Digestive System

1. Digestive System Lecture Packet 19 Chapter 15

2. Outline – Digestive System • Function • Layers of the GI tract • Major parts: mouth, pharynx, esophagus, stomach, small intestine, large intestine, pancreas, liver, gall bladder. • Digestive enzymes • Disorders of the digestive system

3. The Digestive System • The digestive system consists of a long tube, called the gastrointestinal (GI) tract that extends from the mouth to the anus, along with accessory glands • The digestive system is divided into specialized compartments for food processing • Nerves and hormones control digestive activities

4. Function of the Digestive System • The functionof the digestive system is to: • bring food into the body • digest it into nutrients that are absorbed by the body • eliminate wastes out of the body.

5. Terminology • Digestion: The process of breaking complex molecules into simpler molecules which can be absorbed in the GI tract • Absorption: The process of transporting molecules across the wall of the GI tract into vessels to be transported to the liver.

6. Digestion • Mechanical digestion - chewing of food, churning action of the stomach, and segmentation of the small intestine. • Chemical digestion - action of enzymes and chemicals on foods. 7-3

7. The Digestive System ORGANS Mouth • Entrance to digestive system• Teeth chew food• Tongue positions and tastes food Pharynx • Passageway for food (and air) • Plays a role in swallowing Stomach • J-shaped muscular sac • Stores food • Secretes gastric juice(pepsin and HCl) • Mixes food with gastric juice • Protein digestion begins Esophagus • Muscular tube • Moves food from pharynx tostomach Colon • Muscular tube • Absorbs water and somenutrients • Stores waste materials(feces) Small intestine • Long, muscular tube • Mixes food with bile and withintestinal and pancreaticenzymes • Digests most nutrients • Absorbs most nutrients andwater Cecum • Blind pouch at junction ofsmall and large intestines Large intestine Anus • Opening at end of system • Expels feces Rectum • Region of large intestine • Passageway for feces • Stretching of wall stimulatesthe defecation reflex Anal canal • Regulates defecation Figure 15.1 (1 of 2)

8. The Digestive System ACCESSORY STRUCTURES Salivary glands • Three pairs of glands thatsecrete saliva • Saliva moistens food • Enzyme (amylase) in salivabegins starch digestion Liver • Large organ inabdominal cavity • Secretes bile, whichemulsifies fats • Plays role inprocessing and storingcertain nutrients Gallbladder • Small sac • Stores bile • Releases bile into smallintestine Pancreas • Gland located behindstomach • Secretes enzymes thatdigest all majornutrients • Secretes buffers thatneutralize HCl fromstomach • Releases secretionsinto small intestine Figure 15.1 (2 of 2)

9. What type of epithelial tissue lines the GI tract? • Simple cuboidal • Simple squamous • Simple columnar • Stratified sqamous

10. Wall of the Digestive Tract • Along most of its length, the wall of the digestive system has four basic layers • Mucosa • Submucosa • Muscularis • Serosa

11. Wall of the Digestive Tract Lumen The mucosa is a mucousmembrane that lines theGI tract and secretesmucus that lubricates andprotects the GI tract. Bloodvessels Lymphaticvessel The submucosa is a layerof connective tissue thatcontains blood vessels,lymph vessels, and nerves. Nerve The muscularis is madeup of two layers of smoothmuscle—one circular andone longitudinal. The serosa is aconnective tissuecovering that secretesa fluid to lubricate theoutside of the GI tract. Figure 15.2

12. Wall of the Digestive Tract - Mucosa • Mucosa - Mucus membrane layer lines the GI tract • The open area inside the GI tract is the lumen. • Glandular epithelial cells secrete digestive enzymes. • Goblet cells secrete mucus, which lubricates. • Simple columnar epithelial cells line the lumen 7-6

13. Wall of the Digestive Tract - Submucosa • Submucosa – layer of connective tissue with nerves, blood supply, lymph vessels. • Protect us from disease, nerves stimulate muscles, transport of nutrients. 7-6

14. Wall of the Digestive Tract - Muscularis • Muscularis – Layer of smooth muscles. • Has two layers of muscle, one circular and one longitudinal • Functions to mix and moves food. 7-6

15. Wall of the Digestive Tract - Serosa • Serosa – a layer covering the GI tract that secretes serous fluid. • The fluid functions to reduce friction between moving layers of tissue. 7-6

16. Components of the GI Tract • The major GI Tract components • Mouth • Esophagus • Stomach • Small intestine • Large intestine

17. Accessory Organs • The digestive organs are aided by several accessory organs • Salivary glands • Pancreas • Gallbladder • Liver

18. The Digestive System Has Specialized Compartments Table 15.1

19. Parts of the Digestive Tract - Mouth 1. Mouth: specialized for tasting, speech, moistening food, and mechanical and enzymatic digestion. 7-3

