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29. The Digestive System. Learning Outcomes. 29.1 List the functions of the digestive system. 29.2 Trace the pathway of food through the alimentary canal. 29.3 Describe the structure and functions of the mouth, teeth, tongue, and salivary glands.

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The digestive system


The Digestive System

Learning outcomes
Learning Outcomes

29.1 List the functions of the digestive system.

29.2 Trace the pathway of food through the alimentary canal.

29.3 Describe the structure and functions of the mouth, teeth, tongue, and salivary glands.

29.4 Describe the structure and function of the pharynx.

Learning outcomes cont
Learning Outcomes (cont.)

29.5 Describe the swallowing process.

29.6 Describe the structure of the esophagus and tell how it propels food into the stomach.

29.7 Describe the structure and functions of the stomach.

29.8 List the substances secreted by the stomach and give their functions.

Learning outcomes cont1
Learning Outcomes (cont.)

29.9 Describe the structure and functions of the small intestine.

29.10 List the substances secreted by the small intestine and describe the importance of each.

29.11 Describe the structure and functions of the large intestine, including the anal canal and rectum.

29.12 Explain the structures and functions of the liver, gallbladder, and pancreas.

Learning outcomes cont2
Learning Outcomes (cont.)

29.13 List the substances released by the liver, gallbladder, and pancreas into the small intestine and give the function of each secretion.

29.14 Tell what types of nutrients are absorbed by the digestive system and where they are absorbed.

29.15 Describe the causes, signs and symptoms, and treatments of various diseases and disorders of the digestive system.


  • Digestion

    • Mechanical and chemical breakdown of foods into forms that body cells can absorb

    • The organs of the digestive system carry out digestion

  • Two categories

    • Alimentary canal organs

    • Accessory organs

Alimentary canal
Alimentary Canal

  • Wall of alimentary canal

    • Mucosa

      • Innermost layer; epithelial tissue

      • Secretes enzymes and mucus into lumen

      • Absorbs nutrients

    • Submucosa

      • Inferior to mucosa; loose connective tissue, blood vessels, glands, and nerves

      • Blood vessels carry away absorbed nutrients

    • Muscular layer

      • Just outside submucosa; layers of smooth muscle

      • Contracts to move materials through the canal

Alimentary canal cont
Alimentary Canal(cont.)

  • Serosa

    • Double-walled outermost layer: peritoneum

      • Visceral peritoneum

        • Innermost wall of serosa

        • Secretes serous fluid to keep outside of canal moist

      • Parietal peritoneum

        • Abdominal lining

  • Movements

    • Churning – mixes substances in the canal

    • Peristalsis – propels substances through the tract

  • Apply your knowledge
    Apply Your Knowledge

    What are the layers of the wall of the alimentary canal and what do they do?

    ANSWER: The layers are:

    Mucosa: innermost layer; secretes enzymes and mucus into the canal and absorbs nutrients

    Submucosa: inferior to the mucosa; carries away absorbed nutrients

    Muscular layer: just outside the submucosa; contracts to move materials through the canal

    Serosa: double-walled outer layer; secretes serous fluid to keep outside of canal moist


    The mouth
    The Mouth

    • Buccal cavity

    • Mechanical digestion

      • Takes in food and reduces its size by chewing

    • Starts chemical digestion

      • Saliva contains the enzyme amylase, which breaks down carbohydrates

    The mouth cont
    The Mouth (cont.)

    • Cheeks hold food in mouth

    • Lips – sensory nerve fibers that judge temperature of food

    • Tongue

      • Skeletal muscles covered by mucous membrane

      • Lingual frenulum – holds tongue to floor of mouth

      • Mixes food, holds food between teeth, contains taste buds

      • Lingual tonsils– lymphatic tissue destroys bacteria and viruses on back of tongue

    The mouth cont1
    The Mouth (cont.)

    • Palate

      • Roof of mouth

      • Separates oral cavity from nasal cavity

      • Uvula – portion of soft palate that hangs down in throat

    • Lymph tissue

      • Palatine tonsils(oropharynx)

      • Pharyngeal tonsils – adenoids (nasopharynx)

    The mouth cont2

    Teeth – decrease size of food particles

    Incisors– bite off food pieces

    Cuspids – tear tough food

    Bicuspids and molars – grind food

    Salivary glands








    The Mouth (cont.)

