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8.3 & 8.4 - Digestive System
(Ingestion & Digestion)
Adapted by Patrick Shackleford
From a presentation by
Dr. Jared Heidinger M.D. Ph.D
Digestion
• The digestive system is interdependent
with other body systems to function
properly:
muscle system, skeletal system, circulatory
system, nervous system, endocrine system
• How does each help?
What we call “Digestion” is actually 4
processes:
1. Ingestion - Taking nutrients into the body
(eating)
2. Digestion - Breaking down the organic
molecules into smaller complexes
– Two types: physical and chemical
3. Absorption - Transport of digested nutrients
to the tissues of the body
4. Egestion - Removal of waste and the
materials from the food that the body cannot
digest
The Digestive
System
1. Ingestion
Mouth to
Stomach
Mouth
Food enters the
alimentary canal
(digestive tract)
through the mouth
• the mouth starts the physical digestion by
chewing (mastication) with the teeth & tongue
• creates bolus (ball of food)
Saliva
• Contains salivary amylase produced by the
salivary glands breaks down starch into simpler
carbs (chem. digestion).
• Lubricates food for swallowing
• Dissolves food in order to be “tasted”
Chewing tobacco beautiful
images…
• In 2006, cigarette companies spent $12.4 billion on advertising
and promotional expenses in the United States alone.3
• The money cigarette companies spent on U.S. marketing in 2006
amounted to approximately $34 million per day.3
STATS
• Chewing tobacco
contains at least 28
known carcinogens.
• During 2000–2004, total
tobacco use was
estimated to be
responsible for $193
billion in annual healthrelated economic losses
in the United States (
• $96 billion in direct
medical costs
• $97 billion in lost
productivity).10
STATS
• The total economic costs
(direct medical costs and
lost productivity)
associated with cigarette
smoking are estimated
at $10.47 per pack in the
United States.11
• In early 2010, the
average retail price of a
pack of cigarettes in the
United States was
approximately $4.80.
P.S. Chew contains fibreglass.
Why?
To cut open the flesh to allow nicotine in quicker (strengthen addiction further)
From Mouth to Stomach
• Pharynx – section where air and food are
directed to different tubes
• Esophagus – food tube (goes to stomach)
• Epiglottis (small cartilaginous flap) flips down
and covers the trachea so that no food or drink
can go “down the wrong pipe”
I am the Master of my body!...well..
• Voluntary control of food only during first
phase (ingestion – chewing and
swallowing) and last phase (egestion defecation) the rest of the process is
involuntary.
• Ex. You can’t “try” to move or digest food
quicker
Esophagus
• The esophagus connects
the oral cavity to the
stomach and uses
Peristalsis – a rhythmic,
wavelike contraction of the
smooth muscle that moves
food through the digestive/
G.I tract.
G.I. = Gastrointestinal
Candida esophagitis (yeast
infection)
Ulcer in Esophagus
Another Ulcer in Esophagus
Esophagus to Stomach
Sphincters
• Regulate the entry and
exit of food from the
stomach
• Act like drawstrings
• Lower Esophageal
Sphincter (LES)– entry into
the stomach – prevents acid
reflux
• Pyloric Sphincter – regulates move of
food out of the stomach into small intestine
Stomach
• The stomach is the site of
food storage and initial
protein digestion
• Surrounded by 3 layers of
muscle (different directions)
to churn food into chyme.
• J shape & numerous folds allow for 1.5 L
capacity
• Normal pH ranges from 2.0-3.0 (low as 1.0)
Stomach – cells & gastric juices
• Up to 500 mL of juices produced after large
meal
• Mucous cells secrete a protective (alkaline)
mucous coating over stomach lining.
• Parietal cells secrete HCl (hydrochloric acid) to
kill pathogens, denature proteins.
• Peptic cells secrete pepsinogen
– Pepsinogen changes into the enzyme pepsin in the
presence of hydrochloric acid which breaks proteins
into smaller polypeptides
Gastric Ulcers
• Form when the mucous layer breaks
down, cells lining the stomach are
destroyed by acid & pepsin (stomach
literally starts digesting itself)
• Steps must be taken to decrease the
acidity of the stomach or ulcer will grow
(antacids)
• Endoscope can be used to view the
interior of the body
Beautiful isn’t it?
ULCERED!
The Digestive
System
2/3. Digestion
& Absorption
Small Intestines
& Accessory
Organs
Small Intestine and Pancreas
(the digestive duo!)
