lostaquarium (lostaquarium) wrote in ed_ucate,

Food Processing in the Stomach

The stomach acts as a reservoir, releasing contents into duodenum at a controlled rate (controlled by the pyloric sphincter, which is normally contracted and closed).

Entry from oesophagus is controlled by the lower oesophageal sphincter.

In response to stretching in the oesophagus or stomach, the stomach walls actively relax to accomodate up to 1500ml food, with little increase in pressure.

Churning movements help to mix food with gastric secretions --> "chyme".

In the fed state (i.e. after eating), a pacemaker zone near the middle of the stomach generates slow waves at 3/min, which pass to smooth muscle and cause contractions at around 3/min.

Contractions are more forceful near the bottom of the stomach (the "antrum") than at the top.

The pyloric sphincter is never very open. Each contraction of the antrum squirts a little chyme into the duodenum.
- liquid passes through very easily
- larger solid particles tend to be pushed backwards to the stomach centre. This is called "retropulsion" – it allows larger pieces of food to be churned and broken up by the stomach.

Easily-soluble substances (e.g. glucose) have a half-life of 30 minutes. In other words, it take 30 minutes for half of the glucose in your stomach to pass into your duodenum.
Solid food takes longer. 50g cubes of liver, for example, have a half-life of 2 hours. As the liver cubes are gradually digested, they become easier to empty.
The experiment was also carried out with 40 plastic spheres, which are indigestible, so they remained in the stomach indefinitely

I think this answers the questions about the order in which foods come up. Sugar dissolves very quickly (unfortunately) and if a binge is long (like mine are), much of the sugar calories will be beyond purge-ability. What does end up coming up will be the larger particles that can't (yet) pass through the pyloric sphincter, and also the indigestible material i.e. dietary fibre. In other words, purging isn't really value-for-effort :(

Substances absorbed through the stomach:
- some fat-soluble substances.
- aspirin (a weak acid) is protonated at the low pH and can diffuse across the mucosa.
- alcohol.

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