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Chapter 1. Epithelium

A researcher was using reverse transcription polymerase chain reaction (RT-PCR) to screen blood samples for carcinoma cells that had metastasized into the bloodstream of a patient. RT-PCR is a technique used for amplifying a defined sequence of RNA, and can provide a sensitive method of detecting a small number of cells that contain unique mRNAs in a tissue sample. Carcinomas are malignant tumors derived from epithelial cells. Blood can be considered as a specialized connective tissue. The researcher's RT-PCR primers should most likely be designed to amplify the mRNA encoding of which of the following proteins?

A. Actin

B. Collagen

C. Elastin

D. Keratin

E. Vimentin

The answer is D: The only protein in the choices given that is specific for epithelial cells is keratin, making it the most likely target of the researcher's test. Specific keratins are expressed by carcinomas, and identifying these keratins is a useful tool for determining properties of cancer, such as the likely site of origin of metastatic tumors.

Inherited defects in epithelial cell cilia function can result in human infertility; that is, sperm do not swim properly in males and eggs are not transported efficiently in females. A young couple arrives at an infertility clinic because they have not been able to conceive. Because these defects affect many epithelial cells throughout the body, the physician might be able to quickly identify the affected partner simply by asking each of them, "Which of the following symptoms do you experience?"

A. Dry mouth

B. Excessive bruising

C. Fragile skin

D. Frequent diarrhea

E. Numerous colds

The answer is E: Cilia in the large airways of the lungs and the trachea sweep mucus up toward the oral cavity. The mucus traps pathogens that enter the respiratory system and provides an important defense against infection. Therefore, the partner who experiences numerous colds will most likely be the affected partner.

A researcher is studying an epithelial cell line that forms a sheet of cells and resembles gut epithelium in culture. These cells contain a heat-sensitive mutation. In cultures grown at 34°C, a small amount of fluorescent dye injected into one cell quickly diffuses to neighboring cells. At 39°C, however, the dye remains only in the injected cell. Careful microscopic examination shows no differences between the sheets at either temperature. It would be reasonable to expect to find the mutation ...

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