What is the length of the small intestine?
What does the small intestine consist of?
How long is the duodenum?
What are some functions of the duodenum?
Gastric acid neutralisation
How long is the jejunum?
2.5m long (2/5 of total length)
What are some functions of the jejunum?
What percentage of nutrient absorption occurs in the jejunum?
How long is the ileum?
3.5m (3/5 total length)
What is the function of the ileum?
What is the absorptive surface of the small intestine enhanced by?
Folds, villi and microvilli
What are the circular folds of the small intestine called?
What is the relative surface area increase of the small intestine due to plicae?
What is the relative surface area increase of the small intestine due to villi?
What is the relative surface area increase of the small intestine due to microvilli?
What is the classification of the epithelium in the small intestine?
What does villus cells absorb?
What are the functions of crypt cells?
Secrete Cl and water
How much water does the small intestine secrete everyday?
Where does the water that the small intestine secretes come from?
Epithelial cells lining the crypts of Lieberkuhn
How does the small intestine secrete water passively?
Osmotically as a consequence of secreting Cl into the lumen of the gut
Why is H2O secretion important for normal digestive processes?
Maintains luminal contents in liquid state
Promotes mixing of nutrients with digestive enzymes
Aids nutrient presentation to absorbing surface
Dilutes and washes away potentially injurious substances
What happens to H2O secreted by crypts?
Normally reabsorbed by villi
What are the 2 distinct kinds of movements that makes up intestinal motility?
What is segmentation?
Contraction of the circular muscles in the digestive tract
What is perstalsis?
Contraction of the longitudinal muscles in the digestive tract
When is segmentation most common?
During a meal
What is the function of segmentation?
Alterations between contraction and relaxation of short intestinal segments moves chyme up and down into adjacent areas of relaxation
Provides thorough mixing of contents with digestive enzymes
Brings chyme into contact with absorbing surface
How long does each cycle of segmentation last?
A few seconds
Explain the mechanism of segmentation contractions?
1) Initiated by depolarisation generated by pacemaker cells in longitudinal muscle layer
2) Intestinal basic rhythm (BER) produces oscillations in membrane potential
3) Reaches threshold which generates an action potential
4) Causes contraction
What is BER?
Basic electrical rhythm