DIGESTIVE SYSTEM

Digestive System
• Function of the Digestive System
• Part of the Digestive Tube
• Accessory organs
• Processes of the Digestive system
 Function of Digestive System
1.Ingest food
2.Break it down into small
molecules that can cross
plasma membranes
3.Absorb these nutrient
molecules
4.Eliminate non digestible
wastes
 Types of Digestion
As of Action
1. Mechanical Digestion
- food is converted into small pieces by
physical means such as mastication by the
teeth
2. Chemical Digestion
- food is converted into simpler forms by the
 Types of Digestion
As to Location
1. Intracellular Digestion

- Inside the cell particularly in the lysosomes, characteristic

of unicellular organisms
2. Extracelullar Digestion
-outside the cell
-inside the digestive tube
The Digestive Tube
• also called as
Alimentary canal
• over 30ft. long in
human, beginning in
the mouth and ending
in the anus
Digestive glands
Organs that secrete juices
containing enzymes for the
digestion of food
Salivary glands, gastric gland,
pancreas, intestinal gland and the
liver
 Accessory
Parts
includes structures
that help in the
digestion of food
✔ tongue and teeth,
glands
Parts of theDigestive
Tube
A. Mouth
- anterior opening
- guarded by upper
and lower lips
- site of mastication
and lubrication of
food
 B. Pharynx
narrow space behind
the oral cavity
- common passageway
of food and air
-swallow occurs in the
pharynx
-breathing does not
occur when
swallowing
C. Esophagus
- narrow
muscular organ
between the
pharynx and the
stomach
- peristalsis
movement
D. Stomach
- the largest and highly muscular part of the
digestive tube
- maximum capacity of 2.5 pints
- food stays about 3 to 5 hours
- churning movement
-digestion of food thru enzymes and digestive
juices.
Division of Stomach
Cardiac Sphincter

- anterior end
- prevents backward
movement of food to
the esophagus
Division of Stomach

Fundus

- most expanded
part of the
stomach
Division of Stomach
Pyloric Sphincter

- posterior end
- regulates the
movement of food
to the small
intestine
E. Small Intestine
-the longest and most coiled
part of the digestive tube.
- site of final digestion
and absorption.
- about 22ft. long
-food stays for around 4.5
hours
Division of Small Intestine
F. Large Intestine
-posterior part of the
digestive tube
-reabsorbs water and
converts undigested food
into faeces.
-suspended by the mesocolon
- food stays for about 5 to
25 hours or more, houses
500 species of bacteria.
Division of Large Intestine
Caecum Colon Rectum
- anterior - middle - posterior
portion portion portion
- appendix is - divided into
ascending colon
- temporary
located storage of
transverse colon
and descending undigested food
colon and sigmoi
colon
Division of Large Intestine
 I. Anus

- posterior opening of
the digestive tube
- exit of fecal matter
- regulated by the
anal sphincter
Digestive Glands
Salivary Glands

Mucous Glands

Gastric Glands

Intestinal Glands
 Salivary Glands
Produces about 1 liter of saliva a day
✔ saliva contains mucus and a digestive enzyme called salivary
amylase.
✔ teeth carry out mastication by moving the food between
teeth.
mastication breaks down the food into small portions
the tongue forms the chewed food into a small mass called bolus in
preparation for swallowing
Salivary Glands
a. Parotid Glands b. Sublingual Gland

- located in front of and - lie beneath the tongue

below the ears proper and their ducts
c. Submandibular open into the floor of the
Gland oral cavity

- lie in the posterior

floor of the oral cavity
beneath the base of the
Mucous Glands
-found in the oral cavity, esophagus
and small intestine and large
intestine
-secrete mucin for lubrication of
food
 Gastric Glands
-found in the rugae
of stomach
-secrete gastric juices
-controlled by the
medulla of the
brain and by the
hormone gastrin
 Composition of Gastric
Juices
Mucin - lubrication of food

HCl - coverts pepsinogen into pepsin

Pepsinogen - converted into pepsin by HCl ;

digest protein into polypeptide chains
Lipase - digests fat into fatty and glycerol
Intestinal Glands
-found in the intestine
-secreteintestinal juices
Composition of Intestinal
Juice
Mucin - lubrication of food
Enterokinase - activates trypsinogen to trypsin Peptidase - break

polypeptide chains into amino acids

Nucleases - break nucleotides into nitrogen bases, phosphoric

acids and pentoses

Disaccharides - could be maltase to break maltose into glucose,

lactase to break lactose into galactose and glucose or sucrase to break
sucrose into glucose and fructose
 Pancreas
found along the
peripheral surface of the
duodenum
✔ secretes pancreatic juice
to the duodenum
through the pancreatic
duct
✔ The pancreas makes pancreatic
juices and hormones, including
insulin.
✔ The pancreatic juices areenzymes
that help digest food in the small
intestine.
✔ Insulin controls the amount of sugar
in the blood.
Composition of Pancreatic
Juice
Pancreatic Amylase - digests starch and glycerol into maltose

