Understanding Digestive Enzymes: Step-by-Step Process

Enzymes in the Digestive System: A Comprehensive Overview

In our body, digestive enzymes play an important role in the absorption of nutrients. These enzymes are responsible for digesting our food and breaking it down into smaller substrates that can be absorbed by the digestive system. Digestive enzymes are proteins composed of amino acid residues, each of which maintains a specificity for specific macronutrients, meaning that specific enzymes digest specific substrates. For example, starch is digested by amylase, proteins by proteases, lipids by lipase, DNA and RNA by DNAs and RNAs. This article provides a comprehensive review of the types, functions, mechanisms, and importance of digestive enzymes, highlighting their important role in maintaining health and well-being.

Definition and General Characteristics:

Digestive enzymes are biological catalysts that speed up the breakdown of food molecules into their constituent nutrients. Various glands and organs throughout the digestive system, including the salivary glands, stomach, pancreas, and small intestine, secrete these enzymes. Each type of digestive enzyme specializes in acting on specific types of nutrients, such as carbohydrates, proteins, and fats.

Step-by-Step Process of Digesting Food by Enzymes

These digestive enzymes are released in the digestive tract, where they break down food into small pieces that can be absorbed. In this section, we provide a step-by-step guide detailing the specific enzymes and their substrates

01. Ingestion and Mechanical Breakdown

• Mouth
  • Process: when chewing the food particles break down into small pieces which can enhance the surface area which leads to facilitate the enzyme action
  • Enzyme: Salivary amylase
  • Substrate: Starch
  • Action: Enzyme salivary amylase breaks down starch into smaller particles, specifically maltose and dextrins

02. Transportation to the Stomach

• Esophagus
  • Process: In this phase, peristalsis occurs—a process where involuntary contractions and relaxations of muscles move the chewed food (bolus) from the mouth to the stomach.

03. Stomach Digestion

• Stomach
  • Enzymes: Pepsin, Gastric lipase
  • Substrates: Proteins, Fats
  • Action:
    • Pepsin: Pepsinogen activates and forms pepsin under acidic conditions, HCl provides the acidic medium. pepsin breaks down proteins into smaller peptides.
    • Gastric lipase: Begins the digestion of fats into free fatty acids and monoglycerides.
  • pH: the pH range from 1.5-3.5 this acidic environment activates the enzymes and helps to denaturation of proteins

04. Small Intestine Digestion

• Duodenum (small intestine’s first section)
  • Pancreas Contribution
    • Enzymes: Pancreatic amylase, Trypsin, Chymotrypsin, Carboxypeptidase, Pancreatic lipase, Nucleases
    • Substrates: Starches, Proteins, Fats, Nucleic acids
    • Action:
      • Pancreatic amylase: Continues breaking down starch into maltose, maltotriose, and dextrins.
      • Trypsin, Chymotrypsin, Carboxypeptidase: Break down proteins and peptides into smaller peptides and amino acids.
      • Pancreatic lipase: Completes the digestion of fats into free fatty acids and monoglycerides.
      • Nucleases: Digest the DNA and RNA (nucleic acids) into small residues (nucleotides).
  • Bile Contribution
    • Bile Salts: Emulsify fats, increasing the surface area for lipase action.
• Jejunum and Ileum (later parts of the small intestine)
  • Brush Border Enzymes: Maltase, Sucrase, Lactase, Peptidases
  • Substrates: Disaccharides, Peptides
  • Action:
    • Maltase: Converts maltose into two glucose molecules.
    • Sucrase: Converts sucrose into glucose and fructose.
    • Lactase: Converts lactose into glucose and galactose.
    • Peptidases: Break down peptides into amino acids.

05. Absorption

• Small Intestine
  • Process: The small intestine’s lining absorbs the resulting simple sugars, amino acids, fatty acids, and glycerol into the bloodstream and lymphatic system.
  • Mechanism: Nutrients are absorbed through the villi and microvilli, which increase the surface area for absorption.

06. Large Intestine

• Colon
  • Process: Absorbs water and electrolytes, forming solid feces.
  • Enzyme Activity: Some fermentation of undigested carbohydrates by gut microbiota, producing short-chain fatty acids and gases.

07. Excretion

• Rectum and Anus
  • Process: Solid waste is expelled from the body through defecation.