Transcript Ingestion and Digestion - This area is password protected

Ingestion and Digestion
Ingestion and other Mouth
Events
• 3 important events take place in your mouth
(oral cavity):
– mechanical digestion starts the teeth cut, tear,
crush, and grind the food
– chemical digestion starts salivary amylase
begins the hydrolytic digestion of starch
– the food is moistened and lubricated for the
journey through the esophagus (saliva is mainly
water, water is a good lubricant!)
Incisors: cutting &
biting
Canines: tearing
Premolars: grinding
Molars: crushing
The tongue
• Moves food around for chewing proper
type of tooth can be utilized
• Taste buds are located here important for
determining if food is spoiled
• forms chewed food into a bolus for
swallowing
• a giraffe’s tongue is up to 50 cm in
length and can be used to clean the
inside of its own ears!
Saliva and the salivary glands
• there are 3 pairs of salivary glands
• salivary glands are exocrine glands, they
are under the control of the nervous system
• there are 2 types of glands in the body:
exocrine and endocrine
– exocrine: secretes product onto an epithelial
surface (e.g. lining of digestive tract, skin,
mouth) may have a duct
– endocrine: secretes hormone directly into blood
4 important ingredients of saliva
and their functions
• salivary amylase (also called ptyalin)begins the
break down of cooked starch molecules
produces maltose
• water  moistens food which aides in movement
through the esophagus (swallowing)
• mucin slippery lubricant that also aides in
movement of food
• bicarbonate ions buffer the pH of the oral
cavity so that it remains near neutral even when
you eat acidic food
A Spitacular Saliva Fact:
• An adult produces from 1 to
2 litres of saliva in a day
Starch molecule
Remember that starch is a polymer
of glucose
Amylase causes the hydrolysis of starch
to maltose two glucose molecules
joined together
From mouth to stomach
• Tongue pushes food to the pharynx (fancy
term for throat)the food has been shaped
into a ball called a bolus at this point
• air and food both pass through here  air
on its way from oral or nasal cavity to the
lungs via the trachea
• food to the stomach via the esophagus 
swallowing
• Breathing and swallowing must be
separated—even a small amount of water or
food in breathing passages can cause
blockage “café coronary”
The Specifics of Swallowing
• Swallowing is a reflex action  you don’t
have to think about it
• When bolus is swallowed the soft palate
(uvula) is forced upwards  sealing off the
nasal passageway
• Nerves in the pharynx sense contact with
the bolusstimulates glottis to close and
the movement of the bolus down the throat
pushes the epiglottis over the glottis to
protect it further from the entry of food or
H2O
Uvula, Glottis, Epiglottis
This person has a bifid
uvula (unusual but not
uncommon)
This is the glottis 
(opening to the larynx)
The Glottis is bounded by the
vocal cords
The Specifics of Swallowing
Continued…
• Food bolus passes from the pharynx to the
esophagus  usually collapsed but opens
when swallowing occurs
• Peristalsis pushes the food down the
esophagus (peristalsis is important in other
areas of the digestive system too)
• Esophagus passes through chest (thoracic)
cavity and diaphragm to the stomach
• The food is not changed in anyway by the
esophagus—its just a tube
The Particulars of Peristalsis
• Involves two layers
of muscle—circular
muscles (inner) and
longitudinal muscles
(outer)
•Circular muscles in
front of bolus relax
while those behind it
contract
It takes approximately 8 seconds for
a peristaltic wave to reach the
stomach peristalsis continues here
Reverse Peristalsis is also
possible… Drinking is very
bad boys and
girls…
Before the Food Enters the Stomach
There Is One More Obstacle…
• The food must pass through the cardiac
sphincter (although not considered a “true”
sphincter by some sphincter snobs)
• Sphincters are circular muscles that acts as
valves
• Contract: close
• Relax: open
• There is also a sphincter at the other end of the
stomach the pyloric sphincter
Of Course fans
of Wayne’s
World know
the location of
another
sphincter in the
body…
The Stomach…more physical
and chemical digestion
An Empty Stomach
Rugae:
folds that allow
the stomach to
expand as it
fills with food
Physical digestion in the stomach:
• Peristalsis: the rhythmic muscular
contractions of the muscular walls of the
stomach mix the food with gastric juice
• Capacity of the stomach is approximately 1
litre
• Gastric juice is made by the gastric glands
which line the walls of the stomach
Contents of Gastric Juice
• HCl (hydrochloric acid)
gives stomach its low
pH (2--very acidic)
• pepsin an enzyme
that begins the
breakdown of proteins
• mucus made by
Goblet cells in the
lining of the stomach
What the HCl does and does not
do...
• Does activate pepsin pepsin only works at low pH
(acidic conditions)
• the chief cells make pepsinogen (inactive)
converted to pepsin by HCl
• Does kill most bacteria that may have been in the
food
• Does breaks down connective tissue in meat/bone
• Does not digest food!!!
A pH of 2 and a enzyme that
digests proteins How do the
stomach walls survive?
• The thick layer of mucus that lines the walls
produced by the goblet cells
• A gastric ulcer results when the wall is not
protected by mucus
• we know now that most ulcers are caused
by a bacterium  Helicobacter pylori
Summary of the 4 main functions
of the stomach
• Physical digestion of food: the churning of
the stomach is like a blender liquefies
solid food surface area increased even
further!
• Partial chemical digestion of proteins
• kill bacteria in food
• storage of food
The food leaves the stomach in
spurts as chyme a thick soupy
liquid
• Digestion will be finished in the first section
of the small intestine  the duodenum:
approximately the first 25 cm of the small
intestine
• mainly chemical digestion take place here
but there is one nutrient that will still need
to be physically broken down after the
pulverizing in the stomach fats
Bile is released into the
duodenum and emulsifies fats
Bile
Big
glob
of fat
Increased
surface area
of fats
A Whack of Digestive Enzymes
are active in the Duodenum...
•
•
•
•
•
Specific enzymes for: fats
disaacharides
starch
proteins
nucleic acids
• Bile is not an enzyme
Did you get that???
BILE IS NOT AN ENZYME!!!
Bile is involved in the physical
breakdown of fats emulsification is
not a chemical change it is a physical
change
Digestion finishes in the
duodenum portion of the small
intestine --the other function of
the small intestine is absorption
• Absorption is the movement of water,
nutrients, and other substances (toxins,
poisons, synthetic pesticide residues) from
the digestive system into the circulatory
system