Digestive System
Digestion - breaking down food into small molecules that
can
be passed
into your cells. Includes all organs below:
Section
38-2
Mouth
Pharynx
Salivary glands
Esophagus
Liver
Gallbladder
(behind liver)
Stomach
Pancreas (behind
stomach)
Large intestine
Small intestine
Rectum
•Alimentary Canal - a one-way tube that passes through the body.
(mouth, pharynx, stomach, small intestine, large intestine.)
•Accessory structures -do not carry food, but aid in digestion.(salivary glands, pancreas, liver)
• 1. The Mouth:
• Teeth - tear/crush food
• Mechanical digestion - physical
breakdown of food
• Chemical digestion - enzymes
break food into smaller food
molecules. Ex:starch into glucose
• Saliva - moistens food
• Enzyme = salivary amylase breaks down starches into simple
sugars
• Food passes through throat past the
epiglottis
• Q: Do enzymes get used up in
these chemical reactions?
• A: No.
• Q: What is their optimal
temperature and pH?
• A: In humans, 98.6 degrees, and
neutral to slightly basic, except for
stomach enzymes.
2. The Esophagus:
•Muscular tube connecting pharynx
to stomach
•Moves through peristalsis =
rhythmic waves of muscular
contractions
•Squeezes food ball along
esophagus
•Can swallow even when standing
on your head!
•Can begin in absence of food =
“lump in your throat.”
•Food bolus enters stomach through
a sphincter (ring of muscle)
•When sphincter fails to close,
acidic gastric juice may splash up
into esophagus = “heartburn.”
• 3. The Stomach•
•
•
•
•
•
•
•
•
•
•
•
Football shaped, holds 1 liter
Mechanical - smooth muscles churn and
mix food
Lining of stomach produces mucuslubricates/protects stomach wall
Chemical - lining contains gastric glands
which produce:
HCl - kills bacteria,activates pepsin
Enzyme: Pepsin - breaks proteins into
smaller polypeptides/amino acids.
Enzyme: Rennin -curdles milk protein
Final pH of gastric contents = 2.
Chyme - mixture that stomach produces
1-2 hours - out pyloric sphincter valve
(Water, salts, alcohol, some drugs - can be
absorbed through stomach)
Peptic Ulcer - stomach lining is
digested/hole in wall. Most caused by a
bacteria,cured with antibiotics.
Helicobactor pylori Bacteria
causing stomach ulcer
Click to enlarge diagram
• 4. The Small Intestine - 6 m long x 3 cm wide
• Chyme enters the duodenum - (1st of 3 parts of
small intestine.) Enzymes enter here from:
• Liver - makes bile which emulsifies fats (breaks
into small droplets).
• Gall Bladder - stores bile
• Q:What are gall stones?
• Q: Can you live without your gallbladder?
• Pancreas - makes 3 enzymes:
• Pancreatic Amylase - breaks starch into simple
sugars
• Trypsin - breaks proteins into A.A.
• Lipase - breaks fats into fatty acids & glycerol
• Small Intestine enzymes:
• Maltase, sucrase, lactase - breaks down sugars
(disaccharides) into simple sugars
(monosaccharides)
• Peptidase - breaks down proteins into A.A.
• Q: Can you live without your liver or pancreas?
A Close-up: Substances entering the Duodenum
The Liver and the Pancreas
Section 38-2
Liver
Bile duct
Gallbladder
Pancreas
Pancreatic duct
Duodenum
To rest of small intestine
• Absorption in the Small Intestine:
• After duodenum: Jejunum and Ileum
(total 6 meters long)
• Here are villi - fingerlike projections
covered with microvilli.
• These folds and projections provide
large surface area for absorption of
nutrients.
• If the lining were completely unfolded
and spread out, it would be the size of
a tennis court!
• Carbs and Proteins - go from villi to
capillaries to cells
• Fats - go from villi to lymph vessels to
cells
• Now all that is left is water, cellulose,
& other undigestible substances.
Section 38-2
The Small Intestine
Villus
Small Intestine
Circular folds
Epithelial cells
Villi
Capillaries
Lacteal
Vein
Artery
Villi and Microvilli in the Small
Intestine
• 5. The Large Intestine/Colon • These substances pass into appendix, a
small saclike organ
• Clogged and inflamed = appendicitis.
Removal needed.
• Large Intestine -11.5 long x 5 cm wide
- removes water from undigested
material
• Bacteria in colon produce needed
compounds, including Vitamin K.
• Antibiotics can destroy these beneficial
bacteria. (Eat yogurt!)
• Next - eliminate wastes. Go out rectum
and anus = feces
• Disorders:
• Diarrhea - not enough water is absorbed.
• Constipation - too much water is
absorbed - stays in colon too long.(Eat
fiber!)
• Colon polyps or cancer
Review:
Can you trace
this apple through
the digestive
system, naming
each organ and
enzymes involved?
Up Next: Now that we have digested, how
do we excrete our liquid wastes?