QUESTION 1
A pathologist is examining a neoplasm under a microscope. No identifiable structural features are exhibited for the neoplasm (e.g., glandular architecture). To assist in the diagnosis of the tumor type, the pathologist has a desmin immunohistochemical stain performed on the tumor. The desmin stain is positive. Of the following, from which cell type does the tumor most likely derive?
A. Hyaline cartilage
B. Squamous epithelium
C. Mucous producing glandular epithelium
D. Brain
E. Muscle
Answer for Question 1
Answer: E (muscle).
Explanation: Desmin is a type of intermediate filament that is found in the cytoskeleton of muscle cells. Desmin forms scaffolding for the contraction of actin and myosin. The other tissues listed (hyaline cartilage, squamous epithelium, mucous producing glandular epithelium, and brain) should not stain positive for desmin as this form of intermediate filament would not be abundantly present, such as it is in muscle.
QUESTION 2
A pathologist is examining a neoplasm under a microscope. No identifiable structural features are exhibited for the neoplasm (e.g., glandular architecture). To assist in the diagnosis of the tumor type, the pathologist has a desmin immunohistochemical stain performed on the tumor. The desmin stain is positive. Which of the following is the normal cellular constituent in which the desmin is found?
A. Plasma membrane
B. Microfilaments
C. Intermediate filaments
D. Microtubules
E. Nuclear membrane
Answer for Question 2
Answer: C (intermediate filaments).
Explanation: intermediate filaments are components of the cytoskeleton. Common intermediate filaments include vimentin, desmin, neurofilaments, glial fibrillary acidic protein, and cytokeratins. The presence of a specific intermediate filament within a tumor type can help a pathologist identify the cell of origin, and thus, often, the tumor type.
QUESTION 3
After putting out a house fire, firemen find the body of the owner of the house in the bedroom on the bed and with multiple beer bottles on the adjacent night stand. Although he is covered with soot from the fire, he has no thermal injuries of the skin. An autopsy is performed and the cause of death is determined to be carbon monoxide poisoning. Of the following, what was the mechanism of his death?
A. Hypoxia
B. Ischemia
C. Thrombosis
D. Immunologic reaction
E. Sepsis
Answer for Question 3
Answer: A (hypoxia)
Explanation: carbon monoxide binds to hemoglobin, restricting the normal binding of oxygen; thus, although blood is flowing through the vessels, an insufficient amount of oxygen can be delivered to the tissues. The man was hypoxic. There would be no arterial or venous obstruction, and thus, ischemia would not occur. Also, carbon monoxide poisoning in the short term does not cause thrombosis, an immunologic reaction, or sepsis.