Transcript 9.4 Digestion in the Mouth and Stomach


4 main steps in digestion:
 Ingestion - the taking in of nutrients
 Digestion - the physical and chemical breakdown
of complex food molecules into smaller molecules
 Absorption - (the transfer of digested nutrients
from the digestive system to the bloodstream
 Egestion - the removal of waste food materials
from the body

Each animal species has
unique adaptations that
enable it to obtain and digest
food.

The mosquito, for example,
has specialized mouth
structures and a digestive
system that may be used for
sucking blood to obtain
nutrients

http://animal.discovery.com/tvshows/animal-planet-presents/videos/top-10bloodsuckers-female-mosquito.htm
Some simple animals,
such as flatworms or
jellyfish, have a
digestive sac with a
single opening into a
gastrovascular cavity.
 Nutrients are absorbed
by cells lining the cavity
and diffuse into all
other cells

More complex animals have a digestive tract that
has two openings—one for food intake and another
for waste elimination.
Ex. Earthworm
 food ingested in mouth travels through the pharynx
and into the esophagus.
 The esophagus then pushes the food into the crop
for temporary storage.
 Physical breakdown of the food is carried out by the
gizzard.
 The food particles pass into the intestine and are
chemically broken down into smaller molecules to
be absorbed by the cells lining the intestine
 Any undigested wastes eliminated through the
anus.


The human digestive system is
also a complete digestive
system. Unlike that of the
earthworm, the digestive tract
of humans is much longer than
the body (Figure 4).

Often referred to as the
gastrointestinal tract (GI tract),
the human digestive tract is
approximately 7 m to 9 m long,
depending on the age and size
of the individual.
Every organ system depends on the digestive
system for nutrients, but the digestive system also
depends on other organ systems.
 Muscle and bones, for example, enable animals to
catch and ingest food.
 The circulatory system transports oxygen and other
materials to the digestive organs, and carries
digested foods from the digestive system to the
tissues of the body.
 The nervous system and endocrine system regulate
the actions of the digestive organs. Digestion
involves interaction among several body systems.


Make a hypothesis about the evolutionary
origin of taste in humans?
The myth of the
tongue map;
that
1 tastes bitter,
2 tastes sour,
3 tastes salt,
and
4 tastes sweet.

In humans, digestion begins in
the mouth. Food is broken
down into smaller pieces by
the teeth (physical digestion).
Enzymes, like amylase begin
chemical digestion in the
mouth

Flat for grinding and crushing
food

Sharp for grabbing and
cutting food


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The type of teeth an animal has is
directly related to its diet.
Mammalian herbivores have many
molars for chewing plant matter
Mammalian carnivores have canine
teeth that allow them to grab and kill
prey.
HERBIVORE
CARNIVORE
http://www.youtube.com/watch?v=pNcV6yAfq-g
http://www.youtube.com/watch?v=pNcV6yAfq-g

The food stretches the
walls of the esophagus,
activating the smooth
muscles to undergo
rhythmic, wave-like
contractions called
peristalsis

sphincter the circular
muscle that
contracts to close an
opening in the body
There are more than 50 sphincters in the human
body, and several of these are in the digestive tract.
The gastroesophageal sphincter is located where
the esophagus joins the stomach. This sphincter
keeps food and acid from moving up the esophagus,
preventing acid reflux
 The pyloric sphincter is located between the exit
point of the stomach and the first part of the small
intestine (duodenum)

The stomach is an organ where food is temporarily
stored and chemical digestion continues.
 Gastric juice (2 L per day) provides the necessary
acidic environment for enzymes to function. It also
kills most of the bacteria or other micro-organisms
that enter the stomach. Gastrin is the major
hormone that regulates acid secretion in the
stomach.
 Mucus present in gastric juice helps protect the
stomach from acid damage.
 Food in the stomach activates nerves which release
signals that cause an increase in muscular
contractions, which mixes the food with gastric
juice.

Pepsinogen is secreted in the stomach and is
converted to pepsin, a protein digesting enzyme,
when exposed to the acid present in gastric juice.
 Pepsin begins the breakdown of proteins into
separate amino acids. Secreting the inactive
enzyme pepsinogen prevents damage to the
stomach tissue. If gastric glands were to make
pepsin instead of pepsinogen, the stomach would
digest itself.
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http://www.youtube.com/watch?v=URHBBE3RKEs
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Stomach acid is strong enough to kill most bacteria
that enter the stomach.

An ulcer is an open sore in the lining of the stomach
caused by the presence of H. pylori bacteria in the
stomach.

These bacteria prevent mucus-producing cells from
producing enough mucus to protect the stomach
lining

H. pylori may be transmitted through food or water,
but the bacteria have also been found in the saliva
of people with ulcers. H. pylori is usually successfully
eliminated with antibiotics.