1. Why do we need a digestive system?
2. Define autotrophs - how do they intersect w/ heterotrophs?
3. Which is essential to life? Why?
4. What six classes of nutrients does the human body need?
1. Because animals are heterotrophs - require ingestion of biomass to obtain energy and nutrition.
2. Autotroph - organisms that can make their own food (inorganic substances --> organic substances that heterotrophs can use)
3. Autotrophs bc they are primary producers at the base of all food chians
4. Carbs, proteins, lipids, vitamins, minerals, water.
1. Define ingestion
2. Define digestion
3. Til what point is food considered out of your body?
4. Role of digestive system?
1. Ingestion - process of taking food into the digestive system so that it may be hydrolyzed/digested.
2. Digestion - process of breaking down food (mech/chem) in order to utilize nutrients.
3. Until it is broken down and taken up into the enterocyte.
4. To make nutrients accessible from food for absorption and use by the body.
What are the stages of the digestive process?
- 1. Movement
- 2. Secretion of digestive juices
- 3. Digestion - breakdown of food into molecules that can be taken up by enterocytes
- 4. Absorption - passage of molecules into body's interior
- 5. Elimination - removal of undigested foods and wastes.
What are the main structures of the digestive system? (11)
Accessory organs? (3)
What are the 4 components of the oral cavity? 3-3 extras
- 1. Mouth
- 2. Pharynx
- 3. Salivary glands (parotid, submandibular, sublingual)
- 4. Enzymes in saliva
What are the functions of the oral cavity?(5) Each function has a quick description as well.
- 1. Mastication - to cut up food and mix w/ saliva
- 2. Digestion (salivary enzymes)
- 3. Gustatory (chemoreception)
- 4. Speech (larynx, tongue, cheeks, lips)
- 5. Swallowing (hard & soft palate);
How does the mouth contribute to digestion? What is formed?
- 1. Chemical digestion (saliva)
- 2. Mechanical digestion
- 3. A bolus is formed with saliva and tongue
1. What is saliva composed of?
2. How much saliva is produced/day?
3. What are other components of saliva?
- 1. 99.5% water, electrolytes, mucus.
- 2. 1 L
- 3. Amylase, lingual lipase, mucin (protects soft lining of digestive tract & lubricates food), buffers (neutralizes acid to prevent tooth decay), antibacterial/viral compounds
What is the epiglottis? When is it useful? For doing what?
Flap of cartilage.
When swallowing - closes trachea.
Peristalsis - involuntary muscle contractions to move food along.
What does the wall of the esophagus look like?
1. What does esophageal mucosa do? (2)
2. Is it rapidly turned over?
3. What is the lamina propia?
- 1. Provides protection against (1) abrasion of food bolus and (2) refluxed stomach acid
- 2. Yes
- 3. Lamina propia = layer full of lymphoid aggregates and mucosal glands.
1. What is the function of the esophagus? (1)
2. What is the mechanism of the function?
3. Describe 5 steps of the mechanism
- 1. Swallowing
- 2. Peristalsis
- 1. Esophageal sphincter relaxes; esophagus opens
- 2. Epiglottis shifts over glottis
- 3. Voluntary muscles (upper; striated) and involuntary muscles (lower; smooth) are stimulated by parasympathetic nerves.
- 4. Lower esophageal sphincter relaxes
- 5. Bolus of food moves into stomach.
Describe the organization of the wall of the GI tract (4)
- 1. Mucosa (innermost) - produces/releases secretions needed for digestion, also contains lymphoid tissue.
- 2. Submucosa - connective tissue
- 3. Muscularis externa - GI motility
- 4. Serosa - connective tissue
1. What are the four regions of the stomach? What do last two do? 2,3
- 1. Cardia region
- 2. Fundus
- 3. Body (food reservoir/gastric juice production)
- 3. Antrum/distal pyloric region - grinds food & mixes w/ gastric juices to form chyme; strong peristalsis for gastric emptying
1. What is the purpose of muscle in the stomach?
2. What is the role of the lower esophageal sphincter?
3. What is the role of the pyloric sphincter?
1. Forceful contractions of muscle help grind food, mix it with gastric juices to form chyme
2. To regulate flow of food from esophagus to stomach
3. Regulates flow of chyme from stomach --> duodenum.
What are the functional areas of the stomach?
Name functions of #3-4
1. Gastric pits - entrance to the glands
2. Gastric glands - cardiac glands (cardia), oxyntic glands (body), pyloric glands (antrum)
3. Cells in glands
1. Neck (mucus) cells - produce bicarbonate & mucus forming gastric mucosal barrier, protecting mucosal lining from acidity of gastric juice.
