DIGESTIVE SYSTEM I I. IntroductionA. Two main parts: 1. Gastrointestinal (GI) tract – mouth, pharynx, esophagus, stomach, small intestine, large intestine, and anus.2. Accessory digestive organs – teeth, tongue, gallbladder, salivary glands, liver, and pancreasB. Abdominopelvic cavity is lined by 2 serous membranes = Peritoneal membranes = Peritoneum (secretes a watery fluid)1. Parietal peritoneum – attached to body wall and extends to organs.2. Visceral peritoneum – fused to surface of abdominal organs.II. Histology of the GI Tract: All parts of the GI tract have the same four layers (tunics):A. Tunica Mucosa: innermost, 3 parts1. Epithelial Layer: nonkeratinized stratified squamous (oral cavity to the stomach) for protection; Simple Columnar (stomach to anus)a. Absorptionb. Secretioni. of digestion enzymes ii. & mucus from goblet cells 2. Lamina propria - c.t. with lymphatic nodules (aggregations of WBC's) 3. Muscularis mucosae – thin layer of smooth muscleB. Tunica Submucosa - c.t. 1. Highly vascular 2. May contain mucous glands 3. Nerve plexus = submucosal (meissner’s plexus)C. Tunica Muscularis (= muscularis externa) – most common pattern is 2layers of smooth muscle 1. Inner – circular 2. Outer – longitudinalThe tunica muscularis contracts by the means of Peristalsis = waves ofsmooth muscle contraction; controlled by a nerve plexus = myenteric (Auerbach’s) plexusD. Tunica Serosa or Tunica Adventitia: 1. serosa = simple squamous epi. + C.T. = visceral peritoneum 2. adventitia = just C.T.III. Mouth = Oral or Buccal cavityA. Functions1. Receives food2. Initiates digestion a. Mastication b. Saliva – has amylase which breaks down carbs 3. Initiates swallowing = deglutition B. Histology1. Tunica Mucosa; inner epithelial lining = nonkeratinized stratified squamous2. Tunica Submucosa: connective tissue3. Tunica Muscularis: facial muscles (skeletal)4. Skin: outer C. Tongue - has Papillae1. Filiform - most numerous, conical; for tactile sensation (touch, temp, texture, hot, cold, etc.)2. Fungiform – larger; rounded; has taste buds on top 3. Vallate (circumvallate) – very large; 7-12; has taste buds on the sideD. Palate – roof of oral cavity 1. Hard palate - bone (maxilla & palatine) 2. Soft palate = muscular arches a. uvula = end of soft palate b. Palatoglossal arch – anterior c. Palatopharyngeal arch – posterior Between the two arches = palatine tonsils E. Teeth = mastication F. Salivary glands: 3 pairs 1. Parotid - largest, on masseter, secretes serous (watery) fluid, fluid enters mouth through parotid duct.2. Submandibular – secretes serous and mucus (thick)3. Sublingual – secretes primary mucus; in floor of mouthFunctions of saliva: dissolve food, moisten food, cleanse mouth, initiate chemical digestion of carbs, inhibits bacteria The mucosa of the oral cavity contains which of the following?a. Stratified cuboidalb. Simple squamousc. Nonkeratinized stratified squamousd. Keratinized stratified squamouse. Simple
View Full Document
Unlocking...