Human Digestive System

2. Digestion
• Phases Include
1. Ingestion
2. Movement
3. Mechanical and Chemical Digestion
4. Absorption
5. Elimination

3. Digestion
• Types
– Mechanical (physical)
• Chew
• Tear
• Grind
• Mash
• Mix
– Chemical
• Enzymatic reactions to improve digestion of
– Carbohydrates
– Proteins
– Lipids

4. Digestive System Organization
• Gastrointestinal (Gl) tract
– Tube within a tube
– Direct link/path between organs
– Structures
• Mouth
• Pharynx
• Esophagus
• Stomach
• Small intestine
• Large Intestine
• Rectum
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5. Mouth
• Teeth mechanically
break down food into
small pieces. Tongue
mixes food with saliva
(contains amylase,
which helps break down
starch).
• Epiglottis is a flap-like
structure at the back of
the throat that closes
over the trachea
preventing food from
entering it.

6. Esophagus
• Approximately 10” long
• Functions include:
1. Secrete mucus
2. Moves food from the throat to
the stomach using muscle
movement called peristalsis
• If acid from the stomach gets in
here that’s heartburn.

7. Stomach
• J-shaped muscular bag that stores the food
you eat, breaks it down into tiny pieces.
• Mixes food with digestive juices that
contain enzymes to break down proteins
and lipids.
• Acid in the stomach kills bacteria.
• Food found in the stomach is called chyme.
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8. Small Intestine
• Small intestines are roughly 7 meters long
• Lining of intestine walls has finger-like
projections called villi, to increase surface
area.
• The villi are covered in microvilli which
further increases surface area for
absorption.
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10. Small Intestine
• Nutrients from the food pass into the
bloodstream through the small
intestine walls.
• Absorbs:
– 80% ingested water
– Vitamins
– Minerals
– Carbohydrates
– Proteins
– Lipids
• Secretes digestive enzymes
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11. Large Intestine
• About 5 feet long
• Accepts what small intestines don’t
absorb
• Rectum (short term storage which
holds feces before it is expelled).

12. Large Intestine
• Functions
– Bacterial digestion
• Ferment carbohydrates
• Protein breakdown
– Absorbs more water
– Concentrate wastes

13. Accessory Organs
• Not part of the path
of food, but play a
critical role.
• Include: Liver, gall
bladder, and
pancreas

14. Liver
• Directly affects digestion by producing
bile
– Bile helps digest fat
• filters out toxins and waste including
drugs and alcohol
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15. Gall Bladder
• Stores bile from the
liver, releases it into the
small intestine.
• Fatty diets can cause
gallstones

16. Pancreas
• Produces digestive
enzymes to digest fats,
carbohydrates and
proteins
• Regulates blood sugar
by producing insulin

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Organ Function
Mouth Chewing, Digestion of starch by salivary amylase
Esophagus
transport of food from mouth to stomach; lubricated by
mucus
Stomach
Storage of food and initial digestion of proteins + fats;
production of the hormone gastrin (response to protein)
that stimulates stomach's gastric glands to release gastric
juice (including pepsin and HCl)
Small intestine
Continued digestion of carbohydrates, proteins, lipids; most
absorption of nutrients; production of the hormone secretin
(response to HCl) that stimulates pancreas to release
bicarbonate; production of the hormone CCK (response to
fat) that stimulates gall bladder to release bile
Pancreas
Production of digestive enzymes that act in small intestine;
production of the hormones insulin and glucagon which
regulate blood sugar; production of bicarbonate that
neutralizes stomach acid in small intestine
Large intestine
Absorption of water; Production of some vitamins; storage
of undigested food

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Organ Secretion and Function
Salivary glands
salivary amylase - converts starch (a polysaccharide) to maltose (a
disaccharide)
Esophagus mucus - helps movement of food
Stomach
HCL- Converts pepsinogen to pepsin and kills microbes
Pepsinogen - Pepsin, digests proteins to polypeptides & peptides
Lipase - Converts lipids into glycerol and fatty acids
Mucus - Protects stomach from pepsin and HCl
Renin - Coagulates proteins in milk to slow movement
Pancreas;
Small intestine Pancreatic amylase - Converts starch to maltose
Bicarbonate - Neutralizes HCl from stomach
Enterokinase - Converts trypsinogen to trypsin
Trypsinogen - Trypsin, converts proteins into peptides
Erepsin - Converts peptides into amino acids
Lipase - Converts lipids into glycerol and fatty acids
Maltase - Converts maltose (a disaccharide) into two glucose
sucrase - Converts sucrose into glucose and fructose
Lactase - Converts lactose into glucose and galactose
Liver / Gall
bladder
Bile - Emulsifies fat (large globules into smaller ones for lipase to
work)
Large intestine Mucus - helps movement of food
Table 2: Substances Involved in Digestion
Organ Secretion and Function
salivary glands
salivary amylase - converts starch (a
polysaccharide) to maltose (a
disaccharide)
esophagus mucus - helps movement of food
stomach
hydrochloric acid - converts
pepsinogen to pepsin and kills
microbes
pepsinogen - when converted to
pepsin, initiates digestion of proteins
(long chains of amino acids) to
polypeptides and peptides (shorter
chains of amino acids)
lipase - converts lipids (eg.
triglycerides) into glycerol and fatty
acids
mucus - protects stomach from pepsin
and HCl
renin - coagulates proteins in milk to
slow movement
pancreas; small intestine
pancreatic amylase - converts starch
(a polysaccharide) to maltose (a
disaccharide)
bicarbonate - neutralizes HCl from
stomach
enterokinase - converts trypsinogen to
trypsin
trypsinogen - when converted to
trypsin, converts proteins into peptides
erepsin - converts peptides into amino
acids
lipase - converts lipids (eg.
triglycerides) into glycerol and fatty
acids
maltase - convets maltose (a
disaccharide) into two glucose (a
monosaccharide)
sucrase - convets sucrose (a
disaccharide) into glucose and
fructose (monosaccharides)
lactase - convets lactose (a
disaccharide) into glucose and
galactose(monosaccharides)
liver
bile - emulsifies fat (large globules into
smaller ones for lipase to work)
gall bladder
bile - stores concentrated bile from
liver
large intestine mucus - helps movement of food

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20. Facts
• HOW LONG ARE YOUR INTESTINES? At least 25 feet
in an adult!
• Food drying up and hanging out in the large intestine
can last 18 hours to 2 days!
• In your lifetime, your digestive system may handle
about 50 tons!!

22. On a sheet of paper, write the name of
each colored organ:
• Green:
• Red:
• Pink:
• Brown:
• Purple:
• Green:
• Yellow:

23. How’d you do?
• Light Green: Esophagus
• Red: Stomach
• Pink: Small Intestine
• Brown: Large Intestine
• Purple: Liver
• Dark Green: Gall Bladder
• Yellow: Pancreas
Great Job!