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
What is the function of bicarbonate secretion
Neutralises stomach acid to protect the small intestine
Which hormones regulate pancreatic exocrine function
Secretin (bicarbonate) and CCK (enzymes for fat and protein digestion)
What is Type I diabetes
An autoimmune condition where the body produces no insulin
What is Type II diabetes
A condition where insulin is present but the body’s cells don’t respond to it properly (insulin resistance)
A condition where insulin is present but the body’s cells don’t respond to it properly (insulin resistance)
Glucose cannot enter cells, leading to high blood sugar levels
What is the liver’s position in digestion
It is the body’s second largest organ and first processing site for absorbed nutrients
What is the liver primarily made of
Hepatocytes, arranged into lobules
What are three key metabolic functions of the liver
Carbohydrate regulation, fat metabolism, and protein processing (including converting ammonia to urea)
What is the function of bile
To emulsify fats for digestion and excrete bilirubin
What vitamins and minerals are stored in the liver
Vitamins A, D, E, K, B12, iron, and copper
How does the liver detoxify the body
By filtering toxins and metabolising drugs and hormones
How does the liver contribute to Type 2 diabetes
Insulin resistance in hepatocytes causes the liver to overproduce glucose
What is NAFLD
Non-alcoholic fatty liver disease – fat builds up in the liver due to insulin resistance
Non-alcoholic fatty liver disease – fat builds up in the liver due to insulin resistance
NASH (non-alcoholic steatohepatitis), cirrhosis, and liver failure
