Microscopy techniques — MCQs

9 questions

A medical technician is trying to isolate a pathogen from the sputum sample of a patient. The sample is heat fixed to a slide then covered with carbol fuchsin stain and heated again. After washing off the stain with clean water, the slide is covered with 1% sulfuric acid for decolorization. The sample is rinsed again and stained with methylene blue. Microscopic examination shows numerous red, branching filamentous organisms. Which of the following is the most likely isolated pathogen?

An investigator is examining tissue samples from various muscle tissue throughout the body. She notices that biopsies collected from a specific site have a high concentration of sarcoplasmic reticulum, mitochondria, and myoglobin; they also stain poorly for ATPase. Additionally, the cell surface membranes of the myocytes in the specimen lack voltage-gated calcium channels. These myocytes are found in the greatest concentration at which of the following sites?

An investigator is studying neuronal regeneration. For microscopic visualization of the neuron, an aniline stain is applied. After staining, only the soma and dendrites of the neurons are visualized, not the axon. Presence of which of the following cellular elements best explains this staining pattern?

An investigator studying targeted therapy in patients with gastrointestinal stromal tumors requires a reliable test to determine the spatial distribution of CD117-positive cells in biopsy specimens. Which of the following is the most appropriate test?

A group of scientists is studying the mechanism by which the human papillomavirus (HPV) vaccine confers immunity. They observe that during inoculation of test subjects, certain viral proteins are taken up by the organism's antigen-presenting cells (APCs) and presented on major histocompatibility complex (MHC) class I molecules. Which of the following is the correct term for the process that the scientists are observing in this inoculation?

An investigator is conducting a study to document the histological changes in the respiratory tree of a chronic smoker. He obtains multiple biopsy samples from the respiratory system of a previously healthy 28-year-old man. Histopathological examination of one sample shows simple cuboidal cells with a surrounding layer of smooth muscle. Chondrocytes and goblet cells are absent. This specimen was most likely obtained from which of the following parts of the respiratory system?

A 38-year-old man comes to the physician because of a 6-month history of chest discomfort and progressive dyspnea. He cannot do daily chores without feeling out of breath. He was diagnosed in childhood with a milder X-linked dystrophinopathy that has caused progressive proximal muscle weakness and gait abnormalities over the years. Physical examination shows a waddling gait and weak patellar reflexes. Cardiovascular examination shows a holosystolic murmur, displaced point of maximal impulse, and bilateral pitting edema of the ankles. Laboratory studies show elevated levels of brain natriuretic peptide. Which of the following is the most likely underlying cause of this patient's muscle weakness?

A 24-year-old male with cystic fibrosis is brought to the emergency room by his mother after he had difficulty breathing. He previously received a lung transplant 6 months ago and was able to recover quickly from the operation. He is compliant with all of his medications and had been doing well with no major complaints until 2 weeks ago when he began to experience shortness of breath. Exam reveals a decreased FEV1/FVC ratio and biopsy reveals lymphocytic infiltration. Which of the following components is present in the airway zone characteristically affected by the most likely cause of this patient's symptoms?

An 82-year-old woman presents to the emergency department after a fall. Imaging reveals diffuse trauma to the left humerus from the midshaft to the distal metaphysis with shearing of the periosteum. The orthopedic surgeon suggests a follow-up in 2 weeks. In that time, the patient develops worsening pain. At follow-up, she is found to have diffuse bone necrosis from the midshaft of the left humerus to the distal metaphysis, with no involvement of the distal forearm structures. Which of the following structures must have been damaged to cause this diffuse bone necrosis?

Microscopy techniques US Medical PG Practice Questions and MCQs

Question 1: A medical technician is trying to isolate a pathogen from the sputum sample of a patient. The sample is heat fixed to a slide then covered with carbol fuchsin stain and heated again. After washing off the stain with clean water, the slide is covered with 1% sulfuric acid for decolorization. The sample is rinsed again and stained with methylene blue. Microscopic examination shows numerous red, branching filamentous organisms. Which of the following is the most likely isolated pathogen?

