1. The Digestive System ST 120

2. Objectives Sequence of component parts List and describe layers of the tract Mouth to Small Intestines

3. Structure Irregular tube Open at both ends Called the alimentary canal or the gastrointestinal tract (GI) ~29 feet long in the adult Passageway that moves through the body like a hallway Lined with mucous membrane

4. Structure Food must be digested to be used by the body The process of altering the chemical and physical composition of food so that it can be absorbed and used by body cells is known as digestion Food undergoes three kinds of processing: Digestion Absorption Metabolism

5. Organs of the Digestive System Main Mouth Pharynx Esophagus Stomach Small intestine Large intestine Rectum Anal canal

6. Organs of the Digestive System Accessory Teeth and tongue Salivary glands Liver Gallbladder Pancreas Vermiform appendix

8. Wall of the Digestive Tract 4 layers of tissue Mucosa or mucous membrane Submucosa Muscularis Serosa Inside or hollow space is the lumen

9. Wall of the Digestive Tract Mucosa: in the esophagus it is tough and stratified abrasion-resistant epithelium. In the remainder of the tract, it is a delicate layer of simple columnar epithelium. It produces mucus that coats the alimentary canal.

10. Wall of the Digestive Tract Submucosa: connective tissue layer that lies just below the mucosa. It contains many blood vessels and nerves.

11. Wall of the Digestive Tract Muscularis: composed of two layers of muscle tissue. Food material is moved through the digestive system by a wavelike, rhythmic contraction of the muscular coat called peristalsis. Also, the contraction of the muscularis assists in mixing food with digestive juices.

12. Wall of the Digestive Tract Serosa: outermost covering. In the abdominal cavity it is composed of the visceral peritoneum.

13. Wall of the Digestive Tract The loops of the digestive tract are anchored to the posterior wall of the abdominal cavity by a large double fold of peritoneal tissue called the messentery. Blood supply to the bowel runs through this.

15. Mouth Aka oral cavity Lined with mucous membrane Roof of mouth is formed by the hard and soft palates Uvula is the structure that hangs in the back of the throat Uvula and soft palate prevent food and liquid from entering the nasal cavities

16. Mouth Hard palate is formed by parts of the palatine and maxillary bones The tongue is made of skeletal muscle covered with mucous membrane Frenulum attaches the tongue to the floor of the mouth Papillae are the bumps that contain taste buds

19. Teeth 4 major types: Incisors Canines Premolars Molars

20. Teeth Incisors have a sharp cutting edge for mastication Canines are sometimes called cuspids and they pierce or tear food to be eaten Premolars or bicuspids and molars or tricuspids have flat surfaces for grinding or crushing

21. Typical Tooth 3 main parts: Crown Neck Root

22. Typical Tooth Crown- visible portion that is covered in enamel (hardest substance in the body) and dentin and cementum. Neck- narrow portion surrounded by the pink gingiva or gum tissue that joins the crown to the root. Root- fits into the socket of the upper and lower jaw.

23. Typical Tooth Periodontal membrane lines each tooth socket. Dental caries is a disease of the enamel, dentin, and cementum that results in the formation of a permanent defect called a cavity.

25. Salivary Glands Three pairs of these glands secrete most of the saliva produced each day Parotids Submandibulars Sublinguals

26. Parotids Largest Lie just below and in front of each ear at the angle of the jaw People with mumps complain when they chew or open their mouths

27. Submandibular Glands Ducts open into the mouth on either side of the lingual frenulum

28. Sublingual Glands Open into the floor of the mouth Sublingual means under the tongue

30. Saliva Contains mucus and a digestive enzyme called salivary amylase Mucus moistens the food and allows it to pass without friction Salivary amylase begins the chemical digestion of carbs

31. Pharynx Tubelike structure made of muscle and lined with mucous membrane Functions in respiratory and digestive systems

32. Esophagus Muscular, mucus-lined tube that connect the pharynx with the stomach ~10 inches long Serves as a passageway for food

33. Stomach Lies in upper part of the abdominal cavity just under the diaphragm Serves as a pouch that food enters into after it has been chewed, swallowed and passed through the esophagus

34. Stomach Food enters the stomach by passing through the gastroesophageal or cardiac sphincter at the end of the esophagus Sphincters are rings of muscle tissue Cardiac sphincter keeps food from reentering the esophagus when the stomach contracts

35. Stomach If the opening in the diaphragm is enlarged, there may be a bulging of the diaphragm and part or maybe even all of the stomach will move upward into the chest. This is known as a hiatal hernia. May result in gastroesophageal reflux disease.

36. Stomach Contraction of the stomach wall mixes food with gastric juices and breaks it down into a substance called chyme. Gastric juice contains hydrochloric acid. Mucous membranes line the stomach and it contains thousands of microscopic gastric glands that secrete gastric juice and HCl acid

37. Stomach When the stomach is empty, its lining lies in folds called rugae. 3 divisions of the stomach Fundus Body Pylorus

38. Stomach Partial digestion occurs after food is held in the stomach by the pyloric sphincter muscle. Stays closed most of the time thereby closing off the opening of the pylorus into the small intestine.

40. Small Intestine ~7 meters Small in diameter Composed of 3 sections Duodenum Jejunum Ileum This is the order in which food moves through them

41. Small Intestine The mucous lining of the small intestine contains 1000’s of microscopic glands called intestinal glands that secrete intestinal digestive juice. Wall is not smooth, but has multiple circular folds called plicae. (plicate- to fold) These folds are covered with 1000’s of tiny fingers called villi.

