GI Flashcards
Is stage 1 of swallowing voluntary or involuntary?
Voluntary.
What happens in stage 1 of swallowing?
Food is compressed against the roof of the mouth and is pushed to the oropharynx by the tongue.
Is stage 2 of swallowing voluntary or involuntary?
Involuntary.
What happens in stage 2 of swallowing?
The nasopharynx closes off due to soft palate elevation. The trachea is closed off by the epiglottis. Elevation of the hyoid bone shortens and widens the pharynx.
Is stage 3 of swallowing voluntary or involuntary?
Involuntary.
What happens in stage 3 of swallowing?
The pharyngeal constrictor muscles sequentially contract producing peristaltic waves. This propels the bolus of food down the Oesophagus. This is followed by depression of the hyoid bone.
Name 6 muscles/groups of muscles that are involved in swallowing.
- Buccinator.
- Suprahyoids.
- Muscles of the palate.
- Muscles of the floor of the mouth.
- Infrahyoids.
- Pharyngeal constrictor muscles.
Which muscle(s) manipulate food in chewing. Elevate the hyoid bone and flatten the floor of the mouth?
Buccinator and Suprahyoids.
What is the function of the muscles of the soft palate in swallowing?
They act to tense and elevate the soft palate.
What is the function of the muscles of the floor of the mouth in swallowing?
They raise the hyoid bone and larynx.
What is the function of the infrahyoids?
To depress the hyoid bone and larynx.
What is the function of the pharyngeal constrictor muscles?
They contract sequentially producing peristaltic waves which drive food into the oesophagus.
Do parotid glands have mainly serous or mainly mucous acini?
Mainly serous acini.
What is serous acini secretion composed of?
alpha amylase - this is needed for starch digestion.
Do sublingual glands have mainly serous or mainly mucous acini?
Mainly mucous acini.
What is mucous acini secretion composed of?
Mucin - needed for lubrication.
Do submandibular glands have mainly serous or mainly mucous acini?
They have serous and mucus acini.
Which of the main salivary glands is constantly active?
Submandibular.
What is the function of saliva?
It acts as a lubricant for chewing, swallowing and speech. It is important in oral hygiene; has a role in immunity, wash and it can also act as a buffer.
What is the optimum oral pH?
7.2
What is the pH range of saliva?
6.2 - 7.4
Name 4 factors that can affect the composition of saliva.
- Stimulus.
- Age.
- Gender.
- Drugs.
Are serous acini dark staining or pale staining on a histological slide?
Dark staining.
Mucus acini = pale staining
What is the epithelium lining of intercalated ducts?
Simple cuboidal epithelium.
What is the function of intercalated ducts?
They connect acini to larger striated ducts.
What ions are reabsorbed at striated ducts?
Na+ and Cl-
Is saliva hypotonic or hypertonic?
Hypotonic - water reabsorption and ion secretion.
What is the importance of the striated duct basal membrane being highly folded?
It is folded into microvilli for the active transport of HCO3- against its concentration gradient.
What organelle is abundant in striated ducts and why?
Mitochondria. For the active transport of ions.
Name 2 ions that striated ducts secrete.
K+ and HCO3-
Name 2 ions that striated ducts reabsorb.
Na+ and Cl-
What ducts do striated ducts lead on to?
Interlobular (excretory) ducts.
What is the epithelium lining of interlobular ducts?
Simple columnar epithelium.
What is the parasympathetic innervation of the Parotid gland?
Cn 9 - glossopharyngeal.
What is the parasympathetic innervation of the Sublingual gland?
Cn 7 - facial.
What is the parasympathetic innervation of the Submandibular gland?
Cn 7 - facial.
What nerve passes through the parotid gland but does not innervate it?
The facial nerve (Cn 7) gives rise to its 5 terminal branches in the parotid gland.
What artery ascends through the parotid gland?
The external carotid artery.
Does parasympathetic innervation stimulate or inhibit salivary secretion?
Stimulates.
What is the volume of an empty stomach?
50ml
What is the maximum volume of the stomach?
1.5L
What is receptive relaxation?
Smooth muscle in the body and fundus of the stomach relaxes prior to the arrival of food, this allows the stomach volume to increase. There is afferent input from Cn 10. NO and serotonin also influence relaxation.
Where do peristaltic waves begin?
In the gastric body.
Where in the stomach are peristaltic contractions the most powerful?
In the gastric antrum.
Why is the pyloric sphincter closed as the peristaltic wave reaches it?
This prevents chyme entering the duodenum and so the gastric contents are forced back and mixed together in the body of the stomach.
On average, how many peristaltic waves are there a minute?
3 (slow repol/depol cycles).
Name 2 factors that can increase the strength of peristaltic contractions.
- Gastrin.
2. Gastric distension.
Name 5 factors that can decrease the strength of peristaltic contractions.
- Duodenal distension.
- Low pH in duodenum lumen.
- Increased duodenal osmolarity.
- Increased sympathetic action.
- Decreased parasympathetic action.
What do parietal cells secrete?
HCl and intrinsic factor.
What do chief cells secrete?
Pepsinogen and gastric lipase.
What cells secrete Gastrin?
Enteroendocrine cells / G cells.
What cells secrete somatostatin?
D cells.
What cells secrete histamine?
Enterochromaffin like cells.
On average, how much gastric acid do we secrete a day?
2L
What is the hydrogen ion concentration of gastric acid?
> 150mM
Where does the H+ come from in gastric acid?
In parietal cells: H2O + CO2 = HCO3- + H+
What is the mechanism of the H+/K+ ATPase proton pump?
