DIGESTION
What is digestion?

The process in
which food is
broken down into
smaller molecules
that can be
absorbed into the
body and are
usable by cells.
Five Main Digestive Processes
1.
2.
3.
4.
5.
Ingestion – Eat; Intaking of food into
Digestive Tract
Movement – Food travels down digestive
tract.
Digestion – Large molecules  Small
molecules (mechanical or chemical).
Absorption – Transporting digested
nutrients to cells in the body.
Egestion – Removal of materials (waste)
from food that the body cannot digest.
Do you taste different
components of taste with
different parts of your tongue?
The “Taste
Map”: All Wrong
Tongue
Papillae
Circumvallate papillae
Taste Test!





You will be tasting flavoured candies.Yummy 
Catch! –You have to PLUG YOUR NOSE!
One student = facilitator, other = taster
Facilitator chooses 1 candy (don’t show the
taster!), unwrap it while the taster has their eyes
closed and put it in their hands.
60 seconds (keep your nose plugged!) – describe
sensations and try to determine the flavour of
the candy. Guess again after the min is up.THEN
unplug your nose... Switch roles and repeat.
**Remember keep the flavour a secret
until the end**
Taste
What is the difference
between taste and flavour?
 Does smell affect taste?
 If your sense of taste is
impaired, it is possible your
appetite might decrease.
 What things might decrease
your sense of taste?

◦ Cigarettes, illness, medications,
vitamin deficiencies
Why do we eat??
Nutrients!
Body needs energy to do work.
 Nutrients include

◦ Carbohydrates
 Provide energy (growth, warmth, movement).
◦ Proteins
 For growth of cells and tissues.
 Repair of damaged tissues.
 Source of energy if carbohydrates and fats
unavailable.
Nutrients cont…
◦ Fats
 Provide energy
 Two times that of carbohydrates

Nutrients help
◦
◦
◦
◦
in our growth,
by keeping us healthy,
by repairing our cells and tissues,
by giving us energy.
Enzymes : their role

Enzymes are used to digest food.
◦ Carbohydrase / Amylase
 Carbohydrates to Simple sugars.
◦ Protease
 Proteins to Amino acids.
◦ Lipase
 Fats to Glycerol and Fatty acids.
A) Importance of the Digestive
System


Humans/Animals need a digestive system in
order to obtain nutrients for energy.
Digestive system will:
Large
Complex
Molecules
Breaks down
E.g. Cracker (starch)
Small, simple
molecules
Glucose (used by our
cells in the body)
B) Organization of Digestive Tract
From mouth to anus, is on average, 6-9 m or 21-23
ft long.
 Organs are divided into two categories:
1. Gastrointestinal Tract (G.I.)

o
o
2.
Continuous tube from mouth to anus.
Includes: Mouth, esophagus, stomach, small intestine, large
intestine, rectum, anus.
Accessory Organs
o
o
o
Lie outside the G.I tract.
Produce secretions that help in digesting food.
Include: Teeth, tongue, salivary glands, liver, pancreas, gall
bladder, (appendix).
Food must be
mechanically
and
chemically
reduced
before it can
be absorbed
across the
intestinal wall.
Two Types of Digestion

Mechanical Digestion: The physical break
down of food into digestible chunks.
 E.g. Chewing with teeth.

Chemical Digestion: Chemical break down
of food to a form that can be absorbed
(usually by the blood stream).
 E.g. Enzymes cleaving substrates.
Teeth

Primary teeth vs. secondary teeth
Anatomy of a Tooth
Tooth
Enamel – White outer part of the tooth.
Is mostly made of calcium phosphate, a
rock-hard mineral.
 Dentin – has living cells, is porous, and is
like bone (softer than enamel)
 Pulp – the softer, living inner structure of
teeth. Blood vessels and nerves run
through the pulp.

Cementum – connective tissue (bone
like) that binds the root of the tooth to
the gums and jawbone.
 Crown – area of tooth that is visible
(enamel)
 Neck – Where the crown meets root.
Covered by gingiva (gums)
 Root – the anchor of the tooth

Tooth aches
500 species of bacteria inhabit the mouth.
 Certain bacteria thrive on sugar, and produce
lactic acid which destroys tooth enamel.

 Streptococcus mutans
Teeth Questions
What are three types of teeth? What are
they used for?
 Why do Cavities Hurt?
 Analyzing the teeth of animals is a good
indication of their diet. Explain why.
SciShow Videos
 Why do we have baby teeth?
 Why is flouride good for our teeth?
 Why do we have to brush our teeth? List
the two main reasons.

Root Canal
https://www.youtube.com/watch?v=jHHn
52KhBkQ
 https://www.youtube.com/watch?v=YDs848-u-U

Ingestion
and
mastication
Mouth (aka Oral cavity)
Only part of the alimentary canal involved
in ingestion
 Mechanical digestion (chewing) and
chemical digestion (enzymes in saliva)
start here

Tongue

Made up of groups of muscles that run in
different directions. This gives the tongue
its flexibility.

