Chapter 13

1. Chapter 13

2. Applied Learning Outcomes • Use the terminology associated with the digestive system • Learn about the following: • Organization of the digestive system • Structure of the digestive system organs • Function of the digestive system organs • The digestive process • Waste production • Understand the aging and pathology of the digestive system Chapter 13 – The Digestive System

3. Overview The digestive system is composed of the digestive tract and accessory digestive organs. The digestive tract is composed of the mouth, pharynx, esophagus, stomach, salivary glands, small and large intestines, and rectum. The digestive system carries out chemical and mechanical digestion. Chapter 13 – The Digestive System

4. Overview Functions of the digestive system: allows the body to break down complex molecules into simpler molecules Molecules are needed for energy building new cells and tissues

5. The Digestive Tract Is composed of two components The Digestive tract (Alimentary canal) The accessory digestive organs Digestive Tract comprises the mouth esophagus stomach small intestines large intestines rectum Accessory digestive organs salivary glands pancreas liver gall bladder

6. The Digestive Tract One of the first organ systems to develop in the embryo Develops from endoderm This occurs after the 4th week of embryonic development Blastula folds inward in a process called gastrulation.

7. Components of the Digestive Tract Mouth: Contains the salivary glands, teeth, tonsils, and tongue Pharynx: Connects mouth to the esophagus Esophagus: A muscular tube that leads to the stomach Stomach: A muscular sac that stores and digests food Small Intestine: Long, narrow tube that digests and absorbs food Large Intestine: Short, wide tube that absorbs water and electrolytes Rectum: End of the digestive tract; removes undigested materials Chapter 13 – The Digestive System

8. Components of the Digestive Tract Mouth: both mechanical and chemical digestion lips sense temperature and texture of food Cheeks form the lateral walls of the mouth, form the buccal or oral cavity Buccal cavity is where food is moistened in preparation for digestion. Palate forms roof of mouth Uvula is a cone shaped projection that hangs down in the back of the mouth Tongue used in speaking, tasting, and swallowing.

9. Components of the Digestive Tract Mouth: Lingual tonsils are a group of lymphatic tissues located at the base of the tongue. Salivary Glands: lie under the facial skin and buccal cavity they produce saliva which moistens food and starts chemical digestion Three major salivary glands: parotid- largest, located in the cheeks in front of ears watery secretion sublingual- located under the tongue mucous secretion submandibular- located under the mandible mix of water and mucous secretion

10. Components of the Digestive Tract The mouth: Jaws, teeth, and hard palate are responsible for mechanical breakdown of food and assist with speech Teeth: 32 adult or permanent teeth Incisors (8) cut the food Canine (Cuspids) (4) hold and tear teeth Premolars (Bicuspids) (8) assist with breaking food into fine particles Molars (12) used for grinding food into a fine mash people usually have three molars on each side of the jaw The third molar is called the wisdom tooth. It is sometimes removed if it causes crowding.

11. The Mouth

12. The Esophagus and Stomach

13. The Esophagus and Stomach Esophagus a muscular tube that carries food and liquids from the pharynx to the stomach it passes through the diaphragm just above the stomach Contains smooth muscle Moves food down the esophagus by peristalsis. Two sphincters close off the esophagus: Upper sphincter- composed of bundle of smooth muscle closely associated with the larynx Lower sphincter -- cardiac sphincter at the bottom of the esophagus surrounds the esophagus at the entrance of the stomach

14. The Esophagus and Stomach The Esophagus: Both sphincters are usually closed except during swallowing. Helps prevent air from entering stomach Helps prevent reflux- backflow of stomach contents.

15. The Stomach Large saclike organ Three areas: cardiac (upper) fundic (middle) pyloric (lower) Parietal cells- cells in the fundic stomach lining that secretes hydrogen and chlorine which come together to form hydrochloric acid. Chief Cells - cells of the stomach that secrete digestive enzymes. Mucous Neck cells- cells of the fundic stomach that secrete mucus. Gastric stem cells - cells that replace other glandular cells of the fundic stomach.

16. The Stomach Can hold 3 pints of food for digestion Mucous lining keeps the stomach from digesting itself The stomach has muscles that enable squeezing, mixing actions and moving food through it. Cardiac Sphincter is found at the top of the stomach. Pyloric Sphincter is found at the bottom of the stomach.

