1) Ingestion: voluntary process
of placing the food in the
mouth.
 2) Propulsion: food being
moved from one organ to the
next by peristalsis (involuntary
alternating rings of muscle
contraction to squeeze food
through a tube ex: swallowing)
 3) Mechanical Food Digestion:
chewing and segmentation
are examples of physical
processes that break food
apart. Segmentation is a
process that moves the food
within an organ in order to mix
it with digestive juices.

4) Chemical Food
Digestion: sequence of
steps that uses enzymes
to break down
macromolecules into their
building blocks.
 5) Absorption:
transportation of nutrients
from the digestive tract
into the blood stream and
lymph to be circulated
and used throughout the
body.
 6) Defecation: elimination
of indigestible materials.



Some food that is
digested and
nutrients that are
absorbed by the
body are used to
create new cell
structures or replace
worn out cells but
most are used as
metabolic fuels to
create ATP.
A kilocalorie (C) is a
measure of the
energy value of food.


Nutrients are
substances in food that
are used by the body
for normal growth,
maintenance, and
repair.
The six major nutrient
categories include
carbohydrates, lipids,
and proteins which
make up the bulk of
what we eat, vitamins
and minerals which are
needed in minute
amounts, and water
which makes up about
60% of the food we
eat.

Carbohydrates:
› Sugars and starches are derived
from plants with the exceptions
being milk sugar (lactose) and
glycogen in meat.
› Sugars come from fruits, sugar
cane, and milk. Polysaccharide
starches are in grains, legumes,
and root vegetables.
› Polysaccharide cellulose is
found in most vegetables but
the body cannot digest it.
Instead this is used to add
roughage (fiber) and to
increase the bulk of feces to aid
in defecation.

Lipids:
› Most lipids that are
ingested are neutral
fats called triglycerides.
› Saturated fats are
taken in from animal
products such as meat
and dairy and a few
plants such as coconut.
› Unsaturated fats are
present in seeds, nuts,
and most vegetable
oils.
› Cholesterol is found in
egg yolk, meats, and
milk products.

Proteins:
› Animal products contain
the highest quality
proteins that because
they contain all of the
essential amino acids
needed by humans for
tissue repair and growth.
This is called a complete
protein.
› Plant products such as
beans, peas, nuts, and
cereals are also protein
rich but they are
incomplete proteins
because they are missing
at least one of the
essential amino acids.

Carbohydrates are
usually broken down to
make ATP. Fats are
broken down and used
to build membranes,
insulate and cushion
vital body organs, and
to create the myelin
sheath of nerve cells.
They also serve as the
main source of energy
for making ATP when
carbs are inadequate.
Proteins are hoarded
by the body and used
to create cell structures
and enzymes.


Vitamins: Organic
nutrients that are required
by the body in small
amounts. Most work as
coenzymes or molecules
that help enzymes
perform their task.
Minerals: inorganic
substances including
calcium, phosphorus,
potassium, sulfur, sodium,
chloride, and
magnesium. Fats and
sugars have almost no
minerals, cereals and
grains have very little, and
the best sources are
vegetables, legumes, and
meats.

Metabolism refers to all
of the chemical
reactions that take
place in the body
including catabolism or
the breaking down of
large substances and
anabolism or the
building of complex
structures.

The main process used to
break down carbs is cell
respiration. In this process
glucose (blood sugar) is
broken apart into CO2
releasing high energy
electrons and hydrogen
ions. The energy from the
electrons and H+ ions is
used to attach ADP and a
third phosphate creating
ATP. The electrons and
hydrogen are then
attached to an oxygen
molecule to make water.
This process occurs in the
mitochondria and
produces 36 ATP for each
glucose molecule.

Because glucose is the
major source of energy
for the cell maintaining a
homeostatic balance in
the blood is essential. If
there is too much
(hyperglycemia) the
glucose is converted to
glycogen and stored in
liver and muscle cells. If
the problem continues
then the excess sugar is
converted to fat and
stored. If the glucose
level gets too low then
the liver breaks down the
stored glycogen for cell
use.


The liver breaks down fat
for ATP synthesis and to
make lipoproteins,
cholesterol, and
thromboplastin (a
clotting protein). It then
releases the rest into the
blood for body cells to
remove fat pieces and
cholesterol to create
membranes and steroid
hormones.
To be broken down to
make ATP fat is
converted to acetic
acid and then broken
down to release CO2 in
the mitochondria the
same as glucose.

When there are insufficient carbs the
breakdown of fat is accelerated but
incomplete. The substances that are
left accumulate in the blood making it
acidic and giving the breath a fruity
odor. This is common in uncontrolled
diabetes and starvation.

Proteins are broken into amino acids during digestion and
taken to the liver. Once the liver has had enough the
amino acids are transported to the other cells by the
blood stream. The cells use these to build proteins such as
enzymes, membranes proteins, mitotic spindle fibers,
muscle proteins, mucus, and hormones. The cells hoard
amino acids for future use because they are incapable of
making proteins without all 20 amino acids.