20. Parts of the Digestive Tract - Mouth • The mouth contains: • Salivary glands - secretes salivary amylase that begins the process of digesting starch. • Tongue - mixes chewed food with saliva. • Teeth – break food into smaller pieces • Tonsils – protect against infections • Uvula – working with the soft palate, closes off the nasopharynx 7-3

21. Mouth - Salivary glands • Saliva: • Moistens food • Dissolves the chemicals in the food • Contains the enzyme, salivaryamylase • Begins digestion of carbohydrates

22. Salivary glands Figure 15.5

23. Mouth - Tongue • The tongue • A large skeletal muscle with taste buds • Important in speech • Helps form food into a bolus • A soft mass of food, suitable for swallowing

24. Teeth Enamel Dentin Crown Pulp cavity(contains bloodvessels andnerves) Gum (gingiva) Root canal Root Cementum Bone (b) The structure of the human tooth is suited for its function ofbreaking food into smaller pieces. Figure 15.3b

25. Mouth - Pharynx 2. Pharynx: behind the uvula where the nasal and oral cavities join. Common passageway for air, liquids, and food. • Swallowing reflex begins here. • Epiglottis covers opening in the larynx that leads to the trachea when swallowing. 7-5

26. Esophagus 3. Esophagus – passage that connects the pharynx to the stomach. • No digestive processes occur here 7-5

27. Esophagus • Food is pushed through our digestive system by a series of muscular contractions called peristalsis

28. Esophagus Figure 15.7

29. Esophagus • Sphincters - circular muscles that control the entrance and exit of materials to and from the stomach. • Acid reflux - heartburn occurs when partially digested food comes back up into the esophagus and produces a burning sensation. 7-5

30. 4. Stomach • The stomach breaks up food through muscular contractions. There are three layers of smooth muscle • The food that leaves the stomach is only partially digested.

31. Stomach Figure 15.8a

32. 4. Stomach functions • The functions of the stomach include: • Responsible for the storage of food • Turns food into a soupy mixture called chyme • Adds digestive enzymes and acids that begin chemical digestion of proteins

33. Stomach – Storage of food Stomach - Storage of Food • The stomach expands to accommodate amounts of food • When empty the stomach can hold about 50 ml (1/4 cup) • When full, can hold several liters of food 7-8

34. The thick soupy acidic liquid that leaves the stomach is called: • chylomicrons • bolus • chyme • feces

35. Stomach – Secretions • Gastric glands secrete: • The digestive enzyme, pepsin, that begins the digestion of proteins. • Hydrochloric acid (HCl) - strong acid that kills bacteria, aids in the digestion of proteins, begins to break down connective tissues, and activates pepsin. • The wall of the stomach is protected by a thick layer of mucus secreted by goblet cells 7-8

36. Stomach – Storage of food Stomach - Storage of Food • Very little nutrition is actually absorbed into the blood stream from the stomach. • Exceptions include alcohol and some drugs including asprin 7-8

37. Layers of the Stomach Surface epithelium Mucosa Gastric pit Mucus-secreting cell Pepsinogen-secreting cell Submucosa HCl-secreting cell Muscularis Blood vessels Serosa (b) Gastric glands in the wall of the stomachproduce gastric juice, a mixture ofhydrochloric acid and pepsin. Figure 15.8b

38. Gastric Pits Figure 15.8c

39. How many layers of smooth muscle are in the wall of the stomach? • One • Two • Three • Four

40. What is the muscular tube that passes foodstuffs from the pharynx to the stomach? • Trachea • Larynx • Esophagus • Small intestine

41. The primary function of the stomach is: • to break down fats • to store food, liquefy, begin digestion • to absorb major nutrients • package feces

43. 5. The Small Intestine • Small intestine – thin long tube (2.5 cm in diameter and about 6 meters long. • Secretions from the pancreas, liver and gall bladder enter the small intestine • Smooth muscles surround the intestine to push the food through the digestive tract.

44. Parts of the Small Intestine • The small intestine has three regions: • Duodenum • Jejunum • Ileum

45. Function of the Small Intestine • This is the primary site of digestion (mainly chemical, but also mechanical) • Where most (80%) of the nutrients are absorbed into the body.

46. Digestion in the Small Intestine • The digestion of complex molecules (carbohydrates, proteins, fats, and nucleic acids) in the small intestine is aided by: • enzymes released from the pancreas and the small intestine • and by bile from the gall bladder

47. Small Intestine Structure • The lining of the small intestine is • Pleated (has folds) • The pleats have numerous finger-like projections called villi to increase surface area 7-10

48. Small Intestine Figure 15.9a

49. Small Intestine - Villi Figure 15.9b–c

50. Small Intestine Structure - Villi • Villi(villus, singular) - greatly increase the absorption area of the small intestine. • Villi contain blood capillaries and lymphatic vessels called lacteals • Lacteals — absorb fatty acids. • Blood capillaries — absorb nutrients including glucose and amino acids. 7-10