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Leydig Cell Ultrastructure
MCQ questions and answers.
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MCQ Questions
1. Which combination of ultrastructural features most strongly identifies an active Leydig cell specialized for testosterone synthesis?
A.
Abundant smooth endoplasmic reticulum, mitochondria with tubular cristae, and cytoplasmic lipid droplets
B.
Abundant rough endoplasmic reticulum, stacked Golgi cisternae, and secretory granules
C.
Extensive lysosomal compartments, keratin bundles, and desmosomal plaques
D.
Numerous cilia, basal bodies, and mucin-filled secretory vesicles
Correct Answer:
Abundant smooth endoplasmic reticulum, mitochondria with tubular cristae, and cytoplasmic lipid droplets
Explanation:
Leydig cells are steroid-producing cells. Their ultrastructure reflects steroidogenesis: smooth endoplasmic reticulum provides steroidogenic enzymes, mitochondria with tubular cristae participate in early steroid synthesis, and lipid droplets store cholesterol precursors.
2. The tubular rather than lamellar cristae of Leydig-cell mitochondria are most closely associated with which cellular function?
A.
Synthesis and packaging of peptide hormones into secretory granules
B.
Participation in steroidogenic reactions requiring mitochondrial enzymes
C.
Formation of intercellular junctions with adjacent germ cells
D.
Digestion of phagocytosed residual bodies
Correct Answer:
Participation in steroidogenic reactions requiring mitochondrial enzymes
Explanation:
Leydig-cell mitochondria commonly possess tubular cristae, a feature characteristic of steroid-producing cells. Mitochondrial steroidogenic enzymes catalyze early steps in androgen synthesis.
3. A transmission electron micrograph shows a polygonal interstitial cell with an eccentric round nucleus, prominent smooth endoplasmic reticulum, numerous mitochondria with tubular cristae, and lipid inclusions. Which identity is most likely?
A.
Sertoli cell
B.
Peritubular myoid cell
C.
Leydig cell
D.
Primary spermatocyte
Correct Answer:
Leydig cell
Explanation:
The combination of steroidogenic smooth endoplasmic reticulum, tubular-crista mitochondria, and lipid inclusions is characteristic of Leydig-cell ultrastructure. These features distinguish Leydig cells from the other testicular cell types listed.
4. Which ultrastructural observation would most directly indicate that a Leydig cell is adapted for lipid-soluble hormone synthesis rather than protein secretion?
A.
Extensive smooth endoplasmic reticulum with relatively inconspicuous secretory granules
B.
Extensive rough endoplasmic reticulum with abundant dense-core granules
C.
Numerous free ribosomes surrounding a large phagolysosomal compartment
D.
Highly developed ciliary axonemes with radial microtubular spokes
Explanation:
Steroid hormones are synthesized enzymatically and diffuse out of the cell, so Leydig cells contain abundant smooth endoplasmic reticulum but do not depend on large populations of secretory granules. Protein-secreting cells instead show extensive rough endoplasmic reticulum and vesicular packaging.
5. Reinke crystals, when present in an interstitial endocrine cell of the testis, are best interpreted as which finding?
A.
A diagnostic cytoplasmic inclusion associated with Leydig cells
B.
A mitochondrial structure required for testosterone transport
C.
A lysosomal remnant formed from degenerating spermatids
D.
A crystallized component of the blood-testis barrier
Correct Answer:
A diagnostic cytoplasmic inclusion associated with Leydig cells
Explanation:
Reinke crystals are distinctive rod-shaped cytoplasmic inclusions that may occur in Leydig cells. They are useful diagnostically, although they are not present in every Leydig cell and are not themselves the site of steroid synthesis.
6. Which pairing correctly matches a Leydig-cell ultrastructural component with its principal significance?
A.
Lipid droplets — intracellular reservoir of cholesterol substrate for steroidogenesis
B.
Dense-core granules — primary storage site for released testosterone
C.
Desmosomes — mechanism for exocytosis of androgen-containing vesicles
D.
