Digestive System Notes

Oesophagus

  • Also known as the esophagus.

Digestive System

  • The organ system responsible for taking in food and making it available for the body.

Enzymes

  • All enzymes are proteins.
  • Biological catalysts that speed up reactions.
  • Work best at an optimum temperature.
  • pH sensitive (e.g., stomach - acidic, intestine - alkali).
  • Specific to their substrate.
  • Can be reused if not used up in a reaction.
  • Denature at high temperatures.

Lock and Key Model:

  • Enzymes have an active site where the substrate binds.
  • Example: Amylase breaks down starch.

Enzyme-Substrate Complex:

  • Enzyme + substrate → enzyme-substrate complex → enzyme + product

Example:

  • Amylase (enzyme) + starch (substrate) → maltose (product)

Large Intestine

  • Reabsorption of water.
  • Peristalsis movement to move undigested food to the rectum.

Rectum:

  • Temporary storage area for excess and undigested food.

Anus:

  • Removal of fecal product.
  • Sphincter muscle helps control fecal product removal.

Small Intestine

  • Produces enzymes to breakdown nutrients (e.g., maltase breaks down maltose into glucose).

Adaptations for Absorption:

  • One cell thick for efficient diffusion.
  • Villi and microvilli increase surface area.
  • Blood capillaries for effective absorption.
  • Lacteal for absorption of fatty acids/glycerol/fat molecules.

Duodenum

  • Beginning part of the small intestine where most digestion occurs.

Liver:

  • Secretes bile to breakdown fats.

Pancreas:

  • Secretes pancreatic enzymes to breakdown nutrients into smaller forms.

Simplest Forms of Nutrients:

  • Carbohydrates → glucose
  • Proteins → amino acids
  • Fats → glycerol + fatty acids

Pancreas (Pancreatic Juice)

  • Produces amylase (breaks down carbohydrates), lipase (breaks down fats), and protease/trypsin (breaks down proteins).

Enzyme Actions:

  • Pancreatic amylase: starch → maltose
  • Trypsin: polypeptide/peptide → amino acids
  • Lipase: fat droplets → fatty acids + glycerol

Stomach

  • Muscular wall (smooth muscle) for churning.
  • Goblet cells produce mucus for protection.
  • Hydrochloric acid (HCl) kills bacteria and provides an acidic medium (pH 2) for enzymes.
  • Enzymes (chemical digestion), specifically protease.

Enzymes in the Stomach:

  • Pepsin: protein → polypeptide/peptide
  • Rennin: liquid milk → coagulated milk (solid)

Churning Process:

  • Stomach wall contracts and relaxes to mix food with gastric juices, turning it into chyme.
  • Food remains in the stomach for 2-4 hours.
  • Chyme then enters the duodenum.
  • Oesophagus: Sphincter muscle that connects stomach to oesophagus.

Duodenum (continued)

  • Most digestion occurs here due to the release of bile and pancreatic juice.

Bile:

  • Produced by the liver and stored in the gall bladder.
  • Greenish, bitter-tasting substance.
  • Alkali to neutralize the acid of chyme.
  • Emulsifies fats (breaks down fat droplets).
  • Made from broken down red blood cells.

Pancreatic Juice:

  • Contains lipase (fat → fatty acids + glycerol) and protease (protein → amino acids).

Trachea and Oesophagus

  • Two tubes leading down to the throat.
  • Trachea for breathing.
  • Oesophagus for digestion.

Epiglottis:

  • Opens and closes to control food entry.

Peristalsis:

  • Wave-like muscle contractions to move the bolus down the oesophagus.
  • Smooth muscle contracts and relaxes to push food down.

Mouth

  • Physical (mechanical) digestion: teeth crush food.
  • Shape food into a ball (bolus).

Tongue:

  • Forms the bolus.

Saliva:

  • Mucin lubricates food.
  • Enzyme amylase begins to breakdown starch into maltose.

Digestion

  • Process of breaking down food molecules into simpler forms for absorption.

Types of Digestion:

  • Physical/mechanical digestion (e.g., chewing, churning).
  • Chemical digestion (using enzymes).

Chemical Digestion:

  • Breaking down food molecules into the simplest form for absorption using enzymes.
  • Example: Enzymes from saliva mix with starch to break it down into simpler sugars.

Teeth

Types and Functions:

  • Incisors: cut and bite.
  • Canine: hook/pierce/tear.
  • Premolars: crush and grind (1-2 roots).
  • Molars: crush and grind (3-4 roots).

Stages of Digestion

  • Ingestion: Taking in food.
  • Digestion: Breaking down food.
  • Absorption: Absorbing nutrients into the blood.
  • Assimilation: Nutrients delivered to other parts of the body.
  • Egestion: Removal of fecal/faecal & undigested food.

Digestive Tract

  • Includes the mouth, oesophagus, stomach, small intestine, large intestine, salivary glands, liver, gall bladder, and pancreas.

