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
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.
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.
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.
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.
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
Incisors– bite off food pieces
Cuspids – tear tough food
Bicuspids and molars – grind food
SublingualThe Mouth (cont.)
___ 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
Connects nasal cavity with oral cavity for breathing
Pushes food into esophagus
Behind nasal cavity
Behind oral cavity
Continues as esophagusPharynx
___ 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
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
Controls movement of substances into small intestine
Stomach abdominal cavityThe Stomach (cont.)
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.
Absorption of nutrients
Majority of small intestine
Small IntestineThe Small Intestine
Small Intestine intestineThe Small Intestine (cont.)
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.
Large Intestine intestineThe Large Intestine
Large Intestine intestineThe Large Intestine(cont.)
Large Intestine intestineThe Rectum and Anal Canal
___ 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
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.
Pancreatic amylase intestine– digests carbohydrates
Pancreatic lipase– digests lipids
Nucleases – digest nucleic acidsThe Pancreas
Neutralize acidic chyme
Enzyme release stimulated by
Parasympathetic nervous system
Hormones secretin and cholecystokinin (from small intestine)The Pancreas (cont.)
What are the pancreatic enzymes and what do they do?
TApply 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.
Decreased motility – GERD intestine
More likely to develop ulcers and cancers
Decreased ability to detoxify blood
Sense of taste altered
Dietary changes due to
DepressionAging and the Digestive System
___ 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
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.
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.
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.
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.
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.
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.)
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