Transcript Digestive System

Digestive System
A closer look
Digestive Processes
In order for our bodies to use the food we
eat to grow, energize, and repair our cells,
5 digestive processes have to occur.
These include:
Ingestion
Movement
Digestion
Absorption
Egestion (excretion)
Digestive Processes
These processes occur at different
locations along the digestive tract, which is
a continuous tube from mouth to anus.
We are going to discuss what happens at
each site as we go through the stages.
It will be useful to copy the following
concept map and to keep adding to it as
we add more details to help you stay
organized.
NOTE: This should be a straight line in your notes
Stomach
Small
Intestine
Large
Esophagus
Intestine
Tongue
Rectum/
Mouth/
Throat
Teeth
Salivary Glands
Anus
Digestive System
Includes organs which perform
digestion tasks:
Digestive Tract (Gastrointestinal Tract, G. I.
Tract) includes: mouth, esophagus, stomach,
small intestine, large intestine or colon, and
anus.
 Accessory Structures include:, tongue,
salivary glands, liver, gall bladder and
pancreas.
Digestion
The process in our bodies that
breaks down food for use by our
cells. This is done in two ways:
Mechanical: our teeth chewing
through the food
Chemical: enzymes breakdown food
into absorbable molecules.
Mouth (where it all begins)
 Four main parts
of the mouth
Teeth
Tongue
Salivary Glands
Hard and Soft
Palates
Hard Palate
Uvula
Mouth
 Teeth (Chewing)
Mechanical Digestion
Are covered by enamel,
the hardest structure of
the body
Their movements slice,
tear, grind and mix food
Incisors: snap off
pieces of food
Canine: tearing pieces
apart
Premolars & molars:
grind food to a paste
How many teeth in adult
humans?
Tongue
Floor of oral cavity
Composed of voluntarily controlled muscle
tissue
Role: Guides food during chewing and
swallowing
Major taste buds are embedded here.
Salty, sweet, sour, bitter
Salivary Glands
Release saliva in response to the smell,
taste, and thought of food
First example of chemical digestion:
Contains Amylase: an enzyme that begins
breakdown of starch into simple sugars, like
glucose or table sugar.
Interesting Fact: We secrete about 1-2L of
saliva per day!
Hard & Soft Palates
Separate mouth from nasal
cavity, so food doesn’t go up your nose!
Located at the roof of your mouth.
Uvula (dangles)
Just beneath the soft palate
Prevents food from entering nasal
passages by raising up.
Hard Palate
Tongue
Soft Palate
Uvula
Epiglottis
Trachea
Recap (Mouth)
 Food enters
 Teeth rip, tear, and chew into smaller pieces to
swallow
 At the same time, Salivary Glands are stimulated
to release saliva which contains amylase.
 Tongue pushes bolus to back of pharynx (throat)
and the uvula elevates, closing off the nasal
passage. The bolus now pushes the epiglottis
which closes the opening of the larynx,
preventing the food from entering the wrong
tube, which results in choking
Esophagus
 Muscular tube which
extends from pharynx
(throat) to the stomach
 Swallowing initiates
peristalsis, a wave of
contraction which initiates
just above the “bolus”
(substance) and moves it
towards the stomach.
 This movement also
occurs in the stomach
and in the intestines.
http://pennhealth.com/health_info/animationplayer/
Esophagus
Secretes mucus (along with the rest of the
digestive tract)
This lubricant decreases the likelihood of
the esophagus getting damaged by any
sharp edges from the food entering.
Mucus also protects esophagus from acid and
enzymes in gastric juice if reflux were to occur.
http://digestive.niddk.nih.gov/ddiseases/pubs/gerd/
NOTE: This should be a straight line in your notes
Mechanical: Peristalsis
Tongue
Mechanical: Chewing
Chemical: Starch/Amylase
Teeth
Salivary Glands
Stomach
Separated from esophagus by the Gastro
esophageal sphincter
Expandable muscular J-shaped sac that
can hold up to 2-4 liters of food and liquid
Secretes mucous to protect lining cells
Contents are held in the stomach by the
pyloric sphincter, ring of circular muscle,
which separates the stomach from upper
small intestine
Stomach
 3 Functions
Stores food and releases it
gradually into the small
intestine
Assist in mechanical
breakdown of food by
peristalsis and contractions
of muscular walls
Chemical breakdown of
food by enzymes and other
substances.
Stomach
Secretions (continued)
Gastrin: hormone that stimulates secretion of
Hydrochloric acid (HCl)
Pepsinogen: inactive form of enzyme is
activated by HCl and transformed into pepsin
which helps breakdown proteins into amino
acids (smaller units).
