Digestion and absorption 1 Flashcards
what is the main site for digesting CHO
site for carbohydrate digestion is the mouth and intestinal lumen
what are glycosidases ?
Group of enzymes responsible for digesting the CHO
Very specific to the bond that they product
Final product of digestion are MONOSACCHARIDES ( glucose, galactose , fructose )
cuz the intestinal cells lack transporters for disaccharides
what are glycosyltransferase ?
Enzyme that synthesizes glycosidic bonds
what amylase ?
salivary alpha amylase
BREAKS alpha 1,4 glycosidic bond
CANNOT hydrolyze :
Alpha 1-6 ( amylopectin and glycogen )
Beta 1-4 ( cellulose ) –> human cannot digest this
what is the result of amylase digestion ?
Dextrin ( branched and unbranched oligosaccharides )
Disaccharides ( some are resistant to amylase )
Disaccharides need to be disaccharidase enzyme to hydrolyze them into monosaccharides
what is the pancreas role in digestion?
when acidic stomach content reach the small intestine they are neutralized by bicarbonate secreted by pancreas
release Pancreatic amylase
what does pancreatic amylase do?
continue the process of starch digestion :
BREAK DOWN alpha 1-4 linkage
where does the last part of CHO digestion occur?
intestinal brush border
what are the enzymes in brush border?
Isomaltase 6 alpha
Maltase 4 alpha
Lactase 4 beta
Sucrase 2 alpha
Trehalase 1 alpha
I M LA S T
6 4 4 2 1
all of them break alpha except the middle one ( LA ) its B
all of them give 2 glucose except the middle one and sucrase
Lactase –> 1 glucose 1 galactose
Sucrase —> 1 glucose 1 fructose
whats special sucrase and isomaltase ?
its a single enzyme with 2 functional subunits
what is the difference between epimers and anomers?
Glucose and galactose are C-4 epimers
they differ in the configuration of 4th carbon
Alpha glucose and Beta glucose are anomers as they differ in the configuration at 1st anomeric carbon
describe monosaccharides absorption ?
occur at the duodenum and upper jejunum
Different monosaccharides have different hexose transporter
what do glucose and galactose transporters depend on ?
Sodium glucose linked transport -1
Na + / glucose co transporter
what does fructose transport depend on?
facilitated diffusion through GLUT5
How does sugar transport occur ?
Secondary active transport
they dont directly transport using ATP
they use Sodium-potassium pump NA/K atpase
The pump establishes a sodium gradient by actively pumping Na out of epithelial cell into bloodstream
This creates low Na inside the cell allowing sodium to come into the cell and when it comes in glucose will come with it
co transported into epithelial cell via SGLT-1 symporter
Since glucose concentration inside the cell is low compared to outside it needs active
what are types of active transport ?
Uniporter –> one substance across the membrane
Co- transporter : moves 2 substances together :
Symporter in the same direction
Antiporter : opposite directions
why are sugars not transported passively ?
If glucose absorption relied on passive absorption
it will stop once it reaches equilibrium preventing further uptake
this would lead to excess glucose being lost in feces
what are the glucose transport pathways?
from lumen to epithelial cell : via SGLT-1 symporter using sodium gradient
from epithelial cell to bloodstream - facilitated diffusion via GLUT-2
describe lactase deficiency ?
Lactase deficiency results in lactose intolerance
Lactose is fermented by gut bacteria to gas
lactose accumulation leads to increase osmotic pressure in lumen preventing water absorption —> Diarrhea
describe primary lactase deficiency?
Congenital deficiency of lactase
after ingestion of lactose an affected child will typically experience stomach cramps , bloating , excess gas production and diarrhea
These digestive problems can lead to failure to gain weight and grow at the expected rate —> failure to thrive and malnutrition
what are the causes of secondary lactase deficiency ?
possible causes are :
Gastroenteritis - an infection of stomach and intestine
Celiac disease - chronic autoimmune disorder triggered by consuming gluten , a protein found in wheat , barely and rye
in genetically predisposed individual , the gluten ingestion causes the immune system to attack small intestine damaging intestinal villi which is essential for nutrient absorption —> malabsorption symptoms like diarrhea , bloating, pain
Crohn’s disease –> IBD - inflammation of lining of GIT
chemotherapy
long courses antibiotics
downregulation of lactase enzyme
what are relevant tests to diagnose lactose intolerance ?
hydrogen breath test
helps to diagnose :
Intolerance to sugars
Small intestinal bacterial overgrowth ( SIBO )
the test measures the amount of hydrogen present in your breath changes after consuming sugar solution
usually theres little hydrogen in breath
but if u have higher level than usually it indicates a problem either intolerance or bacterial overgrowth
describe congenital sucrase isomaltase deficiency ? CSID
become apparent after an infant is weaned and starts to consume fruit , juices, grains
how is congenital sucrase isomaltase deficiency diagnosed?
Small bowel biopsy
sucrose intolerance hydrogen breath test
13C sucrose breath test – -> person consumes a sugary drink of sucrose that contains carbon 13 —-> if one has little or no working sucrase isomaltase enzymes in their intestine , there will be less 13 CO2 gas exhaled than if working sucrae - isomaltase enzymes were present
The carbon 13 breath test is thought to directly measure sucrase activity
444 oral sucrose challenge test :
simple test that may indicate the possible presence of CSID
fating patient drinks a well dissolved solution of 4 tablespoons of table sugar in a 4 ounce of glass of water
IF sucrase isomaltase activity is diminished or absent within 4 hours the patient will experience the GI symptoms associated with CSID such as gas , bloating , abdominal distention swelling or diarrhea
Test is not appropriate for infants , young children, geriatric patients, those with comorbid condition like diabetes , patients may have severe symptoms if very sensitive to sugar
auto antibodies in celiac disease
