The digestive system has two main parts: the gastrointestinal (GI) tract and accessory organs. The GI tract includes the mouth, esophagus, stomach, small intestine, large intestine, and anus. Accessory organs include the teeth, tongue, liver, gallbladder and pancreas. Food enters the mouth where it is broken down by chewing and saliva before passing through the esophagus into the stomach for further breakdown. Digestion is completed in the small intestine where nutrients are absorbed. Undigested material then passes into the large intestine to be compacted and expelled as waste.

1. DIGESTIVE SYSTEM

3. DIGESTIVE SYSTEM Two main parts: Gastrointestinal (GI) tract - mouth, pharynx, esophagus, stomach, small intestine, large intestine, and anus. Accessory digestive organs - teeth, tongue, gallbladder, salivary glands, liver, and pancreas.

4. Digest. Abdomino-pelvic cavity is lined by 2 serous membranes = Peritoneal membrane(secretes a watery fluid) 1. Parietal peritoneum - attached to body wall. 2. Visceral peritoneum - fused to surface of abdominal organs.

5. GI – 4 Tunics A. Tunica Mucosa: innermost, 3 parts 1. Epithelial Layer; Nonkeratinized stratified squamous (oral cavity to stomach) for protection; Simple Columnar (stomach to anus) a. Absorption b. Secretion i. digestive enzymes ii. mucus from goblet cells 2. Lamina propria - c.t. with lymphatic nodules (groups of WBC's) 3. Muscularis mucosae - thin layer of smooth muscle

6. GI – 4 Tunics B. Tunica Submucosa - c.t. 1. Highly vascular 2. May contain mucous glands 3. Nerve plexus

7. GI – 4 Tunics C. Tunica Muscularis most common type is 2 layers of smooth muscle 1. Inner - circular 2. Outer - longitudinal Contract by Peristalsis (waves of smooth muscle contraction, and are controlled by a nerve plexus)

8. GI – 4 Tunics D. Tunica Serosa or Tunica Adventitia: serosa = simple squamous epi + c.t.; adventitia = just c.t.

9. Mouth = Oral or Buccal cavity Functions 1. Receives food 2. Initiates digestion a. Mastication b. Saliva - has amylase (an enzyme) which breaks down carbohydrates (long chains of sugars into short chains) 3. Initiates swallowing

10. Mouth -Histology 1. Tunica Mucosa; inner epithelial lining = nonkeratinized stratified squamous 2. Tunica Submucosa: c.t. 3. Tunica Muscularis: facial muscles 4. Skin: outer, keratinized stratified squamous

11. Mouth -Tongue - has Papillae 1. Filiform - most numerous, conical; for tactile sensation (touch, temp., texture, heat, cold, etc.) 2. Fungiform - larger, rounded, taste buds on top 3. Circumvallate - very large, 7-12, taste buds on sides

12. Palate 1. Hard palate - bone (roof of oral cavity) 2. Soft palate = muscular arches a. Uvula b. Palatoglossal arch (ant.) c. Palatopharyngeal arch (post.) Between the two arches = palatine tonsils

13. Mouth - Teeth Teeth Mastication

14. Mouth –Salivary Glands Salivary glands: 3 pairs 1. Parotid - largest, on masseter, secretes serous fluid, fluid enters mouth via parotid duct 2. Submandibular - secretes serous & mucous 3. Sublingual - secretes primarily mucus, in floor of mouth

15. Pharynx - Common to resp. & digest. systems. Connects oral cavity to esophagus & nasal cavity to larynx. Parts 1. Nasopharynx - not part of Dig. Sys. 2. Oropharynx - air & food 3. Laryngopharynx - air and food

16. Pharynx –Histo. 1. Tunica Mucosa: contains nonkeratinized stratified squamous 2. Tunica Submucosa: c.t. 3. Tunica Muscularis; composed of 3 bands of skeletal muscle = constrictors 4. Tunica Adventitia: c.t.

17. Esophagus A. Connects pharynx to stomach B. Passes through diaphragm at esophageal hiatus C. Ends at stomach; its muscularis layer forms the Gastroesophageal (cardiac) sphincter.

18. Esophagus – histo. 1. Mucosa - non-keratinized stratified squamous 2. Submucosa - contains mucous glands 3. Muscularis - 3 sections a. Upper 1/3 = skeletal b. Middle 1/3 = sk. & smooth c. Lower 1/3 = smooth 4. Adventitia - c.t. Function: voluntary & involuntary movement of food to stomach

19. Stomach - General 4 regions: cardiac, fundus, body, & pylorus. Ends at pyloric sphincter Begins break-down of food

20. Stomach - histo 1. Mucosa - has Gastric Pits which open up into the Gastric Glands. The Gastric Glands are composed primarily of; a. Simple columnar epi. i. Mucous neck cells - for protection ii. Parietal cells - hydrochloric acid (HCl) iii. Chief cells - pepsinogen (an inactive enzyme that is activated to Pepsin by hydrochloric acid, for protein digestion) 2. Submucosa - c.t. 3. Muscularis - 3 layers of smooth muscle; longitudinal, oblique, & circular 4. Serosa

21. Small Intestine – Major Digest Organ Major digestive organ 8-18 ft long 1. Duodenum: most chemical digestion occurs here because; Duodenal cells make enzymes to break down foodstuffs It receives bile from gall bladder It receives enzymes from the pancreas for the break down of foodstuffs 2. Jejunum - most absorption occurs here 3. Ileum - very little absorption Digestion is completed in Small Intestine. The small intestine ends at the Ileocecal valve

22. Sm. Intestine - Histo 1. Mucosa has finger-like folds = Villi a. Epithelium - Simple Columnar with microvilli (secretion & absorption) and Goblet cells (mucus). b. Lamina propria - contains lacteals Between villi = intestinal glands 2. Submucosa is in folds 3. Muscularis - 2 layers of smooth muscle; outer - long., inner - circ. 4. Serosa

23. Large Intestine – Larger Diameter Regions: Cecum, Apendix, Colon, Rectum, Anal Canal Function Re-absorption of digestive fluids