Announcements
1. writing tutors
* Rob and Bern
2. Biology help sessions with Chelsea and Sarah
* Tuesdays  1-2 pm Library 4300
* Wednesdays   1-2:30 Lab I 1040 and 2033
3. Dr. Rudy Ryser: 12-1:30

Objectives
1. learn how nutrients enter the body (bloodstream)
2. illustrate how cell membranes are selective barriers
3. illustrate how enzymes work

Important concepts
1. absorbable units
2. hydrophobic and hydrophilic substances
* one main objective of Friday's workshop was water soluble substances
3. enzymes

DIGESTIVE SYSTEM   Table 6.3
1. Involved in transferring nutrients, water and electrolytes into the body (bloodstream)

2. Each digestive organ takes part in 1 or more of the 4 digestive processes
* motility: movement of food
* secretion: of digestive enzymes, mucous and other substances by glands through ducts into the GI (gastrointestinal) tract
* chemical digestion: breakdown of foodstuff into absorbable units by enzymes
* absorption: transfer of absorbable material into the bloodstream

3. Chemical digestion occurs in many places
* carbohydrate digestion starts in the mouth and is completed in the small intestine
* protein digestion starts in the stomach and is completed in the small intestine
* fat digestion starts in the small intestine

4. Almost all absorption takes place in the small intestine

5. Large intestine largely involved in extracting water

TOUR OF THE GI TRACT
1. Mouth
* salivary gland secretes saliva containing amylase (which begins carbohydrate digestion)
* mechanical digestion takes place

2. Pharynx
* the common throat: involved in movement

3. Esophagus      Fig. 6.5
* peristalsis: rhythmic, reflexive muscular contractions which force food to the stomach

4. Stomach
* sphincters separate the stomach from the esophagus and small intestine Fig. 6.6
* gastric pits secrete gastric juices containing HCl and enzymes which digest protein
* carbohydrate digestion continues and protein digestion begins
* alcohol and some drugs are absorbed here
* mucous is also secreted
Q: why is mucous secreted?
Q: what would happen if the sphincters did not close properly?
Q: why is there no fat digestion occurring?

5. Small Intestine and Accessory Organs (pancreas and liver)  Fig. 6.8
* most digestion and almost all absorption takes place here
* divided into duodenum, jejunum and ileum
* pancreatic and gall bladder (liver) secretions empty into duodenum Fig. 6.10

6. Pancreas
* secretes enzymes which digest protein, carbs and fats
* secretes hormones (insulin, glucagon) into bloodstream
* absorbable units pass into bloodstream here
Q: If fats are hydrophobic, can't they pass into the bloodstream earlier?

7. Liver
* secretes bile which aids in fat digestion
* produces cholesterol
* detoxifies harmful substances (alcohol, drugs, etc…)
* interconverts nutrients (glucose and amino acids can be converted to fat)
* has other functions

8. Large Intestine
* fecal matter contains undigestible materials, water and bacteria
* water is absorbed in large intestine as well as some vitamins produced by bacteria
* 9 liters of secretions are secreted into the GI tract per day
Q: what would happen if enough water weren't absorbed?
Q: what causes gas (flatulence)?
Q: what happens if the feces moves to slowly through the large intestine?

9. Anus       Fig. 6.11
* internal anal sphincter reflexively relaxes when pressure builds
* external anal sphincter is under voluntary control (thank goodness)

10. The digestive process is regulated by
* muscular system
* endocrine system
* nervous system

Questions
1. If a meal contain simple sugars already in the form of their absorbable units, why can't these monosaccharides be absorbed in the mouth?
2. The absorbable unit of fat does not require a membrane channel through which to enter into the body.  So why aren't fats absorbed in the mouth or stomach?
3. What are some biological principles to consider when designing drugs to be taken orally?
4. What are some principles to consider when designing vitamins and supplements?