Digestive System - Salisbury Composite High School
Digestive System - Salisbury Composite High School
The main role of the digestive system is to metabolize
2 roles of metabolism are:
– Catabolic reactions: breakdown of molecules, energy is
– Anabolic reactions: the making/formation of a molecule,
energy is required
In the digestive tracts the following occurs:
Polmersmonomersabsorbed into the bloodcellsmitcondriaenergy (ATP)
Unlike plants, heterotrophs must consume large
organic molecules and break them down into
smaller molecules that can be transported by the
blood, absorbed and used in the body. This
process of digestion involves four distinct stages:
Ingestion: ‘eating,’ taking in food
Digestion: 2 types:
– Mechanical: Physical breakdown of food into smaller
pieces to increase surface area
– Chemical: breaking of the bonds by enzymes to make
Absorption: movement of food particles into the blood
Egestion: ‘pooping,’ removing waste
adults is about 6-9 m
long. It is responsible
for taking in, storing,
breaking down, and
absorbing food as well
as removing waste
2 ended: mouth anus
Food moves through this
system by peristalsis,
which is just a
Ingestion involves the taking in of nutrients by the
mouth. The early stages of chemical and
mechanical digestion also occur in the mouth as
food is taken in.
Food is taken into the mouth, combined with saliva
and chewed into a soft, slippery mass called a
Saliva – is a watery, slippery
fluid produced by the salivary
glands that contains the
enzyme amylase, responsible
for chemical digestion. This
enzyme breaks down complex
carbohydrates into simpler
sugars. The saliva also
dissolves food particles so that
they can stimulate the taste
buds, and it lubricates the food
bolus so it can travel through
the digestive system more
Teeth – are important for the
physical digestion of foods in the
mouth. The tongue pushes food
toward the roof of the mouth, and
the teeth break it up into smaller
bits. The canine and incisor
teeth are sharper and designed
for chopping and tearing food
while the molars are flat and
broad, designed for grinding food.
Through the teeth, past the gums, look
out stomach, here it comes!
Esophagus – is a long
muscular tube that
contracts in a rhythmic
contractions push the
food bolus towards the
stomach and the
remainder of the gastrointestinal tract.
Stomach – the stomach is a J-shaped sac with a
capacity of about 1.5 L that is also the site of food
storage and digestion. As food enters the stomach
from the esophagus, the cardiac sphincter contracts,
and closes, preventing the stomach contents from
moving back into the esophagus. At the bottom of the
stomach, the pyloric sphincter regulates the exit of
digested food into the small intestine. The stomach
secretes a number of digestive enzymes and gastric
juices to help in the digestion of food particles.
Digestive Secretions of the Stomach
Mucus – Comes from the mucous cells. coats the
inner lining of the stomach, protecting it, from its
own digestive juices.
Hydrochloric Acid (HCl) – comes from the parietal
cells. kills harmful bacteria in the stomach. ***HCl is
also important in activating the protein digesting
enzyme pepsinogen to become pepsin. As a result,
the pH of the stomach is about 1 – 2.
Pepsin – comes from the chief cells. enzyme
responsible for the digestion of proteins. Pepsin,
secreted as pepsinogen, is activated by the
presence of HCl. In the active form, pepsin breaks
down long chain amino acids into shorter chain
Rennin – an enzyme that causes milk to curdle.
Because milk is a liquid, it would pass through
the digestive tract too quickly for nutrients to be
Also, it is at the stomach where alcohol, some
drugs (Such as asprin) and vitamin B is
absorbed into the blood
When food finally exits the stomach and enters
the small intestine, it is now known as chyme.
Acid Reflux – aka “heartburn” is caused
by the movement of gastric juices
(acidic) back into the esophagus. This is
usually caused by failure of the cardiac
sphincter to close.
General Acid Reflux Shockwave™
Peptic Ulcers – are caused by
a breakdown of the protective
mucous lining in the stomach.
This causes lesions (sores) on
the stomach lining that are
irritated by the acidic
secretions in the stomach.
Ulcers are caused by stress,
diet and the bacteria
The stomach can be removed
with any real harm occurring
Digestion involves further chemical breakdown of
macromolecules into smaller components. Most
digestion takes place in the first 25-30 cm of the
small intestine, called the duodenum. Digestion is
primarily a chemical process that is helped by a
number of enzymes secreted by the pancreas,
liver and gallbladder.
Pancreas – when acids enter the small intestine, a
hormone called secretin is released from the
duodenum. This hormone stimulates the
pancreas to secrete enzymes that break down
the three major components of food: proteins,
carbohydrates and lipids.
Proteins – the inactive enzyme trypsinogen is
converted to an active enzyme, trypsin, by the
enzyme enterokinase. Trypsin breaks down
long chain polypeptides into shorter chain
peptides called peptones. A second enzyme
called erepsin is released form the pancreas to
complete digestion of proteins into amino acids.
Carbohydrates – the pancreas also releases
the amylase enzymes to continue with
carbohydrate digestion in the small intestine.
Lipids – lipase enzymes are also secreted from
the pancreas to digest fats into fatty acids and
Zoo 202: Digestive System
Also, the pancreas releases bicarbonate ions
which neutralize the stomach acids that flow into
the small intestine, so that it does not denature
the pancreatic enzymes
Liver and Gallbladder
Liver and Gallbladder – the liver continually
produces a fluid called bile that helps with fat
digestion. This fluid is stored in the gall bladder.
Fats in the small intestine stimulate the release of
a hormone cholecystokinin (CCK), which in turn
triggers the gall bladder to release bile salts.
These bile salts act as an emulsifying agent (like
soap), causing the fat droplets to be broken apart
into smaller particles. The increased surface area
produced by smaller droplets allows the lipase
enzymes to work more effectively.
Concepts in Biochemistry - Interactive Animations
Other Liver Functions
The liver breaks down hemoglobin from red blood
cells and stores the products in the gallbladder.
The resulting pigments give feces its characteristic
color. The liver also stores glycogen and vitamins
A, B12, and D. The liver also removes many
toxins and harmful substances from the body (like
More digestive problems…
Gallstones – crystals of bile salt
the form in the gallbladder.
These may block the bile duct
causing pain and impairing fat
Jaundice – yellowing of the skin
and tissues due to an
accelerated destruction of red
blood cells. Bile pigments are
not excreted and accumulate in
Cirrhosis – chronic inflammation
of the liver caused by nutritional
deprivation or infection.
The stomach absorbs some water, some
vitamins, medications and alcohol. Most
absorption however, occurs in the small
intestine. The small intestine is folded on the
inside, creating fingerlike projections called villi.
The villi are also lined with individual cells
arranged in long extensions of the membrane
called microvilli. Some of the nutrients are
absorbed into the capillary network by active
transport other nutrients are absorbed by
diffusion. Only amino acids, and
monosaccharides can be absorbed here!
Each villus is supplied with a capillary network
that intertwines with lymph vessels called
lacteals, where fats are absorbed. Only glycerol
and the 3 fatty acids are absorbed here!
Once food reaches the large intestine (colon),
chemical digestion is complete. The large intestine
then re-absorbs water, minerals and some
vitamins. Bacteria in the large intestine use waste
materials to make vitamins B and K. Undigested
waste materials accumulate in the large intestine
until a bowel movement is made. The movement
removes potentially toxic waste from the body and
is stimulated by un-digestible fibrous material in the
colon such as plant fiber.
Overview of Digestive Hormones