17. The Small Intestines Main Job: Digestion and Absorption Divided into three sections: Duodenum-receives food from stomach, main area for digestion Jejunum-where most digested food is absorbed into the bloodstream. Ileum-where rest of the digested food is absorbed into the bloodstream before entering the large intestines. Structure: Villi (fingerlike projections) line the mucosa increase surface area for digestion and absorption Microvilli-projections of cell membrane of the villi and give even more surface area. Lacteal -collections of lymphatic vessels found inside the villi. Fat is absorbed by them and they carry it to the liver.

18. The Small Intestines Messentery-is a membranous tissue that connects the small intestines to the peritoneum. Messenteries hold the small intestines in place. Ileocecal valve is a muscular valve separating the small intestines from the large intestines.

19. The Large Intestines and Rectum Also called the colon It is larger in diameter It is shorter than the small intestines It is composed of Five anatomical regions cecum-1st part of large intestines that contains the appendix ascending colon transverse colon descending colon sigmoid colon Main digestive function absorption of water, electrolytes, and vitamins remove undigested waste (feces) from the digestive tract

20. The Large Intestines and Rectum Contains many bacteria and one type of yeast Most of these microorganisms break down waste Some are a source of vitamins Rectum is a muscular storage area for undigested waste located at the end of the digestive tract anal canal is a small portion of the rectum ending in the anus anus is the opening of the rectum to the outside of the body It is surrounded by the anal sphincter. divided into smooth muscle which the person does not have control over and skeletal muscle in which the person does have control over (potty training)

22. Glandular Structures The pancreas and liver are glandular organs. The pancreas produces digestive enzymes and hormones that regulate blood glucose levels. Bile production is the main function of the liver. Bile assists with fat digestion. Chapter 13 – The Digestive System

23. Glandular Structures of the Digestive System Pancreas lies posterior to the stomach Inside of the pancreas is divided into glandular lobules has endocrine and exocrine functions related to digestion Endocrine makes up approximately 2% of the pancreas made up of islets of Langerhans which contain alpha and beta cells alpha cells secrete glucagon-which raises glucose level beta cells secrete insulin-which lowers glucose level hormonal secretions enter directly into capillaries Exocrine consists of saclike cluster of serous glands called acini they make active and inactive digestive enzymes Zymogens-are inactive digestive enzymes they convert to active enzymes once they enter digestive system Keeping them inactive prevents them from degrading the acini cells.

24. Exocrine portion of the Pancreas Pancreatic duct in the pancreas leads to the common bile duct Common bile duct empties into the duodenum Pancreatic Zymogens chymotrypsinogen--- digest protein deoxyribonuclease-- breaks down DNA pancreatic amylase-- digests starch phospholipase-- digest lipids procarboxypeptidase-- digests proteins ribonuclease-- breaks down RNA troacylglycerol lipase--digest lipids trypsinogen --digests protein

25. Liver and Gall Bladder Liver tissue composed of hepatocytes (liver cells) unusual cells because they have two or more nuclei Jobs of the liver: glycogen storage for regulating blood sugar formation of urea formation of blood proteins and clotting factors synthesis of heparin (a blood anticoagulant) metabolism of cholesterol and fatty acids formation of metabolism of vitamin D removal of microorganisms from the blood breakdown of drugs and many poisons breakdown of amino acids destruction of bilirubin(product from hemoglobin being broken down) storage of iron

26. Liver and Gall Bladder Gallbladder: small pear-shaped sac that stores and concentrates bile. found underneath right lobe of the liver receives bile through duct from liver releases bile into the duodenum through the common bile duct Gallstones are formed when the bile containing too much bilirubin, cholesterol, or bile salts accumulate into a mass. they can block the flow of bile and cause pain when they pass through the bile ducts.

27. The Digestive Process CNS has a hunger center and a satiety center located in the hypothalamus Both centers respond to many factors such as blood sugar, amount of fat in blood, appearance and taste of food

28. The Digestive Process--The Mouth First step of the digestive process is Ingestion-the taking in of food into the body through the mouth. The digestive process in the mouth Mastication or chewing ---Mechanical digestion Digestion is most effective when more of the food surface area is exposed to chemical degradation of enzymes. Chemical digestion in the mouth Salivary amylase mixes with food begins to chemically breakdown starch into glucose Saliva wets the food to facilitate swallowing and to assist with chemical action. Bolus-partially digested food in the mouth.

