178. The Stomach & Gastric Acid | Vitamin B12 Absorption and a Brief Conversation on H. pylori

In this episode, we highlight the stomach's role in vitamin B12 absorption and bioavailability, detailing the cellular composition of the gastric mucosa and further highlighting mucous cells, parietal cells, and chief cells. We also briefly discuss Helicobacter pylori and common symptoms, while detailing H. pylori's survival mechanisms in the acidic gastric environment as well as potential impacts on the gastric mucosal barrier.

Topics:

1. Introduction

- Overview of the stomach's role in B12 absorption

- Helicobacter pylori

2. H. pylori Overview

- Gram-negative bacterium, can colonize the stomach lining

- Many individuals remain asymptomatic

- Symptoms

- Can contribute to gastritis and peptic ulcers

- Produces urease, hydrolyzes urea into ammonia (NH₃) andcarbon dioxide (CO₂)

- Ammonia neutralizes stomach acid locally, protective microenvironment

- H. pylori damages the mucosal barrier and contributes to persistence

- Possesses additional virulence factors

3. Gastric Anatomy 

-  Stomach is divided into the cardia, fundus, body, and pylorus

- The gastric mucosa

- The epithelial lining; mucous cells, parietal cells, chief cells, and more

4. Mucous Cells and Mucosal Protection 

- Line the gastric pits and secrete thick, viscous mucus

- Mucus composed of water, mucin glycoproteins, and other low-molecular-weight molecules

- Traps bicarbonate ions (HCO₃⁻)

- Shields the stomach lining

5. Parietal Cells 

- Located in the gastric glands, predominantly in the fundus and body

- Secrete hydrochloric acid (HCl)

- Secrete intrinsic factor (IF)

6. Vitamin B12 Overview 

- Cobalamin: DNA synthesis, red blood cell formation, neurological function, methylation, and more

- Methylcobalamin and 5-deoxyadenosylcobalamin

- Non-active forms include hydroxocobalamin and synthetic cyanocobalamin

  7. Vitamin B12 Absorption Pathway 

- B12 is released from proteins by HCl and pepsin

- Binds first to haptocorrin

- In the small intestine, pancreatic enzymes degrade haptocorrin

- B12 binds intrinsic factor

- Absorption in the ileum

- Impairment

8. Chief Cells 

- Located in the gastric glands

- Secrete pepsinogen, activated by acid into pepsin

- Also secrete gastric lipase

9. Hydrochloric Acid (HCl) 

- Secreted by parietal cells

- Denatures dietary proteins and activates pepsinogen

- Acts as a defense mechanism by aiding in sterilizing ingested food

10. Relevance of H. pylori

- Produces urease that breaks down urea into NH₃ and CO₂

- Ammonia neutralizes acid locally, forming a protective “bubble”

- Enhances mucosal damage and microbial persistence

11. B12 Absorption 

- Multiple factors and root causes can impair absorption

- H. pylori

12. Hypochlorhydria 

- Symptoms

- Absorption: vitamin B12, iron, calcium, magnesium, more

- Small Intestinal Bacterial Overgrowth (SIBO)

13. Conclusion

- Multi-factorial, root cause approach

Thanks for tuning in!

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