M17: Stomach Digestion & Pancreas

Question 1

mechanical digestion in the stomach

Answer 1

• stored in fundus for up to an hour (no contact with gastric juices, salivary amylase still working)
• PERISTALTIC WAVES every 15-20 sec
• pyloric sphincter: slightly open, only liquids go through
• body region: mixing via propulsion and retropulsion
• produces CHYME: broken down liquid form of food

Question 2

propulsion vs retropulsion

Answer 2

PROPULSION: stomach body muscles contract, push food towards sphincter
RETROPULSION: because pyloric sphincter is closed, food pushed back into stomach body

Question 3

chemical digestion in the stomach

Answer 3

• HCL: denatures pr-, kills microbes
• further protection by surface and neck mucous cells
• PEPSINOGEN: activated by HCL, protects against autodigestion
• PEPSIN: digests pr-, very active in low pH areas of stomach
• GASTRIC LIPASE: breakdown of fats, but limited role because optimal pH is higher than stomach
• ABSORPTION: limited except for water, ions, alcohol, drugs

Question 4

how is HCL formed for digestion in the stomach?

Answer 4

parietal cells make H+ and Cl- that combine in stomach to make HCL

HYDROGEN PRODUCTION
- CO2 and water from blood
- carbonic anhydrase converts them to carbonic acid
- carbonic acids -> H+ and bicarbonate ions
- H+ ions via active transport (HYDROGEN-POTASIUM ATPASE) into lumen of stomach
- K+ from pump diffuse back out of cell via ion channels

CHLORIDE PRODUCTION
- when bicarbonate leaves cell, CL- pumped in
- CL- moved to lumen of stomach

Question 5

alkaline tide

Answer 5

increase in blood pH from high amounts of acid being produced fro stomach
- bicarbonate coming into bloodstream as a product of CL- coming into parietal cells to make HCL in stomach

Question 6

pepsinogen and pepsin function

Answer 6

• inactive enzyme so it doesn’t break down cheif cells that produce it
• activated by HCL -> pepsin
• pepsin digests pr-

Question 7

function of gastric lipase

Answer 7

digests triglycerides
limited role in stomach due to suboptimal pH

Question 8

3 accessory organs important to digestion in duodenum

Answer 8

liver, gallbladder pancreas

Question 9

location of pancreas

Answer 9

• retroperitoneal
• posterior to greater curvature of stomach
• head sits in duodenum
• tapers into the tail
• PANCREATIC DUCT - runs through pancreas
  splits into 2 ducts before entering duodenum
  1. ACESSORY DUCT: enters closer to stomach
  2. PANCREATIC DUCT: joins with common bile duct from liver and gallbladder. Opening has a sphincter to control output.

Question 10

histology of pancreas

Answer 10

glandular epithelial cells, form clusters

99% ACINI CELLS: exocrine cells that secrete pancreatic juice
- lead to pancreatic duct

1% ISLETS OF LANGERHANS: endocrine, secrete hormones
connected to blood supply
inside iselets
- ALPHA CELLS: secretes GLUCAGON - tells liver to breakdown glucose
- BETA CELLS: secrete INSULIN - signals glucose uptake via body tissues

Question 11

Pancreatic juice

Answer 11

• contains water, enzymes and sodium bicarbonate (makes juice alkaline)
  DIGESTIVE ENZYMES
• PANCREATIC AMYLASE (starch)
• PANCREATIC LIPASE (trigylcerides)
• PROTEASES (pr-), become activated inside lumen of GI so they don’t digest pancreas

Question 12

purpose of sodium bicarbonate in pancreatic juice

Answer 12

1. Makes it alkaline
   - acts as buffer for acidic chyme leaving stomach
   - helps create optimal pH for enzyme digestion in small intestine
2. Deactivates pepsin

Question 12

proteases within pancreatic juice

Answer 12

• TRIPSINOGEN: activated by ENTEROKINASE (brush border enzyme) to form TRYPSIN
• Tripsin activates all other enzymes
• chymotrypsinogen becomes chymotrypsin
• procarboxypeptidase becomes carboxypeptidase
• proelastase becomes elastase
• ribonuclease - digests RNA
• deoxyribonuclease - digests DNA

Question 12

name for wall of duodenum

Answer 12

brush border