regarding gi function, which of the following best describes the actions of atropine? a. atropine enhance the release of gastric juices. b. atropine is a competetive antagonist of cholinergic muscarinic post- synaptic receptors. c. atropine is a competetive antagonist of adrenergic post- synaptic receptors. d. atropine is secreted by chief cells in the stomach.