2. Parietal (oxyntic) cells - produce HCl and IF to metabolize vitamin B12 and iron.
3. Chief (peptic/zymogenic) cells - needed for protein digestion
4. Enteroendocrine (D&G) cells - produce gastrin (G) stimulating parietal and chief cells. D cells secrete somatostatin.
1. What is in mucin? 4
2. What is in gastric juice? What is its pH?
1. Glycoproteins, glycolipids, water, and bicarbonate
1. Gastric juice contains HCl (pepsinogen-->pepsin, protein denature, nutrient release, bacteriocide); enzymes (pepsin, gastric amylase, gastric lipase); mucus, IF
pH = 2
1. What does HCl do?
1. Converts pepsinogen --> pepsin to cleave proteins, releases nutrients from organic complexes, acts as bacteriocide.
What enzymes are in gastric juice? Describe functions and sources of enzymes
1. Pepsin (chief cells) - pepsinogen --> pepsin; pepsin = endopeptidase. HCl leads to autocatalytic cleavage of pepsinogen --> pepsin. Optimal pH = 3.5
2. A-amylase (salivary glands) - a1,4 hydrolysis of starch, inactivated at low pH
3. Gastric lipase (chief cells) - hydrolyzes short & medium-chain TAGs
4. Intrinsic Factor (parietal cells) - Vitamin B12 absorption
What are the functions of the stomach?(6)
- 1. Temporary food storage
- 2. Secretion of gastric juices
- 3. Layers of muscle that mechanically break up food
- 4. Chemical digestion of food -> limited chemical digestion bc of low pH (i.e., amylase)
- 5. Initiation of protein hydrolysis
- 6. Absorption of water, alcohol, a few drugs, and a few minerals.
What activates gastric motility & secretions? (3)
What inhibits it? (8)
1. Gastrin, gastrin-releasing peptide histamine, motilin, acetylcholine
- Inhibited by:
- 1. CCK
- 2. Enterogastrone
- 3. Gastric inhibitory polypeptide
- 4. Peptide YY
- 5. Vasoactive intestinal polypeptide
- 6. Substance P
- 7. Secretin
- 8. Somatostatin
Control of acid secretions
1. What stimulates acid secretion? (3)
1-4; 2-3; 3-2
2. What inhibits it? (2)
1. Stimulated by:
1. Histamine (ECL) - stimulates by binding to the H2 receptors of parietal cells to release HCl, generates cAMP, inhibited by peptide YY
2. Gastrin (G cells) - increases IC Ca2+ levels; inhibited by somatostatin
3. Acetylcholine (vagus nerve) - increases IC Ca2+ levels
(1) Somatostatin (D cells) - inhibits gastrin & cAMP production
(2) Peptide YY (ileum/colon) - inhibits histamine release.
What regulates gut motility & gastric emptying? (4)
- 1. Stomach relaxation (vagus nerve)
- 2. Antral contractions (pacemaker determines freq)
- 3. Migration motility - motilin
- 4. Gastric emptying - osmoreceptors in duodenum; certain foods have gastric emptying slowing efefct - fat, salt, fiber.
What does antral peristalsis do? Through which 3 mechanisms?
Push foods through pylorus.
Through proplusion, grinding, and retropulsion.
How does chyme move along? (2) Give defs too
1. Segmentation - circular muscles alternate contraction/relaxation creating segments along intestines creating chopping machine --> chyme is pushed back and forth within adjacent segments of the intestine
2. Peristalsis - wavelike rhythmic contractions and relaxations propelling food forward through GI tract.
1. What connects duodenum to diaphragm? What does it designate?
2. What are the two main functions of small intestine?
3. What are the functional parts of the small intestine? (5)
1. Treitz (suspensory) ligament - designates duodeno-jejunal junction.
2. Chemical digestion (major organ for digestion + absorption) & absorption through lining
3. Folds of Kerckring (plicae circulares), villi, microvilli, brush border, crypts of liberkuhn
Name the five functional parts of the small intestine and definitions/functions
1. Folds of Kerckring (plicae circularis) - large circular folds of mucosa to increase SA of intestine
2. Villi - fingerlike projections made of enterocytes (each villus contains capillary & lymphatic network)
3. Microvilli - hairlike extension of enterocytes' plasma membrane to increase SA
4. Brush border - made of microvilli of enterocytes
5. Crypts of Liberkuhn - cells in these crypts migrate up and become absorptive enterocytes on villus tips. Secretes SECRETIN too.
