Transcript Digestion

Digestive, Excretory &
Urinary Systems
DIGESTION & ITS ORGANS
Gastrointestinal Tract

Is the pathway along which the process of
digestion occurs

Digestion is the process of breaking down food
into molecules that the body can use

It begins at the mouth and ends at the anus

It is divided into several distinct organs which
are directly involved in the digestive process

There are additional organs, not part of the
system that aid in digestion by providing
secretions
Digestion
 Includes
the:
Mechanical
& chemical breakdown of food
into nutrients
Absorption
of nutrients
Elimination
of waste
The Mouth
The location of the mechanical phase of
digestion
 Incisors and molars cut & grind up your food
 The tongue keeps food between your chewing
surfaces
 Chemical digestion also begins here
 Salivary glands produce saliva: a mixture of
water, mucus, & salivary amylase

Parts of the Mouth
 Teeth
 Tongue
 Soft
Palate
 Hard Palate
 Salivary glands
 Pharynx
Salivary Glands
3
types:
Parotid
Sublingual
Submandibular
 All
produce saliva & salivary amylase whose
function is to break down starch into
maltose
Next step of Digestion
 After
food has been thoroughly chewed,
moistened, and rolled into a ball: bolus
 It is then forced into the pharynx by
swallowing action
 The bolus passes into the esophagus and
gets pushed down through a series of
rhythmic muscular contractions &
relaxations: peristalsis
Peristalsis
Esophagus
 Is
a muscular tube
approx. 25 cm long
that runs form the
back of the mouth
to the stomach
Esophagus
Step 3 of Digestion
Takes place in the stomach
 By now the bolus is now fairly well minced and
turned into a pulpy mass as it passes into the
stomach
 The mechanical action of the muscles in the
stomach constrict and relax in a continuous
motion blending, whipping, and stirring the
stomach's contents into chyme
 Chyme is a pulpy substance that can be handled
by the small intestine.

Stomach
Is involved in both mechanical & chemical
digestion
 Located in the upper left side of the abdominal
cavity & just below the diaphragm
 It is an elastic bag that is J-shaped, when full
and lies in folds when empty
 It looks like a deflated balloon when empty, but
when full, it becomes about a foot long and six
inches wide
 It is able to hold about two quarts of food and
drink.

Stomach Continued
The function of the stomach is best described
as a food processing unit and a storage cistern
 Various chemicals in the stomach like the
digestive enzymes interact to break down the
food


Digestive enzymes of the stomach include: pepsin,
rennin, & lipase
Hydrochloric acid creates suitable environment
for the enzymes and assists in the digestion
 A watery mucus provides a protective lining for
the muscular walls of the stomach so it will not
be digested by the acid or enzymes

Mechanical Digestion In detail
 As
food enters the stomach, the
esophageal sphincter closes to prevent
food from reentering the esophagus
 Food
remains in the stomach for 3-4 hours
 Muscle
contractions churn the contents,
breaking them down and mixing them with
gastric fluid
Stomach Anatomy

The stomach is composed of six tissue layers

From the outside in they are:

Serosa

Muscularis

Submucosa

Lamina muscularis

Mucosa

Gastric surface
Stomach Anatomy


The walls of the stomach have several layers of
smooth muscle

Circular

Longitudinal

Diagonal
These muscles work together to churn the
contents of the stomach
Internal Stomach Anatomy
The inner lining of the stomach is a thick,
wrinkled mucous membrane composed of
epithelial cells
 Inside of this membrane are small openings
called gastric pits
 Gastric pits: are open ends of gastric glands,
which release secretions from special cells
 These secretions make up the acidic digestive
fluid

Stomach Wall Anatomy
4 Major Secretory Cells
1.Chief
cells
 Produces pepsinogen
 When pepsinogen enters the low pH
environment of the stomach it becomes
the digestive enzyme
pepsin
 Pepsin is responsible for digesting
proteins
4 Major Secretory Cells
2.
Parietal cells
 Produce HCl (hydrochloric acid)
 Antacids work by block the
receptors which control HCl
secretion
 Also produce intrinsic factor, which
binds to and allows B12 absorption in
the intestines
4 Major Secretory Cells
3. G-cell

secretes gastrin hormone

gastrin activates gastric juice
secretion & gastric smooth muscle
“churning”

gastrin also activates the gastroileal
reflex which moves chyme from the
ileum to the colon in the intestines
4 Major Secretory Cells
4. Mucus cells

Produce mucus which protects
against acids and digestive enzymes
Chemical Digestion
 Is
done by gastric fluid which contains
water, mucous, & digestive enzymes
 Pepsin
digests proteins by breaking them
into short amino acid chains known as
peptides
 HCl
provides the necessary low pH of 1.5
to 2.5 to active the enzymes, dissolve
minerals, and kill bacteria
Chemical Digestion
 Peristalsis
forces chyme out of the
stomach and into the small intestine
through the pyloric sphincter
 Each
time the pyloric sphincter opens,
approx. 5 to 15 ml of chyme moves into
the small intestine
 Chemical
intestine
digestion continues in the small
Accessory Organs to Digestion
 The
liver, gallbladder, & pancreas are
accessory organs to the process of
digestion
 They
perform several important
functions including the production of
secretions
 They
do not come directly in contact
with food
The Liver

Is located to the right of the stomach

Not only an organ but the largest gland of the body

Its main functions are to filter and process
nutrient-rich blood & aid in digestion

Additional functions include:

Storing glucose as glycogen
Regulates lipid metabolism: such as making
cholesterol


Making proteins

Breaking down toxins

Secretes & makes bile
Bile

Is a bitter, alkaline, brownish-yellow or
greenish-yellow fluid

It aids in the emulsification, digestion, and
absorption of fats

Made up of bile salts & bilirubin

Bilirubin is the main pigment of bile
Gallbladder
 Is
a 10-12 cm, dark green saclike
organ found underneath the liver
 Also
 Its
known as the cholecyst
functions include:
 Store
& release bile (50 mL)
 Stimulate
the release of cholecystokinin
Pancreas
 Lies
beneath the stomach
 It is an organ & a gland
 It has several functions
 It produces several enzymes &
secretions
Pancreas Functions

Acts as in endocrine gland by producing
hormones to regulate blood sugar levels,
specifically insulin

Two roles in the digestive system:
Produces sodium bicarbonate to neutralize
stomach acid

Produces enzymes to break down
carbohydrates, lipids, proteins & nucleic acids

Pancreas Enzymes
Pancreatic amylase -breaks down carbohydrates
 Pancreatic lipase -breaks down lipids
 Trypsin-comes from the precursor trypsinogen,
and digests proteins
 Chymotrypsin-comes from the precursor
Chymotrypsinogen, and digests proteins
 Nucleases: digests nucleic acids
 DNAase
 RNAase
