Final bits on digestion

We finished up the small intestine and reviewed the rugae of the stomach (these are the folds that expand when food is eaten and help with mechanical digestion in the stomach). Side note: The stomach can actually absorb aspirin and alcohol.


We also discussed how pepsin in the stomach is a positive feedback loop. Pepsin is an enzyme in the stomach that breaks down proteins into "medium size" molecules called peptides (what do you think pepsin's optimal pH is?). These peptides in turn trigger the production of more pepsin thereby speeding up the digestion of the larger protein molecules (Why is this important?).

After we leave the small intestine where food is completely broken down and absorbed (this happens near the end), we move into the colon (or large intestine). The structure of the colon is shorter but with more diameter than the SI. In this organ, water is absorbed into the bloodstream via capillaries. This causes the waste to become bulkier. (why wait until the end to absorb water?). The bile that was provided by the liver to the small intestine, causes the waste to turn brown when the water is taken out.

Why is fiber important?

From the colon we move into the rectum (storage organ for waste, until it can be released) and finally to the anus where waste exits the body.

Can you identify what organs mechanical and/or chemical digestion occurs? What are the enzymes involved in each stage and where are they made?

Monday- Digestion notes!

Monday we delved further into structure and function of the parts of the digestive system.

To start with structure and function, we began with:

Mouth - teeth, tongue, salivary glands. Teeth increase surface area by mechanical digestion, while the tongue moves food to the pharynx. The salivary glands (are they alimentary canal or accessory organs?)  produce saliva which has amylase (what does this break down?) by chemical digestion.

Epiglottis - skin flap made of cartilage that closes off the trachea temporarily when you eat to prevent food from entering.

Pharynx - upper part of the throat. the junction between the alimentary canal and airway.

Esophagus  - muscular tube -transfers food (bolus) to the stomach from the mouth by a series of muscle contractions called peristalsis. tube is closed unless food is inside.

Stomach - muscular sac which has an elastic mucus lining. function - to aid digestion. Mucus lining - helps protect the stomach does not digest itself, lining cells are quickly replaced.
   1. Mechanical - churning of the layers of muscle (which go in different directions).
   2. Chemical - 2 major chemicals involved. a)HCl-breaks down everything. b) Pepsin - breaks down proteins.
We will talk more about Rugae on Thursday!


Small Intestine - muscular tube that contains and moves chyme (liquefied food) where the food is broken down even more and the majority of absorption takes place. We will continue the structure of the SI on Thursday!

Pancreatic Enzymes, made by the pancreas and put into the beginning of the SI
1. Pancreatic Amylase - substrate (what enzyme works on) starches and medium size sugars into the products = Simple Sugars (such as glucose!)
2. Lipase - substrate = fats (lipids) into product = fatty acids (with help from bile (where is this made then stored?)
3. Protease - subsrate = proteins into product = amino acids
4. DNAse - substrate = DNA into product = nucleic acids

Where do the nutrients that are the products absorbed into and by what structure?


Here is a video that may help. (reminder: the enzymes are not discussed in the video, but you should know them!)