A. Cryptococcus neoformans
B. Tropheryma whipplei
C. Nocardia asteroides (Correct Answer)
D. Rickettsia rickettsii
E. Staphylococcus aureus

Explanation: ***Nocardia asteroides*** - The described staining procedure is a **modified acid-fast stain**, indicated by the use of **carbol fuchsin**, heating, and decolorization with **weak acid (1% sulfuric acid)**, followed by a counterstain with methylene blue. - **Nocardia species** are **weakly acid-fast bacteria** that resist decolorization with weak acids (1-3% sulfuric acid), appearing as **red, branching filamentous organisms** under this staining method. - The **modified acid-fast stain** uses weaker decolorizing agents compared to the standard Ziehl-Neelsen stain, making it suitable for detecting weakly acid-fast organisms like Nocardia. - Nocardia are aerobic actinomycetes commonly found in soil and can cause pulmonary infections, especially in immunocompromised patients. *Cryptococcus neoformans* - This is a **yeast** that is typically identified using an **India ink stain** to visualize its polysaccharide capsule, or through fungal stains like Gomori methenamine silver (GMS). - It would not appear as acid-fast red branching filaments with the described technique. *Tropheryma whipplei* - This bacterium is typically identified by **periodic acid-Schiff (PAS) stain** in tissue biopsies, which highlights its cell wall glycoproteins (appears magenta). - It is not acid-fast and would not retain the carbol fuchsin after acid decolorization. *Rickettsia rickettsii* - This is an **obligate intracellular bacterium** that is difficult to culture and is often diagnosed by **serological tests** or **immunohistochemistry** on skin biopsy specimens. - It is not acid-fast and would not be detected by this staining technique. *Staphylococcus aureus* - This is a **Gram-positive coccus** that would be stained **purple** by a Gram stain as it retains crystal violet. - It is not acid-fast and would be completely decolorized by sulfuric acid in the described procedure, appearing blue (counterstain color) rather than red.

Question 2: An investigator is examining tissue samples from various muscle tissue throughout the body. She notices that biopsies collected from a specific site have a high concentration of sarcoplasmic reticulum, mitochondria, and myoglobin; they also stain poorly for ATPase. Additionally, the cell surface membranes of the myocytes in the specimen lack voltage-gated calcium channels. These myocytes are found in the greatest concentration at which of the following sites?

A. Ventricular myocardium
B. Tunica media
C. Lateral rectus muscle
D. Glandular myoepithelium
E. Semispinalis muscle (Correct Answer)

Explanation: ***Semispinalis muscle*** - The described characteristics—**high concentration of sarcoplasmic reticulum, mitochondria, and myoglobin** with **poor ATPase staining**—are hallmarks of **Type I (slow-twitch oxidative) skeletal muscle fibers**. - Postural muscles like the **semispinalis** (part of the erector spinae group) are predominantly composed of Type I fibers adapted for sustained, aerobic contraction to maintain posture. - These fibers appear **red** due to high myoglobin content, have abundant mitochondria for aerobic metabolism, and stain **poorly for ATPase** (distinguishing them from Type II fast-twitch fibers). - While all skeletal muscle does possess voltage-gated calcium channels for excitation-contraction coupling, the overall profile best matches slow-twitch postural muscles. *Ventricular myocardium* - While cardiac muscle has high mitochondria, myoglobin, and sarcoplasmic reticulum, it **does possess L-type voltage-gated calcium channels** on the sarcolemma, which are essential for cardiac excitation-contraction coupling. - Cardiac muscle relies on **both** extracellular Ca²⁺ influx through these channels and calcium-induced calcium release from the SR. - Cardiac muscle typically stains **strongly for ATPase**, not poorly. *Tunica media* - Composed of **vascular smooth muscle** with poorly developed sarcoplasmic reticulum and relatively few mitochondria compared to skeletal or cardiac muscle. - Smooth muscle relies heavily on **extracellular calcium influx** and the calmodulin pathway for contraction. - Not characterized by high myoglobin content. *Lateral rectus muscle* - This extraocular muscle contains predominantly **Type IIb fast-twitch glycolytic fibers** adapted for rapid, precise eye movements. - These fibers have **low myoglobin** (white muscle), fewer mitochondria, and stain **strongly for ATPase**. - Opposite profile from the described tissue. *Glandular myoepithelium* - Myoepithelial cells are specialized contractile cells in secretory glands with minimal sarcoplasmic reticulum and mitochondria. - Function is brief contraction for secretion expulsion, not sustained aerobic work. - Do not exhibit the high oxidative capacity described.