    Apply your knowledge1
    Apply Your Knowledge


    ___ Buccal cavity A. Saliva

    ___ Roof of mouth B. Mouth

    ___ Grind food C. Bolus

    ___ Adenoids D. Palate

    ___ Water, enzymes, and mucus E. Bicuspids

    ___ Mass of food mixed with saliva and mucus F. Pharyngeal gland




    Very Good!








    Connects nasal cavity with oral cavity for breathing

    Pushes food into esophagus



    Behind nasal cavity


    Behind oral cavity


    Behind larynx

    Continues as esophagus


    Pharynx cont
    Pharynx (cont.)

    • Swallowing – automatic process

      • Soft palate rises, uvula covers opening between nasal and oral cavity

      • Epiglottis covers larynx, keeping food out of it

      • Tongue presses against roof of mouth, forcing food into oropharynx

    Pharynx cont1
    Pharynx (cont.)

    • Muscles in pharynx contract, moving food toward esophagus

    • Esophagus opens

    • Food is pushed into esophagus by muscles of pharynx

    The esophagus
    The Esophagus

    • Muscular tube connecting pharynx to stomach

      • Esophageal hiatus– hole in diaphragm through which esophagus passes

    • Cardiac sphincter

      • Circular band of muscle at the opening of the stomach

      • controls movement of food into stomach

    Apply your knowledge2
    Apply Your Knowledge


    ___ Connects nasal cavity with oral cavity A. Cardiac sphincter

    ___ Covers the opening of larynx B. Esophageal hiatus

    ___ Hole in diaphragm C. Sphincter

    ___ Controls movement of food into stomach D. Epiglottis

    ___ Circular bands of muscle E. Pharynx








    The stomach

    Below the diaphragm in the upper left quadrant of the abdominal cavity


    Receive food from esophagus

    Mix bolus with gastric juice

    Start protein digestion

    Move food into small intestine


    Cardiac region




    Pyloric sphincter

    Controls movement of substances into small intestine


    The Stomach

    The stomach cont

    Stomach abdominal cavity

    The Stomach (cont.)

    • Lining of stomach

      • Rugae– folds of the inner lining

      • Gastric glands

        • Mucous cells– secrete mucus to protect the lining

        • Chief cells – secrete pepsinogenpepsin, which digests protein

        • Parietal cells

          • Hydrochloric acid needed to convert pepsinogen to pepsin

          • Intrinsic factorneeded for vitamin B12 absorption

    The stomach cont1
    The Stomach abdominal cavity(cont.)

    • Gastric glands stimulated by

      • Parasympathetic nervous system

      • Gastrin (hormone)

    • Cholesystokinin (hormone) secreted by the small intestine inhibits gastric glands

    • Stomach absorbs alcohol, water, and some fat-soluble drugs

    • Chyme – mixture of food and gastric juices

    Apply your knowledge3
    Apply Your Knowledge abdominal cavity

    What are the functions of the stomach?

    ANSWER: The stomach’s functions are to receive the bolus of food, mix it with gastric juice, start protein digestion, and move food into the small intestine. It also absorbs alcohol, water, and some drugs.

    Right Answer!

    The small intestine

    Tubular organ extending from the stomach to the large intestine



    Absorption of nutrients






    Majority of small intestine

    Small Intestine

    The Small Intestine

    The small intestine cont

    Small Intestine intestine

    The Small Intestine (cont.)

    • Ileum – attached to large intestine

    • Mesentery

      • Fan-like tissue that holds jejunum and ileum in the abdominal cavity

      • Attaches to the posterior wall of the abdomen

    • Ileocecal sphincter

      • Controls movement of chyme from the ileum to the cecumof the large intestine

    The small intestine cont1
    The Small Intestine intestine(cont.)

    • Lining of small intestine

      • Microvilli – increase surface area

      • Intestinal glands

        • Mucus and water

        • Enzymes

          • Peptidases– digest proteins

          • Sucrase, maltase, and lactase– digest sugars

          • Intestinal lipase – digests fats

    • Primary controls

      • Parasympathetic nervous system

      • Stretching of intestinal wall

    Apply your knowledge4
    Apply Your Knowledge intestine

    Your patient states that she is lactose intolerant. What does that mean?

    ANSWER: She cannot produce lactase and cannot digest lactose, which is the sugar in dairy products.

    Nice Job!

    The large intestine

    Large Intestine intestine

    The Large Intestine

    • Extends from the ileum to the anus

    • Cecum

      • Beginning of large intestine

      • Veriform appendix

    • Ascending colon

      • Portion that goes up the right side of the abdominal cavity

    The large intestine cont

    Large Intestine intestine

    The Large Intestine(cont.)

