Digestion and Absorption of Carbs Flashcards
where is glucose found
table sugar
where is fructose found
fruits
where is galactose found
milk sugar
what are glucose, fructose, and galactose?
hexoses (6 carbon sugars)
what are monosaccharides?
simple sugars, building blocks for all carbs
what are pentoses and example
5 carbon sugar, used for deoxyribose and ribose
what is an O-glycoside?
sugars bind to its partner with a glycosidic bond through an oxygen atom
what is a N-glycoside
sugars bind to partners with glycosidic bond through nitrogen
when do glycosidic bonds form?
OH group on anomeric carbon of monosaccharide reacts with an OH or NH group of another compound
what are common O-glycosides disaccharides?
sucrose, maltose, lactose
what bonds does sucrose have?
alpha 1,2 O-glycosidic bond between glucose and fructose
what bonds does maltose have?
alpha 1,4 O glycosidic bond between glucose and glucose
what bonds does lactose have?
beta 1,4 O glycosidic bonds between glucose and galactose
what are oligosaccharides?
sugars with up to 12 monosaccharides
what are poly saccharides?
sugars with more than 12 monosaccharides
examples of polysaccharides
polymer of glucose residues with different types of polymer but same subunits, starch (amylose and amylopectin), glycogen, cellulose
what is starch?
amylose and amylopectin, stores glucose in plant cells
what is glycogen?
stores glucose in animal cells
what is cellulose?
the plant cell wall, or fiber, has beta 1,4 Oglycosidic bonds that make linear chains that pack to form fibers (beta formation)
what is amylose?
a linear starch, has alpha 1,4 O Glycosidic bonds
what is amylopectin?
branched starch, less branches than glycogen, has both alpha 1,4 and alpha 1,6 O glycosidic bonds
clinical significance of cellulose?
we do not have enzymes that break down beta1,4 O-glycosidic bonds, so it helps with GI motility and defecation, prevents absorption of toxins and cholesterol, and helps to slow absorption/digestion and lessens glucose spike
function of salivary gland?
elaboration of fluid, digestive enzymes (amylase)
function of stomach?
elaboration of HCl and digestive enzymes (pepsin)
function of pancreas?
elaboration of NaHCO3 and enzymes for intraluminal digestion
what enzymes does pancreas secrete
propeptidases, amylase, prolipases
function of liver?
elaboration of bile acids
function of gallbladder?
storage and concentration of bile
function of small intestine?
terminal digestion of food (hydrolysis), absorption of nutrients and electrolytes (free AA, dipeptides, tripeptidees, FFA, monoacylglycerols)
what enzymes are secreted in the duodenum?
enteropeptidase (starch, proteins, lipids)
what enzymes are secreted in the jejunum and ileum?
disaccharidases, peptidases, phosphatases
function of the large intestine
absorption of electrolytes (NaCl)
function of alpha-detrinase
make polysaccharides shorter
how does the duodenum neutralize stomach acids at the pyloric sphincter?
the acidic gastric juice enters the duodenum, and the secretions containing HCO3 from the pancreas flow down to the pancreatic duct and enter the duodenum, neutralizes acidic ph and digestive enzymes (pancreatic alpha-amlyase)
function of pancreatic alpha amylase
digestive enzyme from pancreas, cleaves alpha 1,4 glycosidic bonds in starches, NO activity for alpha 1,6 glycosidic bonds at the branch points in amylopectin, l ittle activity for end of polysaccharide chain (alpha detrinase does this)
what juices contain alpha amylase?
saliva and pancreatic juices
what is alpha amylase?
endoglycoside, releases oligosaccharides from glycoproteins and glycolipids
what are the products of amylase breakdown of starches?
2 maltose, 3 maltotriose, and shorter alpha dextrins, which are all then broken down by alpha glucosidases
what makes lactase, sucrase, and alpha glucosidase
intestinal epithelial cells
most common deficient enzyme?
lactase
what causes lactase deficiencies?
genetic, physiological declines with age, injuries to the intestinal epithelial mucosa
what occurs if there is damage to the mucosa after severe food poisoning or severe diarrhea?
patient may have trouble digesting lactose due to the physical damage done to the intestinal epithelial cells
what occurs to make bloating, gas, and watery diarrhea?
the polymers in the lumen that are not broken down bring water into the lumen via the osmotic effects, then bacterial enzymes break them down, causing gas and bloating and watery diarrhea
what is acarbose?
drug that blocks activities of pancreatic alpha amylase and brush border alpha glucosidases that have specificity for glucose
what are the alpha glucosidases?
maltase which breaks down alpha1,4 bonds, and isomaltase which breaks down alpha1,6 bonds
what does lactase cleave?
beta 1,4 O-glycosidic bonds
what does sucrase cleave?
alpha 1,2 O glycosidic bonds
what does maltase cleave
alpha 1,4 O blycosidic bonds
what does isomaltase cleave?
alpha 1,6 O glycosidic bonds
purpose of acarbose?
reduce rate of digestion similar to fiber, so that carbohydrates reach bloodstream slower to reduce glucose spike
side effects of acarbose?
flatulence, diarrhea, caused by bacterial metabolism of nondigested sugars
where is acarbose produced?
a microorganism, is a unique tetrasaccharide
where is GLUT1 found?