1. What % of daily fluid intake is absorbed in SI?
2. What increases surface area of small intestine? (4)
3. How long do enterocytes live?
4. What do enterocytes require? For what? (2)
- 1. Almost 90
- 2. Small intestine in form of cylinder, folds of kerckring, villi of mucosal surface, microvilli
3. 3 days - rapid turnover
4. Energy for processing nutrients & maintaining normal cell processes.
1. What are the two main fuel sources (not compounds) for enterocytes? Which predominates?
2. What are the main compounds? (2)
3. What increases intestinal secretions and motility in SI? (4)
4. What decreases intestinal secretions and motility in SI? (3)
1. Arterial and luminal. Arterial derived fuel sources predominate.
2. Glucose (bc of high hexokinase activity) and glutamine
3. Vasoactive intestinal polypeptide (VIP), substance P, motilin, CCK
4. Glucagon-like peptides, peptide YY, secretin
1. What two main types of tissues protect GI tract immunologically? Abbreviations and what they stand for.
2. What do these tissues contain? (5)
3. What is released from plasma cells? What does it do? (3)
4. What can happen with these tissue layers? Because of what? (3) Which leads to? (1) which then leads to? (2)
5. What are the 3 accessory organs?
1. MALT (mucosa-associated lymphoid tissue) and GALT (gut-associated lymphoid tissue)
2. Leukocytes (T & B lymphocytes), macrophages, NK cells, plasma cells
3. IgA cells - binds w/ food + inhibits growth and translocation of bacteria.
4. Easily destroyed bc of injury, illness, or starvation --> bacterial translocation --> sepsis/organ failure.
5. Pancreas, liver, gallbladder
1. What does pancreas secrete? Which nutrients does it digest?
2. What cells produce pancreatic digestive enzymes?
3. What does pancreatic juice contain? 3
4. What specific digestive enzymes does pancreatic juice contain? 3 What else? (2)
1. Digestive enzymes (exocrine) and hormones (endocrine). All major nutrient types
3. Bicarbonate, electrolytes, pancreatic digestive enzymes
4. Trypsin, chymotrypsin, amylase; buffers (bicarbonate) + somatostatin (endocrine function)
What regulates pancreatic secretion? List substrate, cell source for first 2, and functions. (6)
1. Secretin (S-cells aka enterocytes in crypts of Lieberkuhn) - stimulated by acid chyme released from stach; stimulates pancreas to secrete H2O, bicarbonate, and pancreatic enzymes.
2. CCK (L-cells in intestinal mucosa) - stimulates release of pancreatic juice & enzymes, relaxes sphincter of Oddi
3. Vasoactive intestinal polypeptide (VIP) - stimulates secretion of bicarbonate and water into pancreatic juice
4. Substance P - stimualtes secretion into duodenum
5. Peptide YY inhibits
6. Somatostatin inhibits pancreatic exocrine secretions
1. What are the two overarching functions of liver?
2. What are the 5 functions of liver in the above?
1. Metabolic regulation & production/role of bile.
- (1) Primary organ involved in regulating comp of circulating blood
- (2) Extracts nutrients/toxins from blood before reaching rest of body
- (3) Monitor and adjust circulating levels of organic nutrients
- (4) Stores fat-soluble vitamins (ADKE)
- (5) Makes bile
1. What does bile contain? (6)
2. What is the purpose of bile? (4)
3. What is liver's main function in digestion?
4. What does portal vein do? central vein? bile ducts?
1. Water, ions, bilirubin (pigment from Hb), cholesterol, lecithin, and bile salts
2. To emulsify lipid droplets into smaller pieces --> formation of micelles, detox, excretion of bilirubin
3. Production of bile
4. Portal vein - gets nutrients from GI; central vein - sends nutrients into general circulation. Bile ducts - collect bile
1. What does gall bladder do?
2. What regulates this?
3. What % of bile acids/salts excreted into duodenum are reabsorbed by active transport in the ileum?
4. Where else might bile acids/salts be passively absorbed? What happens to the rest?
5. What happens to the bile acids/salts absorbed in ileum?
6. Where is cholesterol reabsorbed?
7. What compounds decrease reabsorption?
8. How do medicines stop hypercholesteremia?
1. Concentrates (90% of H2O resorbed) bile, stores bile
2. CCk stimulates release of bile; somatostatin inhibits release.
3. 90%. 97% of bile acid/salt reabsorption occurs in ileum too.
