Gastrointestinal system

Structure, function and control of the gastrointestinal system

1. Gastrointestinal system Roger Watson Twitter: @rwatson1955

2. Gastrointestinal system The gastrointestinal system runs from the mouth to the anus. It is responsible for the ingestion and digestion of food and the excretion of waste products. Topologically, it lies ‘outside’ the body.

3. Bozeman biology You Tube link The digestive system

4. Peritoneum Organs of the gastrointestinal system are contained in the: peritoneal cavity Peritoneum: a transparent membrane that lines the abdominal cavity in mammals and covers most of the viscera

5. Mesentery Fold of peritoneum that supports the intestines Also provides blood and nervous supply

6. Gastrointestinal system General structure: Composed of smooth muscle Under control of autonomic nervous system

7. Gastrointestinal system General structure: Composed of smooth muscle Arranged in two planes: longitudinal circular

8. lumen

9. Gastrointestinal system General structure: Composed of smooth muscle Arranged in two planes: longitudinal Circular Muscle arrangement allows PERISTALSIS Waves of contraction and relaxation which propel food along the GI tract

10. Gastrointestinal system General structure: Composed of smooth muscle Arranged in two planes: longitudinal Circular Contains: Lumen (space) Mucosa

11. Mucosa Both secretory and absorbtive. Tends to be: Secretory at the top Absorbtive at the bottom secretory absorbtive

12. Gastrointestinal tract Mouth Oesophagus Stomach Small intestine Large intestine Rectum Anus AND: Pancreas Gall bladder Liver

13. Mouth Contains: Teeth Tongue Salivary glands

14. Mouth Contains: Teeth For breaking food into smaller particles Tongue Organ of taste but also helps in chewing and swallowing Salivary glands Lubricate food in the mouth and begin carbohydrate digestion Process know as MASTICATION

15. Mastication (chewing) Enabled by the muscles of mastication: Temporalis Masseter

16. Temporalis Masseter

17. Mastication (chewing) Enabled by the muscles of mastication: Temporalis Masseter And the temperomandibular joint: Allows movement in three planes

18. Mastication (chewing) Enabled by the muscles of mastication: Temporalis Masseter And the temperomandibular joint: Allows movement in three planes Chewing is a prelude to swallowing

19. Epiglotiss trachea

20. Oesophagus Food is propelled down the oesophagus by peristalsis The trachea (windpipe) is protected by the EPIGLOTTIS

21. The stomach The stomach is a food reservoir: It completes the mechanical breakdown of food It initiates protein digestion It produces CHYME

22. Note US spelling!

23. Convoluted surface (rugae) allows for expansion

24. The stomach The stomach has three muscle layers: Longitudinal Circular Oblique

25. longitudinal circular oblique

26. The stomach The stomach is lined with gastric pits from which is secreted: Mucus Hydrochloric acid Pepsin Gastrin Intrinsic factor

27. The intestines Small intestine Large intestine

28. Small intestine Large intestine Liver Stomach

29. Small intestine Propels food along by peristalsis

30. Small intestine Propels food along by peristalsis Mixes food by segmentation

31. Small intestine Propels food along by peristalsis Mixes food by segmentation Large surface area enabled by: VILLI

32. Small intestine Propels food along by peristalsis Mixes food by segmentation Large surface area enabled by: VILLI Secretions include: Sodium bicarbonate Protein digesting enzymes: Peptidase Trypsin* Fat digesting enzymes: Lipase* Carbohydrate digesting enzymes: Amylase* Maltase Sucrase Lactase

33. Pancreas Lies below the stomach and is linked to the small intestine (duodenum) via the: pancreatic duct ampulla of Vater (controlled by the sphincter of Oddi)

34. Ampulla of Vater

35. Pancreas Lies below the stomach and is linked to the small intestine (duodenum) via the: pancreatic duct ampulla of Vater (controlled by the sphincter of Oddi) Pancreatic secretions: Trypsin Amylase Lipase

36. Gall bladder Stores bile which is produced in the liver Bile is released via the ampulla of Vater Bile is an emulsifying agent

37. Ampulla of Vater LIVER

38. Digestion Breaks large molecules down into smaller ones which can be absorbed in the intestines and used by the body in metabolism The proteins involved in digestion (eg amlyase, lipase, pepsin) are called ENZYMES.

39. Digestion Breaks large molecules down into smaller ones which can be absorbed in the intestines and used by the body in metabolism The proteins involved in digestion (eg amlyase, lipase, pepsin) are called ENZYMES. Digestion is controlled in three phases: Cephalic Gastric Intestinal

40. Cephalic phase Prepares the stomach for incoming food and lasts very briefly. Sight, smell, taste, or thought can stimulate secretions. This stage is directed by the CNS and, under the control of the vagus nerve, parasympathetic fibers innervate the cells which secrete the gastric juices.

41. Gastric phase Begins with the arrival of food, causing the secretion of the hormone gastrin , which is released along with stomach acid and enzymes. This phase may last for several hours.

42. Intestinal phase Begins with the entrance of chyme into the small intestine, causing the secretion of many hormones including secretin , CCK (cholecystokinin), and GIP (gastric inhibitory peptide).

43. Large intestine Acts as a reservoir and as an area for reabsorbtion of water Linked to small intestine by ileo-caecal valve

44. Large intestine Acts as a reservoir and as an area for reabsorbtion of water Linked to small intestine by ileo-caecal valve Movement in large intestine: Peristalsis Haustral churning Mass movement Intestinal bacteria: E.coli Play an important role in digestion of residual products

45. Large intestine Produces waste product: faeces Defaecation: Process of expelling faeces

46. Gastrointestinal system The gastrointestinal system runs from the mouth to the anus. It is responsible for the ingestion and digestion of food and the excretion of waste products. Topologically, it lies ‘outside’ the body.

47. Questions Describe the GI system. What are the four main regions of the GI tract between mouth and anus? Name four organs/structures that are linked to the GI tract. Describe the peritoneum and what is the space that it encloses called? What kind of muscle is found in the GI tract, how is it arranged and how is it controlled? What is the process that moves food along the GI tract? Describe this process.

48. Questions 7. What is the space in the GI tract called and what is the lining of the GI tract called? What are the two functions of  the lining? 8. Name the three pairs of salivary glands. What is the MAIN function of saliva? 9. What is mastication? In addition to saliva what other parts of the mouth are involved? What is the end product of mastication? 10. What are the muscles of mastication? Which joint is involved and what is unique about it? 11. In the process of swallowing, which tube does the bolus of food enter on its way to the stomach?  Which tube is protected by the epiglottis and what is the epiglottis? How is the bolus of food moved to the stomach?

49. Questions 12. What are the functions of the stomach? 13. What are the three muscle layers of the stomach and what are the convolutions on the inner surface of the stomach called? 14. State the three regions of the small intestine in the correct order. 15. What are the functions of the small intestine?

50. Questions 16. What features of the lining of the small intestine provide it with a large surface area? What are the three groups of enzymes ( ie in terms of what they digest) that are secreted into the small intestine? 17. Where do pancreatic secretions enter the duodenum? In addition to sodium bicarbonate what digestive enzymes are produced by the pancreas? 18. Where is bile made? What does the gall bladder do? Where is bile released into the duodenum? What does bile do? 19 . Describe digestion. 20. What do enzymes do? What are the three phases of digestion?

51. Questions 21. What is mainly reabsorbed in the large intestine and what are the three major regions of the large intestine? 22. What are the three types of movement in the large intestine and which bacterium is mainly found here? 23. Describe the structure and function of the internal and external anal sphincters.

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