts as a **competitive antagonist at estrogen receptors in the hypothalamus**.
- By blocking estrogen receptors, clomiphene prevents normal **negative feedback inhibition** of GnRH release.
- This results in increased **GnRH pulsatility**, leading to increased **FSH and LH secretion** from the anterior pituitary, which promotes **follicular development and ovulation**.
*Activation of pituitary dopamine receptors*
- This mechanism is characteristic of **dopamine agonists** (e.g., **bromocriptine**, **cabergoline**), which are used to treat infertility due to **hyperprolactinemia**.
- These agents activate D2 receptors in lactotroph cells, inhibiting prolactin secretion.
- The patient shows no signs of hyperprolactinemia (e.g., galactorrhea, amenorrhea from elevated prolactin).
*Activation of granulosa cell aromatase*
- Aromatase converts androgens to estrogens in granulosa cells.
- While aromatase activity is important in follicular development, **activating aromatase is not a mechanism of any standard ovulation-inducing drug**.
- In PCOS, there is often relative aromatase insufficiency, but drugs do not directly activate this enzyme for fertility treatment.
*Activation of ovarian luteinizing hormone receptors*
- While **exogenous LH or hCG** (which acts on LH receptors) may be used in assisted reproductive technology, this is not the mechanism of **first-line ovulation induction** in PCOS.
- Clomiphene works by increasing endogenous LH/FSH release, not by directly activating ovarian receptors.
*Inhibition of endometrial progesterone receptors*
- This is the mechanism of **mifepristone** (RU-486), an antiprogestin used for medical abortion and occasionally for **endometriosis** or **uterine fibroids**.
- Inhibiting progesterone receptors would **prevent implantation** or disrupt pregnancy, which is opposite to the goal of fertility treatment.
Male sexual physiology US Medical PG Question 7: A 56-year-old man comes to the clinic complaining of sexual dysfunction. He reports normal sexual function until 4 months ago when his relationship with his wife became stressful due to a death in the family. When asked about the details of his dysfunction, he claims that he is “able to get it up, but just can’t finish the job.” He denies any decrease in libido or erections, endorses morning erections, but an inability to ejaculate. He is an avid cyclist and exercises regularly. His past medical history includes depression and diabetes, for which he takes citalopram and metformin, respectively. A physical examination is unremarkable. What is the most likely explanation for this patient’s symptoms?
- A. Testosterone deficiency
- B. Autonomic neuropathy secondary to systemic disease
- C. Psychological stress
- D. Damage to the pudendal nerve
- E. Medication side effect (Correct Answer)
Male sexual physiology Explanation: ***Medication side effect***
- The patient's inability to ejaculate while maintaining normal libido, erections, and morning erections is highly suggestive of **ejaculatory dysfunction** caused by the **citalopram**, a selective serotonin reuptake inhibitor (SSRI).
- SSRIs, like citalopram, are known to commonly cause sexual side effects, including **delayed ejaculation** and **anorgasmia**, by increasing serotonin levels, which can inhibit the ejaculatory reflex.
*Testosterone deficiency*
- Testosterone deficiency usually presents with **decreased libido**, **erectile dysfunction**, and a reduction in **morning erections**, which are not reported by this patient.
- While it can impact sexual function, the specific symptom of inability to ejaculate with preserved erections points away from low testosterone.
*Autonomic neuropathy secondary to systemic disease*
- **Autonomic neuropathy**, often seen in patients with **diabetes**, can lead to ejaculatory dysfunction, including **retrograde ejaculation**.
- However, the patient's normal erections and libido, along with the recent onset coinciding with a stressful event and medication use, make medication a more likely primary cause in this scenario.
*Psychological stress*
- **Psychological stress** can certainly contribute to sexual dysfunction, leading to decreased libido or erectile difficulties.
- However, the patient explicitly states his erections and libido are normal, and he only experiences an inability to ejaculate, which is less commonly the sole manifestation of stress.
