Lecture 1: GI physiology lecture Flashcards
Name the 4 functions of the ailmentary system in order?
- Motility
- Secretion
- Digestion
- Absorption
What are the two intrinsic nerve plexus for the GI tract?
Myentric plexus aka Auerbach’s
Submucosal plexus aka Meissner’s
What are the locations of the Myentric and submucosal plexus?
Myentric: Situated between the circular and longitudinal muscle (muscularis externa layer).
Submucosal: Situated in the submucosal layer.
Define the term Basic Electrical rhythm in relation to the GI tract?
Whats its function
It is the spontaneous depolarisation and repolarisation of the pacemaker (also known as interstitial cells of Cajal) cells in the GI tract.
Function is to control the frequency of contractions in the GI tract.
This depolarisation-repolarisation causes a slow wave (the basic electrical rhythm), which is transmitted to the smooth muscle.
What is the basic electrical rhythm for the stomach?
3 per minute
What is the basic electrical rhythm for the duodenum?
12 per minute
Name the 3 salivary glands?
- Parotid gland
- Submandibular gland
- Sublingual gland
What is the 3 functions of the saliva?
- Lubrication for swallowing and speech
- Antibacterial properties (lysozymes)
- Secretes amylase (digestion of carbohydrate)
What is the function of amylase?
It begins the digestion of complex carbohydrates (i.e. polysaccharids) e.g. glycogen
NOTE: No effect on disaccharides and monosaccharides
Give an example of a polysaccharides?
Glycogen (from animals) or starch (from plants)
Give an example of a disaccharide?
Maltose, sucrose, lactose
Give an example of a monosaccharide?
Glucose
Galactose
Fructose
What are the two controls for salivary secretion?
Simple salivary reflex
Pressure receptors in oral cavity
Acquired salivary reflex
Thinking about food makes you salivate
Describe the primary peristaltic wave in the oesphagus?
Innervated by the vagus nerve
Wave-like contractions that move the bolus towards the stomach
Controlled by the swallowing centre in the medulla
Describe the secondary peristaltic wave in the oesphagus?
This occurs after the primary peristaltic wave
If food is struck, it triggers pressure receptors in the oesphagus, initiating the secondary peristaltic wave.
It is a secondary, more forceful wave-like contractions to remove this leftover bolus to the stomach
What is secretions in the oesphagus?
Mucus- for lubrication and protection
What are the epithelium that covers the oesphagus?
Stratified sqamous epithelium
Describe the phases of swallowing?
Pharyngeal phase:
1 second
Voluntarily
Oesphageal phase:
5-9 seconds
Involuntary
What are the factors that control gastric emptying?
Volume/fluidity of chyme (+ve effect)
Secretin and cholycystokinin (CCK) secreted by the duodenum (-ve effect)
Contents of the chyme (more lipid = slower emptying)
What is the function of pepsinogen?
Pepsinogen - > Pepsin
In the presence of gastric acid
What is the function of pepsin?
Digests protein
What is the difference between surface mucous cells and mucous neck cells?
Surface mucous cells: Secrete mucus and bicarbonate
Mucous neck cells: stem cell compartment
Describe the process of hydrochloric acid production by the parietal cell?
Water and carbon dioxide is converted by carbonic anhydrase into carbonic acid.
Carbonic acid is converted into bicarbonate and hydrogen ion.
The bicarbonate is exchanged for chlorine
Hydrogen ions are exchanged into the lumen from potassium ions
What is the function of hydrochloric acid in the stomach?
Initiates the conversion of pepsinogen to pepsin
Denatures proteins: untangles tertiary proteins into linear proteins so they are easily digested
Barrier immunity: killed pathogens.
Name these different parts of the hydrochloric acid production?
What excretes the hydrogen ions from the parietal cell into the lumen of the gastric pit?
Proton pump
Where is pepsinogen stored in the chief cells?
Zymogen granules
What gets absorbed in the stomach?
Few things are absorbed in the stomach.
Alcohol, aspirins and NSAIDs
Name the controls that stimulate the gastric secretions in the stomach?
Cephalic phase: it is smelling, taste, etc. This increases the acetyl chloine release from the vagus nerve.
Gastric phase: it is the presence of proteins, causing the stomach to be distented
Name the controls that inhibit the gastric secretions in the stomach?
Removal of proteins and distention as the stomach empties
Accumulation of acid (inhibits via D cell somatostatin)
Intestinal phase: enterogastric and enteroendocrine reflex
What is the function of Motilin?
Increases the migrating motility complex
Stimulates the production of gastrin
Overall, improves peristalsis in the small intestine to clear it out in preparation of the next meal
Describe what happens when there is more fat than protein products in the duodenum?
Triggers the release of cholecystokinin (CCK) via the gastroendocrine reflex.
CCKs travel in the bloodstream and stimulates the pancreas to release pancreatic enzymes from the Acinar cells
Describe what happens in the duodenum when chyme enters and gastric acid is still present?
This acidity triggers the release of secretin from S cells (gastroendocrine reflex).
Secretin travels in the bloodstream to the pancreas stimulating the release of bicarbonate from the Pancreatic duct cells
Which cells in the pancreas release bicarbonate?
Pancreatic duct cells
Which cells in the pancreas release pancreatic enzymes?
Pancreatic Acinar cells
Which is the function of bicarbonate in the duodenum?
It neutralises the pH of chyme from the stomach
What is the function of pancreatic proteolytic enzymes?
Continues the breakdown of proteins into small peptide chains and amino acids.
What are the three pancreatic enzymes that are released into the duodenum?
- Pancreatic proteolytic enzymes
- Pancreatic lipase
- Pancreatic amylase
What is the function of the pancreatic lipase?
Breaks down triglycerides into monoglycerids and free fatty acids
What is the function of pancreatic amylase?
Continue the digestion of carbohydrates
Breaks down polysaccharides into disaccharides
What parts of the small intestine perform most of the absorption?
Duodenum and jejunum
