PHYSIOLOGY - The Gastrointestinal System Flashcards
What is mastication?
Mastication is the mechanical processing of food that is mixed with saliva to form a bolus for deglutition
What is the digestive enzyme found in saliva?
Lingual/salivary amylase
What type of gland is the parotid salivary gland?
The parotid salivary gland is a serous gland
What type of gland is the mandibular salivary gland?
The mandibular salivary gland is a merocrine gland
What type of gland is the sublingual salivary gland?
The sublingual salivary gland is a merocrine gland
What are acini?
Acini are the small sacs present at the end of salivary ducts
Which hormone stimulates saliva production?
Aldosterone
What are the three phases of deglutition?
Oral phase
Pharyngeal phase
Oesophageal phase
Which phase of deglutition is a voluntary phase?
Oral phase of deglutition
Which phases of deglutition are involuntary?
Pharyngeal phase
Oesophageal phase
Describe the oral phase of deglutition
During the oral phase of deglutition, the tongue moves the bolus caudally towards the oropharynx
Describe the pharyngeal phase of deglutition
During the pharyngeal phase of deglutition, the bolus stimulates pressure-sensitive sensory cells at the palatopharyngeal arches which stimulate a reflex to relax the cricopharyngeal muscle (upper oesophageal sphincter) and simultaneously contracts the pharyngeal muscles to push the bolus down towards the oesophagus, and moves the hyoid apparatus rostrally to hold the epiglottis over the larynx
Describe the oesophageal phase of deglutition
During the oesophageal phase of deglutition, peristaltic contractions of the oesophagus move the bolus towards the cardiac sphincter
What are the four functions of the stomach?
Food storage
Mechanical breakdown of food
Chemical breakdown of food
Secretion of intrinsic factors involved in Vitamin B12 absorption
What are the three different actions of gastric motility?
Propulsion
Grinding
Retropulsion
Describe propulsion in regards to gastric motility
Propulsion is the movement of the bolus from the fundus towards the pylorus via peristaltic contractions
Describe grinding is regards to gastric motility
Grinding is the peristaltic contractions that mix the bolus with the gastric juices to form chyme
Describe retropulsion in regards to gastric motility
Retropulsion is the action of the pylorus which delivers small quantities of chyme into the duodenum while simultaneously moving most of the chyme back into the stomach
What are the four types of cells found in the stomach mucosa?
Mucin-producing cells
Parietal cells
Chief cells
Neuroendocrine cells
What are the two types of neuroendocrine cells found in the stomach mucosa?
G-cells
Enterochromaffin-like cells
What is the function of mucin-producing cells?
Mucin-producing cells produce mucin which makes up mucus
What is the function of the mucus layer in the stomach?
The mucus layer of the stomach protects the stomach lining from the acidity of the gastric juices
What are the functions of parietal cells?
Parietal cells produce HCL and intrinsic factors for vitamin B12 absorption
What is the function of chief cells?
Chief cells produce pepsinogen (inactive form of pepsin)
What is the function of G-cells?
G-cells produce gastrin hormone
What are the three functions of the gastrin hormone?
Gastrin stimulates HCl secretion from the parietal cells
Gastrin stimulates pepsinogen secretion from the chief cells
Gastrin stimulates pancreatic juice secretion
What stimulates gastrin secretion from the G-cells?
Distension of the stomach stimulates Gastrin secretion from the G-cells
What is the function of Enterochromaffin-like cells?
Enterochromaffin-like cells produce histamine
Which cells are found within the cardiac mucosa?
Mucin-producing cells
Which cells are found within the fundus and corpus mucosa?
Mucin-producing cells
Parietal cells
Chief cells
Which cells are found within the pyloric mucosa?
Neuroendocrine cells (G-cells and Enterochromaffin-like cells)
What is auto-catalysis?
Auto-catalysis is the activation of pepsinogen into pepsin by the presence of HCL or pepsin itself
Describe the process of HCL production in parietal cells
- Carbonic anhydrase within the parietal cells catalyses the production of carbonic anhydrase from CO2 and H2O
- Carbonic acid readily dissociates into HCO3- and H+
- H+ exits the cell into the gastric lumen in exchange for K+
- HCO3- exits the cell into the gastric lumen in exchange for Cl-
- Cl- exits the cell into the gastric lumen and H+ and Cl- react to form HCL
What are the three factors that regulate HCL production in the parietal cells?
Acetylcholine
Gastrin
Histamine
What is cephalic digestion?
Cephalic digestion is when the sight, smell or taste of food triggers the vagus nerve to stimulate HCL production from the parietal cells in anticipation of digestion
How is gastric emptying stimulated?
NEURAL:
- long reflexes via the vagus nerve and short reflexes via the stomach wall which stimulate acetylcholine release, initiating smooth muscle contraction of the stomach
ENDOCRINE:
- gastrin hormone stimulates gastric contractions which relax the pyloric sphincter
Which cells regulate gastric emptying?
Interstitial cells of Cajal
How do the interstitial cells of Cajal regulate gastric emptying?