Question 3: An investigator is studying neuronal regeneration. For microscopic visualization of the neuron, an aniline stain is applied. After staining, only the soma and dendrites of the neurons are visualized, not the axon. Presence of which of the following cellular elements best explains this staining pattern?

A. Microtubule
B. Golgi apparatus
C. Lysosome
D. Rough endoplasmic reticulum (Correct Answer)
E. Nucleus

Explanation: **Rough endoplasmic reticulum** - Aniline stains, particularly basic dyes like cresyl violet or toluidine blue, stain the **basophilic structures** within the neuronal cell body (soma) and dendrites, which are rich in **rough endoplasmic reticulum (RER)**. - The RER, along with free ribosomes, makes up **Nissl bodies**, responsible for protein synthesis, and these structures are largely absent in the axon, explaining the lack of staining. *Microtubule* - **Microtubules** are cytoskeletal components found throughout the neuron, including the axon, and are not preferentially stained by aniline dyes in a way that differentiates the soma and dendrites from the axon. - Their primary role is in **axonal transport** and maintaining cell shape, not in conferring basophilia that would be highlighted by this type of staining pattern. *Golgi apparatus* - The **Golgi apparatus** is involved in modifying, sorting, and packaging proteins and lipids; it is present in the soma and dendrites but also has a more limited presence in axons. - While important for neuronal function, the Golgi apparatus does not possess the same high concentration of **basophilic RER** that gives rise to the characteristic Nissl staining pattern. *Lysosome* - **Lysosomes** are organelles responsible for waste degradation and recycling within the cell; they are found in the soma and dendrites but are less prominent in the axon. - They are not readily visualized by basic aniline stains in the same manner as the highly basophilic RER, and their presence doesn't explain the differential staining observed. *Nucleus* - The **nucleus** contains the cell's genetic material and is prominently stained by basic dyes due to its DNA content. - However, the question specifies visualization of the "soma and dendrites," implying cytoplasmic structures, and the nucleus itself does not extend into the dendrites or axon to explain their staining pattern.

Question 4: An investigator studying targeted therapy in patients with gastrointestinal stromal tumors requires a reliable test to determine the spatial distribution of CD117-positive cells in biopsy specimens. Which of the following is the most appropriate test?

A. Northern blot
B. Immunohistochemistry (Correct Answer)
C. Flow cytometry
D. Fluorescence in-situ hybridization
E. Western blot

Explanation: ***Immunohistochemistry*** - **Immunohistochemistry (IHC)** uses **antibodies** to target specific antigens (like **CD117**) within tissue sections, allowing for **visualization of their spatial distribution** under a microscope. - This technique is ideal for identifying the precise location and quantity of **CD117-positive cells** within a biopsy, which is crucial for assessing targeted therapy in gastrointestinal stromal tumors. *Northern blot* - **Northern blot** is used to detect and quantify specific **RNA** sequences in a sample. - It does not provide information about **protein expression** or the **spatial distribution of cells** within tissue. *Flow cytometry* - **Flow cytometry** is used for analyzing and sorting cells based on their **surface or intracellular markers** by passing them in a fluid stream through laser light. - While it can quantify **CD117-positive cells**, it requires cells to be in suspension and thus **destroys the tissue architecture**, preventing analysis of spatial distribution. *Fluorescence in-situ hybridization* - **Fluorescence in-situ hybridization (FISH)** uses **fluorescent probes** to detect and locate specific **DNA or RNA sequences** on chromosomes or in cells. - FISH is primarily used for genetic analysis and **does not directly assess protein expression** or cellular distribution in the context of targeted therapy. *Western blot* - **Western blot** is used to detect and quantify specific **proteins** from a sample by separating them by size, but it is performed on **tissue homogenates**. - This technique provides information on the **total protein content** but **does not preserve the spatial arrangement** of cells within the original tissue.

