In the digestive tract, what organ is found just inferior to the esophagus?

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A. IgD: IgD is mainly a B-cell receptor on naïve B cells and is not the dominant secretory antibody in mucosal secretions or breast milk.
B. IgA: Secretory IgA is abundant in breast milk (colostrum) and mucosal secretions (tears, saliva, nasal fluid) and helps protect infants’ mucosal surfaces from pathogens.
C. IgE: IgE is involved in allergy and parasitic defense and is not the primary protective antibody in breast milk or mucosal secretions.
D. IgM: IgM is the first antibody produced in primary responses and is mainly intravascular; it is not the dominant secretory antibody passed in milk.

A. Endocardium: The endocardium is the inner endothelial lining of the heart chambers (endothelium + connective tissue), not cardiac muscle, so it does not contain intercalated discs.
B. Parietal pericardium: The parietal pericardium is the outer layer of the serous/fibrous sac surrounding the heart (protective membrane), not muscle tissue, so it lacks intercalated discs.
C. Epicardium: The epicardium (visceral layer of serous pericardium) covers the heart surface and contains connective tissue and fat; it overlies the myocardium but is not the muscle layer itself, so it does not have intercalated discs.
D. Myocardium: The myocardium is the heart’s muscular wall composed of cardiac muscle cells that are connected by intercalated discs (for electrical and mechanical coupling).