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.
