6 - Movement and Coordination of GI Tract Flashcards
What are the three regulatory mechanisms of the GI tract
Endocrine, paracrine, and neurocrine control mechanisms
What systems work together to regulate gastric secretions
The nervous and endocrine systems
What are the three phases of digestion
Cephalic phase, gastric phase, and intestinal phase
What triggers the cephalic phase
Sight, smell, taste, or thought of food
What nervous pathway activates the cephalic phase
Nerve fibres from the medulla stimulate the parasympathetic system
What percentage of gastric acid is secreted during the cephalic phase
Around 20%
What activates the gastric phase
Stomach stretch and chemical stimulation from swallowed food
What percentage of gastric acid secretion occurs in the gastric phase
50–60%
Which cells are stimulated in the gastric phase and by what
G-cells (gastrin – endocrine) and ECL cells (histamine – paracrine)
What occurs in the intestinal phase
Chyme entering the duodenum triggers a reduction in gastric secretion
What hormones inhibit gastric secretion during the intestinal phase
Secretin and cholecystokinin (CCK)
What is the ‘pyloric brake’
A mechanism slowing gastric emptying due to low pH and CCK action
Where is the pancreas located
Behind and beneath the stomach, with the head near the duodenum and tail near the spleen
What are the two main functions of the pancreas
Endocrine (hormone secretion) and exocrine (digestive enzyme secretion)
What are the islets of Langerhans
Clusters of cells that secrete insulin (β-cells), glucagon (α-cells), and somatostatin (δ-cells)
What does insulin do
Lowers blood glucose by promoting uptake and storage in liver, muscle, and fat cells
What triggers insulin secretion
Increased blood glucose levels
What does glucagon do
Raises blood glucose by promoting glycogenolysis and gluconeogenesis
When is glucagon released
During low blood glucose, fasting, or exercise
What is somatostatin’s role in the pancreas
Inhibits both insulin and glucagon secretion
What cells produce digestive enzymes in the pancreas
Acinar cells
What does pancreatic amylase digest
Carbohydrates into sugars
What does pancreatic lipase do
Breaks down fats, with help from bile
What do proteases like trypsin and chymotrypsin digest
Proteins
