Digestive System
Overview
Motility and Mechanical Processing
Secretion & Digestion
Absorption
Elimination
Hormones
Vitamins & Minerals
Overview
The whole goal of
digestion is to produce
monomers (i.e. glucose)
that can be used in cellular
respiration.
 Gastrointestinal (GI) tract
is a hollow tube with
accessory organs.
 Lumen = inside of the
tube. It is still considered
outside of the body.

Overview

5 basic tasks:
1.
2.
3.
4.
5.
Mechanical processing
and motility
Secretion
Digestion
Absorption
Elimination
Overview

5 accessory glands:
1.
2.
3.
4.
5.
Wall of the GI tract
Salivary Glands
Liver
Gall Bladder
Pancreas
Overview

4 layers of the
digestive tract:
1.
2.
3.
4.

Mucosa
Submucosa
Smooth muscle
Serosa
Sphincters control
rate of flow and
prevent backflow.
Motility and
Mechanical Processing

Motility (mvmt)
Peristalsis = wavelike
contractions that move
food
 Segmentation = slower
mixing in the small
intestine that allows for
increased absorption

Motility and Mechanical Processing
 The
breakdown of food into smaller pieces by
mashing and mixing.
 2 main locations:
 Mouth:
 32
teeth and tongue form a bolus
 Swallowing is both voluntary and involuntary
 Stomach:
 Mixes
food with chemicals ultimately making chyme.
Secretion and Digestion



Each organic macromolecule is broken
down by different enzymes at different
locations in the digestive system.
Often many enzymes are involved in the
breakdown of one molecule.
These enzymes operate within a narrow pH
range.
Secretion and Digestion

Carbohydrate Digestion:



Starts in the mouth when salivary amylase, produced
by the salivary glands, breaks down polysaccharides
into oligosaccharides and disaccharides.
Then in the sm intestine pancreatic amylase, produced
by the pancreas, breaks down polysaccharides into
disaccharides and monosaccharides
Finally disaccharidases from the intestinal lining finish
the breakdown into monosaccharides.
Secretion and Digestion

Protein Digestion:




Starts in the stomach with pepsin & HCl being produced by the
stomach lining. This breaks the proteins into protein fragments.
Trypsin and chymotrypsin are produced by the pancreas and
continue the breakdown of proteins into fragments in the sm
intestine.
Also produced by the pancreas, carboxypeptidase also works in
the sm intestine but it breaks proteins further into amino acids.
Aminopeptidase, although produced by the intestinal lining
plays the same role as carboxypeptidase.
Secretion and Digestion

Fat (Lipid) Digestion:


Digestion of fat does not begin until the sm intestine
where the liver is pumping in bile. Bile can be stored
in the gall bladder when not in use and it emulsifies fat
so that it does not glob up.
Lipase is a pancreatic enzyme that is released into the
sm intestine that finishes the breakdown of fats into
fatty acids and glycerol molecules.
Secretion and Digestion

Nucleic Acid Digestion:

Begins in the sm intestine where pancreatic nucleases
and intestinal nucleases break the DNA & RNA into
nucleotides and ultimately into the bases and
monosaccharides that make them up.
Absorption
 Almost
all absorption
occurs in the sm
intestine.
 Villi
 Microvilli
 Substances are
absorbed by active
transport, osmosis, and
diffusion.
Elimination





Large intestine (aka colon)
= absorbs essential salts
and remaining water
Cecum (including the
appendix)
4 parts
Feces = undigested/
unabsorbed food, water, and
bacteria
Rectum
Hormones



Many hormones dictate
when and how food is
digested.
Ex) gastrin increases HCl
production when aa.s are
detected in the stomach.
Ex) cholecystokinin (CCK)
increases pancreas
secretions and gall bladder
contraction.
Hormones
Ex) secretin causes
increased bicarbonate
production
 Ex) glucose
insulinotropic peptide
(GIP) triggers release of
insulin by the pancreas.


View 41Bin Campbell simulation
Vitamins & Minerals

Vitamins = organic substances essential for growth and
survival.
Ex) vit-D = bone growth; enhances Ca absorption
 Ex) vit-C = antioxidant; collagen synthesis; etc.


Minerals = inorganic substances also essential for growth
and survival
Ex) Ca = bone formation; neural and muscle action
 Ex) Fe = hemoglobin; ETC
 Ex) K & Na = muscle and neural function


Shortages or excesses of vitamins and minerals can have
adverse effects.