29. The Digestive Process--The Esophagus Food and liquids travel down the esophagus by peristalsis The epiglottis closes the trachea so no food or liquid can enter. Esophagus lacks mucous membrane so it is damaged if reflux Occurs.

30. The Digestive Process--The Stomach Food enters through the cardiac sphincter Protease zymogens (inactive enzymes) are secreted from stomach lining-Pepsinogen (inactive enzyme) Hydrogen and chlorine are secreted from stomach lining-they come together to produce hydrochloric acid. Low pH of stomach 1-3 causes pepsinogen to become active Becoming pepsin Pepsin digests proteins Mucous lining protects the stomach cells from digestion. Chyme-is partially digested food in the stomach and small intestines.

31. The Digestive Process--The Stomach • Hormones released by stomach cells also stimulate digestion. • Three major hormones that control digestion: • Cholecystokinin (CCK)-causes pancreas to produce enzymes • and the gallbladder to empty • Gastrin-stimulates acid production in the stomach • Secretin-causes the pancreas to release digestive juices • containing bicarbonate (helps protect stomach lining) • stimulates liver to make bile • stimulates stomach to produce protease (pepsinogen)

32. The Digestive Process--The Small Intestines Chyme stimulates the pyloric sphincter to relax In duodenum: chyme is mixed with bile and pancreatic secretions bile breaks fat down in smaller droplets Pancreatic enzymes break down carbs lipids nucleic acids proteins The mucosa of small intestines (lining) releases enzymes called enterokinases to activate zymogens. Peristalsis carries mixture to jejunum. In the jejunum and ileum: Villi facilitate absorption of nutrients into the blood and lacteals.

33. The Digestive Process--The Large Intestines • Any substance that has not been absorbed passes into the • large intestines through the ileocecal valve • Bacteria digest and absorb many undigested waste • The rest of the undigested waste moves through the large • intestines by peristalsis • Most fluids and electrolytes are transported into the blood by • the ascending and transverse large intestines. • The remaining sections of the colon compact the waste into feces.

34. Glandular Structures Pancreas lies posterior to the stomach (under the stomach) inside of pancreas is divided into glandular lobules Endocrine component of Pancreas islets of Langerhans made of alpha and beta cells Alpha cells secrete glucagon Beta cells secrete insulin Exocrine component of Pancreas called acini which are clusters of exocrine cells Common bile duct is a tube through which secretions of the liver and pancreas pass into the duodenum.

35. Glandular Structures Pancreas Produces the following digestive enzymes: Chymotrypsinogen--digests protein Deoxyribonuclease-- breaks down DNA Pancreatic amylase-- digests starch Phospholipase -- digests lipids Ribonuclease-- breaks down RNA Lipase-- digests lipids Trypsinogen-- digests protein These are zymogens-- they are an inactive form of an enzyme Converted to active form when they enter the digestive tract. By being inactive it keeps them from degrading the acini (cells making up the pancreas)

36. Glandular Structures Liver produces bile stores extra glucose as glycogen (animal starch) metabolism of cholesterol and fatty acids formation of urea metabolism of vitamin D breakdown of drugs and many poisons storage of iron synthesis of heparin- a protein that helps prevent blood clotting Gall bladder lies under the right lobe of the liver stores the bile

37. The Digestive Process • Chemical and mechanical digestion begins in the mouth • Peristalsis moves food through the digestive tract • The stomach uses enzymes and acids to digest proteins • Digestion of most food takes place in the proximal portions of the small intestine • The large intestine absorbs water and electrolytes in its proximal components; feces are formed in the distal portions of the large intestine • The rectum forces feces out of the body through the anal sphincter Chapter 13 – The Digestive System

38. Wellness and Illness over the Life Span General abdominal pain is a common symptom of digestive tract disorders. Diseases of the digestive system have various origins, including psychological disorders, allergies, infections, genetic syndromes, and degenerative changes. Digestive system gland disorders include cirrhosis, hepatitis, and pancreatitis. Aging of the digestive system affects the nutrient supply to other organ systems. Most digestive tract aging affects peristalsis. Chapter 13 – The Digestive System

