Transcript Mechanical Digestion

The Digestive System
By Dr Tajdar Husain Khan
Digestive Process
1. Ingestion
2. Propulsion
3. Mechanical Digestion
• Mastication
• Churning food in stomach
4. Chemical digestion
5. Absorption
6. Defecation

Digestion: The process of breaking food down to be
used by the body.
 Why is digestion important?
 Food must be broken down in order for our body to
be able to absorb all of the substances important
for daily functions.
 Food must small enough to be absorbed into the
blood and carried to the cells.
 Two types of digestion:
 Mechanical Digestion: occurs in the mouth
(chewing), and in the stomach (churning of
stomach muscles)
 Chemical Digestion: occurs through the use of
enzymes (substances which chemically act on
food to break it down) in saliva, the stomach, in the
small intestine
Organs of the Digestive System

Mouth: The first step in digestion is actually
getting the food into your body.
 Teeth:
mechanically break food down into smaller
pieces
 Saliva: softens food and chemically breaks food
down further (mucin + amylase + water)
 Tongue: moves food around the mouth, forms a
bolus (ball of food)
Salivary Glands
Teeth
premolars
GI Tract- 4 basic tunics:
GI Tract (alimentary canal)
1. Mucosa- wet epithelial membrane
Major function:
• secretion
• absorption
• protection
• reduce friction
• protect cells from being digested
2. Submucosa- moderately dense connective tissue
Contains:
• blood
• lymphatic vessels
• scattered lymph nodules and nerve fibers
Major function:
• nutrition
• protection
3. Muscularis externa- bilayer of smooth
muscle and superficial longitudinal
muscle
Major function:
• regulate GI motility (churning)
4. Serosa- serous membrane
Major function:
• reduce friction
• anchor and protect the surrounding
GI tract organ
Organs of the Digestive System

Esophagus: a hollow tube at the back of
the throat that connects to the stomach.
To prevent food from “going down the wrong
pipe” a flap of skin called the epiglottis closes
over the opening of the trachea (windpipe)
when we swallow
 Peristalsis: muscular contractions that move
food down the esophagus into the stomach.


Imagine squeezing a tube of toothpaste…

Stomach: a hollow, Jshaped organ located
below the esophagus and
above the small intestine.
 The
stomach uses both
mechanical and chemical
digestion to break food
particles down.
Mechanical digestion: 3 layers
of muscles
 Chemical digestion: digestive
or gastric enzymes


Small Intestine: responsible for absorbing
nutrients from food.
 First
1/3 of the S.I. :Bile from the gall bladder
and digestive enzymes from the pancreas and
walls of the small intestine further break food
down.
 Second 1/3 of the S.I.: contains finger-like
projections called villi
 Villi: increase the surface area of the S.I. so
that more nutrients can be absorbed into the
blood stream

Large intestine: “large” because it is wider
in diameter than the small intestine (about
3” vs. 1”). Responsible for absorbing water
from undigested food.
 Material
found in the large intestine is mostly
food that cannot be digested any further and
water.

Large Intestine: 3 parts
 Colon:
Absorbs water and
nutrients from food, as
the material moves
through the colon it gets
harder and harder-turning
into feces.
 Rectum: Stores feces.
Feces move to the anus
by peristalsis.
 Anus: Eliminates solid
waste from the body
Other Organs

Liver: produces bile, is located to the right
of the stomach.
 Bile:

responsible for breaking down fats
Pancreas: located behind the stomach,
and above the small intestine.
 Secretes

digestive enzymes
Gall Bladder: stores and excretes bile