Introduction to Digestion

We are what we eat!

What is involved in the process of Digestion?

• How would you define digestion?

• Here’s one definition: a process of breaking down food or macromolecules into smaller molecules for absorption

• While watching the demo, try to figure out the four stages of digestion

The Four Stages of Digestion

• What was the first stage that occurred in the demo?

• Hint: without this stage, your system wouldn’t have any food to break down....

1. Ingestion = the taking in of nutrients i.e. the act of eating and putting food into your mouth!

The Four Stages of Digestion

• What happened next?• Hint: without this stage, our body can’t use

the nutrients that we ingest....

2. Digestion = the break down of food by mechanical and chemical processes into molecules small enough for cells of the body to absorb

The Four Stages of Digestion

• And next?• Hint: without this stage, our tissues have no

way of getting the broken down nutrients

3. Absorption = the transport of digested nutrients to the tissues of the body

The Four Stages of Digestion

• And last?• Hint: without this stage, we can be in a lot of

pain and discomfort....

4. Egestion or elimination = the removal of undigested solid waste from the body

But wait – just what the heck are we digesting????

• Q: What is the hotdog? The muffin? The yogurt?

• A: Different forms and combinations of macromolecules that we need to survive!

• We break them down with the help of enzymes and through hydrolysis reactions

What are Macromolecules?

• Macromolecules are very large organic molecules • They are made up of smaller molecules that are

linked together• They are the nutrients and raw materials that are

involved with all cellular functions

• They provide the energyfor metabolism

What are Macromolecules?• Four categories of macromolecules:– Carbohydrates– Proteins– Fats (lipids)– Nucleic acids

• These plus some minerals and vitamins are known as essential nutrients

= a nutrient that cannot be made by the body, and must therefore be obtained from food

Carbohydrates• Contain carbon, hydrogen, and oxygen

generally in the same ratio (C:2H:O)• Provide short-term and long-term energy

storage for organisms• Monosaccarides = one sugar; consists of a

molecule with 3 to 7 carbon atoms (e.g. Glucose or fructose)– Taste sweet

Carbohydrates• Dissacharides = a sugar made up of two

monosaccaride molecules (e.g. Sucrose)

• Polysaccarides = complex carbs, consist of many linked monosaccarides (e.g. Starch, cellulose, glycogen)

Proteins• Found in meats, milk products, eggs,

vegetables, nuts and soy• Macromolecule made up of amino acids• Amino acids join together by peptide bonds

and many joined together = polypeptide• Proteins are needed for cell growth and repair,

and enzymes are proteins, as well as antibodies

Proteins

Fats or Lipids• Found in animal and fish products, nuts and

seeds, avocado and dairy products• Fats are organic compounds that do not

dissolve (insoluble) in water• Basic structure is a glycerol molecule and

three fatty acid chains • Needed for nerve and muscle

function

Fats or Lipids

Nucleic Acids• Nucleic acids direct growth and development

of all organisms using a chemical code• Our body can make them, but there are times

when what we make is not enough, therefore we need to get them from what we eat

• Two types of nucleic acid = • Ribonucleic acid (RNA)• Deoxyribonucleic acid (DNA)

Homework

• Read up on Macromolecules in your text• Section 2.1 (pg 32) to the end of Section 2. 5

(pg. 47)• Answer the questions in the handout.