Digestion and Absorption Basics

Digestion and Absorption

• Digestion converts food into absorbable forms through the breakdown of larger particles.
• Hydrolases are enzymes that catalyze the hydrolysis of nutrients, facilitating the conversion of proteins to amino acids, and nucleic acids to nucleotides.
• Minerals and vitamins are released during the digestion process.

Digestive Enzymes (Hydrolases)

• Amylolytic (Carbohydrate-splitting) Enzymes:

  • Salivary amylase (ptyalin) from salivary glands begins starch digestion in the oral cavity.
  • Pancreatic amylase continues starch digestion in the small intestine.
  • Invertases (disaccharidases) from small intestinal goblet cells further digest carbohydrates.

• Proteases (Protein-splitting) Enzymes:

  • Pepsinogen from gastric glands activates to pepsin in the stomach and breaks down proteins into peptides.
  • Trypsinogen and chymotrypsinogen from pancreas are activated to trypsin and chymotrypsin, respectively, in the small intestine.
  • Peptidases from goblet cells convert peptides into amino acids.

• Lipases (Fat-splitting) Enzymes:

  • Gastric lipase from the stomach acts on emulsified fats, producing fatty acids and glycerol.
  • Pancreatic lipase continues fat digestion in the small intestine.

• Nucleases (Nucleic acid-splitting) Enzymes:

  • Ribonuclease and deoxyribonuclease from the pancreas digest nucleic acids into nucleotides in the small intestine.

Digestion Process

• Carbohydrates:

  • Ptyalin converts starch to maltose in the oral cavity.
  • Pancreatic amylase converts remaining starch to maltose in the small intestine.
  • Maltase, lactase, and sucrase convert maltose, lactose, and sucrose into their respective simple sugars.

• Proteins:

  • Pepsin acts on proteins in the stomach, converting them to peptides.
  • Trypsin and chymotrypsin further break down proteins in the small intestine into peptides.
  • Peptidases convert peptides into amino acids.

• Lipids:

  • Gastric lipase acts on emulsified fats in the stomach to produce fatty acids and glycerol.
  • Bile emulsifies fats in the small intestine before further digestion by lipase.

• Nucleic Acids:

  • Nucleases digest nucleic acids into nucleotides in the small intestine.

Absorption

• Transport Mechanisms Across Membranes:

  • Diffusion: Movement of molecules from high to low concentration.
  • Osmosis: Diffusion of water across a semipermeable membrane.
  • Dialysis: Separation of molecules through a membrane.
  • Carrier-mediated Transport:
    • Facilitated diffusion allows passive transport with assistance from carriers.
    • Active transport requires energy to move substances against a concentration gradient.
  • Bulk Transport:
    • Phagocytosis (cell eating), pinocytosis (cell drinking), and emeiocytosis (cellular uptake processes).

• Intestinal Absorption: Specifics of absorption mechanisms occur in the intestine, facilitating nutrient uptake into the bloodstream.

Test your knowledge on the basics of digestion and absorption processes in the human body, including the role of hydrolases and the transformation of food into absorbable forms.