Chapter 14 – Part 1 The Digestive System

The Digestive System and Body Metabolism Digestion Takes in food (ingests it) Breaks it down physically and chemically into nutrient molecules (digests it) Absorbs the nutrients into the bloodstream Then, it rids the body of the indigestible remains (defecates)

Organs of the Digestive System The organs of the digestive system can be separated into two main groups: Alimentary canal – continuous coiled hollow tube Performs the whole menu of digestive functions (ingests, digests, absorbs, and defecates) Accessory digestive organs Assists the process of digestive breakdown in various ways Includes the teeth, tongue, and several large digestive glands

Organs of the Digestive System

The Alimentary Canal The alimentary canal is also called the gastrointestinal (GI) tract. Continuous, coiled, hollow, muscular tube that winds through the ventral body cavity Is open at both ends Is about 30 feet long in a cadaver

Organs of the Alimentary Canal Mouth Pharynx Esophagus Stomach Small intestine Large intestine Anus

Mouth (Oral Cavity) Anatomy Lips (labia) – protect the anterior opening Cheeks – form the lateral walls Hard palate – forms the anterior roof Soft palate – forms the posterior roof Uvula – fleshy fingerlike projection of the soft palate

Mouth (Oral Cavity) Anatomy Vestibule – space between lips and cheeks externally and the teeth and gums internally Oral cavity proper – area contained by the teeth Tongue – muscle that occupies the floor of the mouth

Mouth (Oral Cavity) Anatomy Tonsils Palatine tonsils Lingual tonsil

Processes of the Mouth Mastication (chewing) of food Mixing masticated food with saliva Initiation of swallowing by the tongue Allowing for the sense of taste

Pharynx Anatomy Nasopharynx – not part of the digestive system Oropharynx – posterior to oral cavity Laryngopharynx – below the oropharynx and connected to the esophagus

Pharynx Function Serves as a passageway for air and food (oropharynx and laryngopharynx only) Food is propelled to the esophagus by two muscle layers Longitudinal inner layer Circular outer layer (constrictor muscles) Food movement is by alternating contractions of the muscle layers This propelling mechanism is called peristalsis

Esophagus Runs from pharynx to stomach through the diaphragm Conducts food by peristalsis (slow rhythmic squeezing) Passageway for food only (respiratory system branches off after the pharynx) About 10 inches long

Layers of Alimentary Canal Organs Mucosa Innermost layer Moist membrane Consists primarily of: Surface epithelium Plus a small amount of connective tissue (lamina propria) Small smooth muscle layer

Layers of Alimentary Canal Organs Submucosa Found just beneath the mucosa Soft connective tissue layer containing blood vessels, nerve endings, lymph nodules, and lymphatic vessels

Layers of Alimentary Canal Organs Muscularis externa – Smooth muscle layer made up of: Inner circular layer Outer longitudinal layer Serosa Outermost layer – visceral peritoneum Layer of serous fluid-producing cells

Layers of Alimentary Canal Organs Serosa Outermost layer Consists of a single layer of flat serous fluid-producing cells

Layers of Alimentary Canal Organs