RBC, BBB, blood retinal border, blood placental border, blood testis border
where is GLUT2 found?
kidneys, liver, pancreatic beta cell, serosal surface of intestinal mucosa cells
where is GLUT3 found?
brain
where is GLUT4 found?
skeletal and cardiac muscle, adipose tissue
how are sugars absorbed?
transported across intestinal epithelial cells and into blood via GLUT and SGLT
where is SGLT1 found?
apical surface of intestinal epithelium
where is SGLT2 found?
kidneys, reabsorbs glucose from the glomerular filtrate in the proximal tubules of nephrons
what occurs if there are mutations in SGLT1
glucose and galactose are malabsorbed
what do SGLT do?
cotransports 2 Na per 1 glucose or 1 galactose via secondary active transport
what occurs if there are mutations in SGLT2?
familial renal glycosuria
what do gliflozins do?
inhibit SGLT2 so that glucose is not reabsorbed into the blood, and is expelled in the urine
what are the gliflozins?
jardiance, farxiga, invokana, steglatro
what is the max capacity of glucose that SGLT2 can reabsorb?
200mg/dl, and then excretes into urine
what is the pathway of insulin release in a pancreatic beta cell?
- glucose is brought into the pancreatic beta cell via GLUT2, and glucose is begun to be metabolized
- elevated ATP from metabolism leads to closing of the K-ATP channel, prevents K from exiting the cell
- charge within cell becomes more positive, depolarizing the cell
- depolarization causes voltage gated calcium channel to open and Ca enters the cell
- increased Ca in cell causes insulin release from B cells of pancreas
what transporter is responsible for glucose entry into pancreatic beta cells?
GLUT2
what is the pathway of glucose uptake in muscle and adipose tissue?
- insulin is released and binds to RTK, which autophosphorylates
- GLUT4 containing vesicles fuse with plasma membrane
- GLUT4 increases on cell membrane and increases rate of glucose transport into the cell
what ways can GLUT4 be recruited?
insulin or AMP-dependent protein kinase during exercise
pathway of GLUT4 activation in exercising muscle
- skeletal muscle uses ATP and makes AMP
- increased AMP increases AMP-dependent protein kinase
- AMPK recruits GLUT4 to promote glucose uptake and utilization
what causes neonatal diabetes?
mutation in KCNJ11 gene
what does KCNJ11 gene encode?
K+ ATP channel
another name for neonatal diabetes
maturity onset diabetes of young (MODY)
what is the consequence of mutating KCNJ11 gene?
eliminates the ATP dependent regulation of the channel and results in a perpetually open channel, therefor K can continually escape and cell hyperpolarizes and cannot open voltage gated Ca channels to cause release of insulin from pancreatic beta cells
MOA of sulfonylureas
close ATP sensitive K channels in the pancreatic beta cells, thus stimulates the release of insulin
what are the sulfonylureas?
glimepiride, glipizide
what is a hypoglycemic response?
light headed, dizzy, sweaty, confusion, nausea
what is the limiting factor for glucose metabolism in the neuronal cells?
glucose transport through GLUT1 and GLUT3, which is slow
what is considered low blood glucose?
18-54mg/dl
what causes hypoglycemic response?
blood glucose levels drop below Km for GLUT1 and then nervous system does not receive sufficient glucose to keep functioning properly
what is unique about neural cells in the blood brain barrier?
- tight junctions betweeen endothelial cells
- narrow intercellular space
- lack of pinocytosis
- continuous basement membrane
- glucose transporters are in both membranes
what is characteristic of non-neural “barrier”
- no tight junctions
- wide intercellular gaps
- pinocytosis is seen
- discontinuous basement membrane
- glucose can diffuse between cells and into ISF
what is GLUT1 deficiency syndrome?
genetic deficiency of GLUT1 results in decreased glucose transport into CSF and brain
sx of GLUT1 deficiency syndrome?
seizures in infancy, developmental delay
