Digestive System Lecture 5 Winter 2014

Transcription

1 Digestive System Lecture 5 Winter 2014

2 This lecture tells the story of the Flow of Matter from Food to Cells. The pictures are only there to help you visualize structures don t worry about names of structures that show up in the picture that are not in the narrative.

3 Mammalian Digestive System 1 Our digestive system is essentially one tube with an opening for bringing food in, and an opening for getting rid of waste. Anything we want to keep for the body must be moved from the digestive tube into our cells of the body. If it is not absorbed, it will go out as waste.

4 Stages of Food Processing 2 There are four stages: 1. Ingestion bringing the food into the digestive system (in the mouth) 2. Digestion breaking the food into smaller pieces (polymers into monomers) so the monomers can be absorbed. 3. Absorption the process of moving nutrients (monomers) from the digestive tract into the blood stream to travel to cells 4. Elimination Anything that stays in the tube is removed as waste

5 Stages of Food Processing 3

6 The Mouth 4 What happens in the mouth when I eat? (in this case, a potato) Mechanical digestion (chewing) This breaks food down into smaller pieces so we don t choke while swallowing Breaking food into smaller pieces also provides more surface area for enzymes to attach to macromolecules (polymers) to break them down

7 The Mouth 5 What happens in the mouth when I eat? Chemical digestion (the chemical part refers to the action of enzymes) Saliva is released into the mouth. It contains: Enzymes to break down (digest) polymers. An example is amylase, an enzyme that digests starch (remember we saw starch in the potato in lab!). It breaks starch (polymer) into glucose (monomer) What kind of reaction is this? Hydrolysis reaction. Mucin (mucus): thick liquid that protects & lubricates the mouth and throat as food travels to the stomach. Buffers: acids or bases to neutralizes ph of what you ate.

8 Next stop - the Stomach 6 Its function is to stores & digest food What happens in the stomach? Secretes digestive juices, which include: HCL (hydrochloric acid). HCL has a ph of 2. This is very acidic. It causes proteins to denature (unfold). Remember that when proteins denature they lose their ability to function.

9 The Stomach 7 Digestive juices also contain enzymes (they do the actual digesting) Pepsin is an enzyme that digests proteins (polymer), breaking the covalent bonds to separate the amino acids (monomers). Because HCL has caused the protein to denature (unfold back to its primary structure), pepsin now has access to it and is able to digests it. What kind of reaction is this? Hydrolysis reaction. It is important to note that HCL cannot digest proteins that requires an enzyme to break the covalent bonds (perform the hydrolysis reaction.

10 The Small Intestine-upper region After the stomach, food arrives in the small intestine. We will break the small intestine into two parts (upper and lower) because they have completely different functions. What happens in the upper small intestine? More digestion (hydrolysis reactions by enzymes). The liver, pancreas & small intestine produce more digestive enzymes to continue to break polymers into monomers. By the time the food has traveled through the upper region of the small intestine, it is now all in its monomer form. simple sugars (e.g., glucose) amino acids glycerol & fatty acids nucleotides 8

11 The Small Intestine lower region Next food goes to the lower region of the small intestine. This is where absorption occurs. Nutrients (monomers) are transported from this lower region of the small intestine into the bloodstream. 9

12 Nutrients brought to cells 10 Our circulatory system (bloodstream) takes the nutrients to all the cells in the body. Once the nutrients (monomers) are in the cells, then other enzymes use the monomers to build polymers. What kind of reaction is this? Dehydration reaction. Simple sugars (e.g. glucose) can be stored as glycogen (or used by mitochondria to make ATP) Amino acids get built into proteins by ribosomes. Nucleotides move into the nucleus to make more DNA and RNA. Glycerol and fatty acids get used to make more complex lipids, like phospholipids, or moved into the smooth ER to make steroid hormones.

13 The Large Intestine 11 What happens to the food that is not absorbed? It stays in the digestive tract and moves through the large intestine (also called the colon). Feces get stored in the rectum, and then expelled. The large intestine also absorbs water. But note that nutrient absorption is done by the lower region of the small intestine, not the large intestine

14 Flow of matter from food 12 to cells Now you can explain how we can take matter from food (e.g., starch from the potato), digest it through a hydrolysis reaction to turn it into its monomer form (glucose), absorb the monomer and send it to our cells, where we then use dehydration reactions to build it into something we need (e.g., the polymer glycogen).