This document summarizes the human digestive system process from mouth to anus. Key points include that digestion involves both chemical and physical breakdown of food using enzymes and movement. Enzymes are produced throughout the digestive tract to break down carbohydrates, proteins and fats into smaller molecules that can be absorbed. Absorption primarily occurs in the small intestine, where nutrients like amino acids, monosaccharides and fatty acids pass into the bloodstream. The role of different organs like the stomach, pancreas, liver and intestines in secreting enzymes and absorbing nutrients is described.

1. Lecture 9: How food gets to your derriere
Tuesday, October 6, 2015
Common rxns:
 A + B -> C + D
o Reactants on left
o Products on right
 A -> B + C
o Reactant: A
o Product: B + C
 A + B -> C
o Reactant: A + B
o Product: C
 Enzymatic rxns are crucial for digestion bc your system can't break anything down w/o
enzymes!
 Substances change during rxns: this produces the product[s]
 We need to speed up rxns, irl ain't nobody got time to wait!
o They do this by making specific proteins
 Enzymes lower the activation energy to speed up the rate of rxn
o In cellular respiration, energy is released, breaking down CO2 & GLUCOSE allowing us to
make ATP!
 Glucose + Oxygen => CO2 + Water
Structure of Enzymes =
 End in "ase"
 Need to be in a specific 3D shape in order to function
 If the shape is destroyed, it's non-functional
o Cooking denatures proteins bc they can't work @ high temps
 You have 3 different genes for lactose: if your gene is turned off, you're intolerant
 Active site: the pocket where the reactant interacts/docks in enzyme
o Substrate = reactants, bind to site
o Products = monomers
 Enzymes building up = Anabolic
o Have smaller components like monosacs
 Monosaccharides dock into active site of that enzyme
 It physically changes shape aka "induced fit"
 This speeds up rxn by 1000s of times!
Metabolism
Anabolic Catabolic
Dehydration synthesis (take away water) Hydrolysis (adding water!)
Endergonic (store energy!) Exergonic (releases ATP)
Ex: Photosynthesis! Ex: Cellular Respiration!
CO2 >>> Glucose Glucose >>> CO2
^opposites
^NOT a 1 step process

2. Metabolic Pathway
 Series of rxns needed to get the end product!
 Along the way, there are intermediates:
o You have to go thru B & C to get to D!
 Certain enzymes work on certain reactants
 If you don't produce lactase enzyme, you can't break down lactose into monomers
o You're intolerant! So microbes break it down and you get diarrhea, gas & bloating (White
Chicks style)
 Good news: your cells are smart and a lot of them are stationary, minimizing distance btw
substrate & enzyme
o Quicker rxn!
Nutrition & Digestion
 We can't just absorb what's out there, we need to digest it
 From mouth >> anus
 Epithelial cells play a big role in absorption !
 Pepsin: (stomach)
o In an acidic environment
o Unique enzyme bc it can work in a low pH (others fall apart, denature!)
Carbs Fats Proteins
Needs to be broken down
into monosaccharides
Needs to be broken into
monoglycerides/fatty acids
Needs to be broken down into
Amino Acids
Bc cholesterol is a fat, it moves freely across the cell membrane (LIKE DISSOLVES LIKE!)

3. Mouth
Chemical Salivary amylase & mucus
Physical Taste buds
Nose
 Informs what enzymes to make later on!
 Chocolate taste test: if you plug your nose,
you can't taste it!
 You can smell many more things than you
can taste!
Teeth
Tongue
Soft & Hard palate
Digestion Salivary amylase digests starch!
 If you let crackers sit on your tongue long
enough, it'll turn sweet
Absorption NONE
Esophagus *food mover*
Chemical Mucus
Physical Peristalsis: wavelike contraction of smooth tube -
moves food in 1direction (towards stomach!)
Upper & Lower sphincter muscles:
Upper shuts down to let peristalsis happen
Lower doesn't always close, causing acid reflux
Epiglottis: right before opening to esophagus.
Shuts off air pipe (respiratory system) so food
doesn't go down the wrong pipe
Digestion NONE
Absorption NONE
Stomach
Chemical Mucus
HCl - acidic conditions denature (unfold) proteins
Pepsin (enzyme to break down proteins!) works @
a low pH
Physical Churns the food
Made up of folds called "rugae" allows stomach to
contort, bathing it in HCl + pepsin (like a washing
machine exc laundry = food, soap = pepsin)
Pyloric Sphincter regulates food moving from
stomach -> small intestine

4. Digestion Proteins
Absorption 10% happens here!
Amino acids & alcohol absorbed here
 Why you eat more when you're drunk!
 Helps you absorb better and compete with it
Small intestine
Chemical Water & mucus come in to bathe food w/ buffer,
enzymes & bile
Physical Long tube has villi & micro villi
 ^Folds that help food get absorbed
 Like peristalsis: moves food in tube in 1
direction
Digestion Proteins
Polysaccharides (carbs)
Big fats (triglycerides)
Absorption Amino Acids
Monosaccharide
Fatty acids
Cholesterol
Minerals & vitamins (< don't need to be digested)
80% of food absorption happens here!!!
Pancreas
Chemical Produces enzymes the stomach needs to break
down large substances
 Lipases (lipid aka fat breakdown)
 Proteases (proteins)
 Carbohydrases (carbs) starch, glycogen
Don’t like acid so it uses a buffer to neutralize pH.
 This lets enzymes function properly
Physical
Digestion Phospholipids -> fatty acids
Triglycerides -> fatty acids
Starch/Glycogen -> glucose
Rule of thumb -> singular components
Absorption
Liver/Gallbladder
Chemical Liver makes bile (fat breakdown!) into single fats
for lipase to take care of

5.  Bile starts the process, (pulls apart fat)lipase
digests/absorbs what's left
Gallbladder stores bile
Physical NONE
Digestion NONE
Absorption NONE
Large intestine
Chemical Mucus
Enzymes have already been deposited by pancreas
Physical Same structure as small intestine:
 Villi, microvilli
 Longer dynamic but shorter distance
Anal sphincter releases everything
Digestion Mutualistic microbes:
 Break down (lactose for ex) which gives you
gas
 Help produce monomers to be absorbed
 Produce vitamins
Remaining enzymes from small intestine
(not much)
Absorption o Vitamin production, minerals
o Water reabsorption (this is where diarrhea
happens if you don't reabsorb)
o Fiber hangs on to fats, and slowly releases
sugars (you'll feel fuller longertm)