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

Organs of the Alimentary Canal

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)

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

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

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

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.

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

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

Accessory Digestive Organs

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

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

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

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.

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.

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

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