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Vagus and the Stomach:

L vagus n: (anterior) gives hepatic branch,

R vagus n: (posterior) gives celiac branch and the 'criminal nerve of Girassi which if undivided can keep elevated acid levels, leading to post vagotomy ulcers


Chief cells: èpepsinogen èpepsin èinitiates proteolysis


Parietal cells: è H+ and IF which binds B12 and is absorbed in T. Ileum.

  • Ach, Gastrin, Histamine are main stimuli for éH+ production
  • ACh (vagus) and gastrin activate PIP, DAG to é Ca, activate protein kinase C which é HCl production
  • Histamine acts on parietal cells via cAMP (H for Happy cAMPers) to é HCl production.
  • PPI’s blocks H/K ATPase of parietal cell

G Cells: from Antrum (hence antrectomy) secrete: GASTRIN.

  • Gastrin is inhibited by H+ in duodenum, Somatostatin, Secretin, VIP & Gastric Inhibitor Peptide
  • Gastrin is stimulated by AA, Ach, ETOH, Distention.
  • Gastrin mainly stimulates Chief and Parietal cells.

D cells: SOMATOSTATIN

  • Stimulated by: Acid in duodenum
  • (Inhibits) Gastrin, Insulin, Glucagon, Secretin, GIP, Motilin, Neurotensin, Enteroglucagon, Pancreatic-Biliary output

K cells: GASTRIC IHIBITORY PEPTIDE

  • Stimulated by: pH, Glucose, Long Fatty acids
  • Decreases: HCL & Pepsin production and increases Insulin secretion.

I cells: (intestinal mucosa) CCK (major action over pancreatic acinar cells)

  • Stimulated by: AA, Fatty acids
  • Contract gallbladder
  • Relax Sphincter of Oddi
  • Pancreatic enzyme secretion
  • Intestinal Motility

S cells: SECRETIN (major action over the pancreatic ductal cells)

  • Stimulated by: Fat, Bile, pH<4
  • Inhibited by: pH>4
  • Bile flow
  • Inhibit G cells to decrease Gastrin =HCL
  • Pancreatic HCO3
  • Primary stimulus of pancreatic bicarb secretion.
    • High flow rate = high bicarb, Low Cl
    • Slow flow allows HCO3/Cl exchange so low HCO3, high Cl concentration

Gut/pancreatic cells: VIP

  • Stimulated by: Fat, Ach
  • Intestinal secretions
  • é Intestinal motility
  • Inhibit G cells-Gastrin = êHCL

All Vagotomies:

  • Abolishes receptive relaxation
  • Which: é liquid emptying (No change for solids)

Type

Division site

Liquid Emptying

Solid Emptying

Truncal vagotomy

Vagal trunks at the level of esophagus

é

ê

éw/pyloroplasty

Selective vagotomy

Nerves of Latarjet

é

ê

éw/pyloroplasty

Highly selective (proximal) vagotomy

Individual fivers

é

Normal

éw/pyloroplasty

Proximal Vagotomy (%)

Truncal Vagotomy + Pyloroplasty (%)

Truncal Vagotomy + Antrectomy (%)

Mortality

0

0.5-1

1-2

Acid reduction Basal'

80

70

85

Acid reduction Stimulated

50

50

85

Ulcer Recurrence

10

12

1-2

Gastric emptying Liquids

Accelerated

Accelerated

Accelerated

Gastric emptying Solids

No change

Accelerated

Slower

Dumping (Mild)

<5

10

10-15

Dumping (Disabling)

0

1

1-2

Diarrhea (Mild)

<5

25

20

Diarrhea (Disabling)

0

2

1-2

Post-vagotomy complications:

  • Most common symptom: Diarrhea (35%) secondary to non-conjugated bile salts in the colon.
  • Dumping syndrome in 10%
  • Can occur after gastrectomy or after vagotomy + pyloroplasty
  • Occurs for rapid entering of carbohydrates into the small bowel
  • 2 phases:
    • Hyperosmotic load causes fluid shift in to the bowel
    • Reactive éin insulin êin glucose
  • Very rarely (1%) dumping syndrome is unresponsive to dietary changes.

Enterokinase: activates trypsinogen to trypsin which then activates other enzymes of digestion.


Enterglucagon: increased in small bowel mucosal hypertrophy, adaptation after small bowel resection.


Peptide YY: released from terminal ileum with mixed meal, inhibits acid secretion "ileal brake"


Bile: 80% bile salts, 15% lecithin, 5% cholesterol.

  • Stones form if increase chol or decrease salts or lecithin.
  • Gallbladder concentrates bile by active resorption of NaCl, H2O then follows.
  • Bile pool 5g, recirculate q4h, lose 0.5g daily (10%)
  • Primary bile acids: (from cholesterol in liver Taurin/Glycin conjugation)
    • Cholic acid
    • Chenodeoxycholic acid
  • Secondary bile acids: (formed by intestinal bacteria):
    • Deoxycholic acid
    • Lithocholic acid
  • Tertiary bile acid: Urodeoxycolic

MMC:

  • Interdigestive motility; 90 minute cycles, starts in stomach, goes to TI.
  • Phases:
    • Phase I quiescence
    • Phase II gallbladder contraction
    • Phase III peristalsis
    • Phase IV subsiding electric activity
  • Motilin is key stimulatory hormone (erythromycin is prokinetic by stimulating motilin receptor)

Jejunum absorbs: most Na and H2O (paracellular), more permeable than ileum.


Fat and cholesterol èbroken down to fatty acids & monacylglycerides èMicelles èIntestinal cells èchylomicrons è(long chain fatty acids) to lymphatics. Short and medium chain fatty acids are released to portal vein

Pages in category "GI Physiology"