4. Jejunum and colon. The rest is excreted (~0.5g/day)
5. Binds to albumin --> blood --> liver. In liver, reabsorbed bile acids are reconjugated to AAs if necessary and secreted into bile along w/ newly synthesized bile acids.
6. Jejunum (~50%)
7. Fiber and plant sterols
8. Binds to bile enhancing its fecal secretion, decreasing recirculation of bile, decreasing absorption of cholesterol requires body to use body's cholesterol stores to synthesize new bile acids.
Describe the roles of gastrin, CCK, and secretin in the stomach (5 steps)
1. Stomach secretes gastrin into blood after meal
2. Gastrin returns to stomach and stimulates muscle contraction & acid production
3. Chyme moves into SI and stimulates secretion of CCK & secretin into the blood
4. CCK & secretin stimulates secretion of digestive enzymes and bicarbonate ions from the pancreas into the small intestine
5. CCK also stimulates contraction of the gallbladder --> releases bile into the SI.
1. How does absorption occur? (5 different mechs)
2. What does absorption depend on? (4)
3. What happens to unabsorbed materials?
1. Diffusion, facilitated diffusion, active transport, pinocytosis/endocytosis
2. Solubility (fat vs. water), concentration/electrical gradient, size of molecule
3. Eliminated in colon
Describe mechanism of dietary starch digestion & absorption (6 steps)
1. Mouth (salivary a-amylase) - carbs --> polysaccharides + oligosaccharides + disaccharides
2. Stomach - low pH halts salivary a-amylase
3. Small intestine (pancreatic a-amylase) - oligosaccharides
4. Brush border (enzymes on luminal surface of SI epithelial cells) - oligosaccharidases/disaccharidases --> monosaccharides
5. Glucose + galactose are absorbed using SGLT (2Na+ ATPase), fructose is absorbed through GLUT 5 (facilitated diffusion)
6. Monosaccharides leave epithelial cells into blood by facilitated diffusion through GLUT 2.
Describe lipid digestion & absorption (4)
- 1. Mouth (lingual lipase)
- 2. SI (bile salts & lingual lipase) yields FFAs and monoglycerides to form micelles (w. bile salts)
- 3. FA and monoglycerides leave micelles and diffuse into epithelial cells.
4.Repackaged to form chylomicrons
5. Chylomicrons are extruded from epithelial cell by exocytosis --> lacteals --> lymph
How do glucose, galactose, fructose, AAs, peptides, short chain FAs, and micelles enter intestine and leave?
1. What are the two main ways that digestive process is regulated?
1. Neural regulation; regulatory peptides.
Describe classification, function, production site, and site of function for the following:
2. HCl (4)
1. IF (glycoprotein); made in parietal cells acts in small intestine for B12 absorption
2. HCl (acid); parietal cells-->stomach breaks down food, denatures proteins, bacteriocide, pepsinogen-->pepsin
3. Pepsin/pepsinogen; stomach--> stomach cleaves carboxyl end of certain AAs.
4. Trypsin & chymotrypsin: pancreas --> SI; cleaves carboxyl end of AAs
5. CCK (hormone): L-cells in intestinal mucosa --> duodenum. Inhibits gastric motility, stimulates release of pancreatic juice, stimulates bile release, relaxes sphincter of oddi, signals satiety
6. Secretin (hormone): S cells in crypts of Lieberkuhn --> pancreas, gastric motility, SI. Stimulatse pancreatic juice/enzyme secretion & inhibits GI motility
Describe classification, function, production site, and site of function for the following:
7. Gastric inhibitory peptide -1
8. Peptide YY -4
9. Somatostatin -4
10. Substance P - 3
11. Vasoactive intestinal polypeptide (VIP) - 3
7. Gastric inhibitory peptide (K cells in duodenum and jejunum): SI --> stomach; inhibits gastric motility & secretions
8. Peptide YY (ileum & colon): inhibits acid secretion via inhibition of histamine, inhibits SI secretions/motility, & pancreatic secretion.
9. Somatostatin (D cells in stomach & pancreas): inhibits pancreatic exocrine secretions, inhibits gastric motility/secretions, inhibits gastrin (inhibits acid secretion), inhibits bile release
10. Substance P (neurons & SI) - inhibits gastric secretions, increases SI secretions & motility, stimulates pancreatic secretion into duodenum.
