Digestion and Absorption in the GI Tract Flashcards
What do digestive juices do?
Breakdown of ingested food (digestion) and intake of the nutrients (absorption)
Very little absorption occurs here
Stomach
What are the folds of the intestinal mucosa called? And how much do they increase the surface area?
Valvulae Conniventes; 3-fold increase in absorptive mucosal surface area
What is found inside the villi of the intestines? How much does villi increase the absorptive surface?
Lymph and blood vessels; 10-fold
Where is the brush border found and what does it contain?
Each intestinal epithelial cell on each individual villus is covered with a Brush Border, which is characterized by as many as 1000 microvilli.
1 micrometer in length protruding into the lumen
Absorption into the lymphatic system through the villi occurs through what structure
Central Lacteal
Three major sources of dietary carbohydrates
Sucrose- A disaccharide known as table sugar
Lactose- A disaccharide found in dairy products
Starches- Large polysaccharides present in almost all non-animal foods (potatoes, corn, grains, etc.)
Saliva contains an enzyme called _____ for digesting carbohydrates. What does this enzyme initiate?
Ptyalin (an amylase); initiate breakdown of starches
What causes the activation of Salivary Amylase?
Low pH in the stomach
20-40% of the starches will have been hydrolyzed to form _____, before what process can happen
Disaccharide Maltose; Salivary Amylase creation
Carbs are very quickly digested in the duodenum by what enzyme
Pancreatic Amylase
The Enterocytes that make up the Brush Border contain these four enzymes that split disaccharides further into monosaccharides.
Maltase, Alpha-Dextrinase, Lactase, and Sucrase
Carbs must reach this state before intestinal absorption can occur
monosaccharide (almost all glucose)
Which form of transport moves glucose into the intestinal cells to be absorbed? what molecule is involved?
Secondary active transport; Sodium moves with glucose into the cell
Which mode of transport moves glucose from the basal surface of the epithelial cells into capillary blood flow?
Facilitated diffusion
Digestion of proteins starts here, and uses what enzymes?
Stomach; hydrochloric acid and pepsin
The acid helps to denature and unfold protein structures.
Pepsin hydrolyzes large protein structures, such as collagen, into small peptones and polypeptides.
What are Trypsin, chymotrypsin, and carboxypolypeptidase and what do they do?
Proteolytic pancreatic enzymes; breakdown proteins into small dipeptides or tripeptides or single amino acids.
What controls the last stage of protein digestion?
Membrane protein peptidases within the microvilli of the enterocytes
These split the remaining polypeptides into smaller amino acid pieces (1, 2, or 3 AAs), which are easily transported into the cell.
Transport utilized for Protein absorption
The majority of the digested proteins are brought into the cell using the secondary active cotransport using Sodium ions or Hydrogen ions as a co-transporter.
Through _______ amino acids are absorbed into the vascular circulation for use by the body
Sodium-Amino Acid Transporter
Dietary fats contain _______ the number of calories that we obtain from carbohydrates and proteins
Twice
Digestion of fats primarily occurs here
duodenum and jejunum
Fats become emulsified by what primarily?
Bile acids
What does pancreatic lipase do to fat?
Pancreatic Lipase is an aggressive digestive enzyme that attacks the emulsified fat, hydrolyzing these fatty lipids into free fatty acids, monoglycerides, and cholesterol.
Fat hydrolysis is highly reversible, so bile acids are available to quickly surround the digested fat, creating _____
Micelles
Micelles act as a good transport medium for ____
cholesterol, glycerides, and fatty acids
Where are triglycerides formed and how?
In the intestinal epithelial cells, fatty acids link with glycerol to form triglycerides
What structure in the cell forms chylomicrons?
Within the Golgi, globules of triglycerides and cholesterol are coated with proteins to form Chylomicrons (transport lipoprotein).
The intestines must absorb roughly _____ grams of sodium each day to prevent a net loss
25-35 grams
Large amounts of sodium can be lost with _____
Diarrhea
How is water absorbed from the intestines?
Diffusion, following the laws of Osmosis
Where does osmotic leakage occur?
Through the paracellular tight junctions, as well as through the cell itself (transcellular).
What are Bicarb-Chloride exchangers and where are they found?
Bicarb-Chloride exchangers in the epithelium result in fecal excretion of Bicarbonate, which is needed to neutralize the acidic end products of bacterial action in the colon.
Where does the brown color of feces come from? The odor?
Color: Derivatives of Bilirubin being excreted
Odor: Bacterial action (gas production)
Water absorption maxes out at _____ daily
5-8 liters daily
An infection like cholera can cause what with water secretion?
The crypts may secrete 10+ liters per day! Major dehydration possible
Epidemiology of Celiac Disease
Most prevalent in Western Europe and the United States.
Bimodal distribution of age at diagnosis:
8-12 months of age
20-40 years of age
Symptoms may become apparent in young infants when they start eating gluten foods.
Symptoms may persist throughout childhood if untreated and then usually diminish in adolescence.
Symptoms then often reappear between 20-40 years of age.
What is Celiac Disease?
Also known as Gluten-Sensitive Enteropathy or Celiac Sprue, this is a chronic digestive disorder characterized by the inability to tolerate Gliadin, an alcohol soluble fraction of gluten.
How is Celiac Disease diagnosed? How is it managed?
Lab studies are the best initial test:
Anti-Tissue Transglutaminase (tTG IgA)
Most common and best predictive value of serology tests
Upper Endoscopy with at least 6 duodenal biopsies is confirmatory.
Management: completely gluten free diet (It takes generally 4-8 weeks of a Gluten-Free diet for patients to notice a difference in their symptoms)
What is Gliadin and what is it’s role in celiac disease?
Gliadin - an alcohol soluble fraction of gluten.
Gliadin-tTG complex is inappropriately presented to helper T cells, which mediates an inflammatory response and antibodies against Gliadin-tTG.
The inflammatory cytokines released into the intestinal epithelium, as well as the presence of antibodies against Gliadin-tTG, triggers epithelial invasion by Lymphocytes, resulting in destruction of the absorptive surface of the intestine.