39. Pathology of the Digestive System Origins of digestive system diseases: allergies infections genetic syndromes degenerative changes from toxins or trauma nervous system disorders lack of certain digestive enzymes-Food intolerance

40. Pathology of the Digestive System • Food intolerance • can restrict a person’s diet because undigested or unabsorbed food • can produce intestinal irritation and painful gas buildup. • Usually due to a genetic disorder • Celiac disease-the inability to digest a certain protein found in wheat. • Abdominal pain is most common digestive system ailment. • Could be from dehydration, flatulence (gas), food • poisoning, infection, overeating, overexertion, stress and trauma • Gastric reflux- backward flow of stomach contents into esophagus • stomach acid can erode and burn the cells of the esophagus. • Gastric dysphagia a condition that causes difficulty with swallowing

41. Pathology of the Digestive System Diarrhea has many causes like allergies, food poisoning, infection, overeating, overexertion, and stress. Different types of diarrhea: Acute diarrhea- rapidly occurring, does not last more than two weeks Chronic diarrhea-long term accompanied by abdominal pain Amoebic dysentery is a long term condition that causes extreme abdominal cramping andregular bouts of diarrhea. Caused by a protozoan found in contaminated food or water. Inflammatory bowel disease(IBD) is a peristalsis disorder with no known cause.

42. Pathology of the Digestive System • Colon polyps found in about 20% of adult population in • North America • They are growths from cells of the large intestines • mucosa that project into the lumen. • People who smoke, eat high fat diets, eat very little • dietary fiber, or are overweight are at risk. • Can cause rectal bleeding and change in bowel • movements. • Most colon polyps do not cause any problems • Some polyps called adenomatous polyps can lead to • colon cancer.

43. Pathology of the Digestive System Ulcer- condition caused by erosion of the inner linings of digestive tract Most common in lower stomach and duodenum Some ulcers are the result of a bacterial infection Hernia not fully a digestive tract disorder they are a protrusion of an organ into surrounding tissues many involve digestive organs that pass into weak spots of the diaphragm and abdominal and pelvic muscles. Hiatal hernia protrusion of stomach through the diaphragm Inguinal hernia occurs lower in the body when a section of the small intestines passes into areas of muscle weakness or openings in the pelvic cavity

44. Pathology of the Digestive System • Liver and pancreatic diseases also plague the digestive system • Hepatitis is a liver disease caused by various viruses that attack • Types are A,B,C, D, and E • B is spread through fecal contamination • Other strains spread through blood contact or sexual activity • Cirrhosis is a condition in which the liver becomes scarred and filled with fat • Result of long term liver damage caused by drug and/or alcohol use or hepatitis • Pancreatitis is inflammation of the pancreas • It has a wide variety of causes. These diseases are more common in the areas of improper food handling and poor sewage treatment.

45. Aging of the Digestive System • Much of the aging of the digestive system is due to decrease in • the neural activity needed for smooth muscle function and • glandular secretion. • Peristalsis becomes weaker • Contractions of the cardiac sphincter decrease • Lining of the stomach loses its ability to resist damage • Stomach becomes more susceptible to peptic ulcers • Peptic ulcers may reduce production of enzymes • Aging has little impact on structure of small intestines • Food intolerances may increase because needed enzymes • to break down nutrients decrease • Bacteria in large intestines can become more prevalent, • competing for food leading to weight loss • Loss of smooth muscle can lead to constipation

46. Aging of the Digestive System Diverticulosis can develop. It is characterized by pouch like pockets in the large intestines. Pancreas ability to regulate blood sugar may decrease with age. Liver and gall bladder may decrease in size with age This reduces liver’s ability to break down hazardous chemical in food A decline in their function impairs body’s ability to digest and absorb fats Decrease in taste and reduced hunger signals from the CNS may increase malnutrition and under- nutrition as people age.

47. Summary The digestive system makes it possible for the body to break down the complex molecules of food into simple molecules needed for energy and raw materials to build cellular components. The blood then transports these nutrients throughout the body by absorbing the digested foods and passing them into the blood stream. Diseases and aging of the immune system decrease the digestive or absorptive capabilities of the digestive system. Chapter 13 – The Digestive System