Ciliary axonemes — apparatus for moving testosterone through the interstitium
Correct Answer:
Lipid droplets — intracellular reservoir of cholesterol substrate for steroidogenesis
Explanation:
Leydig-cell lipid droplets contain neutral lipids, including cholesterol esters that can provide substrate for steroid hormone synthesis. Testosterone is not generally stored in dense-core secretory granules or transported by cilia.
7. Why is a well-developed Golgi apparatus present in Leydig cells but not considered the defining ultrastructural feature of their endocrine specialization?
A.
The Golgi apparatus participates in general membrane and protein processing, whereas steroid synthesis depends primarily on smooth endoplasmic reticulum and mitochondria
B.
The Golgi apparatus is absent from all steroid-producing cells and therefore cannot be observed in Leydig cells
C.
The Golgi apparatus stores cholesterol esters until luteinizing hormone reaches the cell
D.
The Golgi apparatus forms tubular cristae inside Leydig-cell mitochondria
Correct Answer:
The Golgi apparatus participates in general membrane and protein processing, whereas steroid synthesis depends primarily on smooth endoplasmic reticulum and mitochondria
Explanation:
Leydig cells may contain a Golgi apparatus for routine cellular processing, but their defining steroidogenic machinery is the extensive smooth endoplasmic reticulum and specialized mitochondria. The Golgi does not synthesize mitochondrial cristae or serve as the principal cholesterol-storage site.
8. Which change would most likely accompany increased steroidogenic activity in a Leydig cell observed by electron microscopy?
A.
Expansion of smooth endoplasmic reticulum and increased numbers of mitochondria with tubular cristae
B.
Conversion of smooth endoplasmic reticulum into bundles of intermediate filaments
C.
Disappearance of lipid droplets and replacement by ciliary basal bodies
D.
Marked accumulation of mucin granules within the Golgi apparatus
Correct Answer:
Expansion of smooth endoplasmic reticulum and increased numbers of mitochondria with tubular cristae
Explanation:
Greater steroidogenic activity requires more steroidogenic enzymes and mitochondrial capacity. Therefore, active Leydig cells commonly show prominent smooth endoplasmic reticulum and abundant mitochondria with tubular cristae.
9. Which ultrastructural feature best distinguishes Leydig-cell steroid production from the regulated exocytosis used by many peptide-secreting endocrine cells?
A.
Steroidogenic enzymes are concentrated in smooth endoplasmic reticulum and mitochondria, and the lipid-soluble product is not stored in large secretory granules
B.
Steroid hormones are synthesized inside rough endoplasmic reticulum and stored in Golgi-derived vesicles
C.
Leydig cells release testosterone only after fusion of dense-core granules with the plasma membrane
D.
Leydig cells use lysosomes as the principal organelles for androgen synthesis
Correct Answer:
Steroidogenic enzymes are concentrated in smooth endoplasmic reticulum and mitochondria, and the lipid-soluble product is not stored in large secretory granules
Explanation:
Leydig cells synthesize testosterone through enzyme systems associated mainly with smooth endoplasmic reticulum and mitochondria. Because testosterone is lipid soluble, it generally diffuses from the cell rather than being stored in large secretory granules.
10. A Leydig cell contains abundant smooth endoplasmic reticulum and tubular-crista mitochondria but very little rough endoplasmic reticulum. Which inference is most appropriate?
A.
Its organelle profile is consistent with steroid hormone synthesis rather than synthesis of a heavily glycosylated secreted protein
B.
It is specialized primarily for antibody secretion into the seminiferous tubule
C.
It is undergoing spermatid differentiation and acrosome formation
D.
It is specialized for phagocytosis and intracellular digestion of germ cells
Correct Answer:
Its organelle profile is consistent with steroid hormone synthesis rather than synthesis of a heavily glycosylated secreted protein
Explanation:
Abundant smooth endoplasmic reticulum and tubular-crista mitochondria are characteristic of steroid-producing Leydig cells. A cell producing large amounts of secreted protein would instead be expected to have prominent rough endoplasmic reticulum and Golgi-associated secretory machinery.
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