1) A molecule which is lacking in lungs of the premature infant is the ______.  It functions to help to keep alveoli from collapsing.  Positive pressure equipment is necessary in such a situation.

2) Large folds in the stomach known ______ increase its surface area and also enable it to fold on itself when empty.   The ______ is a valve that enables partially digested food out of stomach into the ______.   The ______ enables food to enter the stomach from ______.  Two key cells in wall of the stomach generate the digestive juices.  The ______ cells generate hydrochloric acid and the ______ cells produce enzymes which help to break down proteins.