Lec6 Flashcards
Where are most minerals absorbed?
duodenum
Where are bile acids absorbed?
ileum
Where is cobalamin [B12] absorbed?
ileum
Where is iron absorbed?
duodenum
What are gross folds of the small bowel vs the large bowel called?
small = plicae circulares large = haustrae
How is digestion initiated in the small intestine?
- acid in duodenum –> duodenal S cells secrete secretin –> cause pancreas to secrete bicarb
- fatty acids and amino acids in duodenum –> duodenal I cells secrete CCK –> cause pancreas to secrete enzymes, gallbladder to empty
What is ratio of starch to sucrose to lactose of ingested carbs?
starch 50%
sucrose 30%
lactose 10%
How is starch digested?
- amylase from pancreas/saliva converts to maltose
- maltase on intestinal BBM to glucose
How is sucrose digested?
sucrase-isomaltase on intestinal BBM to glucose and fructose
How is lactose digested?
lactase on intestinal BBM to glucose and galactose
How are carbs absorbed?
glucose/galactose active transported into cell then diffuse into portal vein
fructose facilitated diffusion
unabsorbed carbs converted to short chain fatty acids in colon
What are the components of starch?
maltoses each made of glucose
What are the components of sucrose?
glucose and fructose
What are the components of lactose?
glucose and galactose
How are proteins digested?
in stomach: denatured by acid; pepsin hydrolyzes into polypeptides
in duodenum: digested by pancreatic proteases; duodenal brush border membrane enterokinase activates trypsin which then activated the other pancreatic pro-enzymes
BBM oligopeptidases then hydrolyze into smaller oligopeptides and amino acids
final digestion inside enterocytes by intracellular peptidases that convert everything to amino acids
How are proteins absorbed?
as amino acids and oligopeptides
intracellular pepitdases in enterocytes finish digestion into AAs
AAs absorbed and transported to capillaries into portal vein
What is role of brush border membrane enterokinase in protein digestion?
activates trypsin which in turn activates other pancreatic pro-enzymes
How are lipids digested?
in stomach: churn fats into unstable emulsion
in duodenum/small intestine: emulsion stabilized by phospholipids and bile salts
CCK released in response to dietary fat in duodenum causes bile salt and lipase [panc.] release
pancreatic lipase and co-lipase convert TG–> MG + FFA
mixed micelles form with MGs and FFAs inside; bile salts outside
What is necessary for pancreatic lipase to work?
- CCK causes its release from pancreas in response to fatty acids in duodenum
- requires neutral pH in duodenum to work
How are lipids absorbed ?
passive diffusion across BBM into cell
intracellular resynthesized as cylomicrons and VLDL –> exported into lymphatics
What is exception to the rule that lipids are absorbed into the lymph system?
medium chain TGs are absorbed into the portal vein
What is role of B lipoprotein in fat absorption?
important role in repackaging of fats into chylomicrons inside enterocytes for absorption into lymphatics
How is vit B12 absorbed [steps]?
- dietary B12 complexes with salivary R protein in stomach
- in duodenum trypsin cleaves R-B12 complex
- IF from gastric parietal cells binds B12
- IF-B12 complex absorbed in terminal ileum
- B12 transported into portal circulation
Which vitamins are fat soluble?
ADEK
What happens to B12 with bacterial overgrowth?
luminal bacteria compete for B12; with bacterial overgrowth –> have low serum B12
What are some causes of B12 deficiency
- not enough dietary B12 [rare]
- not enough R
- not enough IF [autoimmune gastritis]
- pancreatic insufficiency [can’t dissociate B12-R]
- ileal disease [can’t absorb]
What happens to folate level if bacterial overgrowth?
high serum folate
How is Ca absorbed?
active transport in duodenum;
calbindin in cell delivers Ca to ATPase for export into circulation
vit D stimulates calbindin synthesis and helps Ca entry into enterocytes
What is major symptom of protein malabsorption?
edema
What major symptoms of fat malabsorption?
steatorrhea
weight loss
What major symptoms of carb malabsorption?
- diarrhea
- bloat
- gas
from bacteria in colon
What major symptoms of vit A malabsorption?
nigh blindness (nyctalopia)
dry scaly skin (zerosis, cutis)
alopecia
What major symptoms of vit D/Ca malabsorption?
tetany = cramping of fingers/toes osteomalacia = thinning of bones
What major symptoms of Vit E malabsorption?
neuropathy
muscle weakness
What major symptoms of Vit K malabsorption?
ecchymoses = non raised discoloration
bruising
What major symptoms of Vit B12 malabsorption?
macrocytic megaloblastic anemia
glossitis
neuropathy; parasthesias
What major symptoms of folate malabsorption?
macrocytic, megaloblastic anemia
glossitis
What major symptoms of iron malabsorption?
microcytic anemia
dyspnea
fatigue
glossitis
When does lactase deficiency present?
lactase almost always present at birth; symptoms occur in adulthood
What is pathogenesis of lactase deficiency?
