WBR0866

Author	[[PageAuthor::Serge Korjian M.D. (Reviewed by Serge Korjian)]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Histology
Sub Category	SubCategory::Pulmonology
Prompt	[[Prompt::A medical student is examining a tissue sample from a human lung. Microscopically, he notices several thin appearing interconnected cells with a few larger interspersed cuboidal granular cells with several intracellular inclusions. If the student was able to isolate the cytoplasmic content of the cuboidal cells, what would he most likely find large contents of?]]
Answer A	AnswerA::Phosphatidates
Answer A Explanation	AnswerAExp::Phosphatidates are the basis for the formation of most modified phospholipids. They are found in large amounts in the cell membrane. They are not components of the pulmonary surfactant.
Answer B	AnswerB::Ethanolamine-based phospholipids
Answer B Explanation	AnswerBExp::Ethanolamine-based phospholipids are important components of the cell membrane particularly in neural tissue. They are not components of the pulmonary surfactant.
Answer C	AnswerC::Choline-based phospholipids
Answer C Explanation	AnswerCExp::The pulmonary surfactant is a choline-based phospholipid known as DPPT. It is contained in large amounts in the cytoplasm of type II pneumocytes. Choline-based phospholipids are also found in the cell membrane.
Answer D	AnswerD::Serine-based phospholipids
Answer D Explanation	AnswerDExp::Serine-based phospholipids are also found in large amounts in the cell membrane and are responsible in part for the process of apoptosis. They are not components of the pulmonary surfactant.
Answer E	AnswerE::Inositol-based phospholipids
Answer E Explanation	AnswerEExp::Inositol-based phospholipids are found in the cell membrane are important as second messengers. They are not components of the pulmonary surfactant.
Right Answer	RightAnswer::C
Explanation	[[Explanation::Type II pneumocytes are important structural and functional components of the lung parenchyma. Structurally, they are responsible for regenerating type I pneumocytes that create the alveolar membrane after damage. They are also the primary cells responsible for the secretion of the pulmonary surfactant. Surfactant is a functional term used to refer to dipalmitoylphosphatidylcholine (DPPT) a choline-based phospholipid that functions to lower alveolar surface tension preventing alveolar collapse. DPPT has the capability of lowering surface tension to approximately zero. Type II pneumocytes contain numerous cytosolic aggregations of DPPT known histologically as lamellar bodies or granules. These granules are also observed in the outer layers of the skin. They are released by keratinocytes an result in the formation of a lipid-containing outer covering that serves as a water barrier. Educational Objective: Type II pneumocytes are cuboidal cells found interspersed among type I pneumocytes that contain high levels of DPPT (surfactant) a choline-based phospholipid. References: Ryan US, Ryan J, Smith D. Alveolar type II cells: Studies on the mode of release of lamellar bodies. Tissue and Cell. 1975;7(3):587-599.]]
Approved	Approved::Yes
Keyword	WBRKeyword::Pulmonary surfactant, WBRKeyword::DPPT, WBRKeyword::Type II pneumocytes
Linked Question	Linked::
Order in Linked Questions	LinkedOrder::