CHAPTER © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 29 The Digestive System

CHAPTER

© 2011 The McGraw-Hill Companies, Inc. All rights reserved.

29The Digestive

System


29-2

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.


29-3

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.


29-4


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.


29-5


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.


29-6

Introduction

• 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


29-7

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


29-8

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


29-9

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

Bravo!


29-10

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


29-11

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


29-12

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)


29-13

The Mouth (cont.)

• Teeth – decrease size of food particles– Incisors – bite off

food pieces– Cuspids – tear

tough food– Bicuspids and

molars – grind food

• Salivary glands– Cells

• Serous• Mucous

– Glands • Parotid• Submandibular• Sublingual


29-14


Matching:

___ 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. Pharyngealgland

D

E

F

A

B

B

ANSWER:


29-15

Pharynx

• Throat

• Functions – Connects nasal

cavity with oral cavity for breathing

– Pushes food into esophagus

• Divisions – Nasopharynx

• Behind nasal cavity

– Oropharynx• Behind oral cavity

– Laryngopharynx• Behind larynx• Continues as

esophagus


29-16

Pharynx (cont.)

• Swallowing – automatic process

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

2. Epiglottis covers larynx, keeping food out of it

3. Tongue presses against roof of mouth, forcing food into oropharynx


29-17

Pharynx (cont.)

Muscles in pharynx contract, moving food toward esophagus

Esophagus opens

Food is pushed into esophagus by muscles of pharynx


29-18

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


29-19


Matching:

___ 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. PharynxC

A

B

D

E

ANSWER:


29-20

The Stomach• Below the diaphragm

in the upper left quadrant of the abdominal cavity

• Functions– Receive food from

esophagus– Mix bolus with gastric

juice– Start protein digestion– Move food into small

intestine

• Sections– Cardiac region – Fundus – Body – Pylorus

• Pyloric sphincter – Controls movement of

substances into small intestine

Stomach


29-21

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 factor needed for vitamin B12 absorption

Stomach


29-23

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


29-24


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!


29-25

The Small Intestine• Tubular organ

extending from the stomach to the large intestine

• Functions– Digestion– Absorption of nutrients

• Duodenum – C-shaped – Short

• Jejunum – Coiled – Majority of small

intestine

Small Intestine


29-26

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 cecum of the large intestineSmall

Intestine


29-27

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


29-29


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

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


29-30

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

Large Intestine


29-31

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 electrolytesLarge

Intestine


29-32

The Rectum and Anal Canal

• Rectum – off sigmoid colon

• Anal canal– Last few centimeters of rectum

– Opening to outside of body is the anus

Large Intestine


29-33

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


29-35


Matching:

___ 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

H

G

F

E

D

C

B

A

ANSWER: Super!


29-36

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


29-37

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


29-38

The Gallbladder• Small sac-like structure

located beneath the liver

• Only function is to store bile

• Cholecystokinin causes the gallbladder to release bile

Gallbladder


29-39


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.


29-40

The Pancreas

Pancreatic amylase – digests carbohydrates

Pancreatic lipase – digests lipids

Nucleases – digest nucleic acids

Trypsin, chymotrypsin, and carboxypeptidase – digest proteins

Located behind the stomach Acinar cells produce pancreatic juice, which contains these enzymes:


29-41

The Pancreas (cont.)


29-42


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!


29-43

The Absorption of Nutrients

• Nutrients are necessary food substances– Carbohydrates

– Proteins

– Lipids

– Vitamins

– Minerals

– Water


29-44

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


29-45

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


29-46


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.

F

F

F

T

T

ANSWER:

Tliver

most

fat-soluble


29-47

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– Isolation– Depression


29-48

Common Diseases and Disorders

Disease/Disorder Description

Appendicitis Inflammation of the appendix; can be life-threatening if not treated promptly

Cirrhosis Chronic liver disease; normal tissue is replaced with nonfunctional scar tissue

Colitis Inflammation of the large intestine; can be acute or chronic

Colorectal cancer Arises from lining of rectum or colon; curable if treated early


29-49

Common Diseases and Disorders (cont.)


Constipation Difficult defecation

Crohn’s disease Inflammatory bowel disease; typically effects small intestine

Diarrhea Watery and frequent feces; usually self-limiting

Diverticulosis Abnormal pouches in the intestinal wall; no inflammation present


29-50



Diverticulitis Inflammation of diverticuli (abnormal pouches in intestinal wall) of the intestine

Gastritis Inflammation of the stomach lining; “upset stomach”

Heartburn Gastroesophageal reflux disease (GERD); stomach acids push into esophagus

Hemorrhoids Varicose veins of rectum or anus

Hepatitis Inflammation of the liver; various types


29-51



Hiatal hernia Portion of stomach protrudes into the chest through an opening (usually the esophageal hiatus) in the diaphragm

Inguinal hernia Portion of large intestine protrudes in the inguinal canal (where thigh and trunk meet) or, in males, into the scrotum

Oral cancer Usually involves the lips or tongue but can occur anywhere in the mouth; tends to spread rapidly


29-52



Pancreatic cancer Fourth leading cause of cancer deaths in the U.S.

Stomach cancer Commonly in cardiac portion of the stomach; occurs more frequently in Japan, Chili, and Iceland

Stomach ulcers Breakdown in lining of the stomach; can be caused by bacteria (H. pylori) or smoking, alcohol, excessive aspirin use, and hypersecretion of stomach acid


29-53


Matching:

___ 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

H

G

F

D

C

B

A

E

ANSWER:


29-54

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.


29-55

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.


29-56

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.


29-57

In Summary (cont.)

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

29.11The 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.


29-58

In Summary (cont.)

29.12The 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.

29.13The 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.


29-59

In Summary (cont.)

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

29.15Common 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.


29-60

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

End of Chapter 29

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CHAPTER © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 29 The Digestive System