Pancreatic Lipase - digests fats into fatty acids and glycerol

Trypsinogen - converted into trypsin by the enterokinase ;

digests proteins into polypeptides, peptones and proteoses

Chemotrypsinogen - activated to chemotrypsin by trypsin;

digests polypeptides to amino acids
 Liver
Secretes bile which is stored in the gall bladder
✔ Bile emulsifies fat into fat globules
The largest gland in the body Storage
of glycogen
Production of fibrinogen in blood clotting
Production of plasma proteins
Liver
Site of protein synthesis
Detoxification of nitrogenous wastes by
changing these wastes into urea
Destruction of worn-out RBC
Formation and storage of vitamins A and D
Functions and Processes of
the DigestiveSystem
The gastrointestinal tract is a long
tube passingthrough the body

The primary function of the GI tract is

to move nutrients, water and
electrolytes from the external
environment into the body's internal
environment

The body meets physiological challenges

by coordinating the four basic processes
Processes of Digestive
System
1. Digestion

- the chemical and mechanical breakdown of

foods into smaller units that can be taken across
the intestinal epithelium unto the body

2. Absorption

- the active or passive transfer of substances

from the lumen of the GI tract to the
extracellular fluid
Processes of Digestive
System
3. Motility

- movement of material in the GI tract as a

result of muscle contraction

4. Secretion

- both the transepithelial transfer of water

and ions from the extracelullar fluid to the
digestive tract lumen and the release of
substances synthesized by GI epithelial cells
Absorption is not regulated "what you
eat is what you get"

Motility and secretion are

continuously regulated to maximize
the availability of absorbable
material

Motility is regulated because if food

moves through the system too rapidly,
thereis not enough time for
Secretion is regulated because if digestive
enzymes are not secreted in adequate amounts,
food in the GI tract cannot be broken down into
an absorbable form

Motility in the GI tract serves two purposes:

moving food from the mouth to the anus and
mechanically mixing food to break it into
uniformly small particles

Most of the GI tract is composed of single- unit

smooth muscle, with groups of cells electrically
connected by gap junctions to create contracting
segments. Different regions exhibit different
 Types of
Contraction
1. Tonic Contraction

- that are sustained for minutes or hours

occur in some smooth muscle sphincter and
in the anterior portion of the stomach

2. Phasic Contraction

- with contraction- relaxation cycles lasting

only a few seconds, occur in the posterior
region of the stomach and in small intestine
Muscle contractions in the GI tract occurs

Between meals when the tract is largely empty, a

series of contractions begin in the stomach and
passes slowly from section to section, each
taking about 90 minutes to reach the large
intestine

This pattern is known as migrating motor

complex, a housekeeping- function that sweeps
food remnants and bacteria out of the GI tract
and into the large intestine
Peristalsis is progressive waves of
contraction that move from one section to
the GI tract to the next. It pushes the bolus
forward into a receiving segment, where the
circular muscles are relaxed
 Secretio
n
In a typical day 9 liters of fluid pass through the lumen of
the GI tract- equal to the contents of 3 liters of softdrink
bottles

Only about 2 liters of that volume enter GI system through

the mouth

The remaining 7 liters of fluid come from body water

secreted along with enzymes and mucus
 Secretio
n
About halfof the secreted fluids
come from accessory organs and
glands such as salivary glands,
pancreas and liver

The remaining 3.5 liters aresecreted

by epithelial cells of the digestive
tract
 Secretio
n
The significance of the secreted volume becomes more
apparent when it is realized that the 7 liters of fluid secreted
equal 1/6 of total body water volume (42 liters) and more
than twice the plasma volume (3 liters) .
These numbers tell that if the fluid secreted into the lumen
is not reabsorbed as it passes along the GI tract, the body
will rapidly dehydrate
 Cephalic
Phase
Digestive processes in the body
begin before food enters the
mouth

Simply smelling, seeing or even

thinking abiut food can makeour
mouths water and stomach
rumble
 Digestion and
Absorption
Digestion of macromolecules into absorbable
units is accomplished by a combination of
mechanical and enzymatic breakdown

Chewing and churning create smaller pieces of

food with more surface area of exposed to
digestive enzymes

Bile, the complex chemical mixture secreted

by the liver, serves a similar purpose by
dispersing lipids as fine droplets with greater
 Digestion and
Absorption
Carbohydrates are absorbed as monosaccharides

Proteins are digested into small peptides and

amino acids

Bile salts facilitate fat digestion

The intestines absorbs vitamins and minerals

The intestine absorbs ions and water

 Chemical and Mechanical
Digestion Begin in the Mouth
When food enters the mouth, it is met by a flood of the
secretion called saliva

Salivary secretion is under autonomic control and can be

triggered by multiple stimuli, including the sight, smell,
touch and even thought of food

The water and mucus in saliva soften and lubricate food to

make it easier to swallow
 Chemical and Mechanical
Digestion Begin in the Mouth
The final function of saliva is protection

Saliva helps wash the teeth and keep the tongue

free of food particles

Mechanical digestion of food begins in the oral

cavity with chewing

The lips, tongue and teeth all contribute to the

mastication of food, creating a softened,
moistened mass (bolus) that can be easily
swallowed
 Swallowing Moves Food from the
Mouth to the Stomach
Swallowing or deglutition is a reflex
action that pushes a bolus of food or
liquid into the esophagus