- lactose osmotically active in lumen –> get diarrhea, gas, bloating, borborygmi [stomach gurgling]
What are symptoms of lactase deficiency?
diarrhea, gas, bloating, borborygmi [stomach gurgling]
Who gets primary lactase deficiency?
asian, african, mediterranean descent
What causes secondary lactase deficiency?
after loss of enterocytes from infection, resection, radiation
How do you diagnose lactase deficiency?
hydrogen breath test
lactose intolerance test
What is treatment for lactase deficiency?
avoid dairy
use exogenous lactase or lactose-free products
What is pathogenesis of pancreatic exocrine insufficiency?
- need to lose > 90-95% of pancreatic function to get this
What are some underlying diseases associated with pancreatic exocrine insufficiency?
cystic fibrosis [in kids]
chronic pancreatitis
pancreatic resection
How does pancreatic exocrine insufficiency present?
maldigestion of fat, protein, carbohydrates
What is treatment for pancreatic exocrine insufficiency?
oral pancreatic enzyme replaement
How does bile salt deficiency present?
maldigestion of fats and fat soluble vitamins
What are some causes of bile salt deficiency?
- severe cholestasis
- distal ileal resection or disease [Crohns]
- bacterial overgrowth
What is treatment for bile salt deficiency?
treat underlying conditions and give medium chain TGs
What is bacterial count in small intestine vs large instestine?
way lower in small intestine; but flourishes if stasis
What are some underlying cause of bacterial overgrowth?
- motility disorder: ileus, pseudo-obstruction
- anatomical disorder: blind loop, fistulae, diverticula
What are consequences of bacterial overgrowth?
- fat malabsorption: bacteria deconjugate bile acids
- vitamin B12 deficiency: bacteria consume vit B12
How do you diagnose bacterial overgrowth?
schilling test
breath tests for bacterial counts
What is short bowel syndrome? effect?
removal of terminal ileum due to crohns, infarct, or cancer, etc
effects: B12 and bile acid malabsorption, rapid transit, cholesterol gallstones due to bile acid depletion; oxalate kidney stones
Why do you get oxalate kidney stones in patient with short bowel?
normally oxalate precipitated by Ca and excreted in stool; but if fat malabsorption –> long chain free fatty acids bind Ca leaving free oxalate to be absorbed by colon and excreted in kidney
What is D-lactic acidosis?
rare syndrome of metabolic acidosis with neurologic symptoms; due to colonic bacteria
occurs in short bowel syndrome
What is treatment for short bowel syndrome?
enteral feeding; total parenteral nutrition; small intestine transplant
What is peptide YY action? from where?
slows gastric emptying
secreted from ileum
What is pathogenesis of celiac?
inappropriate immune response to gliadin
causes malabsorption and villous atrophy
primarily duodenum/jejunum not ileum
What do you see histologically with celiac?
- villous atrophy
- crypt hyperplasia
- intra-epithelial lymphocytes
What HLA types in celiac?
HLA-DQ2
HLA-DQ8
What immune abnormalities associated with celiac?
- selective IgA deficiency
- diabetes
- autoantibodies to tissue transglutaminase, endomysial, and gliadin
What other complications with celiac?
- dermatitis herpetiformis
- T cell lymphoma
collagenous sprue
What are is tropical sprue?
acquired malabsorption syndrome in central america, caribbean, southeast asia
cause unknownl responds to antibiotics
What is treatment for tropical sprue?
replace folate + vitamin B12
antibiotics
What is distribution of tropical sprue vs celiac?
celiac = proximal small intestine
tropical sprue = throughout small intestine
What is clinical picture of tropical sprue?
steatorrhea following diarrhea
What is radiation enteritis?
loss of replicating epithelial cells –> villous atrophy but not hyperplastic crypts
heals over wks to mos
What is abetaliporpoteinemia?
genetic; epithelial cells cannot assemble chylomicrons so lipid accumulates in cell
have fat malabsorption
What is inheritence of abatalipoproteinemia?
autosomal recessive
What is treatment for abetaliporpoteinemia?
- dietary fat restriction
What does CBC tells you?
if microcytic anemia –> iron deficiency
if macrocytic anemia –> B12 or folate deficiency
What does prolonged thrombin time tell you?
vit K deficiency
What does low albumin tell you?
problem absorbing protein
What does low Ca tell you?
vitamin D deficient
What does low cholesterol tell you?
fat malabsorption
What is D-Xylose test of malabsorption?
- drink D xylose [monosaccharide]
50% absorbed –> liver –> circ –> kidney –> at least 25% secreted in urine
What is whipples disease?
rare systemic disease due to tropheryma whippelii causing malabsorption
What do you see in histology of whipple’s?
macrophages with pas positive bacteria in intestinal lamina propria
lymphatic obstruction
“foamy macrophages”
What is pseudo-whipples?
seen in AIDS patients –> macrophages filled with acid fast mycobacteria
What is treatment for whipples?
antibiotics [sulfonamides]
watch for relapse
What are symptoms of whipples?
cardiac symptoms
arthralgias/joint pain
neurologic symptoms
malabsorption symptoms
