Download The Digestive System

The Digestive
System
pH lecture
Functions of Digestive System



Ingestion – active,
conscious process of taking
materials into mouth
Mechanical Processing –
crushing process that
increases the surface area
of the food, exposing it to
more enzymatic activity
(occurs in mouth and
stomach)
Digestion – break down of
food into small fragments
suitable for absorption
Functions of Digestive System
(Continued)
 Secretion –


release of water,
acids, enzymes and
salts by epithelium
of digestive tract
Absorption –
movement of ions,
vitamins, and water
across digestive
epithelium into
interstitial fluid of
digestive tract
Excretion –
removal of waste
from body fluids
Digestive Pathway

Oral cavity (teeth
and tongue)
 Pharynx
 Esophagus
 Stomach
 Small Intestine
– Duodenum,
Jejunum, Ileum

Large Intestine
– Cecum or
(ascending Colon),
Colon or
(Transverse
Colon), Rectum or
(Descending
Colon)
Digestive Pathway
CONT…..
 Don’t forget
to label the
3 parts of
each type
of intestine,
the
pancreas
and the
appendix
Histology of Digestive Tract

Two major types of
tissue that constantly
produce a lubricating
liquid, allowing all
components of
digestive tract to slide
without friction
 Visceral peritoneum –
covers organs
 Parietal peritoneum –
lines inner surfaces of
body wall
Oral Cavity


Also referred to as the
buccal cavity
Functions to:
– Perform sensory
analysis of material
before swallowing
– Mechanically
process material
with teeth, tongue,
and palatal surfaces
– Lubricate material
by mixing it with
mucus and saliva
– Perform limited
digestion of
carbohydrates and
lipids
Anatomy of Oral Cavity
(Continued)

The tongue functions
to:
 Mechanically process
food
 Manipulate food to
assist in chewing
 Sensory analysis
through touch, temp,
and taste
 Secretion substances
including the enzyme
lingual lipase (which
initiates lipid digestion)
Saliva and Salivary Glands

3 pairs of salivary glands:
– Parotid salivary gland – produce
saliva that has high
concentration of salivary
amylase (begins to break down
starches, though no absorption
occurs in oral cavity)
• 25% of Saliva
– Sublingual salivary gland –
produce saliva that acts as
buffer and lubricant
• 5%
– Submandibular salivary gland –
produce saliva rich in buffer,
libricating proteins called
mucins, and salivary amylase
• 70%

Bad Breath
Clinically termed
Halitosis
 Typically caused by
breakdown of epithelial
cells, blood cells, and
bacteria combined with
saliva on tongue
 Low Salivary flow –
dehydration and
morning breath due to
breathing through
mouth during sleep
 Garlic and Onion
Breath – compounds
taken in blood to lungs

Teeth
Perform mastication (chewing)
 Mastication breaks down tough
connective tissues in meat and
plant fibers and helps to saturate
food with saliva
Pharynx and
Epiglottis

Pharynx: common
passageway for food, liquid,
and air

Epiglottis: prevents food
from going into the trachea
and instead directs it to the
esophagus
Esophagus

A hollow muscle tube
approximately 25 cm long
and 2 cm in diameter
 Empties into the stomach
through the cardiac
sphincter, which prevents
backflow from the
stomach into the
esophagus
 Peristalsis= muscle
movement of the
esophagus. Food at this
area is called bolus

Stomach
Performs 4 major
functions:
– Stores ingested food
– Mechanically breaks
down ingested food
– Chemically breaks
down ingested food

Ingested
substances
combine with
digestive juices of
stomach to form
acidic soupy
substance called
chyme
Anatomy of Stomach




Shaped like a J
Lesser curvature (1st
part)
Greater curvature (2nd
part)
Can be divided into four
regions:
–
–
–
–
Cardia
Fundus
Body
Pylorus
• Pyloric sphincter
regulates the release of
chyme into the small
intestine
Stomach’s Volume

Volume of stomach
increases while you
eat and decreases
as it releases chyme
 When full it can
contain between 11.5 liters of material
Mechanical & Chemical Digestion
Digestive System Functions

Digestion—breaking food down both physically
& chemically
 Food breakdown as mechanical digestion
 Mixing food in the mouth by tongue & teeth, churning food in
stomach & segmentation in small intestine
 Mechanical digestion prepares food for further degradation by
enzymes
Digestive System Functions

Digestion—breaking food down both physically &
chemically
 Food breakdown as chemical digestion
 Enzymes break down food
molecules into their building
blocks
 Each major food group uses
different enzymes
 Carbohydrates are broken
to simple sugars
 Mouth & small
intestines
 Proteins are broken to
amino acids
 Stomach & small
intestines
 Fats are broken to fatty acids & alcohols
 Small intestines






Responsible for 90% of
nutrient absorption (most
of rest occurs in large
intestine)
Averages 6 m (19.7 ft) in
length
Averages diameter of 2.54.0 cm
Duodenum – “mixing
bowl” – combines chyme
with digestive secretions
from pancreas and liver
Jejunum – bulk of
chemical digestion and
nutrient absorption occurs
here
Ileum – the longest
segment which ends in
ileocecal valve (separating
ileum from cecum of large
intestine)
The Small Intestine
Histology of Small Intestine
Plicae circulares
are folds that line
the small intestine,
greatly increasing
surface area for
absorption
 Plicae are lined by
tiny fingerlike
projections called
intestinal villi,
which are covered
by simple columnar
epithelium

Pancreas

Lies posterior to the stomach
and is bound posteriorly to
abdominal cavity
 Produces 1000 ml of digestive
enzymes/day (pancreatic juice)
and delivers them to the
duodenum through pancreatic
duct
 When chyme enters the small
intestine, it triggers the
duodenum to release the
hormone secretin, which in turn
stimulates the pancreas to
release these enzymes

Liver
The largest visceral
organ, weighing about 1.5
kg
 Primary function is to
regulate the composition
of circulating blood
 Blood from absorptive
surfaces of digestive tract
enters liver
 Liver cells extract
nutrients or toxins from
blood and then allows
filtered blood to reenter
systemic circulation
 It stores excess nutrients,
and releases these to
correct nutrient
deficiencies
Gallbladder


Stores and
concentrate bile
immediately before it
is released in the the
small intestine
It only releases bile
when stimulated by
the intestinal
hormone
cholecytstokinin
CCK, which is
released when
chyme enters the
duodenum
The Large Intestine

Begins where it
meets the Ilium and
ends at the anus
 Major functions:
 Reabsorption of
water and the
compaction of
intenstinal contents
into feces
 Absorption of
vitamins liberated by
bacterial action
 The storage of fecal
material prior to
defecation
More About the Large Intestine






Approx. 1.5 m long
7.5 cm wide
Divided into three
parts:
Cecum
Colon (ascending,
transverse and
descending)
Rectum
Regions of Colon
The Rectum





Expandable
Temporarily stores feces, as movement of feces
into rectum triggers urge to defecate
Anal canal is last portion of rectum
Internal anal sphincter – involuntary (smooth)
External anal sphincter – voluntary (skeletal)
Constipation






Usually results due to an
infrequent urge to defecate
Infrequent bowel
movements (fewer than 3
per week)
Difficulty in at least 25% of
the movement
Feeling of incomplete
evacuation
Type 1 and 2 qualify as
constipated
Potential Causes
–
–
–
–
Incomplete chewing of food
Insufficient fiber in diet
Dehydration
Quitting smoking (nicotine is
a laxative)
THE END
Vestigial Structures
Click on the
picture to
watch the
movie!