11. VIP (); inhibits gastrin motility/secretions, increases intestinal secretions & motility, stimulates bicarbonate secretion from pancreas
Describe classification, function, production site, and site of function for the following:
12. Gastrin - 5 (regulation 3)
13. Gastrin-releasing peptide
14. Histamine - 2 (1 regulation)
15. Glucagon-like peptides -1
16. Motilin -3
12. Gastrin (G cells stomach) - increases Ca2+ levels (increasing acid secretion), increases SI activity, released in response to meal, inhibited by peptide YY & somatostatin
13. Gastrin-releasing peptide - stimulates gastric motility and secreitons
14. Histamine - (ECL cells) stimulates gastric motility/secretions, inhibited by peptide YY
- 15. Glucagon-like peptides - decreases SI activity
- 15. Motilin (M cells) increase gut motility & gastric emptying, increase SI secretions
1. What passes through large intestine?
2. What happens in ascending colon?
3. What is reabsorbed with water? What is synthesized in colon?
4. What do lactate & short chain FAs do in colon? (2)
5. What gases are produced in colon? (4) What are they used by?
- 1. Undigestible materials (i.e., fiber)
- 2. Reabsorption of water, sodium, chloride, vitamin K and B12
- 3. Vitamin K and B12
- 4. (1) stimulate GI cell proliferation (2) lower luminal pH --> optimal growth conditions for bacteria
5. Gases: methane, hydrogen, CO2, H2S; bacteria
1. What does large intestine contain?
2. How do microflora associate with digestive capabilities?
3. What happens when CHo and protein are broken down anaerobically?
4. Probiotics vs. prebiotics?
- 1. Helpful bacteria - mostly anaerobes; high # of gram negative and positive bacteria stains.
- 2. Augments
3. Fermentation - generates lactate & short chain fatty acids and gases
4. Probiotics - contain live bacterial culture leading to health benefits while prebiotics contain selectively fermented ingredients promoting bacterial growth in colon
1. What are most common examples of probiotics? Purpose?
2. Sources of probiotics? Name a few
3. Purported effects of probiotics? (5)
1. Lactobacillus and bifidobacterium to assist body's naturally occurring gut flora
2. Yogurt, fermented milk, miso, soy, probiotic supplements
- 3. 1. Enhance immune function 2. Antagonize pathogenic bacteria from colonizing 3. increase fecal bulk production 4. lower pH of colon
- 5. Transform/promote excretion of toxic substances
1. What does it resist?
2. Mechanisms? (2)
3. Sources? Name a few
5. What are synbiotics?
1. Host digestoin, absorption and adsorption
2. (1) fermented by microflora colonizing GI system (2) selectively stimulates growth and/or activity of one or a limited # of bacteria within GI system
3. SOurces: soy beans, wheat, unrefined barley, raw oats, yacon
4. Symbiotics = prebiotics + probiotics
1. What is GERD? WHat happens?
2. What is it caused by?
3. Diagnostic criteria?
4. GERD treatment
5. Contributing factors (4)
- 1. Gastroesophageal reflux disease
- 2. Reflux of gastric content from stomach to esophagus, damaging esophageal mucosa --> esophagitis
2. Weak lower esophageal sphincter --> spontaneous opening of LES and increased abdominal pressure
3. Heartburn at least 2x/week
4. Medicines (help muscles empty stomach, stop acid production, antacids) and lose weight, stop smoking, etc.
5. Obesity, pregnancy (both increase gastric pressure), smoking, and large meals (increases gastric volume)
1. What is inflammatory bowel disease?
2. Symptoms? (5)
3. Types? (2) What do they affect? (2)
4. Nutritional guidelines
- 1. GI tract inflammation of unknown etiology
- 2. Excessive diarrhea, cramps, bloody stools, fatty stools, rapid weight loss
- 3. Crohn's disease (mouth to anus, affects whole bowel wall) and ulcerative colitis (starts at nus, affects mucosa)
4. Eat low-fat meals, replace losses associated with IBD (more iron, ca, Mg, vitamins, fluids, electrolytes)
1. What is its key feature? (2)
2. What is gluten?
3. Ingestion of gluten leads to? (2)
- 1. Autoimmune disease AND malabsorption
- 2. Storage protein in grain (wheat, rye, barley)
- 3. (1) Villi of intestine atrophy/become blunted via (2) immune/inflammatory responses
- 4. Avoid gluten containing products
1. Insufficiency of what enzyme?
2. What happens to lactose? (3)
- 1. B-D-galactosidase insufficiency
- 2. Lactose is not digested --> enters colon (osmoticall active) --> fermentation by bacteria leads to increased gas production
- 3. Hydrogen/methane breath test