*Damage to the pudendal nerve*
- **Pudendal nerve damage** typically results in issues with **erectile function**, sensation in the perineum, and potentially urinary or fecal incontinence.
- This patient's preserved erections and specific issue with ejaculation make pudendal nerve damage an unlikely primary cause.
Male sexual physiology US Medical PG Question 8: A couple brings their 1-year-old child to a medical office for a follow-up evaluation of his small, empty scrotum. The scrotum has been empty since birth and the physician asked them to follow up with a pediatrician. There are no other complaints. The immunization history is up to date and his growth and development have been excellent. On examination, he is a playful, active child with a left, non-reducible, non-tender inguinal mass, an empty and poorly rugated hemiscrotal sac, and a testis within the right hemiscrotal sac. Which of the following hormones would likely be deficient in this patient by puberty if the condition is left untreated?
- A. LH
- B. Testosterone (Correct Answer)
- C. FSH
- D. Inhibin
- E. Prolactin
Male sexual physiology Explanation: ***Testosterone***
- **Testosterone** is produced by the **Leydig cells** in the testes. In untreated cryptorchidism, the elevated temperature in the inguinal canal causes progressive damage to both Sertoli cells and **Leydig cells** over time.
- By **puberty**, if left untreated for 11-13 years, the undescended testis will have significant irreversible Leydig cell dysfunction, leading to **reduced testosterone production**.
- While unilateral cryptorchidism may allow the contralateral descended testis to partially compensate, this compensation is often **incomplete during the high testosterone demands of puberty**, resulting in relative testosterone deficiency.
- This is the most clinically significant hormonal deficiency that develops with prolonged untreated cryptorchidism.
*LH*
- **Luteinizing hormone (LH)** is produced by the anterior pituitary and stimulates Leydig cells to produce testosterone. In cryptorchidism with resulting testosterone deficiency, LH levels would be **elevated** (not deficient) as a compensatory response.
- The pituitary responds normally to low testosterone with increased LH secretion via loss of negative feedback.
*Inhibin*
- **Inhibin** is produced by **Sertoli cells** in the seminiferous tubules. While cryptorchidism impairs Sertoli cell function and spermatogenesis, inhibin itself is not typically **deficient**.
- The primary consequence is **impaired spermatogenesis**, which leads to reduced negative feedback and **elevated FSH** levels, but inhibin levels may remain normal or only modestly reduced.
*FSH*
- **Follicle-stimulating hormone (FSH)** is produced by the anterior pituitary. In cryptorchidism, FSH is typically **elevated** (not deficient) due to impaired Sertoli cell function and loss of negative feedback from the seminiferous tubules.
- Elevated FSH is a marker of tubular dysfunction but is not itself deficient.
*Prolactin*
- **Prolactin** is produced by the anterior pituitary and primarily regulates lactation. It has no direct role in testicular function or the pathophysiology of cryptorchidism.
- There is no association between cryptorchidism and prolactin deficiency.
Male sexual physiology US Medical PG Question 9: A 51-year-old man presents to his physician with decreased libido and inability to achieve an erection. He also reports poor sleep, loss of pleasure to do his job, and depressed mood. His symptoms started a year ago, soon after his wife got into the car accident. She survived and recovered with the minimal deficit, but the patient still feels guilty due to this case. The patient was diagnosed with diabetes 6 months ago, but he does not take any medications for it. He denies any other conditions. His weight is 105 kg (231.5 lb), his height is 172 cm (5 ft 7 in), and his waist circumference is 106 cm. The blood pressure is 150/90 mm Hg, and the heart rate is 73/min. The physical examination only shows increased adiposity. Which of the following tests is specifically intended to distinguish between the organic and psychogenic cause of the patient’s condition?
- A. Angiography
- B. Duplex ultrasound of the penis
- C. Penile tumescence testing (Correct Answer)
- D. Biothesiometry
- E. Injection of prostaglandin E1
Male sexual physiology Explanation: ***Penile tumescence testing***
- This test, often performed as a **nocturnal penile tumescence (NPT) test**, measures erections during sleep. The presence of normal nocturnal erections indicates a **psychogenic** cause for erectile dysfunction, as physiological mechanisms are intact.
