70. Nutrition and digestion. Different food types and their biological and nutritional value. Some clinical aspects of feeding. Digestion and absorption of carbohydrates, lipids, proteins, vitamins and minerals. Processes in the colon. Microbiome. Secretory activity of the gastrointestinal tract. Disorders of digestion and absorption.

Saliva

Chemical Composition:

• Water: 99% of saliva, serving as a solvent.
• Electrolytes: Sodium, potassium, calcium, bicarbonate, and phosphate.
• Mucins: Glycoproteins that lubricate food and form a protective mucus layer.

Enzymes:

• Amylase (Ptyalin): Begins the breakdown of starch into maltose.
• Lingual Lipase: Initiates the digestion of lipids, particularly in infants.

Other Components: Lysozyme (antibacterial), immunoglobulin A (immune protection), and various growth factors.

Gastric Fluid

Chemical Composition:

• Hydrochloric Acid (HCl): Lowers pH to 1-2, denatures proteins, activates pepsinogen to pepsin, and kills microbes.
• Pepsinogen: An inactive precursor that is converted to pepsin, a protease, in the acidic environment.
• Intrinsic Factor: Glycoprotein essential for the absorption of vitamin B12.
• Mucus: Protects the stomach lining from acidic environment and digestive enzymes.

Enzymes:

• Pepsin: Breaks down proteins into smaller peptides.
• Gastric Lipase: Contributes to the digestion of lipids.

Pancreatic Fluid

Chemical Composition:

Water: Majority of the fluid.

• Electrolytes: Bicarbonate ions neutralize stomach acid in the small intestine.

Enzymes:

• Proteases:
• Trypsinogen: Converted to trypsin in the small intestine, which then activates other proteases.
• Chymotrypsinogen: Converted to chymotrypsin, further breaking down proteins.
• Procarboxypeptidase: Activated to carboxypeptidase, cleaves amino acids from the carboxyl end of proteins.
• Amylase: Continues the breakdown of carbohydrates.
• Lipase: Breaks down triglycerides into free fatty acids and monoglycerides.
• Nucleases: Degrade nucleic acids (DNA and RNA) into nucleotides.