Stomach
Food is gradually converted into a thick
liquid called chyme which consists of
partially digested food and digestive
secretions.
Chyme is propelled towards small intestine
The Pyloric sphincter lets a teaspoon of
chyme into the small intestine during each
contraction
Takes around 2-6 hours to empty stomach
NOTE: This should be a straight line in your notes
Mechanical: Muscle Contractions
Mechanical: Peristalsis
Mechanical: Peristalsis
Chemical: Pepsin
(Proteins), HCl
Tongue
Mechanical: Chewing
Chemical: Starch
Teeth
Salivary Glands
Small Intestine (S. I.)
 Narrow tube (1-2 inches in
diameter)
 Longest part of digestive
tract
 Split into three parts:
duodenum, jejunum, and
the ileum
 Function: to digest food into
small molecules and absorb
into blood stream and
lymph vessels.
Small Intestine (S. I)
 Helped by three other
sources:
1. Liver: Has many
functions in our bodies.
In digestion, it produces
bile which is stored in
the gall bladder, then
released in the S. I.
Bile is made up of bile
salts, water, and other
salts and assist in the
breakdown of lipids.
http://zap.intergate.ca/images/liver%20image.jpg
Small Intestine (S. I.)
 2. Gall Bladder stores bile until
it’s needed for digestion
http://www.nlm.nih.gov/medlineplus/ency/imagepages/19260.htm
Small Intestine (S. I.)
 3. Pancreas
 Located between stomach and
S. I.
 Cells produce pancreatic juice
which neutralizes the acidic
chyme it receives from the
stomach
 Digests carbohydrates,
proteins, and lipids
 Contains water, sodium
bicarbonate, and many
enzymes
 YouTube - Pancreas - "Weird
Al" Yankovic
http://www.nlm.nih.gov/medlineplus/ency/imagepages/17194.htm
Small Intestine (S. I)
Pancreas (cont’d)
Enzymes include:
Amylase
Lipase
Proteases
Carbohydrates
Lipids
Proteins and peptides
Small Intestine (S. I.)
http://www.udel.edu/biology/Wags/histopage/wagnerart/anaglyph
page/anaglyph.html
 Specialized cells within
the wall complete the
process. At the same
time, nutrients are
absorbed into the blood
stream.
 The numerous folds
and projections, called
villi, give the internal
surface area a much
larger surface for
absorption.
Small Intestine (S. I.)
 The area of absorption is also increased by the
millions of microvilli.
NOTE: This should be a straight line in your notes
Mechanical: Peristalsis
Bile emulsifies lipids
Alcohol absorbed
Mechanical: Muscle Contractions
Peristalsis (3 layers)
Chemical: Amylase-CH2O
Lipase-Lipids
Proteases-Proteins
Macro & micronutrients
absorbed
Mechanical: Peristalsis
Chemical: Pepsin-Proteins
HCl: pH-2
(gastric juices)
Tongue
Mechanical: Chewing
Chemical: Amylase-Starch
Teeth
Salivary Glands
Are We There Yet?
Almost…
While the nutrients are being absorbed by
these cells, chyme is being mixed back
and forth by segmentation movements
within the small intestine.
When absorption is complete, undigested
material moves into the large intestine.
Large Intestine (L. I.)
 Is about 5 feet long and 3
inches in diameter in adults
 Two parts:
Colon
(for most of its length)
Rectum: the final 6”
http://www.nlm.nih.gov/medlineplus/ency/imagepages/19220.htm
 Receives leftovers of digestion: water mixture,
undigested fat and proteins, indigestible fibers
Large Intestine (L. I.)
Contains large populations of bacteria that
thrive on the unabsorbed nutrients and are
also responsible for synthesizing important
vitamins for the body (B12, riboflavin, K).
Remaining water, salts, and vitamins are
reabsorbed by cells in the L. I.
NOTE: This should be a straight line in your notes
Mechanical: Peristalsis
Bile emulsifies lipids
Mechanical: Muscle Contractions
Chemical: Amylase-CH2O
Peristalsis (3 layers)
Lipase-Lipids
Proteases-Proteins
Macronutrients absorbed
Mechanical: Peristalsis
Chemical: Pepsin-Proteins
HCl: pH-2
(gastric juices)
Tongue
Remaining water, salts
and vitamins absorbed
Mechanical: Chewing
Chemical: Amylase-Starch
Teeth
Salivary Glands
Large Intestine (L. I.)
Leftover material is condensed into
semisolid feces which are transported to
the rectum by peristaltic movements.
Expansion of the rectum stimulates the
urge to defecate which is initiated
voluntarily after age 2.
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