The Digestive System

Functions of the Digestive System Process food Extracts nutrients from the food Eliminates the waste

Four Stages of Digestion Ingestionselective food intake DigestionMechanical & Chemical breakdown of food into usable form AbsorptionUptake of nutrient molecules into the blood or lymph DefecationElimination of undigested wastes

Two Subdivisions Digestive Tract Accessory Organs

Digestive Tract Aka alimentary canal About 30 feet long (9 m) Oral cavity Pharynx Esophagus Stomach Small intestine Large intestine

Accessory Organs Teeth Tongue Salivary glands Liver Gall bladder Pancreas

Mouth Also known as oral or buccal cavity Ingestion of food Taste & other sensory receptors for food Mastication (chewing) Deglutition (swallowing) Speech Respiration

Tongue Manipulates food between the teeth Extract food particles from between teeth Contains the taste buds

Teeth Collectively called dentition Adults have 16 teeth in the mandible; 16 teeth in the maxilla Incisorschisel-like cutting teeth Caninespuncture & shred Premolars & Molarsbroad surfaces for crushing & chewing Responsible for mastication or chewing breaking food into smaller pieces so more surface area is exposed for enzymatic activity

Saliva Moistens the Mouth Digests a little starch & fat Cleanses the teeth Inhibits bacterial growth Dissolves molecules for the taste buds Moistens food and binds particles together to aid in swallowing

Saliva contains 97.0% to 99.5% Water Salivary Amylaseenzyme that begins starch digestion Lingual Lipaseenzyme activated by stomach acid & digests food after it is swallowed Mucusbinds to & lubricates the food Lysozymeenzyme that kills bacteria IgAAntibody that inhibits bacterial growth Electrolytessodium, potassium, chloride, phosphate & bicarbonate ions

Salivary Glands Three pairs 1.Parotid glandbeneath skin anterior to earlobe; swells during mumps 2.Submandibular glandhalfway along body of madible 3.Sublinguial glandlocated in the floor of the mouth Secrete about 1 to 1.5 L of saliva a day

Esophagus Tube leading from pharynx to stomach 20 to 30 cm long behind the trachea Sphincter muscle normally prevents gastroesophogeal reflux (backflow of food from stomach into esophagus) which causes heartburn

Swallowing Involves 22 muscles in the mouth, pharynx, and esophagus Controlled by the swallowing center in the medulla oblongata & pons via several of the cranial nerves

Swallowing Buccal phasetongue presses against food to form bolus & push it into the oropharynx The tongue keeps food from re-entering the mouth; the soft palate prevents food from entering the nasal cavity; and the epiglottis prevents food from entering the larynx

Swallowing Pharyngeal-esophageal phaseThe pharyngeal muscles drive the bolus downward, finally into the esophagus The esophagus moves food by peristalsiswaves of muscular contractions that pushes the bolus ahead Liquid reaches the stomach in 1 to 2 seconds Food reaches the stomach in 4 to 8 seconds