    • Transverse colon– crosses abdominal cavity from right to left

    • Descending colon– down left side of abdominal cavity

    • Sigmoid colon – S-shaped portion in pelvic cavity

    • Absorbs water and electrolytes

    The rectum and anal canal

    Large Intestine intestine

    The Rectum and Anal Canal

    • Rectum– off sigmoid colon

    • Anal canal

      • Last few centimeters of rectum

      • Opening to outside of body is the anus

    The rectum and anal canal cont
    The Rectum and Anal Canal intestine(cont.)

    • Feces

      • Leftover chyme

      • Consists of undigested solid materials, little water, ions, mucus, cells of intestinal lining, and bacteria

    • Defecation reflex

      • Triggered by periodic contractions of large intestine

      • Allows anal sphincters to relax

    Apply your knowledge5
    Apply Your Knowledge intestine



    ___ Vermiform appendix A. Feces

    ___ Crosses the abdomen B. Ascending colon

    ___ Up right side of abdomen C. Anal canal

    ___ S-shaped tube D. Defecation reflex

    ___ Down left side of abdomen E. Sigmoid

    ___ Leftover chyme F. Transverse colon

    ___ Last section of rectum G. Cecum

    ___ Allows anal sphincters to relax H. Descending colon










    The liver
    The Liver intestine

    • Lobular organ in right upper quadrant

      • Large right lobe and smaller left lobe

        • Hepatic lobules– contain macrophages

        • Hepatocytes – process nutrients in blood and make bile

    • Part of liver’s function

      • Store vitamins and iron

    The liver cont
    The Liver intestine(cont.)

    • Hepatic portal vein– carries blood from digestive organs to hepatic lobules

    • Hepatic duct– bile from liver

    • Hepatic duct merges with cystic duct from gallbladder and forms common bile duct

    • Common bile duct– delivers bile to duodenum

    The gallbladder
    The Gallbladder intestine

    • Small sac-like structure located beneath the liver

    • Only function is to store bile

    • Cholecystokinin causes the gallbladder to release bile


    Apply your knowledge6
    Apply Your Knowledge intestine

    What is the route of bile through the liver and gallbladder?

    ANSWER: Bile is made in the hepatocytes and leaves the liver through the hepatic duct. The hepatic duct merges with the cystic duct from the gallbladder to form the common bile duct, which delivers bile to the duodenum.


    The pancreas

    Pancreatic amylase intestine– digests carbohydrates

    Pancreatic lipase– digests lipids

    Nucleases – digest nucleic acids

    The Pancreas

    • Located behind the stomach

    • Acinar cellsproduce pancreatic juice, which contains these enzymes:

    • Trypsin, chymotrypsin, and carboxypeptidase– digest proteins

    The pancreas cont

    Also secretes bicarbonate ions into duodenum intestine

    Neutralize acidic chyme

    Enzyme release stimulated by

    Parasympathetic nervous system

    Hormones secretin and cholecystokinin (from small intestine)

    The Pancreas (cont.)

    Apply your knowledge7
    Apply Your Knowledge intestine

    What are the pancreatic enzymes and what do they do?

    • ANSWER: They are:

    • Pancreatic amylase – digests carbohydrates

    • Pancreatic lipase – digests lipids

    • Nucleases – digest nucleic acids

    • Trypsin, chymotrypsin, and carboxypeptidase – digest proteins

    Good Job!

    The absorption of nutrients
    The Absorption of Nutrients intestine

    • Nutrients are necessary food substances

      • Carbohydrates

      • Proteins

      • Lipids

      • Vitamins

      • Minerals

      • Water

    The absorption of nutrients cont
    The Absorption of Nutrients intestine(cont.)

    • Carbohydrates – provide energy

      • Polysaccharides– starches

      • Monosaccharides and disaccharides–simple sugars

      • Cellulose– provides fiber or bulk

    • Lipids – used for energy when glucose levels are low

      • Triglycerides

      • Cholesterol – essential for cell growth and function

    The absorption of nutrients cont1
    The Absorption of Nutrients intestine(cont.)