42. Small Intestine Villi contain capillaries that absorb sugars and amino acids. Villi greatly increase the surface area for contact between the capillaries and the intestinal lining. Each villus has a lacteal (lymphatic vessel) that absorbs lipid or fat materials from the chyme.

43. Small Intestine Each villus is covered by epithelial cells that have a brush-like border composed of microvilli. Microvilli further increase the surface area for absorption.

44. Small Intestine Most chemical digestion occurs in the duodenum. The duodenum is C-shaped and curves around the pancreas. The middle 3 rd of the duodenum has openings in it where pancreas empties digestive juice and the liver empties bile into the small intestine. These openings are the minor and major duodenal papillae.

46. Day 2 Objectives Liver to Extensions Digestion

47. Liver and Gallbladder Liver cells secrete bile into ducts, so it is considered the largest gland in the body. Hepatic ducts drain bile out of the liver. The common bile duct (CBD) drains bile into the small intestine, and is formed by the union of the cystic duct and the common hepatic duct.

48. Liver and Gallbladder Bile contains substances that emulsify or chemically break up fats. Fats in chyme signal the release of cholecystokinin from the mucosa of the duodenum. This stimulates the contraction of the gallbladder and bile flows into the duodenum.

49. Liver and Gallbladder Gallbladder functions to store bile Bile gives feces its color Jaundice is a yellowish skin discoloration

51. Pancreas Lies behind the stomach Exocrine gland that secretes pancreatic juice into ducts and an exocrine gland that secretes hormone into the blood

52. Pancreas Pancreatic juice is the most important digestive juice because it contains enzymes that digest all three major kinds of food. Also contains sodium bicarbonate that neutralizes hydrochloric acid Enters the duodenum where bile enters

53. Large Intestine Only ~5 feet long Larger in diameter than the small intestine Forms lower portion of the digestive tract

54. Large Intestine Undigested and unabsorbed food material enters the large intestine after passing through a sphincter-like structure called the ileocecal valve. This is no longer chyme because chyme is soupy. The material here is the consistency of fecal matter because water and salts are reabsorbed during its passage through the small intestine.

55. Large Intestine Material that escaped digestion in the small intestine is acted on by bacteria which results in additional nutrients and other fibers are absorbed. These bacteria also synthesize vitamin K and some B-complex vitamins

56. Large Intestine Not ideal for absorption- no villi Normal passage takes 3-5 days Diarrhea results when the rate of passage quickens

57. Large Intestine Subdivisions in order of food passage: Cecum Ascending colon Transverse colon Descending colon Sigmoid colon Rectum Anal canal

58. Large Intestine 2 sphincter muscles stay contracted to keep the anus closed The inner anal sphincter is smooth or involuntary muscle The outer one is voluntary muscle

60. Appendix Wormlike, tubular structure Attached directly to the cecum 1. base 2. mesoappendix Appendicitis is the inflammation of the mucous lining of the appendix

61. Peritoneum Large, moist slippery sheet of serous membrane that lines the abdominal cavity and covers the organs located in it Parietal portion lines the abdominal cavity Visceral portion forms the outer layer of each organ

62. Peritoneum Small space between the parietal and visceral layers is called the peritoneal space. Contains fluid to keep both layers moist and able to slide over one another.

63. Extensions 2 most prominent: Mesentery, mesocolon Greater omentum

64. Extensions Mesentery: an extension between the parietal and visceral layers of the peritoneum and is shaped like a giant fan. It anchors the small intestine to the posterior abdominal wall. Blood supply runs through. Mesocolon for Colon

65. Extensions Greater omentum: a pouch-like extension of the visceral peritoneum from the lower edge of the stomach, part of the dupdenum, and the transverse colon. Shaped like a large apron and hangs down over the intestines. Called the lacy apron.

66. Digestion A complex process that occurs in the alimentary canal and consists of physical and chemical changes that prepare food for absorption.

67. Digestion Mechanical digestion breaks food into tiny particles, mixes them with digestive juices, moves them along the alimentary canal, and finally eliminates the wastes. Main processes of mechanical digestion: Mastication Deglutition Peristalsis Defecation

68. Digestion Chemical digestion: breaks down large, nonabsorbable food molecules into smaller, absorbable molecules. Consists of numerous chemical reactions catalyzed by enzymes in saliva, gastric juice, pancreatic juice, and intestinal juice.

69. Carbohydrate Digestion Very little digestion occurs before the small intestine. Pancreatic and intestinal juice enzymes digest carbs.

70. Carbohydrate Digestion Pancreatic enzyme breaks polysaccharides into disaccharides. 3 intestinal enzymes digest disaccharides by changing them to monosaccharides. Most abundant monosaccharide is glucose.

71. Protein Digestion Starts in the stomach Pepsin causes large protein molecules to be broken down into somewhat smaller molecules In the intestine, other enzymes finish the job The end product is amino acids

72. Fat Digestion Most fats are undigested until after emulsification by bile in the duodenum. After this, pancreatic lipase splits up the fat molecules into fatty acids and glycerol End product is fatty acids and glycerol

73. Absorption After food is digested, it is absorbed, that is, it moves through the mucous membrane lining of the small intestine into the blood and lymph Food absorption is the process by which molecules of amino acids, glucose, fatty acids, and glycerol go from the inside of the intestines into the circulating fluids of the body.