Download Digestive system

Digestive system
Why do we need a digestive
system?
• The digestive system uses mechanical and chemical
methods to break complex molecules down into simpler
molecules that can be absorbed into the blood.
• Proteins (meat, diary, nuts) into Amino Acids
• Carbohydrates (starch) into Simple Sugars
• Lipids into fatty Acids and Glycerol
• The process takes time, and therefore the tube is long
and convoluted to allow the food processing to occur.
First site of digestion - mouth
( Biology text page
•
Mechanical breakdown
begins in the mouth by
chewing (Mastication) which
increases the surface area
of the food
•
Chemical breakdown of
Starch by the enzyme
Salivary Amylase.
•
Maltose (glucose-glucose)
is the product of this
digestion.
)
Food is then swallowed as a moist
ball called a bolus
• The epiglottis ensures
food doesn’t go down
our windpipe( trachea)
How is the food moved along the
digestive tract? ( Biology text page )
• Peristalsis is the
muscular contractions
that propel the food
down the esophageus
and along the
digestive tract.
Second site of digestion- stomach
( Biology text page
•
The stomach is a muscular sac with
sphincters at each end. (Cardiac and
Pyloric)
•
The stomach lining secretes about 2
litres of gastric juices per day.
•
This Gastric juice contains
hydrochloric acid, pepsinogen, and
mucus
•
Secretions are controlled by nervous
stimuli (eg smells, thoughts/patterns
of behaviour) and endocrinal signals
( hormones).
)
Stomach wall contains Goblet cells
They secretes hydrochloric acid and
pepsinogen.
•
Hydrochloric Acid (HCl) lowers pH of the
stomach to 2 / 3, which kills most bacteria
and activates the enzyme pepsinogen to
pepsin.
•
Pepsin is a type of protease (protein
enzyme) that breaks down proteins into
peptides (small chains of amino acids
•
The Mucus ensures that the Hydrochloric Acid
does not burn a hole in the stomach lining , ie
stopping ulcer forming
Stomach in Summary ( Biology text page
)
Protein digestion - pepsin begins the process of protein digestion cleaving large
proteins into shorter amino acid chains called peptides .
Storage – It allows a meal to be consumed and the materials released slowly into
the duodenum for further digestion( small intestine). Food may be churned in
the stomach for up to four hours before moving onto the duodenum.
Acidic Environment to assist in activating enzymes and killing bacteria( Mucus is
produced to stop corrosion of the lining
Limited absorption - water, electrolytes, and fat soluble molecules including
alcohol
The Small Intestine ( Biology text page
Small intestine is a coiled tube
over 6 meters long.
Made up of three sections
1. Duodenum
2. Jejunum
3. Ileum
)
Third Site of digestion - Duodenum
( Biology text page
• The pancreas secretes juices
containing bicarbonate to
neutralizing the stomach acid.
•
Brunner's glands also produce alkaline
secretions to counteract the effects of
gastric acids that reach the duodenum.
• Epithelial cells of the duodenum
secrete a watery mucus.
• The liver produces bile, which is
stored in the gall bladder before
entering the bile duct into the
duodenum.
)
Electron micrograph of the Villi
( Biology text page
)
Cross-section of the ileum
Structures and function of a Villus
Summary of Digestion in the
Duodenum
• Protein digestion completed with the
enzyme Trypsin working in an alkaline
environment
• Carbohydrate digestion completed with the
enzyme amylase and maltase reducing
disaccharides to glucose
• Bile (from the liver) emulsifies (breaks into
small particles) lipids (fats), therefore
allowing lipases to digest fats(lipids)
Hormones involved in digestion
Hormone
Gastrin
Secretin
Cholecystokinin
(CCK)
Gastricinhibitory
Peptide
where found
action
results
how stopped
stomach cells
presence of food in
stomach stimulates
stomach glands to
produce more
hydrochloric acid
stomach produces more
acid to aid in the
digestion and
breakdown of food
when acid reaches a pH of
1.5, the stomach cells
stop producing gastrin
duodenal cells
when chyme enters the
duodenum, secretin
enters the blood and
tells the pancreas to
release bicarbonate
to reduce the acid
pH of intestines is increased
so other enzymes can
work and absorption
can take place.
when stomach acid has
been sufficiently
neutralized, secretin is
no longer secreted by
the duodenal walls
intestinal cells
presence of fats in the
intestines stimulates
the gall bladder to
contract, releasing
bile into the small
intestine
bile mixes with chyme and
emulsifies fats so they
can be more easily
absorbed
when fat no longer present
in the intestine,
production of CCK
stops
presence of fats in the
small intestine
triggers release of
hormone
Gastric-inhibitory peptide
slows GI tract motility
and inhibits gastric
acid production.
Digestion and
absorption of fats
takes longer than
carbohydrates or
proteins
when fat no longer present
in the intestine,
production of gastricinhibitory peptide
stops
intestinal cells
The large Intestine - Colon
• Secretions in the large intestine
are an alkaline mucus that
protects epithelial tissues and
neutralizes acids produced by
bacterial metabolism.
• Water, salts, and vitamins are
absorbed, the remaining contents
in the lumen form feces (mostly
cellulose, bacteria, bilirubin).
• Bacteria in the large intestine,
such as E. coli, produce vitamins
(including vitamin K) that are
absorbed.
What you need to know about the
digestive system
• List all parts (in order) of the human digestive system
• List the auxiliary organs that contribute one or more
substances to the digestive process.
• Describe the cross-sectional structure of the small intestine
and explain how its structure is related to its function.
• Describe
– Protein digestion and absorption
– Carbohydrates digestion and absorption
– Lipid digestion and absorption
We are what we eat !!!