The digestive system has two major parts: the gastrointestinal tract and accessory organs. The gastrointestinal tract includes the mouth, esophagus, stomach, small intestine and large intestine. Accessory organs include the teeth, tongue, liver, gallbladder and pancreas. Food is ingested, mechanically and chemically digested, absorbed in the small intestine, and waste is excreted. Digestion involves enzymes from the mouth, stomach, pancreas, and small intestine breaking down food into smaller molecules that can be absorbed and used by the body. Hormones like gastrin and secretin regulate digestive processes.

1. Digestive System

2. Function
●Takes in food
●Breaks food down
mechanically-Digestion
●Breaks food down
chemically-Digestion
●Absorbs nutrients into
bloodstream
●Reclaims water
●Excretes waste

3. Two Major Parts
●Gastrointestinal Tract
●Also called The
Alimentary Canal
●Includes: mouth,
pharynx, esophagus,
stomach, small intestine
and large intestine
●Accessory Organs
●Include: teeth, tongue,
salivary glands, liver,
gall bladder and
pancreas

4. Mouth (Oral Cavity)
●Begins the digestive
process by breaking
down food
●Protected by lips
●Cheeks form the walls
●Hard Palate is the roof
●Soft Palate is the
posterior roof
●Tongue is the floor

5. Tongue
●The tongue attaches to
the hyoid bone and to
the styloid process of
the skull
●The inguinal frenulum
holds the tongue to the
floor of the mouth and
keeps it from sliding
posteriorly

6. Frenulum Medical Problem
●When a child has a
short frenulum or an
attachment that is
farther forward, surgery
is sometimes required
to improve speech

7. Tonsils
●Part of the body’s
defense system
●Palatine Tonsils
●Lingual Tonsils at
the base of the
tongue

8. Salivary Glands
●Food enters the mouth
& teeth break the food
down mechanically
●Salivary Enzymes
Ptyalin and Amylase
work on chemically
digesting starches
●Salivary enzymes also
attack bacteria in the
food.

9. Pharynx
●Passageway that
connects nasal cavity
and oral cavity to the
esophagus
●Respiratory and
digestive function
●Food triggers
involuntary reflexes

10. Esophagus
●Muscular Tube
connecting pharynx to
stomach
●10 inches long
●Between esophagus
and stomach is a ring-
like valve that is closed
until food pushes on it

11. Stomach
●Preparation of food for
digestion
●Mechanically mixes food
●Chemically liquefies food
●Kills Bacteria and Parasites

12. Gastric Pits
●Gastric pits cover the lining
of the stomach
●Secrete gastric juice
●Intrinsic factor- absorption
of Vitamin B12
●Parietal cells produce
Hydrochloric Acid (HCl)
Which provide the protein
digesting enzyme, pepsin

13. Pyloric Sphincter (Valve)
●A full stomach can hold
4 liters or 1 gallon of
food
●Empty, it folds up
●The Pyloric Sphincter
keeps food from being
forced into the intestine
too early

14. Small Intestine
●Stomach empties into
small intestine,
(resembles coiled hose)
●Juices from pancreas
and gall bladder mix in
here

15. Absorption
●This is the site of
nutrient absorption
●Large surface area
covered with projections
(villi)
●Vitamins, minerals,
carbs, protein, fat and
bile salts go to the
bloodstream

16. Large Intestine
●5 feet long
●Water is absorbed with
any remaining nutrients
and feces are formed
●Bacteria plays an
essential role here and
we have about 4
pounds of it

17. Pancreas
●Produces digestive
enzymes
●Also part of endocrine
system producing
hormones: insulin and
glucagon

18. Gall Bladder
●Reservoir for bile
●Secretes bile to break
down fats
●Green and snuggles in
near the liver

19. Liver
●Largest gland in the
body
●Has 4 lobes
●Metabolic and
Regulatory
●Produces Bile
●Secretes through
hepatic duct

20. Function
●Ingestion
●Propulsion
●Mechanical Digestion
●Chemical Digestion
●Absorption
●Defecation

21. Ingestion
●Food is placed in the
mouth
●Physical / Mechanical
breakdown begins with
chewing
●Saliva contributes amylase
(Ptyalin) to break down
starch into maltose
●No Absorption except
sublingual drugs/ vitamins
through oral mucosa

22. Propulsion
●Deglutination =
Swallowing
●Propelled to next
digestive organ by
peristalsis
● Contraction and
relaxation of muscles
that is involuntary

23. Mechanical
●Mixing in mouth by
tongue and teeth
●Churning in stomach
●Prepares food for
further chemical
breakdown

24. Chemical
●Large molecules are broken down into building
blocks
●Hydrolysis = Water molecules are added to split
larger molecules
●Water is also softening agent

25. Absorption
●Nutrients move from
the lumen of the
gastrointestinal tract to
the blood or lymph

26. Defecation
●Elimination of
indigestible portions of
food
●Only happens in the
large intestine
●Water removal is
important

27. Microorganisms
●The gastrointestinal tract contains an
immensely complex ecology of
microorganisms. A typical person harbors
more than 500 distinct species of bacteria.
●The number and type vary dramatically by
region. In healthy individuals the stomach
and proximal small intestine contain few
microorganisms, largely a result of the
bacteriocidal activity of gastric acid.

