Download An overview of the Digestive system of humans

VCE Biology Unit 1: Digestion
Getting the 'Goodness' to our Cells
An overview of the Digestive system of humans
1. INGESTION: Food must be taken into our body. Humans and many other organisms take food into
their body through their mouth. We call this eating.
2. MASTICATION: Food is chewed to break large pieces into small ones*. Food is mixed with saliva
3. DIGESTION: large organic molecules must be chemically broken down into its simplest
components; amino acid (units that make up proteins), monosaccharides eg. glucose (units that
make up carbohydrates), glycerol and fatty acids(units that make up lipids), nucleotides (units that
make up nucleic acids), so that they can be absorbed. Some substances do not need to be
chemically broken down into smaller components e.g. water, vitamins, and minerals
The efficient digestion of food relies on two main forms of breakdown:

Mechanical breakdown:
physical breaking up of large pieces into smaller pieces. (In
humans assisted mostly by teeth (chewing action) and to a lesser
extent by churning of food in stomach)

Chemical breakdown:
breaking of chemical bonds so that larger molecules are broken
into smaller building blocks(molecules)
3. ABSORPTION: nutrients and water must pass across the wall of the stomach (minor role) and
intestine (major role), into the surrounding tissue fluid, and then into the circulatory system (amino acids,
monosaccharides, micronutrients water) or lymphatic system (products of lipid digestion).
Nutrients are then transported, primarily via the circulatory system of the organism, to body cells where
they are utilized.
4. EGESTION: material that is not absorbed as it passes through the alimentary canal are stored
temporarily in the rectum before being eliminated via the anus.
Introducing the Digestive SYSTEM: A summary
Complete the table below: Use sheets, text book, SRAM and video to assist
Under each component are some key words in italics that you must include in your comments about
structure and function. You can use dot points and short hand to complete the table.
Name of Digestive
system component
Mouth
Role: What is the function of this
component
mechanical breakdown of food
How is it suited it to its function.
chemical digestion of cooked
starch in food
Salivary glands: secrete saliva
containing liquids and a type of
amylase called ptyalin. Saliva also
lubricates food to enable it to easily
move through this alimentary canal.
break
moisten
lubricate
nose
trachea
stop
saliva
enzyme
starch
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Teeth: cut tear and grind food to break
it into smaller pieces. This makes
swallowing easier but also importantly
increase the surface area exposed to
enzymes. This enables a faster rate of
chemical digestion than if the food was
not chewed by the teeth.
VCE Biology Unit 1: Digestion
mixing of foods with saliva
Tongue: moves food around the
mouth, forming it into a bolus and
pushing it to the back of the mouth for
swallowing
soft palate: stops food from moving
from the mouth up into the nose during
swallowing
epiglottis: flap that covered the tachea
during swallowing- stops food moving
into the trachea during swallowing thus
ensuring that it moves down the
oesophagus and into the stomach
oesophagus
peristalsis
bolus
cardiac Sphincter
ring
stomach
Muscular layers
pepsin
hydrochloric acid, chyme
glandular layer
mucus
pH
Transports food from the mouth
to the stomach.
Thin tube with a muscular lining
Wave like contractions of the
muscular wall of the
oesophagus, known as
peristalsis, move the bolus of
food from the mouth to the
stomach
Stops or reduces reflux of
gastric juices into the
oesophagus.
short term storage while
digestion is taking place
muscular ring that stops gastric juices
rising
some mechanical breakdown
Stomach wall consist of several
muscular layers. This muscle churns
stomach contents and mixes the food
with gastric juices to form a soupy
mixture called chyme
mixing of food with gastric
juices
Chemical breakdown to proteins
to peptides
absorption of some substances:
