Summarize digestive functions in terms of the hormones and neural systems that regulate it. (Hint: Cephalic, gastric, and intestinal phases)

Summarize digestive functions in terms of the hormones and neural systems that regulate it. (Hint: Cephalic, gastric, and intestinal phases)

1. The cephalic phase comprises those stimuli that originate from the head: sight, smell, taste, or thoughts of food, as well as emotional states. In response, the following reflexes are initiated:
Neural response: Stimuli that arouse digestion are relayed to the hypothalamus, which in turn initiates nerve impulses in the parasympathetic vagus nerve. These impulses innervate nerve networks of the GI tract (enteric nervous system), which promote contraction of smooth muscle (which causes peristalsis) and secretion of gastric juice. Stimuli that repress digestion (emotions of fear or anxiety, for example) innervate sympathetic fibers that suppress muscle contraction and secretion.
General effects: The stomach prepares for the digestion of proteins.
2. The gastric phase describes those stimuli that originate from the stomach. These stimuli include distention of the stomach (which activates stretch receptors), low acidity (high pH), and the presence of peptides. In response, the following reflexes are initiated:
Neural response: Gastric juice secretion and smooth muscle contraction are promoted.
Hormonal response: Gastrin production is promoted.
General effects: The stomach and small intestine prepare for the digestion of chyme, and gastric emptying is promoted.
3. The intestinal phase describes stimuli originating in the small intestine. These include distention of the duodenum, high acidity (low pH), and the presence of chyme (especially fatty acids and carbohydrates). In response, the following reflexes are initiated:
Neural response: Gastric secretion and gastric motility are inhibited (enterogastric reflex). Intestinal secretions, smooth muscle contraction, and bile and pancreatic juice production are promoted.
Hormonal response: Production of secretin, CCK, and GIP is promoted.
General effects: Stomach emptying is retarded to allow adequate time for digestion (especially fats) in the small intestine. Intestinal digestion and motility are promoted.