Digestion and Absorption in the GI Tract Flashcards
What causes lactose intolerance?
when the brush border lactase enzyme activity is deficient or absent, which results in undigested and unabsorbed lactose
what happens when lactose is unabsorbed?
it is converted to SCFAs and hydrogen gas in the SI; it remains in the lumen
how do you get osmotic diarrhea with lactose intolerance?
the lactose remains in the lumen and holds H20 in the lumen as well and that is what causes the osmotic diarrhea
what does the lactose ferments into?
methane and H+ gas
what breaks down starches in the mouth?
salivary amylase
what is starch broken down into?
maltose and then the maltose is broken into glucose
where does most of the starch breakdown occur?
in the small intestine
what breaks down the starch in the small intestine?
pancreatic amylase
the lumen surface of the small intestine is arranged in longitudinal folds known as what?
folds of Kerckring
where are villi longest?
in the duodenum
what is lactose normally broken down into?
glucose and galactose
how does glucose and galactose get into the epithelial cell of the SI duodenum from the lumen?
through the SGLT1 co-transporter- secondary active transporter
how does fructose get into the epithelial cells of the SI duodenum?
through the GLUT5 transporter- facilitated diffusion
how does glucose, galactose, and fructose get into the blood?
GLUT2 transporter (facilitated transport)
what could be used to reduce glucose absorption into the epithelial cell?
sotagliflozin
how can you test for a carbohydrate assimilation disorder (global)?
you can administer D-xylose- it should be in the urine; if you have an absorption issue and you aren’t absorbing the sugars, the d-xylose will not be absorbed- it will go through the SI and end up in the feces
how can you test for a specific sugar enzyme deficiency?
you can use a hydrogen breath test
what are the five protein assimilation disorders we discussed?
chronic pancreatitis, congenital trypsin absence, cystinuria, hartnup disease, and cystic fibrosis
what does chronic pancreatitis lead to?
deficiency of pancreatic enzymes (lack of proteases e.g. trypsinogen)
what does congenital trypsin absence lead to?
the absence of all pancreatic enzymes
why does congenital trypsin absence lead to the absence of all pancreatic enzymes?
pancreatic enzymes are secreted as zymogens and activated by either enterokinase (aka TRYPSINOGEN) or trypsin itself
what is defected in cystinuria?
SLC3A1 or SLC7A9
what is a sign of cystinuria?
AA secreted into the feces or urine
what are three important symptoms of hartnup disease?
3 Ds: diarrhea, dermatitis, and dementia
what results will you see with Hartnup’s disease?
they will have urinary excretion of tryptophan
what are some CFTR mutations associated with?
loss of HCO3- secretion; therefore they can’t move enzymes from the ducts, acute or chronic pancreatitis
what are the brush border enzymes that break down proteins?
aminopolypeptidase and dipeptidases
how are amino acids transported into the epithelial cell of the small intestine from the lumen?
Na+-AA cotransporter
how are dipeptides and tripeptides transported into the epithelial cell of the small intestine from the lumen?
H+ dependent cotransporter
once inside the epithelial cell of the small intestine, what happens to most of the di-/tri- peptides?
they are hydrolyzed to amino acids by peptidase
how do the amino acids get out of the epithelial cell of the small intestine into the blood?
via facilitated diffusion (separate for each amino acid)
what does celiac sprue/ disease lead to?
the destruction of small intestine villi (atrophy) and hyperplasia of the intestinal crypts
what are the common malabsorption deficiencies associated with celiac’s?
folate, iron, calcium, and vitamins A B12 and D
what is tropical sprue and what is it caused by?
it is a loss or decreased number of intestinal epithelial cells; intestinal infection
what are the nutritional deficiencies associated with tropical sprue?
folate and vitamin B12
what is the major symptom of tropical sprue?
diarrhea
how do you treat tropical sprue?
tetracycline and folate for 6 months
what is the digestion of lipids complicated by?
their insolubility
what is the effect of CCK on the stomach?
it inhibits gastric emptying
where does most of the digestion of lipids occur?
in the small intestine
what is pancreatic lipase inactivated by?
by bile salts
what is needed to reactivate the pancreatic lipase?
colipase (which is activated by trypsin)
once the fatty acids are are emulsified by the micelle, how do they get into the epithelial cell of the small intestine from the apical membrane?
there is diffusion of the micellar content across the apical membrane
what happens to the products of lipid digestion once inside the intestinal epithelial cells?
they are reesterified
Inside the epithelial cells of the small intestine, what are the reesterified lipids packaged with and what do these form?
they are packaged with apoproteins and form chylomicrons
failure to synthesize Apo B leads to what?
abetalipoproteinemia, aka no lipid absorption
what happens to the chylomicrons?
they are exocytosed into the lymphatics
problems anywhere along the path of lipid digestion/absorption leads to what?
steatorrhea
What could lead to problems with lipid digestion/absorption? associated with pancreatic enzyme secretion
pancreatitis, pancreatic insufficiency, or zollinger-ellison syndrome (improper acidity in the duodenum contents)
what are two main causes of SIBO?
too little gastric secretion and small intestine dysmotility
what effect does SIBO have on bile salts?
they deconjugate them, so they will not be able to emulsify lipids/micelle formation, leads to lipid digestion/absorption issues
how can you diagnose SIBO?
use a breath test and test for methane and hydrogen
what are the water-soluble vitamins?
b vitamins and vitamin C
when does intrinsic factor bind to the vitamin b12?
not until the small intestine (ileum)
what are the symptoms of a vitamin B12 deficiency?
pernicious anemia, weakness, and nerve conductance issues
what is the common cause of pernicious anemia?
atrophic gastritis
what does vitamin d deficiency result in?
inadequate calcium absorption
how does Fe2+ get out of the enterocyte/ where is the regulation at?
through ferroportin
what is the absorption like in the jejunum?
lots of sodium is absorbed
what is the absorption like in the ileum?
sodium is absorbed and HCO3- is secreted
what is the absorption/secretion like in the colon?
Na absorption and K secretion
what is the effect of cholera?
it increases cAMP, which results in increased Cl- secretion
in cholera, what does the resulting Cl- secretion accompanied by?
secretion of Na+ and H20
what does cholera lead to?
massive secretory diarrhea–> look for chloride