Water

  • Helps remove waste products.
  • 80% of our body.
  • Acts as a solvent.
  • Dissolves enzymes in the alimentary canal.
  • Dissolves chemical for metabolic reactions.
  • Maintains body temperature.
  • Dissolves urea (urine/sweat).

Fiber

  • Mostly cellulose.
  • Cannot be digested by humans (no enzyme).
  • Obtained from vegetables and fruits.

Functions:

  • Helps in removal of undigested food.
  • Deficiency: constipation
  • Excess: diarrhea
  • Peristalsis-After eating, the bolus goes through wave like movement via contraction and expansion to push the bolus down.

Macronutrients

  • Need in large amounts

Examples:

  • Protein
  • Water
  • Carbohydrates
  • Fiber

Micronutrients

  • Need in small amounts

Examples:

  • Vitamins
  • Minerals

Nutrients, Sources, and Deficiencies

  • Calcium: Builds bones and teeth; helps muscles and nerves work.
    • Sources: Milk, yogurt, cheese, salmon, dark veggies.
    • Deficiency: Rickets, weak bones and teeth.
  • Iron: Combines with protein to make hemoglobin; helps cells use oxygen.
    • Sources: Liver, spinach, raisin and molasses, shellfish.
    • Deficiency: Anemia (low blood count).
  • Potassium: Helps nerves and muscles, balances body water.
    • Sources: Potatoes, banana, prune juice, tomato products.
  • Sodium: Helps nerves and muscle function.
    • Sources: Salt, soy sauce, processed food, country ham.
    • Excess: Heart attack and heart disease.

Micronutrients (Vitamins), Sources, and Deficiencies

  • Vitamin A: For healthy skin and night vision.
    • Sources: Orange/yellow veggies, dairy.
    • Deficiency: Night blindness.
  • Vitamin B: Maintains nerve/muscle function.
    • Sources: Fruits, fish, nuts, yogurts, eggs.
  • Vitamin C: Required to produce collagen (a protein to heal wounds).
    • Sources: Citrus fruits, berries, bell peppers.
    • Deficiency: Scurvy (bleeding gums).
  • Vitamin D: Helps body absorb calcium for stronger bones and teeth.
    • Sources: Oily fish, egg yolk, red meat, sunlight.
    • Deficiency: Rickets (softening of bones).
  • Vitamin E: Protects cells from damage.
    • Sources: Nuts, avocado, spinach, kale, broccoli.
    • Deficiency: Uncommon.
  • Vitamin K: Helps blood to clot.
    • Sources: Spinach, Kale, Broccoli
    • Deficiency: Excessive bleeding.

Tests

Biuret test:

  • Protein test = blue violet

Bender's test

  • description missing from context. The test requires water bath at 70-80 degrees celcius.

Tests for carbohydrates

Iodine test

  • For starch. A positive reaction is a colour change yellow/brown to blue/black. The food must be placed on a white tile.

Benedicts test

  • For reducing sugar. The solution should turn from blue --> high suger. The test requires a water bath at 70-80 degrees celcius and two minutes in that water bath.

Protein

  • Macronutrient that is essential to build muscle.
  • Simplest form: amino acid.
  • Made out of C, H, O, N (carbon, hydrogen, oxygen, nitrogen).

Functions:

  • Growth and maintenance.
  • Build and repair.
  • Deficiency: muscle loss, hair loss, fatigue, Kwashiorkor.
  • Excess: kidney damage, weight gain, heart disease.

Types of Protein:

  • Soluble protein (e.g., antibodies, hormones, enzymes).
  • Insoluble protein (e.g., hair, nail, skin, cartilage – keratin).

Amino Acids:

  • Essential amino acids (obtained from diet).
  • Non-essential amino acids (produced by the body).

Fats (Also Known As Lipids)

  • Made out of C, H, O (carbon, hydrogen, oxygen).
  • Simplest form: 1 glycerol and 3 fatty acids.

Functions:

  • Secondary energy source (39kJ).
  • Provides heat.
  • Protects internal organs.
  • Animals in cold weather/ humans under skin use for "Blubber".

Emulsion Test:

*Add Ethanol -> Food ->Water. Mix well. If the mix turns cloudy, they are fats.

Types:

  • Saturated (animal source, solid at room temperature; e.g., lard; less healthy).
  • Unsaturated (plant source, liquid at room temperature; e.g., olive oil, coconut oil; more healthy).
  • Deficiency: brittle nails, dry skin, hair loss.
  • Excess: obesity, heart disease, high blood pressure.

Carbohydrates

  • Made out of C, H, O (carbon, hydrogen, oxygen).
  • Simplest form: glucose.
  • Primary source of energy (17kJ).
  • Energy for daily activities (running, nerve impulses).

Types:

  • Simple carbohydrates (immediate energy, taste sweet).
  • Complex carbohydrates (break down to obtain energy; e.g., rice, potato; usually taste starchy).
  • Excess: Diebetic/Obesity.