The Digestive System Generalities the Mouth and Salivary

The Digestive System Generalities, the Mouth and Salivary Glands

Human Digestive System Digestion – the breakdown of food and absorption of resulting nutrients by cells n Structures n Alimentary canal (mouth, pharynx, esophagus, stomach, small intestine, large intestine, anal canal) n Accessory (teeth, tongue, salivary glands, liver, gall bladder, pancreas) n n Basics: tube, open at both ends, 186 m 2

mouth pharynx

Structure of Wall n Mucosa – mucous membrane of surface epithelium, underlying CT, and small amount of smooth muscle tissue n Folded in some regions to increase surface area in lumen (digestive tube)

Movements of the Tube n Two main types of movement n n Mixing – smooth muscles in small segments of tube contract rhythmically Propelling – wavelike motion called peristalsis n n Ring of contraction appears in wall of tube and wall ahead of ring relaxes Pushes tubular contents ahead of wave

Mouth – primary site of digestion n Reduces size of food particles (mechanical digestion) Mixes with saliva (chemical digestion) Lips, cheeks, tongue, and palate n n Oral cavity – between palate and tongue Vestibule – narrow space between teeth and cheeks

Mouth cont. n Tongue – nearly fills oral cavity when mouth is closed n n n Frenulum – connects midline of tongue to floor of mouth Skeletal muscle helps mix food w/ saliva and moves toward pharynx during swallowing Papillae – rough projects providing friction and taste buds

Mouth cont. n Palate – roof of oral cavity n n Anterior (hard palate) Posterior (soft palate) – muscular arch that extends posteriorly and downward as a cone shaped projection uvula n During swallowing muscles draw uvula upward to close opening between nasal cavity and pharynx you may squirt food out your nose if this action isn’t completed fully before swallowing

Teeth n Two sets during development n n n Primary (baby teeth) – shed in same order they appear root reabsorbed before pressure from secondary teeth pushes out Secondary (permanent) – 32 total (16 in each jaw) Break down food into smaller pieces thus increasing surface area of particles

Teeth cont. n Incisors – 4 central, 4 lateral n n Cuspids – 4 n n Grasping and tearing food Bicuspids – 4 first, 4 second n n Biting off pieces Grinding Molars – 4 first, 4 second, 4 third n Grinding

Teeth cont. n Crown – portion of tooth above gum n White enamel covering – calcium salts (hardest substance in the body) n n Cannot be replaced if damaged Dentin – bone like substance surrounds central cavity (pulp cavity that extends into root)

Teeth cont. n Root – portion below gum n n n Pulp cavity – contains blood vessels, nerves and a CT called pulp Cementum – thin layer of bonelike material encloses root Periodontal ligament – surrounds cementum with dense CT attaching tooth to jaw

Salivary Glands n n Secrete saliva – moistens food particles, binds them, and begins chemical digestion of carbohydrates Two types of cells n Serous cells – produce watery fluid that contains digestive enzyme amylase n n Amylase splits starch and glycogen into disaccharides Mucous cells – secrete thick mucus n Binds food particles and lubricates during swallowing

Salivary Glands cont. n Three major pairs n Parotid glands – largest, lying anterior and somewhat inferior to each ear n n Submandibular glands – floor of mouth, on inside surface of lower jaw n n Secretions rich in amylase Predominately serous, with a few mucous cells Sublingual glands – smallest, floor of mouth, inferior to tongue n Mainly mucous, secretions thick and stringy

Salivary Glands