Download BL 1021 * Unit 1

BL 1021 – Unit 4.1 - 4.5
The Digestive System
4.1 Nutrition Types
• All animals are ingestive heterotrophs, meaning
they consume organic molecules that can then be
used to manufacture their necessary molecules or
can be used for necessary metabolic reactions.
• These organic molecules are found in the food that
animals eat. However, depending on the type of
food, animals will consume different types of
organic molecules. (Recall the organic molecules
important for life include proteins, nucleic acids,
carbohydrates and lipids).
4.1 Nutrition Types
• Herbivores are animals that consume plant material
only. Because plants contain cell walls, these
animals must have a way of breaking through the
cell walls to acquire the nutrition. They will have long
digestive tracts because the digesting and
processing of plant cells requires more work.
• Carnivores are those animals that eat meat. They
are predators and have adaptations such as sharp
pointy teeth for ripping and tearing flesh which is
high in protein.
• Omnivores are animals that consume both plant
material and other animals.
4.2 Animal Nutrition Process
• No matter the type of food consumed or the type
or lack of digestive system, all animals go through
four stages in their overall nutrition.
• Ingestion, the first stage, is the consumption of food
through a mouth. The mouth will often have
adaptations for catching food (tentacles) or
chewing (teeth, jaws) to increase surface area and
mechanically break the food apart.
4.2 Animal Nutrition Process
• Digestion. The process of digestion, the second
stage, involves the use of enzymes to chemically
break the food into their monomers.
• Proteins are broken down to amino acids,
carbohydrates to single sugars, etc.
• Digestion happens outside of the cells of the body.
Even though the digestive tract is inside an animal,
the actual digestion takes place in the cavity inside.
The cells of the digestive tract take up the fully
digested food molecules.
4.2 Animal Nutrition Process
• Absorption is the third stage in which the individual
monomers that resulted from the digestion are
absorbed through the tract and transported
wherever they are needed.
• Elimination. Any material not absorbed is
considered waste and is excreted (in solid form as
feces) in the fourth stage of elimination. Elimination
should not be confused with excretion. Excretion is
the removal of products made from the bodies
chemical reactions. Excretion involves the expelling
of urine or similar substances.
4.3 Human Digestive System
• The human digestive
tract begins at the
mouth cavity where
food is ingested. Teeth
are present to aid in
mechanical
breakdown of food.
• Mechanical digestion
physically breaks down
food.
4.3 Human Digestive System
• The salivary glands
release saliva. This
serves as a lubricant for
the food. The saliva
also contains enzymes
to begin carbohydrate
digestion, buffers to
stabilize pH, and
antibacterial agents to
help in the prevention
of tooth decay.
4.3 Human Digestive System
• Saliva begins the
process of chemical
digestion – the
breaking of chemical
bonds in food to make
it into the simpler forms
the body can use. Most
parts of the digestive
system have both
chemical and
mechanical digestion.
4.3 Human Digestive System
• The food, once
chewed, is
manipulated by the
tongue into a ball
called a bolus.
• The bolus is pushed
down into the
esophagus; a tube that
connects the mouth
cavity to the stomach.
4.3 Human Digestive System
• Smooth muscle exists in
the walls of most of the
digestive system. This
tissue causes periodic
contractions of the
tract that squeeze, mix
and push along food.
These waves of
contractions are called
peristalsis.
4.3 Human Digestive System
• The entrance into the
stomach is called the
cardiac sphincter which
opens to allow food to
enter and then closes.
• Once within the stomach,
longitudinal and circular
muscles within the
stomach 'churn' the food
and the enzymes are
released to continue
chemical digestion.
4.3 Human Digestive System
• The combination of
hydrochloric acid and
digestive enzymes will
begin to break down
proteins as well as
carbohydrates.
• The mixture, at this
point, is extremely
acidic and is a soupy
mixture known as
chyme. It remains in the
stomach digesting for
approximately six hours.
4.3 Human Digestive System
• The sphincters at the
entrance and exit of
the stomach are
important. If the
cardiac sphincter
malfunctions, chyme
will move back into the
esophagus, causing
heartburn and possibly
damaging the tissues of
the esophagus.
4.3 Human Digestive System
• After a while, the
chyme will leave the
stomach through the
pyloric sphincter and
into the small intestine.
• The duodenum is the
top portion of the small
intestine and also aids
in the chemical
digestion of proteins
and fats.
4.3 Human Digestive System
• Accessory glands, such
as the liver, gall
bladder, and pancreas
surround the
duodenum producing
enzymes and releasing
them into the
duodenum to aid
digestion.
4.3 Human Digestive System
• The remainder of the
small intestines are the
jejunum and ileum. In
these two sections, the
final stages of digestion
occur and food
molecules are now
ready to be absorbed.
• Throughout the small
intestine, food is mixed
and pushed along by
peristalsis movements.
4.3 Human Digestive System
• After the small intestine,
the food enters the large
intestine. At this point, the
majority of nutrition has
been extracted from the
food.
• Along the way, a large
amount of water has
been added to the food
(saliva, acids, etc.) and it
is now reabsorbed to
reduce the water lost in
feces.
4.3 Human Digestive System
• After the final journey
through the large
intestine, the undigested
material collects in the
colon until it is eliminated
as feces.
• Feces contains
undigested food and
leftover digestive
materials (acids, bile,
etc.) only. Feces does not
include other wastes
made from metabolic
activity.
4.3 Human Digestive System
• The overall purpose of the digestive system is to
isolate and break down complex organic
molecules into the building blocks needed to build
similar materials.
• As such, animals recycle organic materials (the
protein in it’s food will become proteins in itself).
4.4 Types of Digestive Tracts
• In very simple animals, there is a incomplete
digestive system with only a single-gated cavity
where digestion takes place. In phyla such as
cnidaria and platyhelminthes, a single mouth/anus
gates a cavity that performs all four stages of
digestion with no specialization.
• This is much less efficient than the specialized
digestive regions seen in a complete digestive
system. In incomplete systems, food and waste will
mix, while in a complete system food will flow only
one way.
4.5 Nutrition Problems
• Obesity occurs when an organism obtains too much
stored energy and thus its height to weight ratio goes
outside the norm. This causes strain on the
cardiovascular system.
• Undernutrition occurs when an organism does not get
enough food to obtain enough energy to perform all its
functions. This will cause the organism to have to break
down fat stores (and ultimately muscle) to support itself.
• Malnutrition refers to an organism that is not receiving
enough of one or more particular nutrients. The organism
may have enough calories to live but certain types of
function may be impaired (iron deficiency, low-protein
diet, etc.)