Digestion and Human Health Notes

Digestion and Human Health

Overview of the Digestive System

• Also known as the gastrointestinal (GI) tract.
• Main functions:
  • Ingestion of foods.
  • Physical & chemical breakdown.
  • Absorption of nutrients.
  • Release of solid wastes.

Types of Digestion

• Mechanical Digestion:
  • Grinding/mashing of food to increase surface area for chemical digestion.
• Chemical Digestion:
  • Breakdown of macromolecules by enzymes into building blocks for absorption.

Macromolecules

• Four main types: carbohydrates, lipids, proteins, and nucleic acids.
• Polymer: long molecule made of similar building blocks called monomers.
• Assembling Macromolecules:
  • Dehydration synthesis: removal of water molecule to form a bond between monomers.
• Disassembling Macromolecules:
  • Hydrolysis: addition of water to break the bond between monomers (requires an enzyme).

Carbohydrates

• Functions: energy source, blood glucose control, cholesterol and triglyceride metabolism.
• Building block: monosaccharide.
• Polysaccharide: complex carbohydrate made of many simple sugars.

Lipids (aka Fats)

• Functions: components of cell membranes, sex hormones.
• Made of a glycerol molecule and 3 fatty acid chains.

Proteins

• Functions: enzymes, structural support, carrier molecules, hormones.
• Monomer: amino acid (20 different types).
• Amino acids bonded through peptide bonds form a peptide or polypeptide.

Nucleic Acids

• Functions: genetic material, directs cell growth, carries energy.
• Examples: DNA, RNA, ATP.

Vitamins and Minerals

• Essential for cellular functions and structures.
• Vitamins: organic molecules, function as coenzymes.
• Minerals: inorganic molecules, enable cellular reactions.

Enzymes

• Proteins that increase the rate of chemical reactions (catalysts).
• Bind to a specific substrate (“lock and key model”).
• Function under optimum conditions (temperature, pH, concentration).

Factors Affecting Enzyme Activity

1. Temperature:
   • High temperatures can denature enzymes.
   • Optimum temperature around $37^{\circ}C$ for humans.
2. pH:
   • Changes in acidity can alter enzyme shape.
   • Enzymes have different optimum pH ranges.
3. Concentration of Substrate:
   • More substrate typically increases reaction rate up to a maximum.
4. Concentration of Enzyme:
   • Increased enzyme concentration increases reaction rate if enough substrate is present.
5. Presence of Inhibitors:
   • Competitive inhibitors: compete with substrate for active site.
   • Non-competitive inhibitors: bind to a different location, altering the active site.

The Digestive System

Goals

1. Ingest food.
2. Mechanical breakdown.
3. Chemical breakdown.
4. Absorption of nutrients.
5. Elimination of waste.

Processes

• Physical Digestion: physical breakdown to increase surface area.
• Chemical Digestion: breakdown of macromolecules by enzymes.
• Absorption: movement of small molecules into the circulatory system.

Path Through the Digestive System

1. Mouth
2. Esophagus
3. Stomach
4. Pancreas
5. Liver
6. Gall bladder
7. Small intestine
8. Large intestine
9. Rectum

Organs

• Mouth: teeth and tongue perform mechanical digestion; saliva contains amylase to break down starch.
• Esophagus: peristalsis (muscle contractions) moves food to the stomach.
• Stomach: mechanical digestion (churning); chemical digestion (gastric juice).
  • Gastric juice: hydrochloric acid (activates pepsin, denatures proteins, kills microbes) and pepsin (breaks down proteins).
• Small Intestine: final site of mechanical and chemical digestion; main site of nutrient absorption.
  • Villi and microvilli increase surface area for absorption.
  • Duodenum, jejunum, ileum.
• Large Intestine: concentrates and eliminates waste; absorbs water, salts, and vitamins.
• Rectum: stores feces.

Accessory Organs

• Pancreas: secretes pancreatic fluid (enzymes) into the duodenum; secretes insulin and glucagon.
  • Trypsin and chymotrypsin: hydrolyze proteins.
  • Amylase: breaks down starch.
  • Lipase: digests lipids.
  • Nucleases: digests nucleic acids.
  • Bicarbonate: neutralizes stomach acid.
• Liver: detoxification; produces bile (emulsifies fats).
• Gallbladder: stores and releases bile into the small intestine.

Feedback Inhibition

• End product of a reaction binds to the enzyme, stopping the reaction.

Digestive Disorders

• Ulcers: erosion of stomach lining due to damage of the mucus, often caused by Helicobacter pylori.
• Cirrhosis: scar tissue on the liver, often caused by alcohol or Hepatitis C.
• Hepatitis: inflammation of the liver.
• Gallstones: hard masses in the gallbladder.
• Inflammatory Bowel Disease (Crohn’s Disease): inflammation in the digestive tract.
• Colitis: inflammation and ulcers in the colon.
• Irritable Bowel Syndrome (IBS): abdominal pain, cramps, constipation or diarrhea.
• Celiac Disease: reaction to gluten, damaging the villi of the small intestine.
• Lactose Intolerance: lack of lactase enzyme.

Nutrient Absorption

• Carbohydrates: salivary amylase (mouth), pancreatic amylase (small intestine).
  • Monosaccharides absorbed into the bloodstream; liver converts other monosaccharides into glucose.
• Proteins: pepsin (stomach), trypsin and chymotrypsin (small intestine).
  • Amino acids absorbed into the bloodstream; liver processes amino acids.
• Lipids: bile (emulsification), lipases (hydrolysis).
  • Glycerol and fatty acids absorbed into villi cells, reassembled into triglycerides, and transported via lymph vessels.
• Nucleic Acids: nucleases (hydrolyze nucleic acids), nucleosidases (hydrolyze nucleotides).
  • Nitrogenous bases, sugars, and phosphates absorbed into the bloodstream.

Macromolecule Digestion Summary

The summary of digestion and absorption across the whole entire digestive system.

Important points to know!

• Macromolecules and their enzymes.
• Enzyme action and factors influencing their action.
• Structures and functions of the digestive system.
• Accessory organs.
• Associated disorders.