Human Digestive System Notes

HUMAN DIGESTIVE SYSTEM

Diet

  • Definition: Diet refers to the food we consume daily.
  • Balanced Diet Components:
    • Provides the necessary energy for sustaining life.
    • Contains all essential nutrients:
      • Carbohydrates
      • Proteins
      • Lipids
      • Vitamins
      • Minerals
      • Water

Nutrients

  • Categories:
    • Carbohydrates (Carbs)
    • Proteins
    • Lipids

Carbohydrates

  • Function: Primary energy source.
  • Digestion: Broken down by carbohydrase or amylase.
  • Testing:
    • Iodine test for starch: indicates starch presence with a blue-black color.
    • Benedict's test for reducing sugars: requires heat, positive result shown by a red brick color.

Protein

  • Functions:
    • Enzyme production.
    • Hormone synthesis.
    • Antibody creation.
    • Growth and repair of cells.
    • Energy provision (when carbs and fats are insufficient).
  • Digestion: Broken down by protease that is secreted from the stomach with the help of HCl.
  • Testing:
    • Biuret test: indicates protein presence with a violet color.
  • Deficiency: Kwashiorkor.

Lipids (Fat and Oil)

  • Function:
    • Energy storage.
    • Body warmth maintenance.
  • Types:
    • Fat: solid at room temperature.
    • Oil: liquid at room temperature.
  • Digestion: Broken down by lipase.
  • Testing:
    • Ethanol emulsification test: positive result indicated by a white emulsion.

Enzymes

  • Composition: Made from protein.
  • Denaturation: Can be denatured (lose shape and function) by changes in temperature and pH.
  • Specificity: Highly specific substrate and product.
  • Role: Act as biological catalysts.
  • Catalyst Definition: A substance that accelerates a chemical reaction.

Enzyme and Temperature

  • Optimum Temperature: Typically around 40°C.
  • Denaturation at High Temperatures: Enzyme activity decreases rapidly at high temperatures due to denaturation.
  • Human Enzymes: Optimum temperature is approximately 37°C.
  • Plant Enzymes: Optimum temperature is approximately 25°C.
  • Graphical Representation:
    • A graph shows the rate of reaction versus temperature, peaking around 40°C and then rapidly declining.

Enzyme and pH

  • Gastric Juice Enzymes: Optimum pH is around 2.
  • Mouth and Pancreas Enzymes: Optimum pH is around 7.

Human Alimentary Canal

  • Purpose of Digestion: To break down large, insoluble food molecules into small, soluble molecules through mechanical and chemical processes.
  • Alimentary Canal: A long, continuous tube from the mouth to the anus where digestion occurs.
    • Sequence: Mouth → Esophagus → Stomach → Small Intestine (Duodenum, Jejunum, Ileum) → Large Intestine → Rectum → Anus.
  • Organs Joined to Alimentary Canal: Pancreas, liver, gall bladder.

Alimentary Canal Organs

  • A diagram showing the arrangement of the alimentary canal including:
    • Mouth
    • Esophagus
    • Liver
    • Gall bladder
    • Stomach
    • Pancreas
    • Small Intestine
    • Large Intestine
    • Rectum
    • Anus

Mechanical and Physical Digestion

  • Mechanical Digestion:
    • Utilizes teeth.
    • Peristalsis: Contraction and relaxation of alimentary canal muscles to move food along.

Chemical Digestion

  • Enzymes:
    • Mouth: Amylase.
    • Stomach: Gastric juice containing protease and HCl.
    • Duodenum: Enzymes secreted by the pancreas (amylase, lipase, protease) act in the duodenum.

Summary of Chemical Digestion

  • Mouth:
    • Amylase breaks down starch into maltose.
  • Duodenum:
    • Amylase breaks down starch into maltose.
    • Lipase acts on fats, with bile emulsifying them.
  • Small Intestine:
    • Maltase breaks down maltose into glucose.
  • Stomach:
    • Pepsin (gastric juice) breaks down protein.
  • Duodenum & Small Intestine:
    • Trypsin (from pancreas) and peptidase continue protein breakdown into amino acids.
  • Overall Breakdown:
    • Fats are emulsified and then broken down into fatty acids and glycerol.

Enzyme Functions and Locations

| Enzyme | Function | Location |
| :------- | :-------------------------------------------------------- | :---------------- | # noqa: MD009
| Amylase | Breaks down starch into sugar | Mouth, Duodenum |
| Pepsin | Breaks down protein into peptones | Stomach |
| Trypsin | Breaks down peptones into amino acids | Duodenum |
| Erepsin | | Duodenum |
| Lipase | Breaks down lipids into fatty acids and glycerol | Duodenum |

Mouth

  • Mechanical Digestion: Chewing with teeth.
  • Chemical Digestion: Amylase in saliva (pH around 7).
  • Saliva: Contains water, which helps food to be easily swallowed.

Stomach and Esophagus

  • Esophagus:
    • Mechanical Digestion: Peristaltic movements transport food from mouth to stomach.
    • Chemical Digestion: None.

Stomach

  • Mechanical Digestion: Peristaltic movement.
  • Chemical Digestion: Gastric juice containing HCl and protease (pH around 2).
  • HCl Function: Kills bacteria.
  • Mucus Production: Protects the stomach lining from acid and protease.

Small Intestine (Duodenum)

  • Duodenum's Role: Receives substances from the stomach, pancreas, and gall bladder.
    • Stomach: Delivers food.
    • Pancreas: Adds pancreatic juice containing amylase, lipase, and protease.
    • Gall Bladder: Pours bile (produced by the liver and stored in the gall bladder).
  • Bile Function: Emulsifies lipids, breaking them into small droplets.

Small Intestine (Jejunum & Ileum)

  • Jejunum:
    • Provides time for enzymes to work.
  • Ileum:
    • Contains villi covered by microvilli to increase the surface area for absorption.
  • Absorption:
    • Small substances are absorbed into blood capillaries via diffusion.
    • Large substances pass into the large intestine and are excreted as faeces.

Villi Structure

  • Diagram: Illustrates the structure of villi in the small intestine.
    • Lumen
    • Microvilli
    • Epithelium
    • Capillary bed
    • Lacteal
    • Muscle layers
    • Hepatic portal vein

Large Intestine and Rectum

  • Large Intestine: Water is absorbed from undigested food and faeces.
  • Rectum: Where concentrated faeces is stored before elimination through the anus.

The Liver

  • Function:
    • Detoxifies toxins.
    • Produces bile.
    • Stores sugar as glycogen.
  • Structure: Diagram showing the liver's lobes, gall bladder, and associated vessels.
    • Right and left lobes
    • Gall bladder
    • Hepatic artery
    • Portal vein
    • Hepatic vein
    • Common bile duct

Gallbladder and Pancreas

  • Illustration of the gallbladder and pancreas with their associated ducts.
  • Pancreas Function:
    • Produces pancreatic juice.
    • Neutralizes food.
    • Produces insulin to maintain blood glucose levels.
    • Insulin Function: maintain the blood glucose level