    • Protein – used for growth and repair of tissue

      • Essential amino acids body cannot make

    • Vitamins

      • Fat-soluble

      • Water-soluble

    • Minerals – used to make enzymes, cell membranes, and proteins

    Apply your knowledge8

    ANSWER: intestine


    Apply Your Knowledge

    True or False:

    ___ Carbohydrates are starches, simple sugars, and cellulose.

    ___ Excess glucose is stored in the gallbladder as glycogen.

    ___ Triglycerides are the least abundant lipids

    ___ Linoleic acid is an essential fatty acid.

    ___ A, D, E and K are water-soluble vitamins.

    ___ Minerals are used by cells to make enzymes.










    Aging and the digestive system

    Decreased motility – GERD intestine

    Decreased absorption

    More likely to develop ulcers and cancers

    Decreased ability to detoxify blood

    Sense of taste altered

    Dietary changes due to



    Aging and the Digestive System

    Apply your knowledge9
    Apply Your Knowledge intestine




    ___ Inflammation of the large intestine A. Heartburn

    ___ Inflammatory bowel disease B. Hemorrhoids

    ___ Watery and frequent feces C. Constipation

    ___ Difficult defecation D. Crohn’s disease

    ___ Inflammation of the stomach lining E. Colitis

    ___ Inflammation of pouches in the intestinal wall F. Diarrhea

    ___ GERD G. Gastritis

    ___ Varicose veins of rectum H. Diverticulitis








    Nice Job!

    In summary
    In Summary intestine

    29.1 The digestive system uses mechanical and chemical mechanisms to break down food into forms that the body’s cells can use.

    29.2 The pathway of food through the alimentary canal starts with the mouth through the pharynx, esophagus, stomach, small intestines, large intestines, and anal canal.

    29.3 The mouth takes in food and the teeth assist in reducing its size through chewing. The tongue mixes food and holds it between the teeth. The salivary glands produce saliva to assist in moistening and breaking down food.

    In summary cont
    In Summary intestine(cont.)

    29.4 The pharynx is a long muscular tube extending from behind the nose to the esophagus, connecting the oral and nasal cavities. It also acts to push food into the esophagus.

    29.5 The soft palate rises, closing the opening between the nasal and oral cavities. The epiglottis covers the laryngeal opening. Food is forced into the oropharynx by the tongue, and the pharynx contracts, pushing food to the esophagus.

    29.6 The esophagus is a muscular tube that pushes food toward the stomach through muscular contractions. At the end of the esophagus is the cardiac sphincter, the entrance to the stomach.

    In summary cont1
    In Summary intestine(cont.)

    29.7 The stomach is in the LUQ. It receives food, mixes it with gastric juices, starting protein digestion, and moves food into the small intestine. The stomach has four regions: cardiac region, fundus, body, and pylorus.

    29.8 The stomach’s gastric glands include mucous cells that secret mucus, chief cells that secret pepsinogen, and parietal cells that secrete hydrochloric acid and intrinsic factor.

    29.9 The small intestine carries out most of the nutrient absorption. The sections of the small intestine are, in order, duodenum, jejunum, and ileum.

    In summary cont2
    In Summary intestine(cont.)

    29.10 The small intestine secretes peptidases to digest protein; sucrase, maltase and lactase, which digest sugars; and intestinal lipase, which digests fats.

    29.11 The components of the large intestine are the cecum with its vermiform appendix, ascending colon, transverse colon, descending colon, sigmoid colon, rectum, and anal canal ending in the anus. The large intestine’s primary job is to rid the body of solid waste by defecation.

    In summary cont3
    In Summary intestine(cont.)

    29.12 The liver is in the RUQ. It stores vitamins and iron and produces macrophages to fight infection. The gallbladder stores the bile produced by the liver. The pancreas produces pancreatic juices that assist in carbohydrate, lipid, and protein digestion.

    29.13 The liver secretes bile for fat digestion. Bile is released by the gallbladder for fat digestion. Pancreatic juices contain pancreatic amylase for carbohydrate digestion; lipase for lipid digestion; nucleases to digest nucleic acids; and trypsin, chymotrypsin, and carboxypeptidase to digest proteins.

    In summary cont4

    29.14 Nutrients absorbed by the body include carbohydrates, proteins, lipids, vitamins, minerals, and water. Most of the absorption takes place in the small intestine.

    29.15 Common diseases and disorders of the digestive system include inflammatory disorders such as appendicitis and colitis; cancers including colorectal, oral, and pancreatic cancers; as well as common symptoms such as diarrhea, constipation, and GERD. For more detailed information regarding these and other common disorders, please see the Pathophysiology section at the end of this chapter.

    In Summary (cont.)

    End of chapter 29
    End of Chapter 29 proteins, lipids, vitamins, minerals, and water. Most of the absorption takes place in the small intestine.

    Take all that is given whether wealth, love or language; nothing comes by mistake and with good digestion all can be turned to health.

    ~ George Herbert