those simple enough to be
absorbed without needed
digestion (e.g. water, alcohol,
glucose, aspirin)
it has folds(rugae) that allow for
expansion of stomach as it fills
Glandular layer:
goblet cells in lining of the stomach
produce and secrete mucus. This
mucus provides a protective coating
that reduces the chance of HCl and
proteases damaging or digesting the
stomach lining
glandular cells that secrete HCl. This
creates a very acidic environment
(pH 1-2) in the stomach which is
required for the function of pepsin.
pyloric sphincter
ring
controls
controls the release of chyme
from the stomach into the
duodenum
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glandular cells that secrete the enzyme
pepsin in its inactive form pepsinogen.
If the acidic medium of the stomach
pepsinogen is converted to pepsin.
Pepsin is the enzyme that catalyses the
chemical breakdown of protein.
ring of muscle at the base of the
stomach
VCE Biology Unit 1: Digestion
chemical breakdown of proteins,
lipids and carbohydrates
duodenum
Secretions
enzymes
chemical breakdown
glandular layer that is responsible for
secretion of enzymes that chemically
digest proteins(proteases),
lipids(lipases) and
carbohydrates(amylases)
secretions from liver and gall bladder
Liver
&
Gall bladder
emulsify
lipids
surface area
Pancreas
Bicarbonate ions
pancreatic enzymes
pH
liver produces and secretes bile
which emulsifies lipids, giving
them a larger surface area on
which lipases can act. This
enable an increased rate of
chemical digestion of lipids.
Produce and secrete digestive
enzymes and bicarbonate. The
enzymes enable chemical
digestion of some molecules.
The bicarbonate neutralizes the
chyme and creates a slightly
basic pH(6~8) which is the
optimum pH for the enzymes of
the small intestine and pancreas
to function in.
Large
intestine
colon
Absorption
water
Bacteria
rectum
Anus
Pancreatic duct: carries enzymes and
bicarbonate to the duodenum.
some chemical digestion
villi line the intestinal wall. In the centre
of each villus is a lacteal and a
capillary.
much absorption of
nutrients(amino acids,
monosaccarides, fatty acids
etc), vitamins, minerals and
water (most water is absorbed
here)
Villi and microvilli create a very large
surface area over which absorption of
nutrients can take place. This enables
fast rate of absorption
Ileum
Villi
absorption
capillary
lacteal
fats
amino acids
monosaccharides
Bile duct: bile enters the duodenum
from the gall bladder, via the bile duct
further absorption of water
Amino acids and monosaccharides
pass across the villus and into the
capillary.
fats pass across the villus and into the
lacteal
glandular lining that secretes mucus
bacteria within colon synthesise
some vitamins
storage of faecal matter prior to
egestion
control the release of faeces
from the rectum
muscle
ring
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The anus is a ring of muscle at the
base of the rectum. It expands and
contracts to control the release of
faeces
VCE Biology Unit 1: Digestion
Secretions of the digestive system
Name of
secretion
(~ ph of
secretion)
Saliva (slightly
alkaline)
Gastric juice
(pH 1-1.5)
Site of
production
Site of action
Chemical components
of secretion
(*= an enzyme)
Action
salivary
glands
stomach
lining
mouth
salivary amylase*
a.k.a. ptyalin
Hydrochloric acid
Begins digestion of
cooked starch
creates the acidic pH (1.52) that pepsin need to
function optimally
stomach
(lumen)
pepsin*
Bile (pH 7.5)
Pancreatic juice
(pH 7.1-8.2)
Intestinal juice
(pH 7.6)
liver
pancreas
intestines
chemical digestion of
proteins
rennin*
coagulates milk
bile salts
emulsify lipids
duodenum
duodenum
intestines
Bicarbonate ions
neutralize chyme and
make ph slightly basic
(~8)
Amylase*
chemical digestion of
starch to maltose
trypsin*
chemical digestion of
protein polypeptides
peptidase*
chemical digestion of
peptides into amino
acids
lipase*
chemical digestion of
lipids to fatty acids and
glycerol
digestion of
carbohydrates
various amylases*
peptidase*
chemical digestion of
peptides into amino
acids
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