Mixes food with saliva to form a mass of
wet food called a bolus.

Initiates swallowing by pushing bolus
towards the pharynx
Tongue continued
The top layer of the tongue is covered
with a layer of bumps called papillae
 Papillae helps grips food and contains
taste buds

Taste buds

Can detect the following tastes:
◦
◦
◦
◦
◦
Sweet
Salty
Sour
Bitter
Umami
Why is the tongue important in
choosing the kinds of food you eat?

Tastes has a homeostatic function
◦ Promotes the intake of nutritious foods
that your body needs
◦ Protects you body from possible dangers
◦ Example: Natural poisons and spoiled foods
tastes bitter
Babies response to sour taste

http://www.dailymail.co.uk/news/article2392574/Photographers-April-MaciborkaDavid-Wile-capture-toddlers-reactionstrying-lemon-time.html
Check Your Understanding!
1)
2)
3)
What is the tongue? What function does
it perform?
How many different tastes can the
tongue detect? What are the tastes?
What kind of homeostatic function does
your tongue serve? Explain.
Salivary Glands

There are three types of salivary glands:
1. Parotid Glands
2. Submandibular Glands
3. Sublingual Glands
Salivary Glands continued

Serous cells produce amylase – splits
starch and glycogen into disaccharides
Salivary Glands continued

Mucous cells produce mucus – lubrication
during swallowing
The submandibular salivary glands are the squirters used in
“gleeking”!
“Gleeking” with submandibular gland at
base of lingual frenulum
Swollen
parotid gland
in child with
viral mumps.
This virus can
also infect the
testes.
Parasympathetic
innervation
stimulates salivary
gland secretion
(anticipation of tasty
food).
Sympathetic
stimulation inhibits
normal secretion,
which is why people
who are frightened
experience the
sensation of a dry
mouth.
Check Your Understanding!

Describe the chemical digestion that
occurs in the mouth

Mucus is found in saliva. What might its
function be?
Movement!!
Swallowing
Voluntary
 Tongue pushes bolus to back of throat
(Pharynx)
 Epiglottis closes off the trachea and food
travels down esophagus

Pharynx

The junction between nasal and oral
cavity, part of the throat
Esophagus

Esophagus is made of smooth muscle
that becomes stretched to help food
bolus move along.
•
Causes a wavelike contraction called
PERISTALSIS.
•
Reverse peristalsis = Vomiting
The wall of the esophagus contains both skeletal and smooth muscle.

Can you drink upside down?
Can you drink upside down?
Questions:
1. Is gravity needed to make fluids come down
the esophagus?
2. Can we drink while we stand on our head?
3. How does food go down the esophagus into
the stomach?
4. Why did the fluid not flow out of the mouth
when drinking upside down?
5. What is the muscle action called, which
pushes food into the stomach?
Movement cont.

Smooth muscle contractions also move
food through the rest of the digestive
tract.
Movement cont.

Smooth muscle contractions also move
food through the rest of the digestive
tract.
Digestion / Absorption
Sphincter
A sphincter is a ring of muscle that
controls the passage of material.
Relaxed = open, Contracted = closed
 At the junction of esophagus and stomach
is the cardiac sphincter (AKA Lower
Esophageal Sphincter). Stops stomach
contents from going into esophagus


At the junction of stomach and
duodenum is the pyloric sphincter.
Regulates movement of stomach contents
from stomach  small intestine.
Draw This!
Heart Burn
Caused by a cardiac sphincter that
doesn’t tighten as it should  stomach
acid into esophagus
 Often happens when too much food in
the stomach (overeating) or to much
pressure on the stomach (obesity,
pregnancy)
 Certain foods act as a trigger (relaxes the
sphincter or causes more acid production
 smoking causes both!)

The Stomach
Site of initial protein digestion and food
storage.
 Smooth muscle contractions cause
ingested food to be crushed, ground, and
mixed, liquefying it to form Chyme

Gastric Pits
Gastric Pits
Stomach contains GASTRIC PITS that
have GLANDS and MUCUS cells.
Glands contain:
 Parietal cells – secrete HCl (hydrochloric
acid)
 Chief cells – secrete pepsinogen,
the zymogen (inactive) form of the
digestive enzyme pepsin.(Pepsinogen 
Pepsin under low pH)


Pepsin breaks down proteins into short
amino acid chains
G cells – secretes gastrin, a hormone.
Gastrin stimulates the secretion of HCl and
aids in stomach motility.
 It’s released in response to stomach
stretching or the presence of proteins in
the stomach. It is inhibited by HCl in the
stomach.

