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Digestive System & Digestive
System Disorders
Overview of Key Idea 2
2. The digestion and metabolism of food influences the
absorption and use of nutrients.
• Explore the digestion of food and how process enables nutrients
to be absorbed
• Investigate factors that interfere with nutrient absorption
• Investigate malabsorption syndromes and analyse strategies to
manage the symptoms of these disorders through diet.
•
•
•
•
Understand the importance of metabolism
Identify how excess nutrients are stored
Identify factors that determine BMR
Understand how EER is calculated
What is Digestion?
 ‘Digestion is the process by which food and drink are
broken down into their basic chemical structures in the
gastrointestinal tract…’ (Magee & Oliver 2010)
 ‘Digestion is the mechanical and chemical breakdown of
food to its smaller nutritional components…’ (Burnett- Fell et al
2011)
 ‘Digestion means breaking down foods in to smaller
substances so that the body can absorb them…’ (Home
Economics Association, 2008)
 There are two key parts:
 Ingestion – process of taking food in to the digestive system
 Digestion – the mechanical and chemical breakdown of food
Functions of the Digestive System
 The main tasks of the Digestive System are:
 Mechanical processing:


Secretion


Breakdown of food into nutrient molecules to enable absorption
Absorption


Release of digestive enzymes and other substances
Digestion


Movements that break up, mix and propel food material
Passage of digested nutrients and fluids into blood stream and
lymph
Elimination

Undigested and unabsorbed food residue is expelled from the gut
Human Digestion
Digestion involves a long chain of processes with different
organs doing their individual jobs along the way.
Video – The Journey of the Digestive System
http://www.youtube.com/watch?v=e3O1AdlC8bI
What happens in the mouth?
 Teeth shred the food into smaller pieces by a process
called mastication.
 Saliva is stimulated by the sight and smell of food.
 Salivary glands secrete saliva
into the mouth to moisten the
food and help swallowing.
 Saliva is a watery mixture of
mucin and amylase.
 These enzymes interact with
food and begin the chemical
digestion process.
What happens in the Oesophagus?
 The oesophagus is the tube that joins the mouth to
the stomach.
 Peristalsis moves food a long the
digestive tract

Peristalsis is a series of involuntary wave-like
muscle contracts
 Takes 5-10 seconds for food to pass
from the mouth to the stomach
 No breakdown of food
 Its main function is to prevent acidic
mixture in the stomach from splashing
back up into the mouth.
What happens in the stomach?
 The stomach is a large bag-like
organ
 The muscles lining the stomach
grind the food and mix it with
gastric juices and acid to produce
chyme, a watery paste.
 Small quantities of glucose, water
soluble vitamins and minerals are
absorbed in the stomach.
 Nature of the food and degree of
muscle action can affect the
emptying of the stomach
What are the functions of the Stomach?
 The stomach has three main functions:

Food storage

An empty stomach has a volume of one fifth of a cup, but can
expand to more than 8 cups after eating a large meal
(http://kidshealth.org/teen/your_body/body_basics/digestive_system.html# )

Disinfect food


Hydrochloric Acid kills bacteria
Chemical Digestion

Pepsin is released to
breakdown protein
 When each function is
complete the stomach
empties its contents into the
small intestine (duodenum).
What are the functions of the small intestine?
 Approximately 6 meters long in an
adult
 Most digestion and absorption occurs
here
 The small intestine is divided
into three distinct areas:



Duodenum
Jejunum
Ileum
Small Intestine - Duodenum
 Links the stomach to the small intestine
 Food is digested here in small amounts
 Gall bladder, liver and pancreas release
bile and enzymes to complete the
chemical breakdown of acidic stomach
contents.



