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Digestive System
The digestive system consists
Digestive tract,Oral cavity,Salivary
Ingest food
Break it down
Absorb nutrients and water
Get rid of waste
Supply the body with energy to
Ingestion: materials enter the mouth
Mechanical processing: tearing and
crushing with teeth and squashing with
tongue making it easier for food to travel
through the digestive tract
Digestion: breakdown of food into smaller
Secretion: glandular organs and epithelium
release water, acids, enzymes, buffers,
and salts.
Absorption: the movement of organic
substrates, electrolytes (inorganic
ions), vitamins, and water across the
digestive epithelium and into the
interstitial fluid of digestive tract.
Excretion: eliminate waste products
from body. A process called
*eliminates materials as feces.
Its lining:
The lining of the digestive tract
protects surrounding tissues against
the effects of digestive acids and
*If bacteria reaches the lamina propria
it will be attacked by macrophages
and by other cells of the immune
Major layers of digestive tract
Mucosa: its the inner lining, consists of a
layer of an epithelium moistened by
glandular secretions and an underlying
layer of areolar tissue, called the lamina
Submucosa: layer of dense irregular
connective tissue. Surrounds the
muscularis mucosae.
Has large blood cells and lymphatic
Major layers of digestive tract
Muscularis externa: mostly smooth
muscle. Covered by Serosa.
Responsible for mechanical
processing and movement along the
digestive tract.
Oral cavity
Digestion begins even before food is
ingested. Just by the sight, smell or even
thinking about food.
The sight of food stimulates the salivary
When food is taken into the mouth it gets
prepared for digestion in a process known
as mastication.
Teeth tear down the food making it into
smaller pieces.
Tongue rolls these pieces into boluses.
Parotid, sublingual, and submandibular glands
produce saliva
Breaks down food, Make food easy to swallow
Lubricate the mouth when you eat and moisten
Salivary gland produces 1.0-1.5 liters of saliva
each day.
99.4% water the remaining 0.6% includes
electrolytes, buffers, antibodies, enzymes, and
waste products.
About saliva
mucins is responsible for the lubricating
action of saliva.
Salivary secretions are controlled by
autonomic system.
Nauseas will keep your mouth wet;
increases saliva production.
70% of saliva originates in the
submandibular salivary glands
25% in the parotids
5% in the sublingual cavity.
tongue/taste buds
Detect: sweet, salt, bitter and sour.
Olfactory nerves contribute by
sending the aroma to the brain.
Everyone's taste buds are different.
They will change as you get older.
Fast fact: when you were a baby you
had taste buds, but not only in your
tongue, but on the sides and roof of
your mouth. You were sensitive to
different foods.
Taste buds disorders
smoking, not
getting enough of
the right vitamins,
injury to the head,
brain tumors,
chemical exposure,
and the effects of
radiation can cause
taste disorders.
We have almost 10,000 taste buds
inside our mouths, even on the roofs
of our mouths.
Girls have more taste buds than boys.
Taste is the weakest of the five
The Pharynx
Passageway for solid food, liquids,
and air.
Nasopharynx, oropharynx, and
Food passes through the pharynx and
laryngopharynx to the esophagus.
Voluntarily, automatically once it
Buccal phase
Pharyngeal phase
Esophageal phase
When the bolus of food is swallowed, the
epiglottis closes the trachea.
Food is forced to the esophagus
Epiglottis opens up again
Receives blood from inferior phrenic arteries.
Prevents air from entering.
Movements of Materials: Peristalsis
Smooth muscle tissue is able to
move in a wave of contraction.
Bolus move through the
esophagus with the help of
contractions called Peristalsis.
The contractions occur behind the
bolus pushing it down the digestive
2 or 3 seconds.
Shape of an expanded J.
A short lesser curvature forms the medial
surface of the organ, and a long greater
curvature forms the lateral surface.
The anterior and posterior surfaces are
smoothly rounded.
An average stomach, the lesser curvature
has the length of approximately
10cm (4in.) and the greater curvature
about 40 cm (16 in.)
The stomach extends between the levels of
the vertebrae T7 and L3.
Stomach has four regions:
The cardia: the smallest part of the
stomach. 3 cm (1.2 in.) it contains
abundant mucous glands whose secretions
coat the connection with the esophagus
and help protect that tube from the acids
and enzymes of the stomach.
The fundus: superior to the junction between the
stomach and esophagus. Contacts the diaphragm
The body: between the Fundus and the curve of
the J. the largest region, acts as a mixing tank for
ingested food.