Epiglottis folds down over the opening

of the larynxto prevent food and liquid
from entering the airways at the same
time respiration is inhibited and the
upper esophageal sphincter relaxes as
 Swallowing Moves Food from the
Mouth to the Stomach
If the lower esophageal sphincter does
not stay contracted, gastric acid and
pepsin can irritate the liningof the
esophagus, leading to the pain and
irritation of heartburn

The churningaction of the stomach

when filled with food can also squirt acid
back into the esophagus if the sphincter
 Gastric
Phase

About 3.5 liters of food drink and

saliva enterthe fundus of the
stomach each day. The stomach has
three general functions
 Gastric
Phase
Storage

-the stomach stores food and regulates its passage into the
small intestine where most digestion and absorption take place

Digestion

-the stomach chemically and mechanically digests food into the

soupy mixture of uniformly small particles called chyme

Protection

-the stomach protects the body by destroying many of the

bacteria and other pathogens that are swallowed with food
or trapped in airway mucus
 The Stomach Stores
Food
When food arrives, the stomach relaxes and expands to
hold the increased volume

This neutrally mediated reflex is called receptive

relaxation

Whenever more food is ingested than what is needed from

the nutritional standpoint, the stomach must regulate the
rate at which food enters the small intestine
 The Stomach Stores
Food
Without such regulation, small intestine would not be able
to digest and absorb the load presented to it and significan
amounts of unabsorbed chyme would pass into the large
intestine

The epithelium of the large intestine is not designed for

large-scale nutrient absorption, most of the chyme would
pass out in the feces, resulting in diarrhea
 The Stomach Stores
Food
While the upper stomach is quietly holding food the
lower stomach is busy with digestion

In the half of the stomach, a series of peristaltic waves

pushes the food down toward the pyloric valve, mixing
food with acid and digestive enzymes
 Intestinal
Phase
The net result of the gastric phase is the digestion of proteins in
the stomach by pepsin
The formation of chyme by the action of pepsin Acid and

peristaltic contractions

And the controlled entry of chyme into the small intestine, where
further digestion and absorption take place
 Intestinal
Phase
Once chyme enters the small intestine, the
intestinal phase of digestion begins

The initiation of the intestinal phase

triggers a series of reflexes that feed back
to regulate the delivery rate of chyme from
the stomach and feed forward to promote
digestion, motility and utilization of
nutrients
 Most Fluids is Absorbed in the
Small Intestine
Of the 9 liters that enter the small intestine
daily most is reabsorbed

The transport of organic nutrients and

ions, takes place mostly in the
duodenum and jejunum

Most absorbed nutrients move into

capillaries in the villi and from there into
the hepatic portal system
Most Fluids is Absorbed in the
Small Intestine
This specialized region of the circulation has two sets of
capillary beds: one that picks up absorbed nutrients at
the intestine and the other that delivers the nutrients
directly to the liver

The delivery of absorbed materials directly to the liver

underscores the importance of that organ as a biological
filter
 Most Digestion Occurs in the Small
Intestine

Chyme entering the small intestine has undergone relatively

little chemical digestion
Protein digestion started in the stomach Pancreatic proteases

continue protein digestion

Carbohydrates digestion in the small intestine finishes

converting digestible polysaccharides and disaccharides into
monosaccharides that can be absorbed
 Most Digestion Occurs in the Small
Intestine
Pancreatic amylasecontinues to digest
starch into maltose

Maltose and disaccharides from food,

such as sucrose and lactose (milk
sugar) are digested by the appropriate
brush border disaccharides to their
absorbable end products: glucose,
galactose and fructose
 Most Digestion Occurs in the Small
Intestine

Fats enter the small intestine in the

form of a coarse emulsion

In the duodenum, bile salts coat the fat

droplets to stabilize them so that
digestion can be carried out by
pancreatic lipase
 Large Intestine Concentrates Waste
for Excretion

By the end of the ileum, only about

1.5 liters of unabsorbed chyme
remain

The colon absorbed most of the

volume so that normally only about
0.1 liter of water is lost daily
feces
 Large Intestine Concentrates Waste
for Excretion
Chyme enters the large intestine through
the ileocacal valve

Chyme that enters the colon continues to

be mixed by segmental contractions

Forward movement is minimal during

mixing contraction known as mass
movement
 Large Intestine Concentrates Waste
for Excretion
A wave of contraction decreases the diameter
of a segment of colon and sends a substantial
bolus of material forward

These contractions occur 3-4 times a day and

are associated with eating and distension of
the stomach through the gastrocolic reflex

Mass movement is responsible for the sudden

distension of the rectum that triggers
Large Intestine Concentrates Waste
for Excretion
Defecation, like urination, is subject to emotional influence

Stress may increase intestinal motility and cause psychosomatic

diarrhea in some individuals but decrease motility and cause
constipation in others

When feces are retained in the colon, either through consciously

ignoring a defecation reflex or through decreased motility,
continued water absorption creates hard, dry feces that are difficu
to expel