The Digestive System

Question 1

What is the purpose of saliva?

Answer 1

• Moist, lubricate materials in mouth
• Dissolve chemicals that stimulate taste buds and provide sensory information
• Digest carbs by salivary amylase

Question 2

What are the major functions of the stomach?

Answer 2

• Store ingested food
• Mechanical breakdown of ingested food: churning
• Chemical breakdown via acid and enzymes
• Produce intrinsic factor to absorb vitamin B12 in small intestine
• Nutrients NOT absorbed

Question 3

Describe the four cells of gastric glands

Answer 3

• Parietal cells
  
  • Secrete intrinsic factor and HCl
• Chief cells
  
  • Secrete pepsinogen
  • Pepsinogen is converted by HCl to pepsin
• G cells
  
  • Found in pyloric glands
  • an enteroendocrine that produces gastrin
• D cells
  
  • Found in pyloric glands
  • an enteroendocrine that releases somatostatin (inhibits gastrin)

Question 4

What are the metabolic regulations of the liver?

Answer 4

• Composition of circulating blood
• Nutrient metabolism/storage
• Waste product removal
• Drug inactivation

Question 5

Describe the functions of bile

Answer 5

• Emulsification: break lipid droplets apart
• Increases SA exposed to enzymatic attack
• Creates tiny emulsion droplets coated with bile salts

Question 6

Describe the processes that occur in the digestive tract

Answer 6

• Ingestion: materials enter digestive tract via mouth
• Mechanical processing: crushing and shearing
• Digestion: chemical breakdown of food
• Secretion: release of water/acids/enzymes
• Absorption: movement of substrates into interstitial fluid of digestive tract
• Excretion: removal of waste products

Question 7

Describe the four layers of the digestive tract

Answer 7

• Mucosa
  
  • inner lining
  • folded to increase SA
  • mucous membrane
• Submucosa
  
  • dense irregular connective tissue
  • large blood vessels and lymphatic vessels
  • exocrine glands
• Muscularis externa
  
  • smooth muscle cells
  • for mechanical processing, movement of materials
• Serosa
  
  • serous membrane (outer lining)
  • protective

Question 8

How are digestive materials moved along the digestive tract?

Answer 8

• Peristalsis: waves of muscular contraction move a bolus forward
• Visceral smooth muscle tissue: cells undergo spontaneous depolarization to trigger waves of contraction

Question 9

What are the three factors that control the digestive functions?

Answer 9

• Local
  
  • chemicals released into interstitial fluid
  • coordinate response to changing conditions eg pH
• Neural
  
  • moves materials along digestive tract
  • Motor neurons: controls smooth muscle contractions and glandular secretion
• Hormonal
  
  • produced by enteroendocrine cells
  • reach target organs after distribution in bloodstream

Question 10

Describe the functions of the gallbladder

Answer 10

• Stores bile
  1. Duodenum releases cholecystokinin (CCK)
  2. Hepatopancreatic sphincter dilates
  3. Gallbladder contracts
  4. Bile released into duodenum

Question 11

Describe the three phases of gastric secretion

Answer 11

• Cephalic phase
  
  • sight/smell/taste/thought of food
  • directed by CNS (vagus nerve)
  • increased gastric juice production (pepsinogen and HCl)
• Gastric phase
  
  • due to food presence in stomach
  • Local: distention of gastric wall
  • Hormonal: secretion of gastrin by G cells
• Intestinal phase
  
  • due to food presence in intestine
  • continues small secretion of gastrin from stomach

Question 12

Describe the three segments of the small intestine

Answer 12

• 90% of nutrient absorption
• Duodenum
  
  • Receives chyme from stomach
  • Neutralizes acids
• Jejunum
  
  • Chemical digestion
  • Nutrient absorption
• Ileum
  
  • ends at ileocecal valve
  • controls material flow into cecum of large intestine

Question 13

Describe the intestinal glands

Answer 13

• Enteropeptidase
  
  • Brush border enzyme
  • Activates pancreatic pro enzyme trypsinogen
• Enteroendocrine cells
  
  • Produce intestinal hormones
  • eg gastrin, cholecystokinin, secretin

Question 14

Describe the enzymes produced by the pancreas

Answer 14

• Alpha-amylase
  
  • Breaks down starch
• Lipase
  
  • Breaks down lipids
  • Releases fatty acids and glycerol
• Nucleases
  
  • Breaks down nucleic acids
• Proteolytic enzymes
  
  • Proteases: break down large protein complexes into polypeptides
  • Peptidases: break down small peptides into amino acids

Question 15

What are the six major organs of the digestive tract and their functions?

Answer 15

• Oral cavity (mouth)
  
  • ingestion
  • mechanical processing with teeth and tongue
  • moisten and mix with salivary secretions
• Pharynx
  
  • muscular propulsion of materials into esophagus
• Esophagus
  
  • transport materials to stomach
• Stomach
  
  • chemical breakdown via acid and enzymes
  • mechanical processing via muscular contractions
• Small intestine
  
  • enzymatic digestion
  • absorption of water and nutrients
• Large intestine
  
  • dehydrates and compacts indigestible materials
  • prepares for elimination

Question 16

What are the six accessory organs of the digestive system?

Answer 16

• Teeth
  
  • mechanical processing via chewing (mastication)
• Tongue
  
  • assists mechanical processing with teeth
  • sensory analysis
• Salivary glands
  
  • secretes lubricating fluid (saliva)
  • contains enzymes to break down carbs
• Liver
  
  • secretes bile for lipid digestion
  • stores nutrients
• Gallbladder
  
  • stores and concentrates bile
• Pancreas
  
  • exocrine cells secrete enzymes/buffers
  • endocrine cells secrete hormones

Question 17

Explain hydrochloric acid secretion by parietal cells

Answer 17

1. converts CO2 and H2O to carbonic acid (H2CO3) via carbonic anhydrase
2. H2CO3 dissociates to form H+ and HCO3-
3. H+ exchanged for K+ via proton pump
4. H+ actively transported into stomach lumen
5. HCO3- exchanged for Cl- via bicarbonate chloride antiporter
6. Cl- actively transported into parietal cell
7. Cl- secreted into stomach lumen via channel
8. H+ combines with Cl-

Question 18

Describe the function of the large intestine (colon)

Answer 18

• Reabsorbs water
• Compacts intestinal contents into feces
• Absorbs vitamins produced by bacteria
  
  • Vitamin K
  • Vitamin B7: Biotin
  • Vitamin B5: Pantothenic acid
• Stores fecal material before defecation

Question 19

Describe the enzymatic steps involved in digestion

Answer 19

• Mouth
  
  • Salivary amylase: breaks down starch into maltose
• Stomach
  
  • Pepsin: inactive form, pepsinogen, activated by HCl to break down proteins
  • Gastric lipase: breaks down lipids
• Small intestine
  
  • Pancreatic amylase
  • Pancreatic lipase
  • Nucleases
  • Proteases
• Brush border enzymes (small intestine)
  
  • Maltose: breaks down maltose to glucose
  • Sucrase: breaks down sucrose
  • Lactase: breaks down lactose
  • Peptidases: breaks down peptides to amino acids