Digestion 7 Flashcards
What are the functions of HCl? (3)
- Precipitates soluble proteins for them to remain longer in the stomach (why)
- Denature proteins to be more easily digested
- Activates pepsin and provides an adequate environment
What do parietal cells produce?
HCl
Intrinsic factor
Name the only essential secretion that is essential for life.
Intrinsic factor: it is required for absorption of vitamin B12
How is HCl important in pepsinogen activation?
- HCl transforms pepsinogen into pepsin
Once pepsin is present, it can also feedback to make more pepsin - HCl also maintains the appropriate pH for pepsin activity
What cells produce Mucin? (3)
All surface epithelial cells
Cardiac and pyloric tubular glands
Mucous neck cells in the fundus and corpus tubular glands
How is the stomach protected from acid? (3)
- The surface epithelial cells make mucin which creates a mucous gel called the Muci-Bicarb layer
The cells also make HCO3 and H enter freely due to the concentration gradient. This makes CO2 and H2O in the layer
- there is also a Gastric mucosal barrier which is a specialisation of the apical surface and tight junctions to prevent acid from reaching the cells
- There is a rapid cell turnover to recycle damaged cells
Where can we find the muci-bicarb layer?
Anywhere mucus is secreted in the GIT
What factors can contribute to ulcers?
- A Weak barrier bc of aspirin/ NSAID or Heliobacter pylori
- An excessive HCl output that overwhelms the protective layers
In the cephalic phase, what can regulate secretions?
- Vagal mediation onto ENS
- Sympathetic mediation onto ENS
- Gastrin release because of anticipation of a meal
In the gastric phase, what can regulate secretions?
- Food in the stomach causes stretch and local ENS reflexes activated secretions
- Vago-vagal reflex
- Secretagogues (partially digested proteins) stimulate gastrin-releasing cells
How will gastrin (hormonal regulation) increase secretions?
Gastrin enters circulation to be filtered and then reaches the parietal cells to increase HCl release
It also has a trophic effect to stimulate parietal cell production
How is gastrin regulated?
Gastrin = more HCl
The low pH will decrease gastrin release
The low pH will also secrete somatostatin cells, which inhibit G cells and parietal cells
How is histamine important in HCl release? What are the effects or more/ less?
The histamine has a background amount which interacts with ACh and Gastrin to increase parietal cell sensitivity (more acid released)
When there is less histamine, the sensitivity is decreased (less acid released)
In the intestinal phase, what can regulate secretions?
There is a short excitatory effect on gastrin, followed by an inhibitory effect
What are the functions of the upper intestines? (4)
Chyme neutralisation
Osmotic equilibration
Digestion
Absorption
What is the daily volume of pancreatic juices?
0.5-1.5 L
What are the main electrolytes in the pancreatic juices and what is the tonocity?
Na
K
Cl
HCO3
Isotonic solution
What is the pH of pancreatic juices and what enzymes are in it?
7.2-8.2
Amylase
Protease
Lipase
What is necessary for protease activation in the intestine? name the specificities of what is released where and why
Trypsinogen is made into trypsin with enterokinase
Enterokinase are produced by the intestinal cells to avoid trypsin production in the pancreas (would destroy)
Trypsin will activate other protease
How can trypsin be inhibited?
The pancreas can also release trypsin inhibitor
