1. Digestion

2. Explain why digestion of large food molecules is essential
Explain the need for enzymes in digestion
State the source, substrate, products and optimum pH conditions for one amylase, one protease, and one lipase
Draw and label a diagram of the digestive system
Outline the function of the stomach, small intestine and large intestine
Distinguish between absorption and assimilation
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 food? Ingestion – you eat the food
To start with, this is a breakdown of basic processes:
Ingestion – you eat the food
Digestion – series of chemical reactions that convert food into smaller and smaller molecular forms
Absorption – food molecules absorbed by cells and passed to blood vessels
Transport – you circulatory system moves food molecules throughout your body

4. Many of the foods that we eat are composed of very large molecules and these molecules may be too big to cross the cell membranes and enter your bloodstream
Molecule Type
Ingested Form
After Digestion
Protein
Amino acids
Lipids
Triglycerides
Glycerol/fatty acids
Carbohydrates
Poly, di, monosaccharides
monosaccharides
Nucleic acids
DNA, RNA
nucleotides

5. Proteins to amino acids via hydrolysis reactions

6. Triglycerides into glycerol and fatty acids via hydrolysis reactions

7. Polysaccharides into Monosaccharides via hydrolysis reactions

8. Using enzymes specific for certain tasks, your body is able to breakdown the foods you eat via hydrolysis reactions (your body can then reassemble the monomers into polymers as needed)
Remember, enzymes are protein molecules which act as catalysts for reactions; they don’t cause the reactions, they just lower the activation energy (heat) required to allow the reaction to take place (temperature, pH, substrate levels help determine enzyme effectiveness)

9. Salivary Amylase
Pepsin (Protease)
Pancreatic Lipase
Source
Salivary glands
Stomach cells
Pancreas cells
Substrate
Carbohydrates
Proteins
Lipids
Products
maltose and glucose
Amino acids
Glycerol and fatty acids
Optimum pH
Neutral (pH 7)
Acidic (pH 3)
Neutral (pH 7)

10. Parts of the Digestive System
Much of the digestive system is a tube called the alimentary canal which consists of:
Mouth
Esophagus
Stomach
Small Intestine
Large Intestine
Rectum

11. The Stomach
Food is forced down the esophagus to the stomach via muscle contractions called peristalsis
Food is held in the stomach in order for it to mix with secretions known as gastric juice
Gastric juice is:
- pepsin – a protease enzyme most active in acidic pH
- hydrochloric acid – makes the pH necessary for pepsin to activate and helps break down foods
- mucus – lines the stomach wall to prevent stomach damage from hydrochloric acid

13. The Small Intestine
2-6 hours after a meal, the valve at the bottom of the stomach will start slowly releasing the food/enzyme/acid mixture into the small intestine
The beginning of the small intestine (named the duodenum) is where accessory organs begin secreting juices into the small intestine for the purposes of continuing digestion
What is added includes:
- bile from liver and gall bladder
- trypsin (a protease), lipase, amylase and
biocarbonate from the pancreas
Duodenum is ~25 cm of 6 m of small intestine (most digestion compete by the end of duodenum)

14. Absorption in Small Intestine
In the small intestine food molecules are small enough to be absorbed into the bloodstream/lymphatic system
This can happen b/c inner wall of small intestine is made up of thousands of finger-like extensions called villi and each villi contains a capillary bed and lacteal (this increases surface area for maximum absorption of monomers)
Most molecules go into bloodstream via capillaries but fatty acids are absorbed into lacteal (remember diffusion/active transport from earlier this year) because they are too large to pass through the membranes of capillaries

16. Assimilation of Molecules
After molecules are absorbed into bloodstream via capillaries or into lymphatic system via lacteals it is transported around the body by the circulatory system
Once a molecule has reached a body cell where it is needed, it will leave the bloodstream the same way it entered (diffusion or active transport across membranes) into the cell
The molecule may be used for energy (e.g. glucose) or it may be used to build a polymer inside the cell (e.g. amino acids used to make proteins)
The process of bringing a molecule to a body cell and then using it to make larger molecules (polymers) is called assimilation

18. The Large Intestine
Most useful nutrients are absorbed in the small intestine but the H2O we drink/eat is still present
The primary function is water absorption (this makes sense b/c having our undigested foods in an aqueous environment for as long as possible aids in movement)
contains many bacteria including E. coli (these are mutualistic organisms – we provide food/H2O,warm enviro and they help us synthsize vitamin K and maintain healthy intestines)
Any undigested food by us or the bacteria (e.g. cellulose) is eliminated as solid waste