________ act as hydrogen acceptors during cellular respiration.

A. elastic fibers:Elastic fibers are present in the skin, lungs, and blood vessel walls, providing resilience and the ability to stretch and recoil. In the skin, they maintain flexibility; in the lungs, they allow expansion and recoil during breathing; in blood vessels, they help accommodate pressure changes from blood flow.

B. reticular fibers:Reticular fibers form supportive networks in organs like the spleen, liver, and lymph nodes, but they are not a common feature of skin, lungs, or blood vessel walls.

C. simple squamous epithelium:Simple squamous epithelium is found lining blood vessels (endothelium) and alveoli in the lungs, but it is not present in the skin, so it is not a shared characteristic of all three tissues.

D. simple columnar epithelium:Simple columnar epithelium lines parts of the digestive tract and some glandular ducts but is absent from skin, lungs, and blood vessels, making it irrelevant as a shared feature.

A. intercalated discs:Intercalated discs connect cardiac muscle cells and contain desmosomes and gap junctions. Desmosomes provide mechanical strength to prevent cells from pulling apart during contractions, while gap junctions allow coordinated electrical signaling.

B. stroma:Stroma refers to the supportive connective tissue framework in organs. While it provides general support, it does not directly prevent cardiac muscle cells from separating during contraction.

C. myofilaments:Myofilaments, including actin and myosin, generate the contractile force in muscle cells. They are essential for contraction but do not provide structural adhesion between cells.

D. flana:Flana is not a recognized anatomical or histological structure in cardiac tissue, so it has no role in maintaining the cohesion of heart muscle cells.