Gastric glands secrete most of the acids and the
The pylorus: the curve of the J. it's divided into
pyloric antrum that is connected to the body and
pyloric canal, which empties to the duodenum.
When the mixing movements occur the pylorus
changes shape.
Pyloric sphincter regulates how much chyme its release into
the duodenum.
The volume of the stomach increases while you eat, then
decreases when chyme enters the small intestine.
When stomach is relaxed (empty), the mucosa is thrown into
prominent folds called rugae
Rugae is a temporary feature that lets gastric lumen expand.
When your stomach fills the rugae flattens out. When its full
the rugae almost disappears. When full: it can expand to
contain 1-1.5 liters of material.
Active stomach
Mixes w/ gastric juices for 3 hours.
When filled up its walls begin to
contract downward in a swaying
The oblique layer assist in the mixing and churning
essential to the formation of chyme.
Alkaline mucous layer protects epithelial cells against the
acids and enzymes in the gastric lumen.
The stomach receives blood from the left gastric artery,
which supplies the left gastroepiploic artery and the
common hepatic artery supplies the right gastric Then
drained by the gastric and gastroepiploic veins.
*When food is liquefied in the stomach, it is slowly
released into the small intestine for further processing.
Stomach lining
It contains
Hydrochloric acid
(HCI) and enzymes
(pepsin) that break
down food.
When food enters HCI
is released.
Gastric pits openings
to the gastric mucosa.
Gastric epithelial cells
has a life span of 3-7
Parietal and chief
Together they
secrete 1500 ml of
gastric juice each
Parietal cells secrete intrinsic factor.
This facilitates the absorption of
vitamins B12. They also secrete
hydrochloric acid. HCI is not produced
in the cytoplasm because it's such a
strong acid that would destroy the
H+ and C1- form HCI and are
transported by different mechanisms
Parietal/ G Cells
The acidity of gastric juices kills most of the
microorganisms ingested in food.
The acidity break down plant cell walls and
the connective tissues in the meat.
G cells produce gastrin.
Gastrin stimulates the secretion of both
parietal cells and chief cells.
They also help the contractions when
mixing the food .
Chief cells
pepsinogen, then
converted to
Pepsin functions as
a strong acidic pH
of 1.5-2.0
Three phases of gastric control
Cephalic phase: Begin when you see, taste, or
smell food. Prepares your stomach to receive
food. Only lasts minutes.
- increase volume of gastric juices by stimulating
mucus, enzyme and acid prod.
Gastric phase: begins with the arrival of food. 3 –
4 hrs.
-consists of Neural response, Hormonal response,
Local response.
Intestinal phase: starts when chyme enters the
small intestine.
Small Intestine
6 m (20ft.) in length
Absorb minerals, vitamins, carbohydrates,
proteins, and fats.
Divided into three sections: Duodenum,
Jejunum, and Ileum.
90% of the absorption of nutrients occur in
Duodenum: a mixing bowl that receives chyme
from the stomach. It curves in a C that
encloses the pancreas. It's between vertebrae
L1 and L4
Enzymes released from liver, gallbladder,
pancreas break bolus down.
Jejunum: chemical
digestion and
nutrient absorption
occur in the
Ileum: final
segment of the
small intestine.
Undigested food
enters the large
Intestinal villi
Has folds of Plicae.
Does not disappear
when stomach fills.
Small intestine
contains 800 Plicae.
It increases the
area available for
Villi Structure
Each villus is covered by
epithelial cells which
contain microvilli.
Increases absorption
The Lamina Propria of
each villus contain a
network of capillaries.
Carry absorbed nutrients
& deliver it to the liver &
send it to the bloodstream
to get to the body cells.
Contractions move the villi back and forth.
The movements of the villi squeeze the lacteals,
and they move lymph out of the villi.
Capillaries contain lymphatic capillary called
Transport materials that aren't able to enter
blood capillaries.
Small intestine: movements
When chyme enters the duodenum it
is then moved with peristaltic
contractions towards jejunum.
Nervous system controls this.
Has two distinct functions: endocrine and
Produces digestive enzyme and buffers
Pancreatic duct: delivers secretions to the
Three enzymes in pancreatic juice which
digest carbohydrates, lipids, and proteins.
Lipases and pancreatic juices break down
fat into fatty acids and glucerol, while
proteinases continue to breakdown
proteins into amino acids.
