Digestive System
50 cm=
1.7 ft
Alimentary Canal
One long continuous tube
from mouth to anus
Small intestine
550- 600 cm=
18.3 – 20 ft.
Colon
150 cm=
5 ft.
Gall bladder, liver and
pancreas dump enzymes
into the canal via ducts
Two Phases of Digestion
Mechanical –
physically breaking down food
a. chewing (mastication)
b. churning
c. peristalsis
d. segmentation
e. propulsion
Chemicalusing enzymes to chemically break
down food
a. carbohydrates  monosaccharides
b. proteins  amino acids
c. fats  fatty acids and glycerol
Peristalsis vs. Segmentation
The Mouth
Saliva - 95 % water, 5% salivary amylase (breaks down carbs)
Starch  maltose (disaccharide)
Salivary Glands
1. Parotid- in front of ear;
ducts empty near second
molars in upper jaw
2. Submaxillary- at angle of
jaw; ducts empty near bottom
molars
3. Sublingual- ducts empty
under tongue
The Teeth
Children= 20 deciduous teeth
Adults= 32 teeth (including 4 wisdoms)
** enamel is the hardest substance in the body
The Esophagus
about 1 foot long (30 cm)
Connects mouth to stomach
Coats food with mucus=
Bolus- mucus covered food ball
Moves food to stomach by peristalsis
Pushing food to the stomach via peristalsis
The Stomach
Made of 3 layers of
muscles- running in
different directions
Inside lining has
mucosal folds
(rugae) with
gastric glands
Protein digestion begins here
Gastric fluids (secreted by gastric glands):
a.
pepsin- breaks down proteins (only at low pH)
b. HCl- activates the pepsin
c. mucus- protects the lining of the stomach
Food usually stays in the stomach for 2-6 hours
The stomach churns the food to a green pea soup consistency= chyme
then sends it to the small intestine
Main
cause of
ulcers=
bacterium
The Small Intestine
Main function: chemical digestion
absorption of nutrients from chyme
3 sections:
1. Duodenum- shortest section;
only about 25 cm (10 in.)
•enzymes empty into this
section via ducts;
neutralizes chyme
2. Jejunum- middle section
-8 ft.
bulk of chemical digestion
and nutrient absorption
occurs here
3. Ileum- joins large intestine
-10 ft.
absorbs vitamin B12 and bile
salts and whatever products
of digestion were not
absorbed by the jejunum
The Small Intestine
One layer of
epithelial cells
Villus= fingerlike projection where
food is absorbed into bloodstream
or lymph vessels
4 enzymes secreted by the small intestine:
Uses peristalsis to move
food along and segmentation
to break it up.
a. peptidase- breaks down protein
b. maltase- breaks down maltose
c. lactase- breaks down lactose
d. sucrase- breaks down sucrose
The Liver and Gall Bladder
Liver- makes bile
These organs are not
directly on the alimentary
canal; their ducts empty
into the small intestine
Pancreas- has exocrine and endocrine
functions
secretes digestive enzymes (exocrine):
Gall bladder- stores bile
a . trypsin- breaks down protein
b. lipase- breaks down fat
c. amylase- breaks down carbs
The Large Intestine
bands of
longitudinal
muscle
fibers
Instead of having the
evaginations of the small
intestine (villi), the large intestine
has invaginations (the intestinal
glands). While both the small
intestine and the large intestine
have goblet cells that
secrete mucin to form mucus in
water; they are abundant in the
large intestine.
No digestive enzymes are secreted here
Main purpose= reabsorb water back into
bloodstream
About 1.5 meters long
Feces= undigested cellulose (plant cell
walls), fats, connective tissue, bacteria,
mucus, unabsorbed food
Uses peristalsis to move material toward
anal sphincter (made of skeletal muscle)
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