- The absence of nocturnal erections, despite adequate sleep, suggests an **organic** cause, as the body's natural erectile reflex is impaired.
*Angiography*
- **Angiography** is an invasive procedure used to visualize blood vessels and identify arterial blockages or abnormalities. It is typically reserved for cases where vascular disease is strongly suspected as the cause of erectile dysfunction and often considered before revascularization surgery.
- While it can identify **vascular organic causes** of erectile dysfunction, it does not directly differentiate between psychogenic and organic causes universally; it focuses specifically on arterial flow.
*Duplex ultrasound of the penis*
- **Duplex ultrasound** evaluates blood flow within the penile arteries and veins, assessing both arterial inflow and veno-occlusive function. It aids in diagnosing **vascular abnormalities**, such as arterial insufficiency or venous leakage.
- Similar to angiography, duplex ultrasound identifies specific **organic vascular pathologies** but does not definitively distinguish between psychogenic and organic causes of erectile dysfunction if vascular function is normal.
*Biothesiometry*
- **Biothesiometry** measures penile vibratory sensation threshold, which assesses **neurological function** of the penis. It helps detect peripheral neuropathy, a potential organic cause of erectile dysfunction, especially in diabetic patients.
- While useful for uncovering **neurological organic causes**, biothesiometry does not differentiate between psychogenic and organic etiologies in cases where neurological function is normal.
*Injection of prostaglandin E1*
- The **injection of prostaglandin E1** (alprostadil) is a diagnostic and therapeutic tool that induces an erection by relaxing smooth muscle in the penile arteries, increasing blood flow. A strong response indicates intact vascular smooth muscle function.
- A successful response to prostaglandin E1 suggests that vascular smooth muscle and neurological pathways are largely functional, which can indirectly point away from severe organic causes, but it's not a definitive differentiator between **psychogenic and organic** causes as it by-passes some physiological mechanisms.
Male sexual physiology US Medical PG Question 10: Research is being conducted on embryoblasts. The exact date of fertilization is unknown. There is the presence of a cytotrophoblast and syncytiotrophoblast, marking the time when implantation into the uterus would normally occur. Within the embryoblast, columnar and cuboidal cells are separated by a membrane. Which of these cell layers begins to line the yolk sac cavity?
- A. Hypoblast (Correct Answer)
- B. Epiblast
- C. Syncytiotrophoblast
- D. Inner cell mass
- E. Endoderm
Male sexual physiology Explanation: ***Hypoblast***
- The **hypoblast** is a layer of cuboidal cells that forms from the inner cell mass around day 8 post-fertilization.
- It plays a crucial role in forming the **primary yolk sac** by migrating to line the exocoelomic cavity.
*Epiblast*
- The **epiblast** is composed of columnar cells located dorsal to the hypoblast and forms the floor of the **amniotic cavity**.
- It is the source of the **three primary germ layers** during gastrulation (ectoderm, mesoderm, and endoderm), not the yolk sac lining itself.
*Syncytiotrophoblast*
- The **syncytiotrophoblast** is the outer, invasive layer of the trophoblast that facilitates implantation and forms the fetal component of the placenta.
- It is not involved in lining the yolk sac cavity but rather in **invading the uterine endometrium** and producing hCG.
*Inner cell mass*
- The **inner cell mass (ICM)** is the cluster of cells within the blastocyst that gives rise to the embryoblast (which further differentiates into epiblast and hypoblast).
- The ICM itself does not line the yolk sac; rather, its derivative, the hypoblast, does.
*Endoderm*
- The **endoderm** is one of the three primary germ layers that forms during gastrulation from the epiblast derivative.
- It ultimately forms the linings of the **gastrointestinal and respiratory tracts**, not the primary yolk sac lining.
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