Transcript 07 T5.1 Digestion

Topic 5.1
N in
ammals
M
utrition
Intake of food & processes
that convert food substances
into living matter
Nutrition
Feeding on ready-made
complex organic matter:
Holozoic nutrition
Well developed organ
system for nutrition in
mammals (digestive
system)
Consists of the:
Alimentary canal (gut)
Associated glands
Physical
Chemical
A journey through the gut: Overview
A journey through the gut:
The mouth & buccal cavity
What happens
when you chew a
piece of bread for
1 minute?
A journey through the gut:
The mouth & buccal cavity
Food is chewed &
mixed with saliva
Jaws:
Upper jaw is fixed
Lower jaw is movable
A journey through the gut:
The teeth
Mastication: The mechanical
process of breaking up food
into small particles by the
chewing action of the teeth
4 types:
• Incisors
• Canines
• Premolars
• Molars
A journey through the gut:
The mouth & buccal cavity
Why is mastication important?
Mixes food with saliva
Food is more easily swallowed
Increases surface area for enzyme action
Saliva: Secreted by the
salivary glands
A journey through the gut:
The mouth & buccal cavity
Saliva:
Water & mucin softens food, lubricates food
Saliva contains salivary amylase
Starch
Maltose
Salivary Amylase
Slightly alkaline:
• Provides correct pH for amylase to work
• Helps to prevent tooth decay
A journey through the gut:
The mouth & buccal cavity
Tongue
Mixes food with saliva
Rolls food into a bolus (pleural: boli)
Pushes food down into pharynx
Has sense cells (taste buds)
A journey through the gut:
The pharynx
Leads from the mouth to the:
Oesophagus
Trachea (windpipe) by the
larynx (voice box)
Junction of respiratory and
digestive passages: common
passage for food & air
Think about it:
Does food go into the lungs
when we swallow?
A journey through the gut:
Breathing & Swallowing
A journey through the gut:
Oesophagus
A journey through the gut:
Oesophagus
Also known as the gullet
A narrow, muscular tube
Extends from the pharynx
through the thorax &
diaphragm to join the
stomach
Carries food to the stomach
Does food drop into the
stomach due to gravity?
A journey through the gut:
The layers of the gut: Pg 5
A journey through the gut:
The layers of the gut: Pg 5
The muscular wall is
made up of
Outer longitudinal
muscles
Inner circular muscles
A journey through the gut:
Peristalsis
The muscle layers cause rhythmic,
wave-like contractions called peristalsis
which move food along the gut
A journey through the gut:
Peristalsis
The involuntary
rhythmic waves of
muscular contractions
which pass along the
gut to move the food
along it
The process is
initiated by the
presence of food
A journey through the gut:
Oesophagus
Is it true that the
oesophagus does not
secrete anything?
Wall produces mucin to
lubricate food during
peristalsis
Salivary amylase continues
to digest starch
A journey through the gut:
Stomach
A journey through the gut:
Stomach
Stores food and digests
protein
A distensible, muscular
bag with thick & welldeveloped muscular walls
Very powerful muscular
contractions (churning)
Mixes food with gastric juice
to form chyme
A journey through the gut:
Stomach
Gastric glands secrete
gastric juice:
Hydrochloric acid
Gastric enzymes
Mucin
A journey through the gut:
Stomach: Hydrochloric acid
Provides acidic
medium (pH 2) for
gastric enzymes to
function
Stops the action of
salivary amylase
Changes the inactive
forms of gastric
enzymes to active
forms
A journey through the gut:
Stomach: Hydrochloric acid
Denatures proteins, unfolding the
polypeptide chains, exposing more
peptide bonds to enzyme action
Kills some bacteria / germs
A journey through the gut:
Stomach: Enzymes
Prorennin
Pepsinogen
HCl
HCl
Rennin
Soluble
milk
Protein
(Caseinogen)
Insoluble
milk
Proteins
(Casein)
Pepsin
Proteins
Polypeptides
Can remain in
stomach long enough
A journey through the gut:
Why doesn’t the stomach digest itself?
Proteases are produced in inactive
forms
Enzymes & acid are produced by
different cells
Mucus protects the stomach wall from
enzyme action and corrosiveness of the
acid
A journey through the gut:
Stomach
A journey through the gut:
Stomach
The food normally remains in the
stomach for about 3 to 4 hours.
The partly digested food becomes
liquefied, forming chyme
After 1 or 2 hours, the pyloric sphincter
relaxes and opens at intervals to let the
chyme into the duodenum
A journey through the gut:
Stomach: Pyloric sphincter
Muscular valve where stomach joins the
small intestine
A journey through the gut:
Small Intestine
A journey through the gut:
Small Intestine
About 6 metres long!
Consists of
U-shaped duodenum (1st part)
Jejunum
Ileum (very coiled)
Liver & pancreas discharge
secretions into the duodenum
The intestinal wall also
secretes intestinal juice
A journey through the gut:
Associated Gland: Liver
Largest gland in the body
Three blood vessels:
Hepatic portal vein, Hepatic vein, Hepatic artery
Liver cells secrete bile:
Bile salts and pigments
Greenish-yellow colour
Alkaline
Stored in gall bladder
A journey through the gut:
Associated Gland: Pancreas
Produces pancreatic juice
Contains digestive enzymes
Produces insulin (hormone)
Control of blood sugar levels
Utilization of carbohydrates
A journey through the gut:
Liver & Pancreas
Liver &
pancreas
discharge
their
secretions via
the bile duct
& pancreatic
duct
respectively
A journey through the gut:
Duodenum
The chyme stimulates
The intestinal glands to secrete intestinal juice
The pancreas to secrete pancreatic juice
The gall bladder to release bile
All 3 fluids are alkaline:
Neutralize chyme
(acidic)
Provide suitable
alkaline medium
for enzyme action
A journey through the gut:
Small Intestine
Nutrients
Liver
Pancreas
Carbohydrates
-
Amylase
Intestinal
glands
Maltase
Lactase
Sucrase
Proteins
-
Trypsin
Enterokinase
Erepsin
Fats
Bile
Lipase
Lipase
A journey through the gut:
SI: Carbohydrate digestion
Starch
Maltose
Pancreatic
Amylase
Lactose
Glucose
Maltase
Glucose
Galactose
Glucose
Fructose
Lactase
Sucrose
Sucrase
A journey through the gut:
SI: Protein digestion
Protein
Trypsinogen
Trypsin
Enterokinase
Polypeptides
Erepsin
Amino Acids
A journey through the gut:
SI: Fat digestion
Fats
Emulsification
Bile
Fat globules
Pancreatic &
Intestinal
Lipase
Fatty
Acids
Glycerol
So far, what have we learnt?
Next lesson…
What happens to
the digested and
undigested food?