Pancreatic juice
Secrete about 1000 ml (1 qt) of pancreatic
Pancreatic enzymes:
-pancreatic alpha- amylase, a
carbohydrate. Breaks down starches.
Identical to salivary amylase.
- Pancreatic lipase:break down complex
lipids, release products like fatty acids.
- Proteolytic Enzyme: break proteins apart
Secrete insulin and glucagon into the
The largest organ in the body
Functions: metabolic regulation,
hematological regulation, and bile
The liver has more than 200 functions.
It controls the excretion and production of
Stores iron, maintains the hormone
balance, fights infections, regulates blood
Bile functions
Bile salts break down droplets apart.
90% of the bile salts are reabsorbed
in the ileum.
This reabsorbed bile salts are
collected and recycled by the liver
Stores bile; releases bile
into small intestine. It can
store 2 oz.
Divided in three sections:
-the Fundus
- Body
Two major functions: bile
storage and bile
When full it can contain 4070 ml of bile
The major hormones that control the
functions of the digestive system
are produced and released by cells in the
mucosa of the stomach and small intestine.
These hormones are released into the blood of
the digestive tract, travel back to the heart and
through the arteries, and return to the digestive
system where they stimulate digestive juices and
cause organ movement
Gastric causes the stomach to produce an acid for
dissolving and digesting some foods. Gastric is
also necessary for normal cell growth in the lining
of the stomach, small intestine, and colon.
Secretin causes the pancreas to send out a
digestive juice that is rich in bicarbonate. The
bicarbonate helps neutralize the acidic stomach
contents as they enter the small intestine. Secretin
also stimulates the stomach to produce pepsin, an
enzyme that digests protein, and stimulates the
liver to produce bile.
CCK causes the pancreas
to produce the enzymes of
pancreatic juice, and
causes the gallbladder to
empty. It also promotes
normal cell growth of the
Ghrelin is produced in the stomach
and upper intestine in the absence of
food in the digestive system and
stimulates appetite.
Peptide YY is produced in the
digestive tract in response to a meal
in the system and inhibits appetite
Intestinal absorption
Takes about 5 hours for materials to
pass from duodenum to the end of the
The cecum, the first part of the large intestine, the inner
side of the ilium (the upper part of the hipbone).
a pouch or large tube like structure in the lower
abdominal cavity that receives undigested food material
from the small intestine and is considered the first region
of the large intestine. It is separated from the ileum (the
final portion of the small intestine) by the ileocecal
valve which limits the rate of food passage into the
cecum and may help prevent material from returning to
the small intestine.
main functions: absorb fluids and salts that remain after
completion of intestinal digestion and absorption & to mix
its contents with mucus.
The ileocecal valve
has two main
functions. The first is
to prevent the back
flow of fecal contents
from the colon to the
small intestine. The
second is to prevent
the contents of the
ileum from passing
into the cecum
Large intestine
Begins at the end of the ileum ends at the anus.
Major functions: reabsorption of water and
compaction of intestinal contents into feces.
-Absorptions of important vitamins.
- storage of fecal material prior to defecation.
Length of 1.5 meters (5ft.)
Four regions
ascending colon
transverse colon
Descending colon
Sigmoid colon
l. intestine
10% nutrient absorption
Most of the bile salts that are in the
large intestine are absorbed in the
cecum and transported in blood to the
liver for secretion into bile.
Three parts
Divided in three parts
Cecum- first portion of the large
The colon- largest portion
Rectum- end of the digestive tract.
Absorption in l. intestine
1500 ml of material enters your colon
each day, only about 200 ml of feces
is ejected.
- its 75% water 5% bacteria & rest a
mixture of indigestible material and
remains of epithelial cells.
Takes hours for
material to turn into
Mass movementsoccur a few times
each day.
Contractions forces
feces into the rectum
and causes an urge to
Peristaltic contractions
force feces towards
the anus.
Integration with other systems
Nervous: transmit signals to the digestive
system to perform properly at a given time.
Cardiovascular: absorbs fluid to maintain
normal blood volumes. Absorbs vitamin K;
liver excretes heme.
Endocrine: provides nutrients and
substrates to endocrine cells; endocrine
cells of pancreas secrete insulin and
Fun Facts
You get a new stomach lining every three
Digestive problems cost Americans $50
billion each year in both direct costs and
absence from work.
Our saliva glands produce 2 liters of saliva
everyday and we en up gulping most of
them down. That's an average of 50,000
liters (5,500 gallons) for a lifetime.