Question 5: A group of scientists is studying the mechanism by which the human papillomavirus (HPV) vaccine confers immunity. They observe that during inoculation of test subjects, certain viral proteins are taken up by the organism's antigen-presenting cells (APCs) and presented on major histocompatibility complex (MHC) class I molecules. Which of the following is the correct term for the process that the scientists are observing in this inoculation?

A. Priming of CD4+ T cells
B. Ubiquitination
C. Endogenous antigen presentation
D. Cross-presentation (Correct Answer)
E. Adhesion

Explanation: ***Cross-presentation*** - **Cross-presentation** occurs when an **antigen-presenting cell (APC)**, typically a dendritic cell, takes up **exogenous antigens** (like viral proteins from a vaccine) and presents them on **MHC class I molecules** to activate **CD8+ T cells**. - This process is crucial for generating a strong **cytotoxic T lymphocyte (CTL) response** against viruses and tumors when the pathogen does not directly infect the APC. *Priming of CD4+ T cells* - **Priming of CD4+ T cells** involves the presentation of antigens on **MHC class II molecules**, which are typically loaded with **exogenous antigens** that have been internalized by the APC. - The scenario describes antigen presentation on **MHC class I**, which points towards activation of CD8+ T cells, not CD4+ T cells directly. *Ubiquitination* - **Ubiquitination** is a process where the protein **ubiquitin** is attached to another protein, often marking it for degradation by the **proteasome**. - While ubiquitination is involved in preparing **endogenous antigens** for MHC class I presentation, it is a *step within* the broader antigen processing pathway, not the overall process of an APC presenting exogenous antigen on MHC class I. *Endogenous antigen presentation* - **Endogenous antigen presentation** refers to the presentation of **peptides derived from proteins synthesized within the cell** (e.g., viral proteins in an infected cell) on **MHC class I molecules**. - In this scenario, the viral proteins are *inoculated* into the organism, meaning they are initially **exogenous** to the APC before uptake, making cross-presentation the more accurate description. *Adhesion* - **Adhesion** refers to the process by which cells attach to other cells or to the extracellular matrix, often mediated by **adhesion molecules**. - While cell-cell interactions are important in immune responses, "adhesion" does not describe the specific mechanism of an APC taking up an antigen and presenting it on MHC class I.

Question 6: An investigator is conducting a study to document the histological changes in the respiratory tree of a chronic smoker. He obtains multiple biopsy samples from the respiratory system of a previously healthy 28-year-old man. Histopathological examination of one sample shows simple cuboidal cells with a surrounding layer of smooth muscle. Chondrocytes and goblet cells are absent. This specimen was most likely obtained from which of the following parts of the respiratory system?

