1Lab 41Digestive System AnatomyFor Lab Practical 2• Be able to identify the following tissues microscopically: esophagus, stomach, small intestine (identify section), liver (identify central vein and triads), pancreas, salivary glands. Instead, identify large intestine• Be able to identify the following structures on a model: esophagus, stomach, small intestine, large intestine, pancreas, liver, gall bladder, salivary glands.Digestive System• Mouth (oral cavity)– Salivary glands– Teeth– tongue• Throat (pharynx)• Esophagus•Stomach• Small Intestine• Large Intestine• Accessory Organs:–Liver– Gallbladder– PancreasHistologyof the Digestive Tract• Major layers of the digestive tract:– mucosa– submucosa– muscularis externa– serosaSalivary glands• This is a composite slide, with three different tissues. Look at all three, but sketch one (pick your favorite). Do your best to label any cells or ducts. Hint: serous cells tend to stain darker than mucous cells. The parotid gland contains predominantly serous cells, while the sublingual and submandibular glands have a mixed population of cells. Take an educated guess as to which salivary gland you are looking at, and label it as such. Salivary Glands• Parotid Salivary Glands– Inferior to zygomatic arch– Produce serous secretion:• enzyme salivary amylase (breaks down starches) • Sublingual Salivary Glands– Covered by mucous membrane of floor of mouth– Produce mucous secretion:• buffer and lubricant• Submandibular Salivary Glands– In floor of mouth– Secrete buffers, glycoproteins (mucins), and salivary amylase• Each have their own ducts to reach the mouth2Salivary GlandsParotid – serous secretionsSublingual and submandibularEsophagus• Esophagus • Draw and clearly label the esophagus. Remember to include the total magnification used for your sketch. Label: the mucosa (yes, bracket the entire mucosa), and then within the mucosa, label: the epithelia (label the TYPE of epithelia), lamina propria (note the TYPE of connective tissue), and muscularis mucosae. Label the submucosa (note glands if seen), and muscularis externa (label the two different muscle layers here). The EsophagusFigure 24–10Histology of the Esophagus• Wall of esophagus has 3 layers:– mucosal– submucosal–muscularisCharacteristics of the Esophageal Wall • Mucosa contains nonkeratinized, stratified squamousepithelium • Mucosa and submucosa:– both form large folds that extend the length of the esophagus and allow for expansion• Muscularis mucosae consists of irregular layer of smooth muscle• Submucosa contains esophageal glands:– produce mucous secretion which reduces friction between bolus and esophageal lining • Muscularis externa:– has usual inner circular and outer longitudinal layers – Superior portion has some skeletal muscle fibers• No serosa (adventitia instead)Stomach• The box of ‘stomach’ slides contains a variety of slides. If you choose the composite slide, it contains three stomach regions. The first sample (left most) is from the fundus, the third sample (right most) is from the pyloricregion. Sketch and clearly label these two regions of the stomach. • For the fundus, label: epithelia (what type), gastric pits, gastric glands, the thin muscularis mucosae, submucosa, and external muscularis layers. Indicate the area in the tissue where you expect to find parietal and chief cells. • For the pyloric region of the stomach, label similarly as above. Indicate where you would expect to find G cells.3The StomachFigure 24–12bRegions of the Stomach• Cardia: – smallest part; superior, medial portion within 3cm of esophagus– abundant mucus glands• Fundus– portion superior to esophageal junction•Body– Area between fundus and curve of the “J”– Many gastric glands• Pylorus – The curve portion of the “J”, ends at pyloric sphincter– Glands here secrete gastrinFigure 24–13The Stomach LiningStomachHistology of the Stomach• Rugae = folds of empty stomach• Muscularis mucosa and externa contain extra oblique layers of smooth muscle• Simple columnar epithelium lines all portions of stomach, is a secretory sheet: produces mucus that covers interior surface of stomach• Gastric Pits– shallow depressions that open onto the gastric surface– Mucous cells found at base, or neck, of each gastric pit actively divide, replacing superficial cellsGastric Glands• Found in fundus and body of stomach, extend deep into underlying lamina propria• Each gastric pit communicates with several gastric glands • Two types of secretory cells in gastric glands secrete gastric juice:– parietal cells– chief cells4Gastric Gland cells• Parietal Cells– Mostly in proximal portions of glands–Secrete intrinsic factor and hydrochloric acid(HCl)• Chief Cells– Most abundant near base of gastric gland:–Secrete pepsinogen (inactive proenzyme)– Pepsinogen Is converted by HCl in the gastric lumen to pepsin (active proteolytic enzyme) Pyloric Glands• Pyloric Glands in the pylorus produce mucous secretions• Enteroendocrine Cells are scattered among mucus-secreting cells:– G cells• Abundant in gastric pits of pyloric antrum•Produce gastrin: stimulates both parietal and chief cells and promotes gatric muscle contractions– D cells• In pyloric glands •Release somatostatin, a hormone that inhibits release of gastrinSmall Intestine• This is a another composite slide. The three regions of the small intestine are presented on the slide in order of appearance in the body. Please sketch the first and third. • For the first (duodenum), label: epithelia (what type), goblet cells (if you see any), crypts(intestinal glands), Brunner’s glands (these are large glands of the submucosa), a lacteal, and a villus. • For the third (ileum), label the same things as above (if present), and the Peyer’s patches. Segments of the S.I.• The Duodenum is the 25 cm (10 in.) long segment of small intestine closest to stomach– “Mixing bowl” that receives chyme from stomach, digestive secretions from pancreas and liver• The Jejunum is the 2.5 meter (8.2 ft) long middle segment – the location of most chemical digestion and nutrient absorption• The Ileum is he final 3.5 meter (11.48 ft) long segmentThe Intestinal WallFigure 24–17Intestinal Folds and Projections• Largest = Plicae: transverse folds in intestinal lining– permanent features (they