Digestion and Stomach Function

Digestion in the Stomach

Introduction

• The stomach is where protein digestion begins.

• Carbohydrates and lipids start chemical digestion in the mouth due to enzymes in saliva (amylase for carbohydrates, lipase for fats).

• Protein digestion doesn't occur until food reaches the stomach.

Importance of Protein

• Increasing protein intake enhances satiety and prolongs the feeling of fullness.

• This helps reduce the likelihood of consuming sugary snacks.

• Protein takes longer to digest, contributing to longer-lasting satiety.

Enzymes in the Stomach

• Proenzymes, such as pepsinogen, are present in the stomach.

• Pepsin, derived from pepsinogen, is crucial for protein breakdown.

Absorption in the Stomach

• Absorption starts in the stomach, but the small intestine is the primary site for nutrient absorption.

• Vitamin B12 is an exception, beginning absorption in the stomach with the help of intrinsic factor.

Stomach Functions

• The stomach stores and churns food, facilitating mechanical digestion.

• Bolus (food in the oral cavity) becomes chyme in the stomach after mixing with hydrochloric acid.

• The name of the food changes as it moves through the digestive tract.

Stomach Lining

• The stomach is lined with simple columnar epithelium, which is effective at withstanding acid.

• The stomach's pH can be as low as 2.

Gastric Pits and Cells

• The stomach lining contains gastric pits with specific cells:

  • Chief cells: Produce pepsinogen and gastric lipase (enzymes).

    • Gastric lipase continues fat digestion.

    • Pepsinogen is converted to pepsin, which digests protein.

  • Parietal cells: Produce hydrochloric acid and intrinsic factor.

    • Hydrochloric acid converts pepsinogen to pepsin.

    • Intrinsic factor is a protein that binds to vitamin B12, facilitating its absorption in the stomach.

Intrinsic Factor and Vitamin B12

• Intrinsic factor is not an enzyme; it's a delivery protein for vitamin B12.

• Pernicious anemia results from a deficiency in intrinsic factor, leading to inadequate vitamin B12 absorption.

• Vitamin B12 deficiency can cause significant fatigue.

Medications and Stomach Function

• Proton pump inhibitors (e.g., omeprazole) reduce hydrochloric acid production.

• Long-term use of proton pump inhibitors can impair parietal cell function, affecting vitamin B12 absorption and leading to fatigue.