28. Microorganisms
●Most are located in the illeum (pH 7.5) and
colon (pH 6.8)
●bacterial populations in the large intestine
digest carbohydrates, proteins and lipids
that escape digestion and absorption in
small intestine. This fermentation,
particularly of cellulose, is of critical
importance to herbivores.
●Assists in absorption of Vitamin K

29. Enzymes
●Salivary amylase (also called Ptyalin)
breaks starch (a polysaccharide) down to
maltose (a disaccharide)
●Bicarbonate ions in saliva act as buffers,
maintaining a pH between 6.5 and 7.5.
●Mucins (mucous) lubricate and help hold
chewed food together in a clump called a
bolus

30. Gastric Juice
●Pepsinogen is converted to pepsin, which
digests proteins. Pepsinogen production is
stimulated by the presence of gastrin in the blood
(discussed below).
●Hydrochloric acid (HCl) converts pepsinogen to
pepsin which breaks down proteins to peptides.
HCl maintains a pH in the stomach of
approximately 2.0.
●It also dissolves food and kills microorganisms.
●Mucous protects the stomach from HCl and
pepsin.

31. Enzymes
●Pancreatic Juice
●Pancreatic juice contains sodium bicarbonate
which neutralizes the acidic material from the
stomach.
●Pancreatic amylase digests starch to maltose.
●Trypsin and Chymotrypsin digest proteins to
peptides. Like pepsin (produced in the stomach),
they are specific for certain amino acids, not all of
them. They therefore produce peptides.
●Lipase digests fats to glycerol and fatty acids.

32. Enzymes
●Liver
●The liver produces bile which is stored in
gallbladder and sent to the duodenum
through a duct.
●Bile emulsifies fats (separates it into small
droplets) so they can mix with water and be
acted upon by enzymes.

33. Enzymes
●Small Intestine:
●Peptidases complete the digestion of
peptides to amino acids.
●Maltase completes the digestion of
disaccharides.

34. FOOD TYPE ENZYME SOURCE PRODUCT
CARBOHYDRATES Salivary amylase
Pancreatic amylase
Maltase
Salivary glands
Pancreas
Small intestine
Maltose
Maltose
Glucose
PROTEINS Pepsin
Trypsin
Peptidases
Stomach mucosa
Pancreas
Intestinal mucosa
Peptides
Peptides
Amino acids
FATS Lipase Pancreas Fatty acids
and glycerol

35. SOURCE ENZYME FOOD PRODUCT
MOUTH (salivary
glands)
Salivary
amylase
Polysaccharides Maltose
STOMACH Pepsin Proteins Peptides
PANCREAS Pancreatic
amylase
Trypsin
Lipase
Polysaccharides
Proteins
Fats
Maltose
Peptides
Fatty acids
and glycerol
SMALL INTESTINE Maltase
Peptidases
Maltose
Peptides
Glucose
Amino acids

36. Hormones
●Hormones, reach their target cells by the
circulatory system.

37. Gastrin
●The presence of food in the stomach
stimulates stretch receptors which relay this
information to the medulla oblongata. The
medulla stimulates endocrine cells in the
stomach to secrete the hormone gastrin,
into the circulatory system. Gastrin
stimulates the stomach to secrete gastric
juice.

38. Secretin
●Secretin is produced by cells of the
duodenum.
●It’s production is stimulated by acid chyme
from stomach.
●It stimulates the pancreas to produce
sodium bicarbonate, which neutralizes the
acidic chyme. It also stimulates the liver to
secrete bile.

39. Polyps
●Polyps are small growths in the epithelial lining of the colon.
●They can be benign or cancerous and can be removed individually.
●A low-fat, high-fiber diet promotes regularity and is recommended as a
protection against colon cancer.

40. Ulcers
●An ulcer is an irritation due to
gastric juice penetrating the
mucous lining of the stomach or
duodenum. It is believed that
ulcers are caused by the
bacterium Helicobacter pylori,
which, can thrive in the acid
environment of the stomach. The
presence of the bacteria on
portions of the stomach lining
prevents it from secreting
mucous, making it susceptible to
the digestive action of pepsin.