The Digestive System

1. The Digestive System The Anatomy

2. Anatomy • We have what we call an alimentary canal • This means we have 2 holes • One for import, one for export • This is in contrast to organisms such as jellyfish who have a gastrovascular cavity • You guessed it…..just one hole for both in AND out • Moral of the story: be glad you have 2 holes!!

3. Anatomy • Connecting our 2 holes we have a series of tubes PLUS a bunch of accessory organs that assist in the digestion of foods

4. The Tubes • Our alimentary canal, aka our gastrointestinal (GI) tract, consists of a continuous, coiled, hollow, muscular tube • Organs • Mouth • Pharynx • Esophagus • Stomach • Small intestine • Large intestine

5. Let’s Draw a Picture!

6. 1) Mouth • Lined with a mucous membrane • Question: What type of membrane is that? • Epithelial membrane • Means it is comprised of epithelial tissue and connective tissue • Important components • Tongue • Teeth • Salivary glands

7. Ms. Mueller’s Teeth

9. 2) Pharynx • Passageway for food, fluids, and air • Muscular passageway to propel food • Called peristalsis

10. CAREFUL!! • Do NOT confuse this structure with the larynx • The pharynx is for phood (food) and air • The larynx is for voice (we will talk about this in the respiratory system) • Food should NOT be found here!!

11. True or False Food passes through the larynx on the way to the stomach.

12. 3) Esophagus • Runs from the pharynx to the stomach • 4 layers (innermost to outermost) called tunics • Mucosa • Moist membrane that lines the lumen (the hollow part of the tube) • Epithelial tissue, connective tissue, smooth muscle layer • Submucosa • Connective tissue • Blood vessels, nerve endings, lymph organs

13. 3) Esophagus • Muscularisexterna • Inner circular layer and outer longitudinal layer of smooth muscle • Serosa • Outermost layer consisting of flat serous fluid-producing cells • Visceral peritoneum and parietal peritoneum

14. Question • What are the 4 tunics, in order, from external to internal? • Serosa, muscularisexterna, submucosa, mucosa

15. Location Matters • Notice the location of the esophagus to the trachea

16. Question • What prevents our food from “going down the wrong tube”? • Answer: the epiglottis!! • Flap of cartilage that directs food to the stomach and air to the lungs

17. 4) Stomach • C-shaped organ • Has the same 4 tunics as the esophagus • What were those again? • Mucosa, submucosa, muscularisexterna, serosa

18. 4) Stomach • Has 2 sphincters • These acts as gatekeepers letting things in and out of the stomach • Cardioesophageal sphincter connects the cardiac region of the stomach (closest to the heart) with the esophagus • the pyloric sphincter connects the stomach to the small intestine • Let’s add to our picture!

19. 4) Stomach • Contains large folds of mucosa called rugae • This enables it to be flexible in its diameter • When full, it can hold up to ONE GALLON of food

20. Surgery: Gastric Bypass • Treatment for obesity • Involves decreasing the size of the available storage space of the stomach • Intended to make you feel full faster so that way you can eat less • Surgery Squad! • http://www.surgerysquad.com/surgeries/rny-gastric-bypass-surgery/

21. 4) Stomach: Microscopic • Pitted appearance called gastric pits that lead to gastric glands • There is also a variety of cells that assist in digestion • (We will get to those when we get to the physiology of digestion )

22. 5) Small Intestine • Connects to the stomach via the pyloric sphincter • Coiled tube • Average length: 8-18 feet!! • Same 4 tunics of the stomach and esophagus • 3 subdivisons • Duodenum (5% of length) • Jejunum (40% of length) • Ilium (55% of length)

23. 5) Small Intestine • Contains ducts that connect to accessory organs • Both ducts merge into 1 duct • Pancreatic duct • Connects the pancreas to the small intestine • Common bile duct • Connects the liver/gall bladder to the small intestine • The gall bladder, liver, and pancreas are accessory organs to the GI tract

24. 5) Small Intestine: Microscopic • The small intestine has folds in it, just like the stomach • Called circular folds • Difference: these folds are not for stretching like the rugae of the stomach • These folds are for increased surface area

25. 5) SI: Microscopic • More microscopically, villi are fingerlike projections of mucosa found facing the lumen of the SI on the circular folds • Again, these function to increase the surface area

26. 5) SI: Microscopic • Even more microscopically, there are a series of microvilli on each villus • Projections of the plasma membrane of the mucosa cells • Often referred to as the “brush border”

27. Let’s Draw a Picture • Circular folds • Villi • Microvilli

28. Question • Which of the following has the 4 tunics? • A) esophagus • B) SI • C) stomach • D) LI • E) all except D

29. 6) Large Intestine • Larger in diameter than the SI, but shorter in length • Frames the SI on 3 sides • Subdivisions • Cecum attaches the SI to the LI • The appendix hangs off of this structure • Called vermiform appendix because it looks like a rat tail • Colon • Ascending colon • Transverse colon • Descending colon • Sigmoid colon • Rectum • Anal canal

30. Interesting….. • Your anus is a sphincter • That is, it has a muscular gatekeeper • It has both voluntary and involuntary muscle so technically you can’t always control your elimination • Elimination=defecating=going #2

31. Let’s draw a complete picture putting it all together!

32. Quiz Yourself • Put the following organs in order: pharynx, mouth, small intestine, large intestine, stomach, esophagus • Mouth, pharynx, esophagus, stomach, SI, LI • Where does food pass through first: the cardioesophageal sphincter or the pyloric sphincter? • Cardioesophageal and then pyloric • What are the three accessory organs and how are they connected to our GI tract? • Liver, gall bladder, and pancreas; SI • What allows our stomach to expand? • Rugae folds • What is the purpose of the circular folds, villi, and microvilli? What organ contains these structures? • Increase surface area; SI