The interstitial cells of Cajal produce spontaneous oscillations within the smooth muscle of the stomach and the small intestine, synchronising the smooth muscle activity and this the rate of gastric emptying with the absorption capacity of the small intestine. Neural, hormonal or mechanical input can bring these oscillations up to threshold value, triggering an action potential, smooth muscle contraction and gastric emptying
What has the greatest impact on the rate of gastric emptying?
The conditions within the duodenum have the greatest impact on the rate of gastric emptying
What is the main function of the pancreas within the digestive system?
Exocrine secretions of pancreatic juices
What are the two pancreatic ducts and where do they run into the duodenum?
Pancreatic duct joins with the common bile duct and empties into the major duodenal papilla
Accessory pancreatic duct empties into the minor duodenal papilla
What are the two cell types involved in pancreatic juice secretion?
Pancreatic intercalated duct cells
Acinar cells
What is produced and secreted by pancreatic intercalated duct cells?
Pancreatic intercalated duct cells produce and secrete bicarbonate
What is produced and secreted by acinar cells?
Acinar cells produce and secrete pancreatic enzymes
What is the function of the hormone secretin in pancreatic function?
Secretin is produced by the duodenum in response to acidic chyme to stimulate bicarbonate secretion from the pancreatic intercalated cells
What is the function of the hormone cholecystokinin (CCK) in pancreatic function?
Cholecystokinin (CCK) is produced by the duodenum is response to increased lipid concentrations to stimulate the secretion of pancreatic enzymes from the acinar cells of the pancreas
What are the three phases of pancreatic juice secretion?
Cephalic phase
Gastric phase
Intestinal phase
Describe the cephalic phase of pancreatic juice secretion
The sight, smell or taste of food triggers the vagus nerve to stimulate gastrin production which stimulates pancreatic juice secretion in anticipation of digestion
Describe the gastric phase of pancreatic juice secretion
Bolus distends the stomach stimulating a reflex which triggers further pancreatic juice secretion
Describe the intestinal phase of pancreatic juice secretion
Acidic chyme enters the duodenum stimulating secretin to stimulate further secretion from the pancreatic intercalated duct cells and increased lipid concentration stimulates cholecystokinin (CCK) which stimulates further secretion from the acinar cells
What are the two main functions of the liver within the digestive system?
Bile synthesis and secretion
Regulation of nutrient absorption into the systemic circulation
What is the function of bile salts (the primary component of bile)?
Bile salts are involved in the emulsification of lipids
What is the role of secretin in liver function?
Secretin is produced by the duodenum is response to acidic chyme and stimulates bile production in the hepatocytes
What is the role of cholecystokinin (CCK) in liver function?
Cholecystokinin (CCK) is produced by the duodenum in response to increased lipid concentration in the duodenum and stimulates the contraction of the gallbladder to allow for stored bile secretion
What is the main function of the small intestine?
The small intestine is the main site of nutrient degradation and absorption
Which macromolecule is exclusively absorbed by the small intestine?
Lipids are exclusively absorbed by the small intestine
What are the three different actions of small intestinal motility?
Segmentation
Peristalsis
Migrating mobility complex
Describe segmentation in regards to small intestinal motility
Segmentation is the action of circular muscle within the muscularis externa which contracts to segment the chyme within the small intestine, moving it backwards and forwards
Describe the migrating mobility complex in regards to small intestinal motility
When the nutrients are absorbed within the small intestine, segmentation stops and the migrating mobility complex contractions clear the indigestible residue from from the small intestine into the large intestine
What are the cells which regulate small intestinal motility?
Interstitial cells of Cajal
What are the two cells involved in small intestinal secretions?
Paneth cells
Goblet cells
What is produced and secreted by paneth cells in the small intestine?
Paneth cells produce and secrete antimicrobial peptides
What is produced and secreted by goblet cells in the small intestine?
Goblet cells produce and secrete mucus
Where are goblet cells and paneth cells found within the small intestine?
The crypts of Leiberkuhn
What is the function of the Brunner’s glands in the small intestinal muscosa and submucosa?
Brunner’s glands produce of an alkaline mucous secretion to neutralise the acidic chyme exiting the stomach through the and so preventing acidic damage to the mucosa of the small intestine
Describe the process of small intestinal emptying
When indigestible residue reaches the ileocolic orifice, the orifice is relaxed by the pressure of the residue. When this residue enters the colon, the colon is distended which closes the ileocolic orifice
What are the two main functions of the large intestine?
Absorption of water and ions from indigestible residue
Microbial digestion of any remaining carbohydrates or proteins
What are the four different actions of large intestinal motility?
Segmentation
Peristalsis
Retroperistalsis
Mass movements
What is the purpose of retroperistaltic contractions of the large intestine?
Retroperistaltic contractions of the large intestine ensure that all of the nutrients are absorbed from the ingest before defecation occurs
What are mass movements of the large intestine?
Mass movements are contractions of the terminal colon and the rectum resulting in defecation
