The red stained circular tissue component in the image is which tissue type?

• A. smooth muscle
• B. collagen
• C. liver
• D. adipose

Answer: (A)

Recognizing tissue types by cell shape, organization, and how they take up stain is key here. The red, eosinophilic staining of the circular bands points to smooth muscle cells, which have a non-striated, spindle-shaped appearance and are organized in circular layers around lumens. In a cross-section of a tubular organ, these circular smooth muscle fibers form distinct rings that encircle the lumen, and their cytoplasm stains pink to red with hematoxylin and eosin due to actin-myosin content.

If this were collagen, you’d see wavy, fibrous pink ribbons of extracellular matrix rather than tightly packed circular bands of cells. Adipose tissue would show large, pale, intracellular lipid droplets with nuclei pushed to the periphery, not dense circular muscle rings. Liver tissue would display hepatocytes in plates with central veins, not circular muscle layers.

So the circular, red-stained component is smooth muscle.