Usmle 1 Stomach

• • Orad region- fundus and proximal portion of the body
•   • Thin muscle wall

• • Caudad region - distal portion of the body and the antrum
•   • Thicker muscle wall
•   • Region responsible for mixing the food

• • Mechanoreceptors detect distension of the stomach and relay this information
• to the CNS via sensory neurons

• • CNS then sends efferent information to
• the smooth muscle wall of the orad
• stomach, causing it to relax

• • Neurotransmitter released from the
• postganglionic vagal nerve fibers is VIP

• • Vagotomy eliminates receptive
• relaxation

• Hydrochloric acid (HCL): function is to reduce pH for the conversion of pepsinogen to pepsin

• Pepsinogen (inactive): Low pH converts it to the active form- pepsin for protein digestion

• Intrinsic factor: for the absorption of Vit. B12 in the ileum (essential)

• Mucus: protects the gastric mucosa from HCL

• • produce H+
• • Intrinsic Factor (for B12)

• take up water and CO2 from plasma

• produce H2CO3 with carbonic anhydrase

• Break down to H+ and HCO3

• HCO3 will leave the cell, and float around stomach lining to protect it (Alkaline tide: efflux of HCO3−)

• Cl- will enter instead of the HCO3

• H+ will pump out into stomach via H/K ATPase (works like Na/K pump)

• Will make electrochemical gradient that will push Cl into the stomach

• Make HCl in the stomach

• Will continue to produce HCl until pH is 1-2

• #1 protection from acid erosion of GI lining is Mucus → most abundant Goblet cells

• • #2 protection is Prostaglandins: (+) mucous production
•    • That’s why ASA which blocks PG,PGE2 will cause ulcers.
•    • ASA=acetylsalicylic acid (aspirin)
•    • irreversible block Cox 1 & 2
•    • NSAIDs - reversible inhibit COX
•      • (Nonsteroidal anti-inflammatory drugs)
• • #3 protection is HCO3: alkaline tide

• • COX 1 – GI
• • COX 2- Joints

• • release Pepsinogen
• • activate Pepsin

• • Main enzyme that digests protein (protein digestion begins in stomach)
•   • sugars and fat stop digestion in the stomach

• all digestion ends in the small bowel

• • Fat digestion is in the Small intestine
•   • Dumping syndrome → eat small frequent meals high in fat!!!

• Empty their secretory products via ducts

• Opening of the glands are called pits

• Lined with epithelial cells

• its the lowermost part of the stomach

• • Contain 2 cell type:
•   • Mucous cells- mucus and HCO3 are protective. pepsinogen
•   • G-cells (secrete gastrin into circulation)

• relaxation of the lower esophagus sphincters and the orad region to accept food into the stomach. 

• • Auerbach plexus uses VIP to relax LES
•   • Vasoactive intestinal polypeptide

• begins in the middle 1/2 of the BODY of the stomach

•­ ↑ pH is the signal to the G-Cells to produce Gastrin to make more acid

• is in the Small intestine

• Dumping syndrome → eat small frequent meals high in fat!!!

• • periodic gastric contractions occur, MMC
•    • “ migrating myoelectric complexes”

• Mediated my Motilin

• Occur ever 90 minutes

• Function to clear the stomach of any residue remaining from a previous meal

• Takes approximately 3 hours to empty

• • Rate must be regulated to provide adequate time to
•   • neutralize the gastric H+ in the duodenum
•   • adequate time for absorption of nutrients

• • Two factors slow or inhibit gastric emptying:
•   • Fat and H+ in the duodenum
•     • Fat mediated by CCK (secreted by duodenum)
•     • H+ mediated by reflexes of the enteric nerves (myenteric
• plexus) ensures content is delivered to the duodenum
• slowly

• • Misoprostol
•    • replace PGE
•    • Vasoconstricts
• • Alprostadil
•     • Vasodilation 

• • Cox 2 inhibitors
•   • Celecoxib only one left
•   • problem if on > 18 mo)
•   • block prostacyclin
•   • inhibit platelet agg

• • due to lack of blood supply
• • sympathetic output causes vasoconstriction

• • CUSHING’S ULCER
• • CURLING’S ULCER
• • STRESS ULCER