Trypsin converts protein to amino acids
Amylase breaks down starch
Lipase breaks converts fats to fatty acids
or glycerol.
Small intestine – Jejunum & Ileum
 Jejunum is the coiled mid section
 Ileum is the final section that leads to
the large intestine.
 Increase of villi and
micro villi.
 Fats are absorbed through
the intestinal wall and
carried to the liver via the
bloodstream.
Liver & Gallbladder
The liver produces bile:
 Bile is an alkaline fluid
stored in the gallbladder,
which is discharged into
the duodenum upon
eating.
 Breaks up fats by acting
like detergents

Bile emulsifies fats
 The gall bladder, a
small sac that is
attached to the
undersurface of the
liver, holds bile.
Pancreas
 The pancreas
 Produces enzymes (pancreatase) to
digest protein, starch and fat.
 Pancreatic secretions neutralise
stomach acids.
The lining of the small intestine contains finger like projections
called villi. Through these villi nutrients are absorbed.
What are the functions of the large intestine?
 Large intestine and rectum make up
1.5m of the gastrointestinal tract
 4 X thicker than the small intestine
 Contains no digestive juices and all
food has been absorbed by this
time.
 Main function is to remove food
residue and waste from the body.
 The residue includes cellulose,
digestive juices, excess water
soluble vitamins and bacteria.
What are the functions of the large intestine?
 Large intestine produces no
enzymes, but digestion still
occurs due to bacteria.
 Soluble fibre is digested by
bacteria in large intestine.

This provides nourishment for the
cells in the walls of the intestines
and helps protect against diseases.
What is the function of the rectum?
20
 Last section of colon (Large intestines)
 Mucus
is secreted to aid the passage of faces
to the rectum
 Eliminate faeces 12 to 24 hours after eating.
 Undigested
materials which is mainly
cellulose from plants (fibre)
 Masses of dead bacteria
Summary of where nutrients are absorbed
Mouth
Digestion of cooked
starchy carbohydrates
Stomach
Digestion of protein
Absorption of glucose, alcohol and water soluble vitamins and
minerals
Small Intestine
Digestion of protein, carbohydrate, and fat
Absorption of all nutrients except fibre
Large Intestine
Digestion of Fiber
Absorption of Water
Bowel
(Rectum & Anus)
Elimination of faecal matter
Summary of Macronutrient Absorption
Macronutrient
Carbohydrate
Protein
Lipids
Site
of Digestion
Digestive chemicals
involved
Product(s) of
Digestion
Mouth
Small Intestine
Amylase
Glucose Fructose
Galactose
(Monosaccharides)
Stomach
Small Intestine
Hydrochloric Acid
Pepsin
Amino Acids
Fatty Acids and Glycerol
Small Intestine
Bile
Lipase
Digestive System Disorder - Ulcers
 ‘A stomach or gastric ulcer is a break
in the tissue lining of the stomach.
The term 'peptic ulcer' refers to
those that occur in either the
stomach or… the duodenum.’ (Betterhealth
Channel 2011)
 Commonly thought stress, smoking
and diet were responsible for
stomach ulcers; however
Helicobacter pylori (H. pylori)
bacterium is now known to be
responsible for most duodenal
ulcers and 60 per cent of stomach
ulcers. (Betterhealth Channel 2011)
Digestive System Disorder - Constipation
 ‘Constipation is the passing of hard,
dry bowel motions (stools) that may
be infrequent or difficult to pass.’
(Betterhealth Channel 2011)
 Occurs when food stays in the
intestine too long; thus, too much
water is absorbed.
 The most common causes of
constipation include a change in
routine, not enough fibre in the daily
diet, not enough fluids and lack of
exercise.
Digestive System Disorder – Diarrhoea
 Diarrhoea is the frequent passing of
loose, watery and unformed faeces.
 The most common cause of
diarrhoea is an infection of the
intestines, such as gastroenteritis or
food poisoning.
 The intestinal lining becomes
irritated and inflamed, which hinders
the absorption of water from food
waste.
 Can result in severe dehydration,
especially in infants
Video – Poo Analysis
http://www.youtube.com/watch?v=tw6eme3ozQU
Digestive System Disorder – Gall Stones
 ‘Gallstones (biliary calculi) are
small stones made from
cholesterol, bile pigment and
calcium salts…’ (Betterhealth Channel 2011)
 Treatment depends on the size
and location of the gallstones, but
may include:


Surgery
Limiting fatty products and dairy
products
Digestive System Disorder – Heartburn
 Heartburn or reflux happens
when the contents of the
stomach back up into the
oesophagus, causing a burning
sensation.