The Digestive System
Stages of Food Processing
Ingestion
Taking in of nutrients
Digestion
Breakdown of complex organic
molecules into smaller components by
physical and chemical means
Absorption
Taking up of digested molecules into
the cells of the digestive tract
Egestion
Removal of waste food materials from
the body
Appearance of the
Digestive System
Humans
● Digestive system is one long
tube, open at both ends
● Gastrointestinal
tract/alimentary canal
Birds
● One long tube that will store,
grind up, and absorb food
Perch (Fish)
● One long tube similar to humans
Rat
● Very similar to humans – really only size that varies
● One long tube that goes from mouth to anus
Let’s Start at the Top
Mouth
● Digestion begins here
● Teeth begin the physical
breakdown of food
● Action of chewing stimulates
salivary glands (parotid,
sublingual & submandibular)
● Saliva: water, mucus (mucin)
& enzymes that breaks down
carbs into maltose (amylase)
● Tongue: forms bolus out of
food
Neck Area
● Pharynx: double purpose tube
– bolus from mouth comes to
pharynx to get to digestive tract
● Epiglottis: flap over your
airway to make sure food does
not go down
● Esophagus: tube that joins
the mouth and the stomach.
Food moves down by smooth
muscle contractions
“peristalsis”
Stomach
● Movement in and out of the stomach is controlled by
sphincters – like drawstrings on a bag
● Stomach has 3 muscle layers – contract/relax to
churn food
● Cells in stomach lining secrete gastric juice (HCl +
enzymes) and mucus
● HCl + enzymes break down fibrous food
● HCl kills foreign invaders
● Mucus protects the stomach lining
Stomach
● Our stomach is super acidic – without mucus barrier,
our stomach would digest itself
● Damage to the mucus – gastric ulcers
● Pepsin – breaks down proteins, needs an acidic
environment
● Minimal absorption (small amounts of water,
medicine, alcohol)
A Small Detour
A Small Detour – the Liver
● Produces bile – emulsifying agent – digest fats
● Bile contains bile salts that break large fat globules
into small ones
● Bile is secreted continuously by the liver and stored
in the gallbladder
● Liver stores carbs, vitamins, and is a detox organ
A Small Detour – the Pancreas
● Produces sodium bicarbonate to raise the pH of
chyme from 2.5 to 9.0 (acidic to basic)
● Also secretes digestive enzymes such as lipase (fat
digesting), pancreatic amylase (carb digesting),
trypsin (protein)
Small Intestine
● Duodenum: receives secretions from the pancreas
and the liver
● food from the stomach is called chyme – water,
food, gastric juice
● UH OH! Chyme is very acidic but the small intestine
can’t handle it...what do we do?
● Thankfully, the pancreas secretes sodium
bicarbonate to raise the pH
● Structure contains ridges and folds as well as villi
and microvilli to increase surface area for absorption.
Small Intestine
● Secretes maltase (converts maltose to glucose)
● Secretes peptidases (complete digestion of protein –
amino acids)
● Once digestion is complete, the products are ready
to be removes from the digestive tube and
transported
● Most absorption takes place in the small intestine –
villi increase surface area, microvilli further increase
surface area for absorption
● Lacteals transport materials
Large Intestine (aka Colon)
● Shorter than the small intestine
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but larger in diameter
Absorbs usable materials –
primarily water
Has bacteria that produce
vitamin K and some B
Cellulose (from plants) reaches
large intestine pretty much
undigested
Feces = cellulose, living/dead
bacteria, water
As waste builds up, CNS
prompts to void the waste
What about the End?
Rectum and Anus
● Bowel (large intestine) movements propel waste
through the rectum and anus
● Allow our bodies to get rid of potentially very toxic
wastes
Where does Homeostasis fit?
● Seeing, smelling, tasting, thinking about food will
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stimulate glands to produce hormone secretions
Stimulation of salivary glands – saliva
Gastrin (hormone) stimulates gastric juice release
Secretin (hormone) travels to the pancreas to initiate
release of sodium bicarbonate
Large meal – more forceful stomach contractions, faster
emptying
Fatty meal – slow peristalsis – more time for fat digestion
and absorption – feel full longer after a high fat meal
What happens when
things go wrong?
Case Study
● Jess came to the hospital with significant weight loss
and fever.
● She was also was bleeding from the rectum (both
red and black)
● She was found to be anemic
● What’s wrong?
Let’s look at her symptoms:
● Weight loss
● If she’s eating properly, something may be wrong with her
digestive system
● Ideas?
● Fever
● Infection
● Inflammation (body trying to attack invader)
● Rectal bleed
● Red – small intestine
● Black – large intestine
● Anemia
● Low iron
● Nutrients may not be getting where they need to go?
How do we figure out the cause?
● Blood tests – anemia
● Colonoscopy – insert camera into the anus – look for
inflammation or bleeding in the large intestine
● Upper Gastrointestinal examination – look at small
intestine
● patient drinks Barium solution that coats lining of the
small intestine
● shows up white on X-ray film to show abnormalities or
inflammation
Crohn’s Disease
● Chronic inflammation of the intestines
● Causes ulcers
● Can affect anywhere in the digestive system
● Kids can have stunted growth and development
● Treatment: correct nutritional deficiencies, relieve
symptoms
● Treatment: drugs, nutrition supplements, surgery,
combination
● NO CURE! Chronic means will act up again and
again
Other Digestive System Disorders
● Appendicitis - appendix
● Tape Worm – stomach/intestine
● Dysentery - intestine
● Gallstones – gallbladder, liver, pancreas
● Gingivitis - mouth
● Hiatus Hernia - stomach
Digestive System
● Our digestive system is an open ended tube that
starts at the mouth and ends at the anus
● It is necessary to receive nutrients to keep our
bodies running with the energy that we need
● Each area of the digestive system has a particular
role to play in the big picture
● The nervous and endocrine systems control the
actions of the digestive system in various ways
Fetal Pig Pictures