What increases the surface area in the stomach?

A. Endocardium: The endocardium is the innermost layer of the heart wall, lining the chambers and valves, and is not in contact with pericardial fluid.

B. Fibrous pericardium: This is the outermost layer of the pericardium but is not part of the heart wall. It provides protection and support but does not come into direct contact with pericardial fluid.

C. Epicardium: The epicardium is the outer layer of the heart wall and is in direct contact with pericardial fluid, which is found between the epicardium and the pericardium.

D. Myocardium: The myocardium is the middle muscular layer responsible for heart contractions and is not in contact with pericardial fluid.

A. Marrow: The hollow spaces within long bones contain bone marrow, which is responsible for the production of blood cells.

B. Natural killer cells: Natural killer cells are a type of lymphocyte found in the bloodstream and tissues but not directly within the hollow spaces of bones.

C. Enzymes: Enzymes are not found specifically in the hollow spaces of long bones; they are present throughout the body and are involved in metabolic processes.

D. Plasma cells: Plasma cells are derived from B cells and are primarily located in lymphatic tissue and bone marrow but do not fill the hollow spaces of long bones.