1. The Digestive System
The organs of the digestive system can be separated into two groups
The alimentary canal or gastrointestinal tract – perform all the functions of digestion as the long, coiled, hallow, muscular tube winds through the body
Accessory digestive organs – assist the digestive process

2. Organs of the Alimentary Canal

3. Mouth Also known as the oral cavity
This is where food enters the body. As it enters the body it is mixed with saliva and masticated (chewed)
It is a mucous membrane lined cavity
It is protected by the lips
The cheeks form the sides of the mouth, the hard palate forms the anterior roof, and the soft palate forms the posterior roof
The floor of the mouth is occupied by the muscular tongue
At the anterior portion of the mouth are the paired palatine tonsils (sides) and lingual tonsil (base)

4. Pharynx Subdivided into three parts
Nasopharynx – the section that part if the respiratory system
Oropharynx – posterior to the oral cavity
Laryngopharnyx – part that connects to the esophagus
This area helps to propel food, which is also known as peristalsis

5. Esophagus Also known as the gullet
Runs from the pharynx, through the diaphragm, and to the stomach
It is essentially a passageway for peristalsis
It is composed of the same four basic layers of all the other organs from the esophagus to the large intestine

6. The Four Layers
Mucosa – the moist, innermost layer that lines the cavity
Submucosa – a soft connective tissue layer just below the mucosa that contains blood vessels, nerve endings, and lymphatic vessels
Muscularis externa – the smooth muscle layer which is made up of a circular inner layer and longitudinal outer layer
Serosa – the outermost wall

7. Stomach
C-shaped organ on the left side of the abdominal cavity that is hidden by the liver and diaphragm
The stomach acts as a temporary storage tank for food as well as a site for food breakdown
The stomach has an additional muscle layer so that it can move and churn its contents
It also has various cells that produce digestive enzymes and gastric juice to break down the food as well as mucous producing cells to protect the stomach.
The processed food is called chyme as it leaves the stomach and heads for the small intestine.

8. Small Intestine It is the main digestive and food absorption organ
It is the longest part (8-18 feet) of the alimentary canal and is a long twisted passageway
It is composed of three areas called the duodenum, jejunum, and ileum
Walls of the small intestine have microvilli, villi and circular folds to help increase the surface area and therefore increase absorption

9. Large Intestine
Larger in diameter, but shorter in length than the small intestine
Its main purpose is to dry out the indigestible food residue by absorbing water and to eliminate this residue from the body as feces through the anus

10. Accessory Digestive Organs

11. Salivary glands Produce saliva – a mixture of mucus and serous fluids
Saliva moistens and binds food together into a mass called a bolus
Amylase in the serous fluid begins the digestive process by breaking down the starch in food

12. Teeth
Helps process food by breaking the food down into smaller pieces while helping the food mix with the saliva
Normally an adult will have 32 teeth

13. Pancreas
A soft, pink, triangular gland that extends across the abdomen from the spleen to the duodenum
Produces a multitude of enzymes that chemically break down food
The enzyme secretions form the pancreas enter the small intestine at the duodenum

14. Liver Largest gland of the body
Its function in digestion is bile production, which emulsifies fats
This means the large fat molecules are separated into smaller molecules. This increases the surface area and gives fat digesting enzymes more places where they can work.

15. Gallbladder Small, thin-walled green sac
Stores bile while digestion is not occurring
While being stored, the bile is concentrated by removing water
If bile is stored too long or too much water is removed, the cholesterol it contains may crystallize forming gallstones.

16. Functions of the Digestive System
Ingestion – the voluntary act of putting food in the mouth
Propulsion – movement of materials through the digestive system by peristalsis
Food Breakdown by Mechanical Digestion – physically fragmenting the materials
Food Breakdown by Chemical Digestion – chemically fragmenting the materials
Absorption – moving usable digested food into the body
Defecation - moving unusable digested food out of the body

17. Comic Strip Project