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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

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


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 (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

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

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 (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

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

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

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

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 (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



___ 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
  • 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 (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
  • 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

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– 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

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

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
  • Nutrients are necessary food substances
    • Carbohydrates
    • Proteins
    • Lipids
    • Vitamins
    • Minerals
    • Water
the absorption of nutrients cont
The Absorption of Nutrients (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 (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



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

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




___ 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

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 (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 (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 (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 (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

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