A. Terminal bronchiole (Correct Answer)
B. Alveolar sac
C. Main stem bronchus
D. Bronchiole
E. Respiratory bronchiole

Explanation: ***Terminal bronchiole*** - Terminal bronchioles are lined by **simple cuboidal epithelium** and contain surrounding **smooth muscle** but lack cartilage (chondrocytes) and goblet cells, matching the histological description. - They represent the most distal purely conducting airways before respiratory bronchioles, where gas exchange begins. *Alveolar sac* - Alveolar sacs are primarily composed of **Type I and Type II pneumocytes** for gas exchange, and would not have a prominent smooth muscle layer or cuboidal cells in this described pattern. - They are the terminal structures of the respiratory tree where gas exchange occurs, defined by very thin walls lacking cartilage and goblet cells. *Main stem bronchus* - The main stem bronchi are characterized by **pseudostratified ciliated columnar epithelium** with abundant **goblet cells** and contain **hyaline cartilage** (chondrocytes) in their walls. - The presence of goblet cells and cartilage (chondrocytes) makes this option inconsistent with the given histological findings. *Bronchiole* - Bronchioles are generally lined by **ciliated columnar to cuboidal epithelium** with scattered goblet cells in larger ones, and they possess smooth muscle but lack cartilage. - While they share some features with terminal bronchioles, the presence of goblet cells (even if sparse) distinguishes bronchioles from terminal bronchioles. *Respiratory bronchiole* - Respiratory bronchioles are distinguished by their walls having occasional **alveoli**, indicating the beginning of gas exchange. Their epithelium is cuboidal. - They would not be described as having a "surrounding layer of smooth muscle" in isolation as clearly as a terminal bronchiole, and the presence of alveoli would be a key distinguishing feature.

Question 7: A 38-year-old man comes to the physician because of a 6-month history of chest discomfort and progressive dyspnea. He cannot do daily chores without feeling out of breath. He was diagnosed in childhood with a milder X-linked dystrophinopathy that has caused progressive proximal muscle weakness and gait abnormalities over the years. Physical examination shows a waddling gait and weak patellar reflexes. Cardiovascular examination shows a holosystolic murmur, displaced point of maximal impulse, and bilateral pitting edema of the ankles. Laboratory studies show elevated levels of brain natriuretic peptide. Which of the following is the most likely underlying cause of this patient's muscle weakness?

A. Increased number of CTG repeats in the DMPK gene
B. Interruption of microtubule depolymerization through stabilization of GDP-tubulin
C. Impaired connection of cytoskeletal actin filaments to membrane-bound dystroglycan (Correct Answer)
D. Cell–mediated cytotoxicity against skeletal muscle antigens in the endomysium
E. Defective lysine-hydroxylysine crosslinking of tropocollagen

Explanation: ***Impaired connection of cytoskeletal actin filaments to membrane-bound dystroglycan*** - The description of a **milder X-linked dystrophinopathy** with progressive muscle weakness and gait abnormalities, coupled with cardiac manifestations like a **holosystolic murmur** and elevated **BNP**, is characteristic of a **dystrophinopathy**, such as **Becker muscular dystrophy**. - **Dystrophin** is a critical protein that links the **cytoskeletal actin filaments** to the **dystroglycan complex** at the sarcolemma, providing mechanical stability to muscle fibers. Impaired connection leads to muscle fragility and degeneration. *Increased number of CTG repeats in the DMPK gene* - This describes **myotonic dystrophy type 1**, which is an autosomal dominant condition, not X-linked. - While it causes muscle weakness, it is also associated with **myotonia**, testicular atrophy, and cataracts, which are not mentioned. *Interruption of microtubule depolymerization through stabilization of GDP-tubulin* - This mechanism is associated with **chemotherapeutic agents** like taxanes (e.g., paclitaxel, docetaxel), which interfere with cell division. - It does not explain a genetic, progressive muscle weakness disorder. *Cell–mediated cytotoxicity against skeletal muscle antigens in the endomysium* - This describes the pathophysiology of **polymyositis**, an **inflammatory myopathy**. - Polymyositis is an autoimmune condition and does not typically present as an X-linked inherited disorder diagnosed in childhood. *Defective lysine-hydroxylysine crosslinking of tropocollagen* - This mechanism is characteristic of disorders affecting **collagen synthesis** and cross-linking, such as **Ehlers-Danlos syndrome**. - These conditions primarily affect connective tissue, leading to joint hypermobility, skin hyperextensibility, and tissue fragility, not primarily progressive muscle weakness due to dystrophin deficiency.

