Lactose intolerance pathophysiology: Difference between revisions
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== Pathophysiology == | == Pathophysiology == | ||
===Physiology=== | |||
Without lactase, the [[lactose]] [[disaccharide]] in many dairy products remains uncleaved and can not be absorbed through the intestinal wall into the bloodstream, so remains in the intestines. Enteral [[bacterium|bacteria]] adapt to the relative abundance of this undigested sugar and their [[operon]]s quickly switch over to lactose [[metabolism]], which produces copious amounts of gas by [[fermentation (biochemistry)|fermentation]]. | |||
This also causes a range of unpleasant abdominal symptoms, including stomach [[cramp]]s, [[bloating]], [[flatulence]] and [[diarrhea]]. As with other unabsorbed sugars ([[mannitol]]), the lactose raises the [[osmotic]] pressure of the [[colon (anatomy)|colon]] contents, preventing the colon from reabsorbing water and hence causing a [[laxative]] effect to add to the excessive gas production. | |||
===Genetics=== | ===Genetics=== | ||
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[[Category:Disease]] | [[Category:Disease]] | ||
[[Category:Needs overview]] | [[Category:Needs overview]] | ||
Revision as of 20:19, 25 March 2013
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [2]
Pathophysiology
Physiology
Without lactase, the lactose disaccharide in many dairy products remains uncleaved and can not be absorbed through the intestinal wall into the bloodstream, so remains in the intestines. Enteral bacteria adapt to the relative abundance of this undigested sugar and their operons quickly switch over to lactose metabolism, which produces copious amounts of gas by fermentation.
This also causes a range of unpleasant abdominal symptoms, including stomach cramps, bloating, flatulence and diarrhea. As with other unabsorbed sugars (mannitol), the lactose raises the osmotic pressure of the colon contents, preventing the colon from reabsorbing water and hence causing a laxative effect to add to the excessive gas production.
Genetics
The gene is expressed and the enzyme synthesized if at least one of the two genes are present. Only when both gene expressions are affected is lactase enzyme synthesis reduced, which in turn reduces lactose digestion.[1] Lactose tolerance(lactase persistence) is the dominant allele. Lactose intolerance is an autosomal recessive trait.
The normal mammalian condition is for the young of a species to experience reduced lactose (milk sugar) production at the end of the weaning period (a species-specific length of time). In non dairy consuming societies, lactase production usually drops about 90% during the first four years of life, although the exact drop over time varies widely. However, certain human populations have a mutation on chromosome 2 which results in a bypass of the common shutdown in lactase production, making it possible for members of these populations to continue consumption of fresh milk and other dairy products throughout their lives.
Pathological lactose intolerance can occur due to coeliac disease, which damages the villi in the small intestine that produce lactase. This lactose intolerance is temporary. Lactose intolerance associated with coeliac disease ceases after the patient has been on a gluten-free diet long enough for the villi to recover.
Certain people who report problems with consuming lactose are not actually lactose intolerant. In a study of 323 Sicilian adults, Carroccio et al. (1998) found only 4% were both lactose intolerant and lactose maldigesters, while 32.2% were lactose maldigesters but did not test as lactose intolerant. However, Burgio et al. (1984) found that 72% of 100 Sicilians were lactose intolerant in their study and 106 of 208 northern Italians (i.e., 51%) were lactose intolerant.