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The Digestive System
Every cell in your body needs a continuous supply of energy and
nutrients to survive. Your digestive system extracts these materials
from the foods you eat, and your circulatory system delivers them to
the cells of your body.
Digestive System: the organ system that is composed of the
digestive tract and other accessory organs responsible for the digestion
of food and the excretion of waste.
The accessory organs include the liver, gall bladder, and pancreas.
Digestive Tract: the tube through which food moves as it is digested
(mouth at one end and anus at the other).
Organs include: the mouth, esophagus, stomach, small intestine and
large intestine.
Layers of the Digestive Tract (see Fig. 2 p. 80)
 epithelial tissue lines the digestive tract and is made of many
different kinds of cells
o eg. goblet cells secrete mucus to protect tract from acid and
digestive enzymes, and to keep material moving easily
 layers of muscle tissue and nerves that can contract and expand in a
rhythmic manner to keep food moving forward
What happens if you eat spoiled food?
 outside of tract is also covered with epithelial tissue
 a layer of connective tissue is located between the other layers
Tissues of the Digestive Tract
Parts of the Digestive Tract
The Mouth
 mechanical digestion involves the teeth and the tongue breaking food
up into smaller pieces to increase the surface area
 enzymes are also produced here that starts the chemical digestion of
the molecules in the food into smaller molecules that the body can
use
o enzymes are proteins that speed up a chemical reaction without
being used up in the process
o the digestion of food would happen too slowly if not for the
presence of digestive enzymes
 saliva is a mixture of water and enzymes that softens the food, and
starts chemical digestion
 saliva is produced by cells in the epithelial tissue that lines the mouth
The Esophagus
 tube that connects mouth to stomach
 surrounded by smooth muscle tissue which can contract and relax
without conscious thought
 nerve tissue controls the muscle contractions
 the muscle contractions slowly move the food along
The Stomach
 function is to hold food and churn it
 lining contains cells that produce digestive enzymes and acid
 layers of smooth muscle tissue contracts to mix stomach contents
The Intestine
 lining contains cells that produce mucus
 lots of fine blood vessels to receive absorbed nutrients and transport
them around the body
 layers of smooth muscle to keep food moving forward without
conscious thought
Small Intestine
 first section after stomach
 about 6m long (narrow)
 goblet cells secrete mucus
 site of most digestion of food
Large Intestine (colon)
 about 1.5m long (wider than small
intestine)
 absorbs water from material
remaining after digestion is done
 site of most absorption of
nutrients
 solid waste exits from the anus
(end of large intestine)
Accessory Organs
 liver, pancreas, and gall bladder all secrete digestive enzymes that
help with the process of digestion
 liver produces bile (green liquid) that helps with the digestion of fats
 bile produced in the liver is stored in the gall bladder until it is
needed
 bile and enzymes leave the accessory organs and enter the digestive
tract through a duct that leads to the small intestine
 the pancreas also secretes insulin which controls the amount of sugar
in the blood
Homework
 use your textbook to find out what causes heartburn, colitis and
diabetes
Specialized Tissues and
Cells of the Stomach
Human Digestive System
Digestive System Worksheet
Place the following structures in order:
_____Anus
_____Duct from accessory organs
_____Esophagus
_____Large intestine
_____Mouth
_____Small intestine
_____Stomach
Match each structure with the substance they secrete:
Structure
_____ Liver
_____Goblet Cells
_____Stomach lining cells
_____Epithelial cells of mouth
_____Pancreas
Secretion
a)Saliva
b) Digestive enzymes and acid
c) Bile
d) Digestive enzymes and insulin
e) Mucus
Match each structure with its main digestive function:
Structure
_____Mouth
_____Stomach
_____Esophagus
_____Liver
_____Small intestine
_____Gall bladder
_____Large intestine
_____Pancreas
a)
b)
c)
d)
e)
f)
g)
h)
Function
produce enzymes and bile
deliver food pieces to stomach
digest food and absorb nutrients
absorb water and eliminate waste
break food into smaller pieces
produce enzymes and insulin
hold food and churn it
store bile