Question 8: A 24-year-old male with cystic fibrosis is brought to the emergency room by his mother after he had difficulty breathing. He previously received a lung transplant 6 months ago and was able to recover quickly from the operation. He is compliant with all of his medications and had been doing well with no major complaints until 2 weeks ago when he began to experience shortness of breath. Exam reveals a decreased FEV1/FVC ratio and biopsy reveals lymphocytic infiltration. Which of the following components is present in the airway zone characteristically affected by the most likely cause of this patient's symptoms?

A. Pseudostratified columnar cells
B. Goblet cells
C. Simple cuboidal cells (Correct Answer)
D. Stratified cuboidal cells
E. Cartilage

Explanation: ***Simple cuboidal cells*** - The patient's symptoms, history of a lung transplant, and biopsy findings of **lymphocytic infiltration** suggest **bronchiolitis obliterans**, a form of chronic lung allograft dysfunction. - Bronchiolitis obliterans primarily affects the **small airways** (bronchioles), which are characterized by an epithelial lining of **simple cuboidal cells** and lack cartilage. *Pseudostratified columnar cells* - These cells line the **trachea** and **main bronchi** (larger airways), which are typically not the primary site of damage in bronchiolitis obliterans. - They are part of the **mucociliary escalator** and are also associated with cartilage. *Goblet cells* - While present in the **larger airways** along with pseudostratified columnar cells, goblet cells are less prominent or absent in the small bronchioles primarily affected by bronchiolitis obliterans. - Their characteristic function is mucus production, not the specific epithelial type of the affected bronchioles. *Stratified cuboidal cells* - This cell type is **rare** in the respiratory tract and is not characteristic of the small airways affected by bronchiolitis obliterans. - Stratified epithelia are typically seen in ducts of glands or specialized transitional zones, not the functional bronchioles. *Cartilage* - Cartilage provides structural support to the **trachea and main bronchi**, but it is **absent** in the small airways (bronchioles) that are the primary target of bronchiolitis obliterans. - The presence of cartilage would indicate a larger airway, contradicting the pathophysiology of this condition.

Question 9: An 82-year-old woman presents to the emergency department after a fall. Imaging reveals diffuse trauma to the left humerus from the midshaft to the distal metaphysis with shearing of the periosteum. The orthopedic surgeon suggests a follow-up in 2 weeks. In that time, the patient develops worsening pain. At follow-up, she is found to have diffuse bone necrosis from the midshaft of the left humerus to the distal metaphysis, with no involvement of the distal forearm structures. Which of the following structures must have been damaged to cause this diffuse bone necrosis?

A. Volkmann’s canal
B. Haversian canal
C. Epiphyseal plate
D. Brachial artery (Correct Answer)
E. Ulnar nerve

Explanation: ***Brachial artery*** - Damage to the **brachial artery** can compromise the blood supply to the entire distal upper limb, leading to **ischemia** and subsequent **bone necrosis**, particularly in the humerus as described. - The extensive necrosis from the midshaft to the olecranon process suggests a significant vascular insult affecting a large portion of the bone. *Volkmann’s canal* - **Volkmann’s canals** primarily house small blood vessels and nerves that run perpendicular to the long axis of bone, connecting Haversian canals. - Damage to these microscopic canals alone would not typically cause such a widespread and diffuse pattern of macroscopic bone necrosis. *Haversian canal* - **Haversian canals** contain the blood vessels and nerves within the osteons, the basic structural units of compact bone. - While essential for local bone viability, damage to individual Haversian canals would lead to microscopic areas of necrosis, not the widespread bone death observed here. *Epiphyseal plate* - The **epiphyseal plate (growth plate)** is responsible for longitudinal bone growth and is typically found in growing children, not an 82-year-old woman. - Damage to this structure in a child would primarily affect bone development and length, not widespread necrosis in an adult. *Ulnar nerve* - The **ulnar nerve** carries motor and sensory fibers to parts of the forearm and hand and does not supply blood to the bone. - Damage to the ulnar nerve would result in neurological deficits, such as numbness and weakness, but would not directly cause bone necrosis.

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