9 21 Nutrient digestion and absorption 1-Table 1 Flashcards
what are the common maronutrients found in a “western” dite.
Carbohydrates (polysaccharides, Disaccharides, monosaccharides); Proteins; Fats (Triacylglycerol, phospholipids; cholesterol).
Carbs that can not be digested by human enzymes – exemplified by a beta sugar configuration.
Dietary Fiber
describe how carbs are digested/absorbed
Mouth(Amylase); Duodenum (Pancreatic amylase); Small intestine (Maltase, Sucrase, Lactase). Break the carbohydrates down to monosacharides.
explain lactose intolerance
70% of population Hypolactasia; don’t absorb lactase, lactase will get absorbed and digested by the gut bacteria.
explain fructose malabsorption.
GLUT 5 mutation could lead to inability to inability to absorb Fructose.
average amount of this macromolecule in western diet is 300 g/day
Carbohyderates
what are the constituents of a carbohyderate?
polysaccharides (starch, glycogen); disaccharides (sucrose, lactose, maltose); monosaccharides (fructose, glucose, galactose);; non-digestible carbs (fiber)
polysaccharides
starch (65%)/ glycogen (.0%)
what is starch
glucose linked together, mostly linear, some branches. (flour, corn, potatoes)
Disaccharides
sucrose(25%) lactose (6%); maltose
what is sucrose
Glucose -alpha(1,2)-Fructose
what is lactose
Galactose-beta(1,4)-glucose
what fructose
fruit sugar,, and the monomer of sucrose.
Monosaccharides
fructose,glucose (3%) and galactose
non-digestible carbs
fiber!
Amount of proteins in day avg.
100g/day
where do we get glycogen?
meat!
amount of fats in day?
80g/day triclyglycerol;phospholipids’cholesterol
what are the three components of fats?
triachyglycerol; phospholipids’; cholesterol
what is starch?
mostly unbranched amylose linked alpha 1,4: plus some occasionally branched amylopectin linked alpha 1,6;
what is sucrose?
glucose with alpha 1,2 link to fructose
what is lactose?
galactose beta 1,4 link to glucose
so what links do we break to break starch?
alpha 1,4, and some alpha 1,6
what is digestion in general
the way that we break polymers to monomers
carbohyderate digestion and absorption summary!
h (picture on slide 9)
what is the first digestive enzyme?
salivary amylase
describe the basic path of digestion
salivary amylase; pancreatic amylase; maltase;surase,lactase.
pancreatic amylase
breaks long chains of the startch to disacerides
what does maltase do?
breaks matose to glucose molecules (2 of them)
they break the disacherides to monosacherides
what is a disacherideases
what does sucrase do?
they breack sucrose to glucose and fructose
what does lactase do?
break lactose to glucose and galactose.
what are the monomers that can be absorbed?
glucose, fructose, galactose, and D-Xylose
why is the small intestine not at pH 2 like the stomach
secrete bicarbonate in the small intestine to buffer back to around 7 pH
moves glucose and gallactose into the epitheilial
SGLT1 (Na cotransporter)
moves glucose and galactose into the epithelial cell when eat alot of sugars
GLUT2
move the fructose down its concentration gradient into the epithelial cells
GLUT 5
move glucoes fructoes and galactose from the epithelial to the interstitial space
GLUT2
that is in table sugar?
Sucrose or (glucose -alpha 1,2 bound to frutose)
corn syrup
mostly glucose, some maltose and isomaltose (hydrolyzed corn starch
high fructose corn syrup
corn syrup processed to convert 50% of glucose to fructose
Honey
82% carbohydrate. (38% fructose 31% glucose, 13% di and oligosaccharides)
agave syrup
55%-90% fructose, remainder of carbohydrate is mostly glucose.
under what condition might cane sugar and highfructose corn syrup affect the body differently?
you need a disaccharidase to hydrolize this (sucrase). (it is about the same as table sugar). If sucrase is the rate limiting step, then there will be a difference between high fructose corn syrup and sugar (there doesn’t seem to be much evidence for this. Therefore it really doesn’t matter that much.
why change glucose to fructose
fructose tastes sweeter than glucose
how do we effectively get all digested macronutrients absorbed?
about 9000 m2 surfacd area in the villi and microvilli
what transporter is likely to cause fructose malabsorption?
GLUT 5
what could lead to bloating, intestinal cramps and gas after the consumption of pizza and ice-cream
lactose intolerance! not enough lactase! don’t break down lactose (milk sugar), but the gut bacteria aborb it and emit a lot of gas!
what does lactase do?
break lactose into the monomers galactose and glucose
what is hypolactasia
it is a lack of lactase in the brush border microvilli
what percent of people are hypolactaseic?
70% of people.
what happens to the blood glucose of a hypolactasia person when consume milk?
it goes up a tiny part
what happens to the blood glucose of a non-hypolactasia person when consume milk?
it spikes why up!
how is the blood glucose different after absorbing milk? (for hypolactasia/ normal)
normal would spike and hypolactasia would not!
after lactose consumption: why blood sugar spike for “normal” and why H2 spike fore “hypolactasia”
the blood sugar goes up as lactate broken down and H2 is from bacterial metabolism
compare the mean breath H2 for hypolactasia vs. non-hypolactasia (“normal”)
the breath pH would spike for hypolactasia and pretty flat for “normal”
what is the difference in a alpha vs. a beta sugar conformations
the OH of the #1 carbon is oriented “down” on an alpha glucose, and “up” on a beta glucose. (in reference to the carboxy group on the #6 carbon.
why do you get diarrhea with a lactose intolerance?
extra lactase not absorbed and raises the osmolarity of the intestines
why do we care if the sugar is oriented alpha or beta?
digestive enzymes are specific for either the alpha or the beta configuration.
what is digestible vs. non digestible fiber?
insoluble fiber has only the beta 1,4! and soluble fiber has some beta 1,3 (looks like an alpha bond)
what is dextrose/
Glucose! (D-Glucose)
Soluble fiber?
gummy, viscous. digeste/partially metabolized by intestinal bacteria. binds cholesterol and inhibits its absorption
insoluble fiber
richer in wheat bran. prevent constipation, possibly diverticular disease.
what type of enzymatic activity is most likely responsible for beano’s effectiveness?
probably an alpha galactosidase to break the alpha bond between the galactose and glucose and galactose and galactose molecules found in the carbs in beans.
what happens when you can’t fully digest carbs?
excessive colonic bacterial fermentation: gas, bloating, discomfort, and diarrhea (osmotic diarrhea).
