Lactose Intolerance Flashcards
Lactose intolerance
- lactose not broken down in small intestine due to a lack of lactase enzyme activity
- no lactase activity in colon
- microbiota ferments non-digested lactose in colon
Name the monosaccharides making up these disaccharides:
* lactose
* sucrose
* maltose
- lactose = galactose + glucose
- sucrose = fructose + glucose
- maltose = glucose + glucose
Where is lactase expressed?
jejunum and ileum
What are the two membranes of the intestinal epithelial cell? What is on the opposing side of each?
- apical membrane: opens into intestinal lumen
- basolateral membrane: opens into blood
At which membrane are the microvilli brush border enzymes located?
Apical membrane of the intestinal epithelial cell
What are the characteristics of the SGLT1 transporter (what does it transport, where does it transport it, how does it transport it?)
- glucose and galactose
- across the apical border
- by co-transport (2Na+ and 1 glucose enters cell)
What are the characteristics of the GLUT5 transporter (what does it transport, where does it transport it, how does it transport it?)
- transports fructose
- across the apical membrane
- by facilitated diffusion
What are the characteristics of the GLUT2 transporter (what does it transport, where does it transport it, how does it transport it?)
- transports ALL monosaccharides (glucose, galactose and fructose)
- across the basolateral membrane
- by facilitated diffusion
How is the concentration gradient required for SGLT1 maintained?
- Na+/K+ pump
- removal of Na+ from inside of cell maintains low Na+ inside of cell, high Na+ outside of cell
GLUT5 is encoded by the ____ gene
SLC2A5
Fructose malabsorption
deficient or low expression of GLUT5 in small intestine
Hereditary fructose intolerance
- no expression of aldolase B
- leads to accumulation of fructose-1-phosphate
- accumulation of F-1-P results in the death of liver cells
Primary lactase definciency (inherited)
- loss of lactase expression after weaning
- IRREVERSIBLE
Secondary lactase deficiency (acquired)
- loss of lactase expression due to GI mucosal injury
- REVERSIBLE
Lactase non-persistence
- WILDTYPE
- low lactase expression or activity
Lactase persistence
- MUTANTS
- retained neonatal level of lactase activity into adulthood
SNPs
- single nucleotide polymorphisms
- 1-base mutation in the DNA sequence
What chromosome is the lactase gene on?
chromosome 2
SNPs in the ____ gene cause lactase persistence. It modulates ____ expression/protein level
MCM6 ; LCT (lactase gene)
What SNP is common in caucasian populations that causes lactase persistence? Is this a rare or common occurrence?
intron 13 of the MCM6 gene -> LCT13910 C>T
What SNP is common in Asian and African populations that causes lactase persistence. Is this a rare or common occurrence?
intron 13 of the MCM6 gene -> LCT13915 T>G
Is the lactase persistence or non-persistence gene dominant?
lactase persistence (only one copy of this allele will result in lactase persistence)
What is/are the activator(s) of lactase gene expression that only bind(s) at the LCT gene?
- HNF1-a
- Cdx-2
- GATA-4, GAT-5, GATA-6
What is/are the activator(s) of lactase gene expression that bind(s) at the LCT gene and the MCM6 gene?
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