Management of the Bariatric Surgery Patient

Publication Date: March 1, 2023

Gastrointestinal Hormones

Gastrointestinal Hormones

TOP 10 TAKEAWAY MESSAGES: Gastrointestinal (GI) Hormones

  1. Gastrointestinal hormones regulate caloric balance, hunger/satiety, food digestion, and nutrient utilization via central nervous system signaling, effects on GI motility, and GI enzyme release.
  2. Common GI hormone action in response to eating include decrease in hunger and facilitative digestion (delayed gastric emptying, digestive enzyme release, and post-absorptive nutrient metabolism).
  3. The jejunum is the second longest segment of the small intestine, and absorbs the greatest amount of simple sugars, fatty acids, proteins, minerals and vitamins.
  4. The ileum is the longest segment of the small intestine, and absorbs bile salts, bile acids, vitamin B12, some vitamins and some minerals.
  5. After food intake, most GI hormones decrease hunger/increase satiety.
  6. Among the few GI hormones that increase hunger between meals are ghrelin (“hunger hormone”) and neuropeptide Y (NPY); positive caloric balance may not always be hunger-related.
  7. Illustrative GI hormones produced by the stomach include ghrelin and gastrin.
  8. Illustrative hormones produced by the pancreas include insulin, glucagon, pancreatic polypeptide (PP), amylin, and somatostatin.
  9. Illustrative GI hormones produced by the small intestine include cholecystokinin (CCK), secretin, motilin, and glucose-dependent insulinotropic peptide (GIP — also known as gastric inhibitory peptide).
  10. Illustrative GI hormones produced by the ileum and/or large intestine include fibroblast growth factor (FGF) 19, glucagon-like peptide-1, glucagon-like peptide-2, oxyntomodulin, and peptide YY (PYY).

Nutrient Absorption

GI Hormone Regulation of Caloric Balance, Food Digestion, and Nutrient Utilization

a The biologically active PYY and PP are expressed by endocrine cells in the digestive system. Animal studies suggest NPY endocrine cells are found throughout the small and large intestine, with NPY thus being involved in both gut-brain and brain-gut axis (bidirectional signaling). NPY is mainly described as a highly abundant orexigenic peptide found throughout the brain.

Illustrative Gastrointestinal Hormones and Function

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Where Secreted Gastrointestinal Hormone Effect of Hormone on Eating Behavior Effect of Eating on Hormone Secretion Notes Effect of Gastric By-pass and Sleeve Gastrectomy
Stomach Ghrelin (secreted by P/D1 cells) Hunger With fasting
Gastric emptying/growth hormone (GH)
Ghrelin likely to decrease with sleeve gastrectomy (not so with gastric bypass)
Stomach Gastrin (secreted by G cells in antrum) Hunger Hydrochloride (HCI) acid and pepsinogen Gastric bypass
–/↑ Sleeve
Pancreas Insulin (secreted by pancreatic beta cells) Hunger Hunger with hypoglycemia
Glucose transporter 4 in adipose tissue/muscle, glycogenesis, lipoprotein lipase activity, lipogenesis
Insulin resistance / fasting insulin
Insulin sensitivity / insulin responsiveness
Pancreas Glucagon (secreted by pancreatic alpha cells) Hunger Glycogen to glucose
Postprandial glucagon in patients with type 2 diabetes mellitus (glucagon not suppressed)
Pancreas PP [secreted by PP (F) cells] Hunger Pancreatic exocrine secretion Variable
Pancreas Amylin
(secreted by pancreatic beta cells)
Hunger Gastric emptying, glucagon –/↓
Pancreas Somatostatin (secreted by D cells pylori antrum, duodenum, and pancreatic islets) Hunger Growth hormone, gastrin, HCI, secretin, CCK, insulin, glucagon –/↑
Small Intestine (Mainly Duodenum and Jejunum) CCK (secreted by I-cells) Hunger Gall bladder contractility and bile, pancreatic enzymes
Gastric emptying
Small Intestine (Mainly Duodenum and Jejunum) Secretin (secreted by S cells) Pancreatic bicarbonate and bile
Intestinal motility and gastric acid
Small Intestine (Mainly Duodenum and Jejunum) GIP; Also known as Gastric Inhibitory Peptide – secreted by K cells Insulin
Glucagon postprandial
Small Intestine (Mainly Duodenum and Jejunum) Motilin (secreted by M or Mo cells) Hunger
( with
Gastric motility, interdigestive migratory contractions (borborygmi) ?
Ileum and/or Large Intestine FGF 19 [FGF 21 is produced by the liver](secreted by ileal cells and regulated by farnesoid X receptors [FXR]) Hunger Bile acids, glucose production
Insulin sensitivity, glycogen synthesis
Ileum and/or Large Intestine Glucagon like peptide-1 (secreted by ileum/colon L-cells) Hunger Insulin
Glucagon, gastric emptying
Ileum and/or Large Intestine Glucagon like peptide-2 (secreted by ileum/colon L-cells) Hunger
Glucose metabolism, intestinal mucosal growth, increases absorptive surface, epithelial brush-border nutrient transporters and digestive enzymes, intestinal blood flow, postprandial chylomicron secretion
Gastrointestinal motility
Ileum and/or Large Intestine Oxyntomodulin (secreted by ileum/colon L-cells) Hunger Glucagon-like peptide-1 (GLP-1) and glucagon receptor activity
Gastric acid and gastric emptying
Gastric bypass − Sleeve gastrectomy
Ileum and/or Large Intestine Peptide YY (secreted by ileum/colon L-cells) Hunger Gall bladder and pancreatic secretions, gastric emptying

Bariatric Surgery

...riatric Surgery...

...TAKEAWAY MESSAGES: Bariatric Surgery...

...ic Surgery Poor Candidates...

...ential Bariatric Surgery...

...ic Surgical ProceduresHaving trouble v...

...ic Surgical Procedures...

Endoscopic Sleeve Gastroplasty... Endoscopic suturing of the stomach cre...

...ndoscopic Sleeve Gastroplasty (ESG) - Illus...

...echanisms of Weight Loss with ESG...

...iction of gastric expansion induce...

...perative and Post-Operati...

...ions Some medications that increase periope...

...Diet Progression Clear liquid die...


...First 30 Days) General post-operative...

...Days) Gastro-gastric fistula (RNY)...

...te Intestinal (small bowel) obst...

...erations After Surgery Hair loss: Any weight lo...

Nutrient Considerations

...nt Considerations...

...AY MESSAGES: Bariatric Surgery Nutrient Consi...

...P 10 TAKEAWAY MESSAGES: Microbiome...

...Micronutrient Deficiencies...

...utrient Deficiency Replacement After Ba...

...utrient Deficiency Replacement After Bariatric...