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Summary: Digesting the Microbiome
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Summary Digesting theMicrobiome
Name: Abduallah Lemdjad
Course: Digesting the microbiome
Date: 15-04-2024
, Chapter 1 – Intestinal physiology: secretion
The entry point of the human intestinal tract starts with the mouth, where
the salivary glands produce enzymes (among them amylases) that help
breakdown carbohydrates in either polysaccharides or disaccharides.
Next, the food travels via the oesophagus to the stomach, where the food
is further digested. The stomach produces various enzymes among them
pepsin, in combination with high pH due to the presence of gastric acid
proteins are digested into polypeptides by the pepsin enzyme. The
stomach, liver and pancreas are responsible for the breakdown of
polypeptides into smaller peptides and for the breakdown of remaining
polysaccharides into disaccharides. Finally, the small intestines are
responsible for the digestion and absorption of disaccharides into
monosaccharides, the uptake of fatty acids (monoglycerides) and for the
digestion and absorption of polypeptides into amino acids. Interestingly,
the further the food travels the higher pH it encounters, with the stomach
having a pH between 1-3, the small intestines between 6-7, and finally the
large intestines pH 7.
The digestive tract has multiple functions with as main goal to digest
ingested food, to absorb nutrients from the food, and finally to excrete the
remains (faeces). This is a complex process with interplay between many
different cell types, enzymes, and bacteria. Digestion can be categorized
in four different phases:
1) Cephalic phase
2) Oral phase
3) Gastric phase
4) Intestinal phase
1.1 The cephalic and oral phase of digestion
The cephalic phase is characterized by the
anticipation of food. This phase is triggered by the
sight, smell, thought, or taste of the food, leading to
the activation of the cerebral cortex, sending signals
to the hypothalamus and then to the medulla. The
brain signals the three-pair salivary glands
(sublingual, parotid, and submandibular) in the mouth,
to start producing saliva. Saliva contains enzymes like
amylase that help breakdown carbohydrates as well
as mucus which helps with lubricating and binding
food particles together making it easier to swallow.
The composition of the final secretion depends on the
secretion rate. The initial fluid released by the
secretory cells in the ducts are usually rich in Na+
when the blood levels of Na+ are high. After the initial
secretion the fluid undergoes modification, during the
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