Human Physiology · MU Plovdiv

62. Digestion and absorption of Proteins, Fats and Carbohydrates in the Gastrointestinal Tract. Absorption of Salts, Water and Vitamins.

Inside: 14 sections · 11 labelled pictures · 49 flashcards · 12 min

Topic 62 of 80 in the MU Plovdiv syllabus for Human Physiology (Medicine, Year 2). The free AceMed note covers it in 13 sections, about 1,675 words (12 min of reading), with 49 flashcards.

In this note

  1. Digestion in the gastrointestinal system: general characteristics. Digestion of carbohydrates, proteins, nucleic acids and lipids.
  2. General Characteristics.
  3. Digestion of Carbohydrates.
  4. Digestion of Proteins.
  5. Digestion of Nucleic Acids
  6. Digestion of Lipids.
  7. Recap Questions
  8. Absorption in the gastrointestinal system: general characteristic. Absorption of the carbohydrates, proteins and lipids. General Characteristics
  9. Absorption of electrolytes, water, vitamins and bile acids in the gastrointestinal tract.
  10. Electrolyte Absorption.
  11. Water Absorption
  12. Vitamin Absorption.
  13. Bile Acid Absorption.

General Characteristics.

The goal of the gastrointestinal (GI) system is the digestion and absorption of nutrients. Digestion, the process of breaking down food into absorbable molecules, is achieved through the action of enzymes present in:

  • Saliva
  • Gastric juice
  • Pancreatic juice
  • The apical membrane of the intestinal epithelium

Digestion of Carbohydrates.

  • Goal: Breakdown of carbohydrates into monosaccharides (glucose, fructose, and galactose), which are the absorbable forms.
  • Process:
  1. Amylases break down polysaccharides into disaccharides.
  • Salivary amylase begins this process in the mouth.
  • Pancreatic amylase continues the breakdown of starch in the small intestine, yielding disaccharides like maltose and maltotriose, as well as α-limit dextrins.
  1. Disaccharidases further break down disaccharides into monosaccharides.
  • Enzymes like maltase, sucrase, and lactase, located on the intestinal brush border, complete the digestion of disaccharides into their respective monosaccharide components.
  • Absorption: Monosaccharides are absorbed into the capillaries through the villi.

Digestion of Proteins.

  • Goal: Breakdown of proteins into amino acids, dipeptides, and tripeptides, the absorbable forms.
  • Process:
  1. Pepsin initiates protein digestion in the stomach, breaking proteins into polypeptides.
  2. Pancreatic and brush-border proteases continue protein digestion in the small intestine.
  • Endopeptidases (e.g., trypsin, chymotrypsin, elastase) cleave peptide bonds within the polypeptide chain.
  • Exopeptidases (e.g., carboxypeptidase A and B) cleave peptide bonds from the ends of the polypeptide chain.
  1. Key enzymes like pepsin, trypsin, and chymotrypsin are primarily secreted in inactive forms and are activated in the duodenum.
  • Absorption: Occurs in the small intestine through various mechanisms, including:
  • Na+-driven transport
  • H+-driven transport
  • Pinocytosis

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