The liver :
› manufactures bile for
›
›
›
›
›
fat emulsification in the
small intestine
detoxifies drugs and
alcohol
degrades hormones
removes ammonia and
converts it to urea
makes cholesterol for
the construction of
hormones and plasma
membranes
processes nearly every
nutrient absorbed by
the digestive system
› Maintains glucose levels:
the liver removes excess
glucose from the blood
and constructs
glycogen to store it in a
process called
glycogenesis. Liver cells
will break down this
glycogen in times of
need in a process
called glycogenolysis to
put glucose into the
blood. They can also
create glucose from fats
or proteins in a process
called gluconeogenesis
if necessary.
› Makes blood proteins
such as albumin (holds
fluid in the blood to
prevent edema),
clotting proteins, and
lipoproteins which help
transport water insoluble
substances such as fats
and cholesterol through
the blood stream

The hypatic portal
circulation brings
nutrient rich blood from
the digestive system
directly to the liver. This
ensures the livers needs
are met first.
The alimentary tract also
known as the
gastrointestinal (GI) tract is
a continuous hallow tube
that is open at both ends.
This includes the mouth,
pharynx, esophagus,
stomach, small intestine
and large intestine.
 Accessory organs are used
to aid in digestion but are
not part of the path of food
such as glands, teeth, the
pancreas, gallbladder and
liver.

Lingual frenulum: attaches tongue limiting
posterior movement.
 Teeth tear and grind food. The
deciduous/baby/milk teeth emerge
between 6 months and 2 yrs. As perminant
teeth develop the root of the baby tooth is
reabsorbed so the tooth loosens and falls
out. Food enters the mouth, is mechanically
broken down by the tongue and teeth,
chemically broken down by amylase
(starch  maltose) and voluntarily
swallowed.




Pharynx: peristalsis begins here. The alternating
contractions of the two layers of muscle push
food through the pharynx to the esophagus
involuntarily. This process is controlled by the
parasympathetic nervous system.
Esophagus: involuntary peristalsis continues to
push food down to the stomach. Because of
the constant abrasion the esophagus is lined
with stratified squamous cells while the rest of
the GI tract has simple cuboidal or columnar.
Glands: produces saliva which contains mucus
and serous fluid. Serous fluid contains salivary
amylase that starts to digest starch. This mix
helps moisten and bind food together into
bolus to be swallowed, the lysozyme and
antibodies inhibit bacteria and dissolves food
chemicals to allow taste.






Crown: covered in enamel which is made with
calcium salts to be very hard.
Dentin: bone like bulk of tooth.
Pulp cavity: contains pulp that has blood
vessels, connective tissue and nerves that
supply the tooth with nutrients and sensation.
Cementum: attaches root to the periodontal
membrane.
Periodontal membrane: ligaments that hold
tooth in the jaw bone
Root canal: creates path for blood vessels and
nerves to pulp cavity




Mucosa: inner most lining that is moist and
includes epithelium, connective tissue and
smooth muscle, can be folded to increase
surface area for ansorption
Submucosa: second layer that contains blood
vessels to provide nutrients, nerve endings,
lymph nodules, and vessels.
Muscularis externa: two layers of muscle one
circular and one longitudinal that alternate
contraction to create a wave of motion
Serosa: outer most layer that may be modified
into a membrane that is used to anchor the
organ in place






Cardioesophageal sphincter: opening through which food enters the
stomach from the esophagus
Layers of muscularis externa that move the food through the stomach
and churn in the mix it with digestive juices to break down
Rugau: folds of mucosa that appear when the stomach is empty
Pylorus: peristalsis of this portion pushes chyme through the sphincter
Pyloric sphincter: opens slightly to allow small amounts of chyme
through. Takes 4-6 hrs to empty stomach contents.
About 25 cm long and able to expand to hold 4 liters the stomach acts
as a storage tank, site of chemical protein digestion, and site of
mechanical digestion. After the stomach processes food it resembles
heavy cream and is called chyme. Production of gastic juices is
regulated by the parasympathetic nervous system that is stimulated by
the sight, smell, and taste of food and by hormone gastrin that is
produced when food enters the stomach changing the pH. This
hormone encourages the glands to produce more gastric juices.
Normally the stomach produces 2-3 liters a day. The stomach does not
absorb nutrients other than things like alcohol and aspirin.






Gastic gland: produces gastric juices to begin
chemical digestion of food
Chief cells: produces protein digesting enzymes like
pepsinogen
Gastric gland duct: transport juices to the surface
Parietal cells: produces hydrochloric acid (HCl) which
raises the acidity of the stomach activating enzymes
like pepsin
Mucous neck cells: produce a sticky alkaline
substance that coats the stomach lining to protect it
from the HCl and digestion enzymes like pepsin
Simple columnar epithelium: produces mucus

Creates enzymes that complete
macromolecule breakdown once in the
duodenum. Amylase finishes the break
down of sugars that started in the mouth.
Trypsin, chymotrypsin, and
carboxypeptidase carry out half of the
protein digestion. Lipase completely breaks
down lipids and nuclease breaks down
nucleic acids. Bicarbonates produced here
help to neutralize the chyme from the
stomach and activate the enzymes.
Made of four lobes the liver makes bile.
Bile works like a detergent to emulsify
(break apart) large fat globules into
smaller fat globules providing more
surface area for enzymes to work on.
Also helps absorb fat and fat soluble
vitamins like K, D, and A once in the small
intestine.
 Gallbladder: stores and concentrates
bile


Produces “brush border” enzymes that
help break down sugars. Also produces
the hormones secretin which travels
through the to stimulate the pancreas
and liver to increase output and the
enzyme cholecystokinin (CCK) that
prompts the gallbladder and pancreas
to release stored substances.