Into where does the stomach empty chyme?
What happens to chyme in the duodenum?
It is conditioned
What features of chyme are modified in conditioning?
- Partly digested
How is the acidity of chyme modified in conditioning?
It is corrected by HCO3-
Where does the HCO3- used to correct the acidic nature of chyme in conditioning come from?
Secreted from the pancreas, liver, and duodenal mucosa
When is the HCO3- used to correct the acidity of chyme in conditioning produced?
During the production of gastric acid
How is hypertonicity of chyme modified in conditioning?
Corrected by the osmotic movement of water into the duodenum across its wall
How is the partly digested nature of chyme modified in conditioning?
Digestion is completed by enzymes
Where do the enzymes used to finish digestion of chyme in conditioning come from?
The pancreas and duodenal mucosa
Other than enzymes, what is required from the completion of digestion of chyme in conditioning?
Bile acids from the liver
What conditions does absorption require?
A large surface area, to which the luminal contents of the small intestine needs to be exposed to through gentle agitation for hours
How is the surface area of the small intestine maximised?
- Very long
- Increased by millions of villi projecting into the lumen
How do epithelial cells (enterocytes) arise?
By rapid division in the crypts between the villi, and migration towards the tips
What happens to enterocytes at the tips of the villi?
They are shed
What happens to newly formed enterocytes as they migrate to the tip?
What covers the luminal surface of the enterocytes?
What is the purpose of the microvilli present on the enterocytes?
- Further increase surface area
- Form the brush border
What does the brush border form?
An 'unstirred layer'
What happens at the unstirred layer?
Nutrients meet and react with enzymes secreted by the enterocytes, completing digestion prior to absorption
Label this diagram
- A - Muscle layers
- B - Villi
- C - Hepatic portal vein
- D - Lumen
- E - Capillary bed
- F - Lacteal
- G - Microvilli
- H - Villi
What is the function of the large intestines?
Absorb water from the indigestible residues of chyme
What do the large intestines do to the indigestible residues of chyme?
Convert them into semi-solid stool or faeces
What happens to the faeces formed by the large intestines?
It is stored temporarily and allowed to accumulate until defecation occurs
What are teniae coli?
The thickened bands of smooth muscle of the large intestines
What do the teniae coli constitute?
Most of the longitudinal coat of the large intestines
Where do the teniae coli run?
The length of the large intestine
What is the effect of the teniae coli on the part of the wall they are associated with?
They shorten it
Why do the teniae coli shorten the part of the wall they are associated with?
Because of their tonic contraction
What does the shortening of the wall due to teniae coli form?
What are haustra?
Where the colon becomes sacculated, or 'baggy', between the teniae