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Lectures of Digesting the Microbiome
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Lectures from the course Digesting the Microbiome
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Digesting the MicrobiomeLecture 1 – 9-04-2021
The answers of the test yourself;
1. What is the main function of the parietal cell in the stomach? → production of gastric acid
2. Which hormone inhibits gastric acid secretion? → somatostatin
3. By which mechanism are carbohydrates absorbed? → luminal breakdown by enzymes and
absorption as monosaccharides.
4. Which ion can provide the driving force for small peptides (co-transport) → proton
5. Which enzyme can digest lipids ? → lipase
6. Which ions are actively secreted in the intestinal lumen during secretory diarrhoea? →
chloride
7. Which ions are secreted in the duodenum to neutralize the pH? → bicarbonate
8. What is a prebiotic? → fibres stimulating the growth of the microbiome
9. What is referred to as the alpha diversity of the microbiome? → variation of microbes in a
single sample
10. Which genetic material is generally sequenced to determine the microbiome composition?
→ ribosomal RNA
For the function of the digestive tract you have to consider four processes:
1. Secretion
2. Motility (of in the intestinal system)
3. Absorption and digestion of carbohydrates, protein and fats
4. Absorption water and ions
Screening for colon cancer in the Netherlands, since it is a western disease that is growing.
In total we have a volume of about 9Liters in our intestinal system. You get about 2Liters from food
and drinks, so the rest (7L) is created by our own body, so for example saliva, bile, gastric secretions,
pancreatic secretions or intestinal secretions. In faeces there is about 0.1L, so there is a huge task for
the intestine to reabsorb all the fluids. Mostly reabsorption is done by the small intestine, but also
little bit by the large intestine. The compounds that are present in most of the fluids are; enzymes,
mucus, H2O, ions, H+ and HCO3-. These enzymes are for importance of the digestion of our foods
(carbohydrates, proteins and fats). Each type of nutrient have another enzyme, and all these
enzymes are produced/active at a different location.
There are 4 phases of digestion:
1. Cephalic phase
2. Oral phase
3. Gastric phase
4. Intestinal phase
Cephalic and oral phase:
Cephalic phase is the anticipation of food (thinking of what kind of food you will eat, can give a
reaction on for example the production of saliva).
The oral phase is when the food is located in the mouth, so when you are eating.
Saliva is important in both phases. Saliva is produced by three saliva glands, called sublingual gland,
submandibular gland and parotid gland. Saliva consists water, mucoprotein and salivary amylase (the
most known enzyme, important for carbohydrate digestion). With saliva there is dilution and
,transport of food (allow taste), there is start of starch digestion. Further it has a antimicrobial effect
and a cleansing effect (cleaning your mouth).
The production of saliva is done via two types of secretion. There is secretion in the glands and
secretion in the mouth. In the primary secretion there is secretion of sodium (Na+), this sodium will
attract water and then in this water you can also secrete the enzymes required. In the secondary
secretion (mouth) there can be absorption of sodium and secretion of potassium (K+) and HCO3-.
These secretions are regulated by the parasympathetic nervous system.
In the oral phase the central nervous system has long reflexes.
The cells in the intestine have short reflexes.
Further in the oral phase there is digestive tract secretion and
motility.
Cephalic phase → Pavlov experiment, ringing bell starts
production of saliva in dogs.
Types of cells in gastric mucosa:
- Superficial epithelial cell
- Mucous neck cell
- Stem/regenerative cell
- Parietal (oxyntic) cell
- Chief cell
- Endocrine cell
Mucus production important to
protect the stomach.
Gastric phase: the stomach
First there is storage in the stomach, about 4 hours. The storage makes sure that the food is going
into the intestine a bit by bit and not everything at once. The there is digestion in the stomach, here
the parietal/wall cells are producing HCl, the chief cells are producing lipase and they produce
pepsinogen. There is also protection of the stomach wall by HCO3- (mucus, mucin) and the mucus
neck cells / goblet cells. At last there is also production of the intrinsic factor, which is important for
vitamin B12.
, Acetylcholine is a neurotransmitter.
So that is the part where the CNS
starts to produce the gastric acid,
which is important for the cephalic
and oral phase. So this is that thinking
of food starts the production of gastric
acid.
this is a parietal cell. By the way this cell are formed and
proliferating you can see if there is an active acid secretion. At
the active state there is a larger surface where the proton
pump can excrete protons. People who have too much acid
secretion, have often also more parietal cell presents.
Regulation of gastric acid production → there is a cocktail of three substances;
- Acetylcholine → vagus nerve
- Gastrin → G-cells in antrum and duodenum mucosa
- Histamin → mast cells and gastric mucosa.
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