1. Topic 6.1: Digestion

2. Assessment Statements
6.1.1: Explain why digestion of large food molecules is essential
6.1.2: Explain the need for enzymes in digestion
6.1.3: State the source, substrate, products and optimum pH conditions for one amylase, one protease, and one lipase
6.1.4: Draw and label a diagram of the digestive system
6.1.5: Outline the function of the stomach, small intestine and large intestine
6.1.6: Distinguish between absorption and assimilation
6.1.7: Explain how the structure of the villus is related to its role in absorption and transport of the products of digestion

3. Why do we digest?
When you eat a snack or a meal, you begin a set of events that leads to your body cells being provided with needed nutrients
Ingestion
Digestion
Absorption
Transport

4. Digestion Digestion solves a problem of molecular size
Food is too large to pass through cell membranes
Food must be chemically digested to a suitable size
Molecule type
Molecular form ingested
Molecular form after digestion
Protein
Amino acids
Lipids
Triglycerides
Glycerol and fatty acids
Carbohydrate
Polysaccarides, disaccharides, and monosaccharides
Monosaccharides
Nucleic acids
DNA, RNA
Nucelotides

5. Digestion Digestion allows you to turn molecules into ‘your own’
All the food that you eat is composed of plant or animal cells, thus containing molecules characteristics of a living organisms that is not a human being
Each type of living organism has its own set of proteins, nucleic acids, and carboydrates

6. Digestion
When we digest food molecules, we break them down (hydrolyze them) into smallest components.
The components can be reassembled into larger molecules that are useful to you!!

7. Digestion
As food moves through your alimentary canal, many digestive enzymes are added along the way
Each digestive enzyme is specific for a specific food type
Examples:
Lipase: is an enzyme is specific for lipid molecules
Amylase: is specific for amylose (starch)

8. Digestion
The real function of enzyme is to lower the activation energy of reactions that they catalyze
Digestive enzymes all help to catalyze hydrolysis reactions

9. Examples of digestion enzymes
Salivary Amylase
Pepsin (a Protease)
Pancreatic Lipase
Source
Salivary glands
Stomach cells
Pancreas cells
Substrate
Amylose (starch)
Proteins (polypeptides)
Lipids
Products
Maltose and glucose
Amino acids
Glycerol and fatty acids
Optimum
Neutral (pH 7)
Acidic (pH 3)

10. Human Digestive System
Much of the human digestive system is a tube called the alimentary canal
Alimentary canal consists of:
Mouth
Esophagus
Stomach
Small Intestine
Large Intestine (colon)
Rectum
Any foods that you ingest must either be digested and absorbed for use by the body or remain undigested and be eliminated as solid waste

11. Stomach
Food is brought to your stomach by a muscular tube called the esophagus
When you swallow, the food is forced down to your stomach by a sequential series of smooth muscle contractions called peristalsis

12. Stomach
Once in the stomach, the food is held for a period of time in order to mix it with a variety of secretions collectively known as gastric juice

13. Stomach
Gastric juice is a mixture of three secretions form the cells of the stomach inner lining:
Pepsin- a protease enzyme most active in acidic pH
Hydrochloric acid- helps degrade and break down foods and creates the acidic pH necessary for pepsin to be active
Mucus- lines the inside the stomach wall to prevent stomach damage from the hydrochloric acids

14. Stomach
The muscular wall of the stomach creates a churning motion in order to mix food with the gastric juice
After a period of time, a valve at the lower end of the stomach opens and the food enters the small intestine

15. Small Intestine
The first portion of the small intestine is called the duodenum
Three different accessory organs secrete juices into the small intestine in order to continue the digestive process
These secretions include:
Bile from the liver and gall bladder
Trypsin (a protease), lipase, amylase, and bicarbonate from the pancreas

16. Small Intestine
As the digestive process continues in the small intestine, molecules are produced that are small enough to be absorbed
The inner wall of the small intestine is made up of thousand of finger-like extensions called villi

17. Small Intestine
Each villus contains a capillary bed and a lacteal
Lacteal is a small vessel of your lymphatic system
If the inner lining of your small intestine were smooth, you would have a fairly limited membrane surface area for absorption
The function of the villi is to greatly increase the surface area for absorption of molecules such as glucose, amino acids, and fatty acids

18. Small Intestine
Most molecules absorbed are taken into the capillary bed within each villus
Except fatty acids which are more efficiently absorbed into the lacteal
All absorbed molecules are taken to a wide variety of body cells by the circulatory system

19. Large Intestine
The vast majority of useful nutrients are absorbed while food is still inside the small intestine
Much of the water that we drink or that is naturally contained in many food is also present

20. Large Intestine
The primary function of the large intestine is water absorption
Leaving water in the alimentary canal as long as possible is beneficial because it keeps the moving food in a fluid environment

21. Large Intestine
The large intestine is also home to a very large number of naturally occurring bacteria including Escherichia coli.

22. Large Intestine
These bacteria are examples of mutualistic organisms within us.
We provide nutrients, water, and a warm environment for them while they synthesize vitamin K and maintain a healthy overall environment for us in our large intestine
Any food undigested by us or the bacteria is eliminated from the body as solid waste or feces