What kind of feedback is this??
The J-shaped
stomach stores
food (the semidigested mass is
called chyme),
initiates the digestion
of proteins, has only
minimal absorption,
and moves materials
on to the small
intestine.
Absorption

Some water, specific vitamins and alcohol
Stomach Composition

The stomach has four layers that surrounds the
space called the lumen.
1)
2)
3)
4)

Mucosa
Submucosa
Muscle layer
Serosa
The stomach has folded membranes on the inside
called Rugae  allows stomach to expand
Why doesn’t the stomach digest
itself?
Mucus cells in the gastric pits secrete a
thick layer of mucus which protects the
walls of the stomach
 also secrete bicarbonate solution which
neutralizes stomach acid (acid base
reaction)

Peptic Ulcers
Peptic Ulcer
Most commonly caused by bacterial
infection  Helicobacter pylori
 NSAIDS (non-steroidal anti-inflammatory
drugs)  aspirin and IBProfen
 Smoking
 Alcohol
 Genetics

A Very Famous Stomach!
Alexis St. Martin, 1822
 https://www.youtube.com/watch?v=pqgcEI
aXGME

Mechanical vs Chemical recap
Mechanical – churning of stomach
Chemical :
 HCl  denatured proteins and kills
ingested bacteria
 Pepsin  begins protein digestion
Liver & Gall Bladder
Liver produces Bile  mainly water and
some bile salts
 Bile is stored in the Gall Bladder  the
gall bladder absorbs water making the bile
more concentrated
 Bile releases into duodenum via bile duct

Bile Salts

Emulsify Fats (Emulsify - To make a
suspension of small globules of one liquid in a
second liquid in which the first will not mix)
Bile continued
Mechanical digestion:

Emulsification – bile salts break down fat
globules into smaller droplets so that they
can be digested by enzymes.

Purpose – To increase surface area!
Check your understanding
What is the function of the 2 sphincters
in the stomach
 What role does each cell in the gastric pit
play?
 Describe the chemical digestion that
occurs in the stomach
 What is the main purpose of bile salts.
Explain.

Other Liver Functions
Regulate blood glucose levels (stores
glycogen)
 Breakdown and synthesis of lipids and fats
 Protein breakdown and amino acid synthesis
 Stores vitamins (A, B12, D) and iron
 Breaks down hormones, antibiotics, and
other toxic substances (detoxifier)
 Breaks down the by-products of RBC
recycling

Note** these are main functions. Liver is
thought to do about 500 separate functions
Gall Stones
Crystalline mass formed from bile
pigments, cholesterol, and calcium salts.
 Cause severe pain and blockage of bile
duct

Liver Cirrhosis
Most commonly caused by alcohol,
hepatits B, hepatits C, and fatty liver
disease.
 Gradual build up of scar tissue that
replaces normal tissue
 Leads to liver failure

Ethyl alcohol is toxic to the liver
Healthy Liver
Liver cirrhosis
Note extensive scarring
Cirrhosis of the liver
Chronic
alcoholism will
typically lead to
damage of the liver
characterized by
scarring. The damaged
liver often turns an
orange color. This
damage of the liver is
called “cirrhosis”.
Jaundice
One of the by-products of RBC
destruction is bilirubin (yellow color)
 The liver filters out bilirubin from blood,
and excretes in bile.
 If liver is failing, or bile duct is blocked,
bilirubin builds up in body, causing
jaundice  a yellowing of skin and whites
of eyes.

Gastrointestinal Disorder Project

So now that you
know (almost) a lot
about the normal
functioning of the
digestive system, it’s
time to investigate
some disorders!
Plagiarism
Source all the materials you use!
 In University if caught plagiarizing you will
automatically receive a zero on the
assignment with the potential of receiving
a failing grade in the course or a
suspension from the University!


http://www.youtube.com/watch?v=yQHx9
WEfT-Y&safe=active
Small Intestine
Small Intestine is 7 meters in length
• Three parts to small intestine:
1. Duodenum – first 25-30 cm.
- Area of most digestion.
2. Jejunum
3. Ileum
•
When chyme enters the small intestine it
stimulates the release of secretin and
cholecystokinin by the duodenum walls.
 Secretin regulates pH  inhibits gastric
HCl production and stimulates
bicarbonate ion secretion (pancreas)
Cholecystokinin causes release of bile
(gall bladder) and digestive enzymes
(pancreas).

Pancreas

Secretes pancreatic juice into the
duodenum
Pancreatic juice contains:

Bicarbonate –
◦ changes pH of chyme from highly acidic (pH
2) to weakly basic (pH 8)
◦ Important pH for pancreatic enzymes to
function
Enzymes
lipase - breaks down triglycerides into fatty
acids and glycerol.
•
Protease – to digest proteins
Amylase – to digest carbohydrates


Insulin
Glucagon
Regulation of
blood glucose levels
Check your understanding!

