Download The Digestive System

The Digestive
System
Chapter 11 page 352 -373
MHR
Obj. 17 - Why do we have a digestive
To system??
break large ingested (eaten)
molecules into smaller, more simple
compounds that can be easily
absorbed into the circulatory system.
What are the molecules that we need
to break down?? Coming soon :)
Obj. 18 - Mechanical and Chemical Digestion
Mechanical Digestion
Physically breaking down food into smaller particles.
Occurs in the mouth where the teeth chew and the
tongue manipulates food.
Chemical Digestion
Separation of food into molecular components by chemical means.
Begins in the mouth with saliva, continues in the stomach, and completes in the
small intestine.
Both work together to provide the nutrients that are absorbed into the body.
Major Organs and the Pathway of food
through the Digestive System
pg 359-362 (fig 11.3 pg 359)
Mouth - food is chewed by the teeth, manipulated
by the tongue, and mixed with saliva
The top of the tongue is covered with Papillae
which house the taste buds
allow us to tell if food is sweet, sour, salty, or bitter.
The uvula (“hangy ball”) hangs in the back of the
throat and prevents food from entering the
pharynx.
Salivary Glands - secretes saliva which
lubricates food (pass easier through the
digestive system) & is the beginning of
chemical digestion
Esophagus (fig 11.3, pg 359) - a tube-like
structure that connects the mouth and stomach.
Mucus produced by mucous lining
lubricates food
it is lined with muscles that push food
down to the stomach.
Stomach (figs 11.5, pg 359; 11.6, pg 360)
muscular J-shaped sac
stomach wall has millions of gastric glands that secrete
gastric juices which chemically breakdown food.
stomach muscles help breakdown food into a thick liquid
called chyme.
At the junction of the stomach and the next part of the tract, a valve
is present to control the amount of chyme leaving the stomach
called the Pyloric Sphincter
Small Intestine (figs 11.5, pg 359; 11.7, pg 361) - After the stomach, food enters
the small intestine
tiny villi increase the surface area of the intestine to absorb as many nutrients
as possible.
has total absorptive surface area of a tennis court!!
it has three sections: 1) duodenum, 2) jejunum, and 3) ileum
1) Duodenum (25-30 cm long) -The first part of the small intestine (shortest and
widest of the three sections)
the pancreatic and bile ducts open into this section
it has many folds lined with villi - high surface area for absorption
2) jejunum (2.5m long) - middle part; also has
many folds (and villi)
it breaks down remaining proteins and
carbohydrates so their end products can
be absorbed.
3) Ileum (3m long) - fewer folds, absorbs
remaining nutrients, pushes undigested
material to the large intestine.
Large Intestine (1.5m long) see fig 11.3 pg 359
much shorter than small intestine but has a larger
diameter
consists of the caecum, colon, rectum, and anal
canal.
1) Caecum blind end of the large intestine; the
appendix hangs from the caecum.
2) Colon - Undigested food travels up, across, and
down the colon
water and dissolved minerals are absorbed
material that remains is now called feces.
3) Rectum - last 20 cm of the large intestine
stores feces until it is eliminated from the body
4) Anus - Feces passes out of the body through the
anus
anal sphincter allows the body to control the
elimination of feces to some extent.
Note: Food moves through the digestive system
by wavelike muscular contractions known as
peristalsis (Fig. 11.8 pg 362).
Related Organs (pg365-368) - Organs that are not directly in the digestive tract
but which play an important role in digestion.
The Liver (pg 365-368; fig 11.11
pg 368)
produces bile salts which break
up fat globules into tiny droplets
that can be absorbed by the
small intestine
Other functions: breaks
down/recycles some cells,
stores some chemicals &
detoxifies poisons
The Gall Bladder (pg 368; fig 11.3 pg 359)
stores bile that the liver produces - a hormone
causes it’s release into the duodenum
The Pancreas (pg 368; fig 11.3 pg 359)
Contains enzymes & produces a basic
solution to neutralize chyme as it comes from
the stomach into the small intestine
Essential Nutrients (page 354-358)
A healthy diet must include the six essential nutrients.
carbohydrates
fats
proteins
minerals
vitamins
water
A diet where these nutrients are present in the right
proportions is called a Balanced Diet.
Carbohydrates
made of atoms of carbon,
hydrogen and oxygen
a source of energy that can be
accessed quickly
can be simple (glucose) or
complex (starch).
Sources: pancakes, bread,
pasta, cakes, and cookies.
Carbohydrates
two or more simple sugars combine to form
a polysaccharide.
Glycogen performs the important function
of energy storage in animals.
stored in the liver.
Chemical digestion
mouth - salivary amylase breaks glycogen
into maltose.
small intestine - maltase breaks maltose
down into two glucose molecules
See structure of glycogen p. 44
Lipids
fats used for energy and building
materials for cell membranes and
hormones
layers of fat protect the body against
cold and cushion against organ
damage.
Sources: nuts, meat, cheese,
milk, butter, eggs, and cooking
Lipids (fats)
fats are broken down into fatty
acids and glycerol in the small
intestine by the enzyme lipase.
here they are absorbed by
microvilli
some are transported to the liver
and converted to glycogen
others are passed to fat cells where
they can be reconverted to fat.
Proteins
Made up of peptides (made up of amino acids).
we can’t make 8 out of the 20 amino acids we need
these 8 are called essential amino acids
they must come from food. A food source containing all
eight is called a complete protein.
Complete protein sources: meat, legumes, eggs,
cheese, milk, and whole grain products.
proteins in your body include enzymes & antibodies
proteins build & repair muscles & cell membranes
Protein
After digestion they are
broken down into amino acids.
absorbed into the bloodstream
carried to the liver
transported to cells to make new proteins
the liver also breaks down amino acids for energy when fat and glycogen stores
are low.
Chemical Digestion
Stomach: protein break down to peptides by pepsin
Small intestine: peptides - break down to simpler peptides by trypsin.
Minerals
inorganic compounds the body
needs in small amounts
enable certain chemical reactions
help build bones and cartilage
are essential components of
hemoglobin, hormones, and
enzymes
Vitamins
required in relatively small amounts.
function as coenzymes i.e. are needed to
make enzymes function.
involved in tissue growth
help the body fight and resist disease.
Of the four fat soluble vitamins (A,D,E
and K) only A and K can be stored. The
others must be consumed on a regular
basis.
Water
You obtain water by drinking and eating.
Water dissolves food materials so they
can pass to the bloodstream.
Most of the body’s chemical reactions
occur in water solutions.
Digestive Enzymes pg 363-365
chemical digestion involves hydrolysis, or
the breakdown of bonds by adding water
occurs with carbohydrates, lipids and
proteins
breaks these down into smaller, absorbable
molecules
is made faster by enzymes
3 types: carbohydrases, lipases, and
proteases
they are formed in secretory cells and
secreted into the digestive tract in
several locations
Fig 11.10 pg 364
Maltose + water → glucose + glucose
Dehydration Synthesis
● Dehydrate - ‘remove water’
● Synthesis - ‘to make’
● Join together simpler molecules to make more complex ones
by removing water
● When used - storing glucose for ‘later’
maltose
Digestive Enzymes pg 363-365
carbs. + H2O → simple sugars
proteins + H2O → amino acids
lipids + H2O → glycerol + fatty acids
Digestive enzymes = chemical
digestion.
Begins in the mouth and ends in the
small intestine.
No chemical digestion in the large
intestine.
Bacteria here are producers of vitamin
B and K