Digestion and Absorption in the GI Tract Flashcards
Lactose intolerance
Lactase enzyme activity is deficient or absent
Lactose converted to SCFAs and hydrogen
Remains in lumen, holds H2O in lumen resulting in osmotic diarrhea
Ferments into methane and H+ gas
Type of transport for glucose, galactose and fructose in small intestine
Concentration gradient established by Na/K ATPase
Secondary active transport for glucose and galactose via SGLT1 cotransport w/Na
Facilitated diffusion for fructose via GLUT5
GLUT2 facilitated transport of these sugars into blood
Most starch breakdown occurs where
Small intestine via pancreatic amylase
Breaks starch down into maltose and longer (3-9) polymers of glucose
Congenital trypsin absence
All pancreatic enzymes are gone because trypsin cleaves/activates the pancreatic enzymes
Trypsinogen (enterokinase) catalyzes trypsinogen–>tryspin
Cystinuria
Defect in transport or absence of di-basic AA transporter
Cystine, lysine, arginine, ornithine are not reabsorbed at proximal tubule
Cystine is most problematic because it is not very soluble and aggregates
Hartnup disease
Cannot absorb neutral AA
Symptoms resemble pellagra (niacin deficiency)
High excretion of tryptophan & its byproducts like serotonin
Diarrhea, mood changes, neurological problems, red/scaly skin, photosensitivity
Cystic fibrosis
CFTR Cl channel is defective
Pancreatic problems early in life
Some CFTR mutations associated w/loss of HCO3 secretion which means pancreas cannot move enzymes from ducts - leads to acute/chronic pancreatitis
Pancreas protein digestion - enzymes/functions
Mostly breaks proteins into di/tripeptides and some AAs
Trypsin, chymotrypsin, carboxypeptidase, elastase
Small intestine protein digestion
Aminopolypeptidase, dipeptidases
AAs, di/tri-peptides are absorbed into enterocytes
Amino acid vs Di/tri-peptide cotransport
AAs cotransported with sodium
Di/tripeptides cotransported with hydrogen
Folds of Kerckring
Longitudinal folds in the small intestine containing villi and microvilli
Increasing surface area for absorption
Duodenum has longest villi
Fat digestion in the stomach
Lingual and gastric lipase act on TAGs
10% of TAG digestion
Cholesterol ester hydrolase separates cholesterol from FAs
CCK inhibits gastric emptying for more mixing along with activating gallbladder emptying
Small intestine fat digestion
Most digestion of lipids occurs here - bile salts emulsify
Pancreatic lipase - inactivated by bile salts - colipase prevents pancreatic lipase from being inactivated by bile salts
ApoB
Found on chylomicrons
Lack leads to abetalipoproteinemia - no lipid absorption leading to steatorrhea
Overlying theme of pancreatic insufficiency, Zollinger-Ellison syndrome and Pancreatitis
Duodenum is too acidic due to lack of HCO3 containing pancreatic secretions
SIBO
Bacteria deconjugate bile salts, impairing micelle formation
Can damage intestinal mucosa
Too little gastric secretion and small intestinal dysmotility
Methane and hydrogen detected in breath test
Causes of IF deficiency
Atrophic gastritis- chronic inflammation of stomach mucosa leading to loss of parietal cells
Autoimmune metaplastic atrophic gastritis- immune system attacks IF protein or parietal cells
Water soluble vitamin vs fat soluble vitamin absorption
Fat soluble ADEK- same mechanisms as lipids
Water soluble BC- most are absorbed via Na depended cotransport except B12
Iron absorption
Occurs in duodenum
Liver secretes apotransferrin into bile, enters duodenum
Apotransferrin binds free iron and hemoglobin forming transferrin
Transferrin binds intestinal epithelial cell receptors and is absorbed via pinocytosis
Ferroportin transports iron into the blood and transferrin transports to liver/spleen/bone marrow
Jejunum vs ileum electrolyte absorption
Jejunum- absorbs lots of sodium
Ileum- sodium absorbed, HCO3 secreted
Colon electrolyte absorption
Na absorption and K+ secretion
Aldosterone modulates- stimulates Na absorption
Cholera
Increases cAMP causing increased Cl secretion, accompanied by Na and H2O secretion
Volume of fluid secreted into the intestinal lumen overwhelms the absorptive mechanisms of the small intestine/colon leading to massive secretory diarrhea
Calcium absorption occurs where
Small intestine - duodenum/jejunum