What accessory gland produces a
secretion with no digestive enzymes?

What kinds of foods are broken down by
the pancreas?

Most enzymes are secreted as zymogens
(inactive), why do you think that is?
Check your understanding!

Explain two functions of pancreatic fluid.

Someone recently has had a
cholecystectomy, a surgical procedure to
remove his gall bladder. Now he must
take medication to prevent diarrhea. Why
would the removal of the gall bladder
cause diarrhea?
Mesentery
Tissue that supports the intestinal tract.
 A double layer of connective tissue in
which blood vessels, nerves, lymphatics
and other structures are contained.

Thin walls of small intestine with blood supply.
Mesentery
Adhesions often
form following
abdominal surgery
or after an
abdominal
infection
(peritonitis).
Peritonitis can also
follow a penetrating
abdominal injury.

Small Intestine
Made up of three
parts:
◦ Duodenum
◦ Jejunum
◦ Ileum
Segmentation

Smooth muscle contractions in both
directions that mix and further break
down contents of small intestine (chyme)

Is this mechanical or chemical digestion?
Absorption
The small intestine absorbs the majority
of nutrients
 such as

◦ The breakdown products of
 Carbohydrates
 Protein
 Fats
◦ Vitamins
by active and passive mechanisms
Intestinal villi
Each villus contains blood capillaries
and a lymph capillary (lacteal). Each
villus is covered with microvilli.

Villi – tiny, finger-like projections on the
walls of the small intestine

Microvilli – “brush border”  further
increases surface area

Within villi structures are blood vessels
that carry the absorbed nutrients to the
rest of the body

Also contain in the villi are structures
called lacteal, which absorbs fats to be
delivered into the bloodstream
The Colon (AKA large intestine)
Main Functions of the Large
Intestine
Water absorption
 Absorption of vitamins produced by
bacteria
 Mass movements (defecation) – removes
undigested food

Chemical Digestion
Indigestible food matter (e.g. cellulose) is
digested by enteric bacteria (ex. E. Coli)
that thrive in the large intestine.
 These bacteria produce vitamin K and
some B vitamins.

Appendix
Vestigial organ  has lost function but
retained structure
 However, some scientists now think it
does serve a function stores good
bacteria to help repopulate gut after
infection.

http://www.flickr.com/photos/moonjazz/3530268320/
Endoscopic view of appendix
Cecum
Rectum

Connected to the sigmoid colon of the
large intestine

Damp Mass of indigestible food remaining
in large intestine is called FECES.

Temporarily stores feces before
elimination (egestion)
Anus
The ending portion of the gastrointestinal
tract in which feces (undigested food
matter) leaves the body
 Anal sphincter controls opening of anus.

Bowel Movement
Receptors in the walls of the large
intestine give the central nervous system
(brain) signals when a bowel movement is
needed.
 Some substances stimulate the bowel
movements like caffeine.

Defecation
to eliminate
feces.
Summary
Digestion Time Summary
Digestion takes different lengths of time depending on the food
being consumed. For healthy adults, it's usually between 24
and 72 hours.
◦ Mouth (20 sec)
 Starch is digested to maltose by carbohydrase / amylase.
◦ Esophagus (10 sec)
 Muscles squeeze food along the canal.
◦ Stomach (2-6 hours)
 Gastric juice mixes food when stomach churns.
◦ Small intestine (5 hours)
 Intestinal juice contains enzymes that complete the digestion process.
◦ Large intestine and anus (min of 24 hours)
 Undigested food reaches the large intestine
 Lots of water is removed and taken back into the body
Washing your hands is essential!
(Return to regular notes booklet for this)
Bacteria
 Food poisoning
 Parasites
 Worms (Tapeworms)
* All can be transferred
through the mouth!

The Bacteria in your Gut?
Good, bad or ugly?
Good √
E.coli helps you digest food that you
could not digest otherwise.
 Bad √
 The bacteria that help you out, also
produce flatulence as a by-product.
Gas is a normal part of digestion.
 Ugly √
 Some bacteria cause food poisoning,
resulting in severe stomach cramps,
vomiting and diarrhea.


More important stuff...

Our bodies make two hormones that
contribute to homeostasis.
1. GASTRIN: Releases gastric juice (HCl) and
relaxes gastric sphincter.
2. SECRETIN: Help release bicarbonate ions that
neutralize HCl.

Our pancreas also helps with homeostasis in
regulating blood glucose.
Insulin and Glucagon in Digestive
System
Two hormones secreted by pancreas.
 Work with liver to control level of glucose in
body (blood).
 Insulin released after meal  allows cells to
become permeable to glucose.
 Excess glucose stored by liver as glycogen.
 Can change back to glucose if blood glucose
becomes too low  Glucagon