• Small Intestine - small diameter,
large in length (up to 7m)
3 Sections
1st – Duodenum
– The majority of chemical Digestion
occurs here
– Bile and Pancreatic ducts
connect (add fluids)
2nd – Jejunum
3rd - Ileum
Hormones
• Part of Endocrine system (bio 30)
• Chemicals released by cells that affect
cells in other parts of the body (required
in small amounts)
• Travel through the blood stream
• Ex. Secretin (small intestine to pancreas)
Digestive Duo cont.
Digestive Duo cont.
• Pancreatic secretions contain bicarbonate
ions HCO3- (basic)
• Released into duodenum via pancreatic
duct.
• Neutralizes low pH of the chyme (contains
HCl) raising pH from 2.5 to 9.0
• Pepsin becomes inactive in the high pH,
protects duodenum from digestion. If this
function of the pancreas is inhibited, a
duodenal ulcer can form
Pancreatic Secretions: Enzymes
• Trypsinogen is released from pancreas, when it
enters the small intestine, an enzyme called
enterokinase activates the trypsinogen into
trypsin which continues digestion on proteins.
Pancreatic Enzymes cont.
• Lipase – Breaks down fats into component
glycerol and fatty acids.
• Pancreatic Amylase – Completes the break
down of carbs started in the mouth.
Small Intestine Secretions
• Disaccharidases – Breaks down Disaccharides
into monosaccharides.
• Ex. Maltase breaks maltose down into glucose.
• Erepsin – Completes breakdown of proteins
into individual amino acids.
Absorption of Nutrients
• Stomach absorbs some water,
specific vitamins and alcohol
• Large Intestine absorbs some
vitamins and water
• Small Intestine absorbs the most
nutrients of all the organs in the
digestive system
Absorption cont.
• Villi - small finger like projections
that extend into the small intestine.
Villi increase
surface area
for absorption.
Microvilli - infoldings of the cell
membrane on the cells. Look like
fine hairs covering the
cell.
The cells that make up
the villi in the digestive
system also have
microvilli on them.
Increase S.A. Again!
Lacteals
• Each villus is supplied with a capillary
network that intertwines with lymph
vessels called lacteals
• Carbohydrates and amino acids are
absorbed into capillary
network
• Fats absorbed into
lacteals
Liver and Gallbladder
• Liver has many functions
• Main function related to digestion produces fluid called Bile which contains
bile salts - aid in fat digestion by
physically emulsifying fat into smaller
particles (more S.A. For lipase to
chemically digest)
• Gallbladder stores and concentrates bile
salts when the stomach is empty.
Liver and Gallbladder cont.
Cholecystokinin (CCK) – hormone released by
small intestine in response to fats, stimulates
gallbladder to release bile salts.
Nice liver man!
Liver cont.
• Secondary function related to digestion
- acts as a storehouse for glycogen and
vitamins (A, B12, D)
• Also detoxifies the blood (deactivates
poisons) the body
• alcoholism causes cirrhosis of the liver
where the liver becomes inflamed from
an increase of non-functioning fibrous
tissue and fat.
Alcoholic liver
Liver and Gallbladder cont.
• Crystals of bile salts which form on cholesterol
can build up and become a very large mass
called a gallstone
• Can get stuck in the bile duct when it is on its
way to the small intestine (huge amounts of
pain)
• Can cause Jaundice – Yellow discoloration of
skin and eyes due to backup
of bile salts in the
blood
The Digestive
System
4. Egestion
Large Intestine
to Anus
Lets take a journey through the colon!
Large Intestine - Colon
• Chemical digestion of food is complete by the
time it reaches the large intestine
• Colon - The largest segment of the large
intestine
• Functions: stores wastes and absorbs water
into the body (along
with some organic salts)
• also houses bacteria
which synthesize
vitamins B and K
Fibre in the colon
1. Fibre is important because it
helps to keep water in the large
intestine which aids in Egestion (removal)
2. Binds cholesterol, lowers
cholesterol levels
3. Adequate fibre intake keeps
you “regular” (makes bowel
movements regular) which means that toxins are
removed from the body on a regular basis. Helps
avoid conditions like colon cancer
Control of Digestion
• Exerted by Nervous and Hormonal systems
• Sight, Smell, Taste, Physical, Chemical
• Gastrin – secreted by the stomach - stimulates
the release of HCl by parietal stomach cells.
• Enterogastrone – secreted by small intestine slows peristaltic movements allowing time for
fat digestion
Control of Digestion
GASTRIN
ENTEROGASTRONE