Success Criteria

1. Describe the parts and functions of the human digestive system.

2. Outline the process of digestion.

3. State the end products of digestion.

Overview of Digestion

• Definition: Digestion is the breakdown of food into smaller particles that can be absorbed into the blood or lymph.

• Pathway: Takes place along the digestive tract (alimentary canal).

• Ingestion: Taking food into the alimentary canal.

• Egestion: Taking undigested food out of the alimentary canal.

Types of Digestion

1. Physical (Mechanical) Digestion: Breaking food into smaller pieces (e.g., chewing).

   • Advantages:

     • Eases swallowing.

     • Increases surface area for enzymes.

2. Chemical Digestion: Breaking down large molecules into smaller molecules through enzyme action.

   • Advantages:

     • Makes food absorbable into the bloodstream.

Human Digestive System Parts and Functions

1. Mouth

   • Functions:

     • Teeth break down food physically.

     • Salivary glands produce saliva (contains water, mucus, and enzyme ptyalin).

   • Saliva Functions:

     • Softens food.

     • Begins starch digestion.

2. Oesophagus

   • Function: Transports food to the stomach; lubricated by mucus.

   • Note: No digestion occurs here.

1. Stomach

   • Functions:

     • Prevents food from returning to the mouth (cardiac sphincter) and entering the duodenum too quickly (pyloric sphincter).

     • Secretes gastric juice (mucus, hydrochloric acid, and enzymes like renin, chymotrypsin, and pepsin).

   • Hydrochloric Acid Functions:

     • Creates acidic environment for enzyme activity.

     • Kills germs.

     • Softens hard food particles.

2. Duodenum

   • Secretions:

     • Bile: Produced by the liver, stored in the gall bladder; emulsifies fats.

     • Pancreatic Juice: Contains sodium hydrogen carbonate and enzymes (lipase, trypsin, pancreatic amylase).

       • Functions:

         • Lipase: Breaks down fats into fatty acids and glycerol.

         • Trypsin: Digests polypeptides into peptides.

         • Pancreatic Amylase: Digests starch into maltose.

End Products of Digestion

• Carbohydrates: Broken down into simple sugars (e.g., glucose).

• Proteins: Digested into amino acids.

• Fats: Converted into fatty acids and glycerol.

5. Jejunum

• Function: No enzymes are released; food is passed to the ileum.

6. Ileum

• Secretions: Releases intestinal juice (succus entericus) containing:

  • Maltase: Breaks down maltose into glucose.

  • Peptidase: Breaks down peptides into amino acids.

  • Sucrase: Breaks sucrose into glucose and fructose.

  • Lactase: Breaks lactose into galactose.

  • Cellulase: Breaks down cellulose into glucose.

Food Absorption

• After digestion, the small intestine has a higher concentration of food substances than the surrounding blood capillaries.

• Movement: End products move from the small intestine into the bloodstream via diffusion and active transport.

• Transport: Nutrients are carried to the liver through the hepatic portal vein, where they are processed before entering general circulation.

Functions of the Small Intestine

1. Digestion of Food

2. Absorption of Food Substances

Adaptations for Absorption

• Villi: Increase surface area.

• Length: More surface area for absorption.

• Blood Vessels: Dense network facilitates nutrient transport.

• Thin Walls: Allows for easy diffusion.

Villi

• Structure: Small projections in the walls of the small intestine.

• Function: Absorb nutrients; have very thin walls (one cell thick) for quick diffusion.

Adaptations of Villi

• Thin Walls: Facilitate faster diffusion.

• Mitochondria: Provide energy for active transport.

• Blood Capillaries: Enhance nutrient diffusion.

• Permeability: Lacteals absorb fatty acids and glycerol.

• Nutrient Absorption:

  • Fatty Acids and Glycerols: Absorbed by lacteals and stored as adipose tissue.

  • Glucose, Amino Acids, Vitamins, and Minerals: Absorbed by blood vessels and transported to the liver.

Final Products of Digestion

• Carbohydrates: Glucose

• Fats and Oils: Fatty Acids/Glycerol

• Proteins: Amino Acids

Undigested Food in the Large Intestine

• Undigested food enters the large intestine, where water is absorbed, and feces are formed.

• Storage: Feces are temporarily stored in the rectum before egestion.

Functions of the Liver

• Produces bile.

• Stores vitamins A, D, and iron.

• Converts excess glucose to glycogen.

• Deaminates excess proteins.

• Neutralizes toxic substances (detoxification).

Functions of the Large Intestine (Colon)

• Absorption of water.

• Absorption of mineral salts.

Problems in Digestion

1. Constipation

   • Causes:

     • Lack of roughage in the diet.

     • Stress and anxiety.

     • Insufficient water intake.

     • Illness.

   • Treatment and Prevention:

     • Increase water intake.

     • Use appropriate medications.

     • Engage in regular exercise.

2. Ulcers

   • Causes: Excess hydrochloric acid production in the stomach.

   • Treatment and Prevention:

     • Consume a diet rich in roughage.

     • Manage stress.

     • Seek medical assistance when necessary.