9. Digestion and Absorption in the GI Tract Flashcards
What is lactose intolerance
- Failure to digest dairy carbohydrates
- Brush border LACTASE enzyme activity is deficient or absent
What happens when lactose passes unabsorbed through the small intestine
- Lactose is converted to SCFAs and hydrogen gas
- Sugar remains in lumen holding H2O resulting in OSMOTIC DIARRHEA
- Sugar ferments into methane and Hydrogen gas (bloating and gas)
What are the primary sugars in human diet
Sucrose
Lactose
Starch
What carbohydrate digestion occurs in the mouth
Begin breaking down starch into maltose and glucose by salivary amylase
What carbohydrate digestion occurs in the small intestine
Most starch breakdown in maltose and glucose by pancreatic amylase
(many disaccharides reach small intestine in tact)
What transporters are responsible for absorption of Fructose, galactose and glucose
Fructose- GLUT5
Galactose/Glucose- uptake via secondary active transport SGLT1
Galactose/Glucose- into blood via GLUT2
What does the D-xylose test check
D-xylose is absorbed but not used so if 5g is administered then kidneys should secrete >4g
If there is a problem with sugar absorption then D-xylose will be in feces not urine
What defines protein assimilation disorders
Deficiency of pancreatic enzymes or defect in transporters of intestinal epithelial cells
Compare and contrast Chronic Pancreatitis with Congenital Trypsin Absence
Chronic Pancreatitis: deficiency of pancreatic enzymes - lack of proteases (trypsinogen)
Congenital Trypsin Absence: absence of trypsin - all pancreatic enzymes are gone
What causes Cystinuria
Defect in transport (SLC3A1) or absence of dib-basic AA transporter (SLC7A9)
COLA
What is Hartnup Disease
- Cannot absorb NEUTRAL AA
- Symptoms like pellagra
How does Cystic Fibrosis affect the pancreas
Loss of HCO3- secretion is associated with some CFTR mutations
Where are amino acids, di/tri-peptides absorbed
Enterocytes
What type of transporters are used by epithelial cells of the small intestine
Separate Co-Transporters for each amino acid type to get into the cell
-Neutral/Basic/Acidic/Imino
Separate Facilitated Diffusion mechanisms for each amino acid type to get into lumen
-Neutral/Basic/Acidic/Imino
What establishes the sodium (ion) gradient needed for protein absorption
Na+/K+ ATPase
Needed because AA transporters move H+ and Na+ also
What is Celica Sprue
Autoimmune disorder causing problems with fat digestion and absorption
Antibodies develop against a gluten component - Gliadin
-Leads to destruction of small intestine villi and hyperplasia of the intestinal crypts
What is Tropical Sprue
Loss or decreased number of intestinal epithelial cells result in problems with fat digestion and absorption
Where is the site of activity of a number of digestive enzymes
brush border
What is the significance of the structure of intestinal mucosa
- Ideal for absorption of large amounts of nutrients
- Lumen surface arranged in longitdunial folds (folds of Kerckring)
- Villi and microvilli increase SA for absorption
What is the basic concept behind fat digestion
Bile salts and lecithin emulsify fat products into micelles
Where is the most digestion of lipids occuring
Small intestine via pancreatic enzymes
- Pancreatic lipase
- Cholesterol Ester Hydrolase
- Phospholipase A2
What is the overlying theme behind problems with fat digestion and absorption
Improper acidity of duodenum contents - lumen must be neutralized by HCO3- containing pancreatic secretions
What can cause a deficiency in bile sales and interfere with formation of micelles
- Ileal resection
- Small intestinal bacterial overgrowth (SIBO)
What are fat-soluble vitamisn
ADEK
What are water-soluble vitamins
B vitamins and C
What can cause B12 deficiency
- Atrophic gastritis
- Autoimmune metaplastic atrophic gastritis
- Gastrectomy
- Gastric bypass
What key concept defines/regulates electrolyte absorption
absorbate is always ISOSMOTIC
Where are electrolytes absorbed
Jejunum- lots of sodium
Ileum- sodium absorbed, HCO3 secreted
Colon- Na absorption and K secretion
