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The Digestive System
Life Science
FLSS
All images used are taken from copyright-free sources e.g. Wikicommons Media or produced by UWS staff.
nutrients
Used as “building material” & as energy
source
problem:
• nutrients in food not in form accessible to
body cells
solution:
• digestive system extracts nutrients from
food for use by cells
Digestive system processes
• Ingestion
• Propulsion
• Digestion
– Mechanical (action of teeth and muscles)
– Chemical (enzymes)
• Absorption
• Elimination
Digestive system
1. Gastrointestinal tract (GIT)
• Tube through which food passes
(mouth to anus)
• Also called alimentary tract
2. Accessory organs
• Glands secrete chemicals into GIT to
aid digestion
The Digestive System
USA Department of Health and Human Service (2014)
http://commons.wikimedia.org/wiki/File:Gastrointestinal_system.gif
The Digestive System
LadyofHats: (2011) digestive system
:http://commons.wikimedia.org/wiki/File:Digestive_system_simplified_az.png
Basic anatomy of GIT wall
• Same layered tubular structure
throughout
• 4 main layers
• Variations for specialised functions
• Lumen – hollow cavity
• Narrowing of the lumen can obstruct
food from passing along the GIT
Intestinal anatomy - GIT Wall
National Cancer Institute (2013) Mucosa:
http://commons.wikimedia.org/wiki/File:Mucosa.jpg?uselang=en-gb
OpenStax College (2013)
http://commons.wikimedia.org/wiki/File:2402_Layers_of_the_Gastrointestinal_Tract.jpg
Basic anatomy of GIT wall
1. Mucosa (includes epithelial layer,
cell types vary in different regions)
• Protection
• Secretion
• Absorption
2. Submucosa
• supports mucosa,
• contains blood vessels, lymph
vessels, nerves
Basic anatomy of GIT wall
3. Muscle layer
– Inner layer (circular)
– Outer layer (longitudinal)
mixes and propels food along GIT
4. Adventitia
– Thin outer layer, fibrous tissue
– In abdomen it is a double serous
membrane, the peritoneum
– It secretes fluid to moisten & lubricate outer
surface of GIT so that it slides freely within
abdomen
Intestinal anatomy
Submucosal
plexus – controls
glandular secretion
http://commons.wikimedia.org/wiki/File:2402_Layers_of_the_Gastroint
estinal_Tract.jpg
Myenteric
nerve
plexus –
controls
intestinal
movements
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OpenStax College (2013)
http://commons.wikimedia.org/wiki/File:2402_Layers_of_the_Gastrointestinal_Tract.jpg
Mouth chewing/ mastication
BruceBlaus. (2013)
http://en.wikipedia.org/wiki/File:Blausen_0780_SalivaryGlands.png
•
•
US Gov (2011)
https://commons.wikimedia.org/wiki/File:Illu_mouth.jpg
Swallowing (deglutition)
Swallowing:
Soft palate
Raised
Epiglottis
lowered
Glottis
Closed
Larynx
raised
Diagram
shows
neutral
position
Arcadian (2007)
http://en.wikipedia.org/wiki/File:Illu01_head_neck.jpg
National Cancer Institute (2013) Head & Neck overview:
http://training.seer.cancer.gov/head-neck/anatomy/overview.html
Breathing
Soft palate
lowered
Epiglottis
raised
Glottis
open
Larynx
lowered
Diagram shows neutral
position
Arcadian (2007)
http://en.wikipedia.org/wiki/File:Illu01_head_neck.jpg
National Cancer Institute (2013) Head & Neck overview:
http://training.seer.cancer.gov/head-neck/anatomy/overview.html
Boumphreyfr (2009) Peristalsis:
https://commons.wikimedia.org/wiki/File:Peristalsis.png
Oesophagus
After swallowing the chewed food or BOLUS moves through the
LUMEN of the oesophagus by waves of alternate contractions of
the longitudinal and circular muscle called PERISTALSIS
The bolus eventually passes into the top end of the stomach
through the Lower oesophageal sphincter, not a true sphincter.
Boumphreyfr (2009) Peristalsis:
https://commons.wikimedia.org/wiki/File:Peristalsis.png
Auawise (2008)
http://en.wikipedia.org/wiki/File:Peristalsis.gif
Stomach
Arcadian (2006)
http://en.wikipedia.org/wiki/File:Illu_stomach2.jpg
Indolences (2010)
http://en.wikipedia.org/wiki/File:Regions_of_stomach.svg
GASTRIC JUICE
Contains:
Mucus
Hydrochloric acid
Pepsin
Boumphreyfr (2009)
http://commons.wikimedia.org/wiki/File:Gastric_anatomy.png
Gastric acid is corrosive and can damage
the stomach wall.
• How is this protected against in the
stomach?
• mucous covering of the internal surface of
the GIT wall
• What condition arises when acid does
does damage the wall?
• (peptic) ulcers)
• What is meant by “heartburn”?
• burning sensation in oesophagus caused
by reflux of gastric acid
Small intestine
BruceBlaus (2013)
http://en.wikipedia.org/wiki/File:Blausen_0817_SmallIntestine_Anatomy.png
Pancreas, liver
and gall bladder
BruceBlaus (2013) Gallbladder, Liver, and Pancreas
http://commons.wikimedia.org/wiki/File:Blausen_0428_Gallbladder-Liver-Pancreas_Location.png?uselang=en-gb
Pancreas
BruceBlaus (2013)
http://en.wikipedia.org/wiki/File:Blausen_0701_PancreaticTissue.png
Liver
Jiju Kurian Punnoose (2007)
http://en.wikipedia.org/wiki/File:Anatomy_of_liver_and_gall_bladder.png
Absorption of nutrients
Snow93 (2008)
https://commons.wikimedia.org/wiki/File:Intestinal_villus_simplified.svg?uselang=en-gb
すじにくシチュー (2015)
https://commons.wikimedia.org/wiki/File:Small_intestine_and_villus_jp.svg?uselang=en-gb
Brush border of villi
Pdeitiker (2008)
https://commons.wikimedia.org/wiki/File:Protein_digestion.PNG
Large intestine
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BruceBlaus (2013)
http://en.wikipedia.org/wiki/File:Blausen_0604_LargeIntestine2.png
Armin Kubelbeck (2013)
http://en.wikipedia.org/wiki/File:Anatomy_of_human_rectum_and_anus-2.png
GIT motility
• Functions
– mix food with GIT secretions
– move food along length of GIT
– bring food in contact with wall for
absorption
Peristalsis
• Peristalsis
– Muscle contraction
“upstream” from
food, relaxation
“downstream”
– Waves move food
onwards
OpenStax College (2013)
http://commons.wikimedia.org/wiki/File:2404_PeristalsisN.jpg
Types of movement
• Segmentation
– Segments contract &
relax in rhythmic pattern
– Stationary contractions
of circular muscle layer
– Usually after a meal
– Mixes food with
secretions, increases
absorption
– Food NOT propelled
along GIT
OpenStax College (2013)
https://commons.wikimedia.org/wiki/File:2419_Segmentation.jpg