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Intratesticular Testosterone
MCQ questions and answers.
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MCQ Questions
1. Why is the testosterone concentration within the seminiferous tubules normally much higher than its concentration in peripheral blood?
A.
Leydig cells secrete testosterone directly into the tubule lumen, where it accumulates
B.
Sertoli-cell androgen-binding protein retains testosterone near the seminiferous epithelium
C.
Spermatozoa synthesize testosterone from cholesterol during spermatogenesis
D.
The blood-testis barrier actively transports circulating testosterone into the tubules
Correct Answer:
Sertoli-cell androgen-binding protein retains testosterone near the seminiferous epithelium
Explanation:
Sertoli cells produce androgen-binding protein, which binds testosterone and helps maintain a high local intratesticular androgen concentration required for efficient spermatogenesis.
2. A selective reduction in Leydig-cell testosterone synthesis would most directly impair spermatogenesis because it would:
A.
eliminate follicle-stimulating hormone receptors from Sertoli cells
B.
lower the androgen concentration acting on Sertoli cells and developing germ cells
C.
prevent Sertoli cells from forming the blood-testis barrier immediately
D.
increase the conversion of testosterone into inhibin by Sertoli cells
Correct Answer:
lower the androgen concentration acting on Sertoli cells and developing germ cells
Explanation:
Leydig cells are the principal source of intratesticular testosterone. A reduction in their testosterone output decreases local androgen action needed for the progression of spermatogenesis.
3. Which experimental finding would best demonstrate that high intratesticular testosterone, rather than merely normal circulating testosterone, is important for spermatogenesis?
A.
Spermatogenesis remains normal when intratesticular testosterone is low but plasma testosterone is normal
B.
Spermatogenesis is impaired despite normal plasma testosterone when intratesticular testosterone is selectively reduced
C.
Spermatogenesis is impaired only after inhibin concentrations rise in the circulation
D.
Spermatogenesis increases whenever testosterone is excluded from Sertoli cells
Correct Answer:
Spermatogenesis is impaired despite normal plasma testosterone when intratesticular testosterone is selectively reduced
Explanation:
This result would separate local testicular androgen action from systemic androgen status and show that the high testosterone concentration within the testis has a specific role in supporting spermatogenesis.
4. Luteinizing hormone supports intratesticular testosterone primarily by acting on which cells and stimulating which immediate process?
A.
Sertoli cells; secretion of androgen-binding protein
B.
Peritubular myoid cells; conversion of testosterone into dihydrotestosterone
C.
Leydig cells; steroidogenesis from cholesterol
D.
Developing spermatocytes; synthesis of testosterone from progesterone
Correct Answer:
Leydig cells; steroidogenesis from cholesterol
Explanation:
LH acts on receptors of Leydig cells and stimulates steroidogenic pathways that convert cholesterol into testosterone, thereby maintaining the intratesticular androgen environment.
5. If Sertoli cells could no longer synthesize androgen-binding protein, which change would be most likely within the testis?
A.
A rise in the effective free testosterone concentration near the seminiferous epithelium
B.
A fall in the ability to maintain the high local testosterone concentration required for spermatogenesis
C.
Complete cessation of testosterone synthesis by Leydig cells
D.
Conversion of intratesticular testosterone into follicle-stimulating hormone
Correct Answer:
A fall in the ability to maintain the high local testosterone concentration required for spermatogenesis
Explanation:
Androgen-binding protein helps concentrate and retain testosterone in the seminiferous-tubule environment. Without it, local androgen availability would decline even if Leydig cells continued producing testosterone.
6. Which combination most accurately describes the local cooperation required to sustain a high intratesticular testosterone concentration?
A.
Leydig-cell testosterone production and Sertoli-cell androgen binding
B.
Sertoli-cell testosterone production and Leydig-cell inhibin secretion
C.
Germ-cell testosterone production and peritubular-cell androgen degradation
D.
Leydig-cell follicle-stimulating hormone secretion and Sertoli-cell testosterone degradation
Correct Answer:
Leydig-cell testosterone production and Sertoli-cell androgen binding
Explanation:
Leydig cells supply testosterone, while Sertoli cells produce androgen-binding protein that helps preserve a high local testosterone concentration around the seminiferous epithelium.
7. A drug blocks androgen receptors in Sertoli cells without directly reducing Leydig-cell testosterone secretion. Which interpretation is most appropriate?
A.
Intratesticular testosterone production must immediately stop because Leydig cells require Sertoli-cell androgen receptors
B.
Testosterone may remain high inside the testis, but its functional signaling to Sertoli cells is reduced
C.
Circulating testosterone must become zero because receptor blockade increases testosterone clearance
D.
Androgen-binding protein will necessarily increase enough to restore Sertoli-cell signaling
Correct Answer:
Testosterone may remain high inside the testis, but its functional signaling to Sertoli cells is reduced
Explanation:
Intratesticular testosterone concentration and androgen-receptor signaling are distinct. Receptor blockade can impair testosterone action in Sertoli cells even while Leydig cells continue producing testosterone.
8. Why can testosterone replacement that restores plasma testosterone fail to restore normal sperm production when gonadotropin secretion is suppressed?
A.
Exogenous testosterone always destroys Sertoli cells directly
B.
Plasma testosterone cannot enter any part of the testis
C.
Suppressed luteinizing hormone reduces Leydig-cell stimulation and therefore lowers intratesticular testosterone
D.
Testosterone replacement selectively increases androgen-binding protein degradation in the epididymis
Explanation:
Systemic testosterone replacement can provide normal circulating levels while failing to recreate the very high local testosterone concentration generated by LH-stimulated Leydig cells inside the testis.
9. Which observation most strongly indicates that Sertoli-cell androgen-binding protein functions locally rather than as the principal systemic carrier of testosterone?
A.
It is produced by Sertoli cells and concentrates testosterone within seminiferous tubules
B.
It is secreted by the liver and distributes testosterone throughout the circulation
C.
It is produced by germ cells and transports testosterone into Leydig cells
D.
It is released by the pituitary and stimulates Leydig-cell steroidogenesis
Correct Answer:
It is produced by Sertoli cells and concentrates testosterone within seminiferous tubules
Explanation:
Sertoli-cell androgen-binding protein acts within the testicular microenvironment, helping maintain high intratesticular testosterone near developing germ cells rather than serving as the main plasma transport protein.
10. If Leydig cells remain structurally intact but their LH receptors are experimentally blocked, which sequence best predicts the effect on intratesticular testosterone and spermatogenesis?
A.
Increased testosterone production followed by enhanced spermatogenesis
B.
Unchanged testosterone production because Sertoli cells synthesize most testicular testosterone
C.
Reduced testosterone synthesis followed by impaired androgen-dependent support of spermatogenesis
D.
Increased androgen-binding protein followed by testosterone-independent spermatogenesis
Correct Answer:
Reduced testosterone synthesis followed by impaired androgen-dependent support of spermatogenesis
Explanation:
Blocking LH receptors prevents normal stimulation of Leydig-cell steroidogenesis. The resulting fall in intratesticular testosterone compromises the androgen-dependent functions of Sertoli cells during spermatogenesis.
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