It pumps H+ into the stomach lumen and K+ into the parietal cell.
What ions are exchanged on the side of the parietal cell in contact with the capillaries?
Cl- is pumped into the parietal cell and HCO3- moves out of the parietal cell into the capillary.
What is the importance of HCO3- being exchanged for Cl-?
HCO3- moving out of the cell increases the rate of the forward reaction and so more H+ are produced. Cl- moving into the cell then moves into the stomach lumen via Cl- channels and combines with H+ to form HCl.
What are the 4 phases important in regulating gastric acid secretion? Do these phases turn secretion on or off?
- Cephalic phase - turning ON.
- Gastric phase - turning ON.
- Gastric phase - turning OFF.
- Intestinal phase - turning OFF.
Regulating gastric acid secretion: What stimuli are involved in the cephalic phase?
Sight, smell, taste of food. Chewing.
Regulating gastric acid secretion: What stimuli are involved in the gastric ON phase?
Gastric distension, presence of peptides and amino acids in the stomach.
Regulating gastric acid secretion: What stimuli are involved in the gastric OFF phase?
Low pH in gastric lumen.
Regulating gastric acid secretion: What stimuli are involved in the intestinal phase?
Low pH in duodenal lumen, duodenal distension, presence of amino acids and fatty acids in the duodenum.
Briefly describe the cephalic phase.
The parasympathetic nervous system is triggered by stimuli. This releases Ach. Ach acts on parietal cells and on gastrin and histamine. HCl secretion increases.
Briefly describe the gastric ON phase.
Gastrin is released in response to the stimuli. This acts on parietal cells and triggers release of histamine (histamine then acts on parietal cells too). HCl secretion increases.
Briefly describe the gastric OFF phase.
Gastrin is inhibited in response to stimuli and histamine is therefore indirectly inhibited. Somatostatin is also released and this inhibits parietal cells. HCl secretion decreases.
Briefly describe the intestinal phase.
The enterogastrones secretin and CCK are released in response to stimuli. Secretin inhibits gastrin and stimulates further somatostatin release. HCl secretion decreases.
What neurotransmitter is involved in regulating gastric acid secretion?
Ach.
What hormone is involved in regulating gastric acid secretion?
Gastrin.
What paracrine factors are involved in regulating gastric acid secretion?
Histamine and Somatostatin.
What enterogastrones are involved in regulating gastric acid secretion?
Secretin and CCK.
Name the 4 main defence mechanisms against gastric acid secretion.
- Alkaline mucous.
- Tight junctions between epithelial cells.
- Replacing damaged cells.
- Feedback loops.
Define ulcer.
A breach in a mucosal surface.
Name 3 things that can cause peptic ulcers.
- Helicobacter pylori.
- NSAIDS.
- Chemical irritants.
Why do NSAIDS cause peptic ulcers?
They inhibit cycle-oxygenase 1.
Cycle-oxygenase 1 is needed for prostaglandin synthesis, prostaglandins stimulate mucus secretion. Without cycle-oxygenase 1 there is less mucus and so the mucosal defence is reduced.
Why does helicobacter pylori cause peptic ulcers?
Helicobacter pylori lives in gastric mucus. It secretes urease. Urease breaks into CO2 and NH3. The NH3 combines with H+ to form NH4+. NH4+ damages the gastric epithelium, an inflammatory response is triggered and mucosal defence is reduced.
Name 2 drugs that can be used to reduce gastric acid secretion.
- Proton pump inhibitors.
2. H2 receptor antagonists.
If water input is 9L, how much is reabsorbed and how much is excreted in the faeces?
8.8L is reabsorbed and 0.2L is excreted in the faeces.
How does water move across the small intestine?
It moves freely by osmosis and also via aquaporins.
How does Na+ move across the small intestine?
Na+ is actively transported from the lumen by pumps located in the cell membranes in the ileum and jejunum.
How does K+ move across the small intestine?
Via passive diffusion. Movement is determined by the potential difference between lumen and capillaries.
Where does Cl- and HCO3- reabsorption mainly take place?
In the ileum and colon.
What is the mechanism for Cl- and HCO3- reabsorption?
Cl- is actively reabsorbed in exchage for HCO3-. The intestinal contents therefore become more alkaline.
What enzyme digests starch in the small intestine?
Pancreatic amylase.
What bonds does pancreatic amylase break?
alpha 1-4 linkages.
What are the end products of starch digestion?
Maltose!
Also maltotriose, glucose polymers and alpha-dextrins.
Where in the small intestine are bile salts absorbed?
Jejunum.
What enzyme(s) hydrolyse peptide bonds in the stomach?
Pepsins.
What is the optimum pH for pepsins?
1.6-3.2
Why is pepsin action terminated in the small intestine?
The pH in the small intestine is too alkaline and so it denatures.
What enzyme(s) further break down peptides in the small intestine?
Pancreatic proteases.
What is the precursor molecule for pepsin?
Pepsinogen.
What activates pepsinogen?
Low pH.
What 2 groups can pancreatic proteases be divided into?
- Endopeptidases e.g. trypsin.
2. Exopeptidases e.g. carboxy dipeptidases.
How do amino acids get absorbed into the blood?
Passive diffusion.
What enzyme(s) hydrolyse cholesterol esters in the intestinal lumen?
Pancreatic esterases.
What emulsifies lipids?
Bile salts.
What is the advantage of emulsifying lipids?
It increases the SA for digestion and so digestion is more efficient.
What digests lipids in the small intestine?
Pancreatic lipases.
Are lipids hydrophobic or hydrophilic?
Hydrophobic.