Digestive System
Function
• Takes in food
• Propulsion of food
• Breaks food down
Mechanically and
Chemically-Digestion
• Absorbs nutrients into
bloodstream
• Reclaims water
• Excretes waste
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
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
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
Frenulum Medical Problem
• When a child has a
short frenulum or an
attachment that is
farther forward,
surgery is sometimes
required to improve
speech
Tonsils
• Part of the body’s
defense system
• Palatine Tonsils
• Lingual Tonsils at
the base of the
tongue
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.
Pharynx
• Passageway that
connects nasal cavity
and oral cavity to the
esophagus
• Respiratory and
digestive function
• Food triggers
involuntary reflexes
Esophagus
• Muscular Tube
connecting pharynx to
stomach
• 10 inches long
• Between esophagus
and stomach is a ringlike valve that is
closed until food
pushes on it
Stomach
• Preparation of food for
digestion
• Mechanically mixes food
• Chemically liquefies food
• Kills Bacteria and
Parasites
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
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
Small Intestine
• Stomach empties into
small intestine,
(resembles coiled
hose)
• Juices from pancreas
and gall bladder mix
in here
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
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
Pancreas
• Produces digestive
enzymes
• Also part of endocrine
system producing
hormones: insulin and
glucagon
Gall Bladder
• Reservoir for bile
• Secretes bile to break
down fats
• Green and snuggles
in near the liver
Liver
• Largest gland in the
body
• Has 4 lobes
• Metabolic and
Regulatory
• Produces Bile
• Secretes through
hepatic duct
Function
•
•
•
•
•
•
Ingestion
Propulsion
Mechanical and Chemical Digestion
Absorption of nutrients
Absorption of water
Defecation
Ingestion
Food is placed in the mouth
• Physical / Mechanical
breakdown = chewing
• Chemical = Saliva
contributes amylase
(Ptyalin is one type) to
break down starch into
maltose or to predigest
fruit and grain
(carbohydrates)
• No Absorption except
sublingual drugs/ vitamins
through oral mucosa
Propulsion
• Deglutination =
Swallowing
• Propelled to next
digestive organ by
peristalsis
– Contraction and
relaxation of muscles
that is involuntary
Mechanical
• Mixing in mouth by
tongue and teeth
• Churning in stomach
• Prepares food for
further chemical
breakdown
Chemical
• Large molecules are broken down into building
blocks
• Hydrolysis = Water molecules are added to split
larger molecules
• Water is also softening agent
Absorption
• Nutrients move from
the lumen of the
gastrointestinal tract
to the blood or lymph
Defecation
• Elimination of
indigestible portions
of food
• Only happens in the
large intestine
• Water removal is
important
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.
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
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
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.
More 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.
Even More 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.
Yes! More Enzymes
• Small Intestine:
• Peptidases complete the digestion of
peptides to amino acids.
• Maltase completes the digestion of
disaccharides.
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
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
Hormones
• Hormones, reach their target cells by the
circulatory system.
• Examples are Gastrin and Secretin
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.
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.
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.
Ulcers
• An ulcer is an irritation due to
hydrochloric acid and pepsin found
in 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.