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Chapter 9

Digestive System

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Points to ponder

• What are the digestive system structures and their functions?

• Where does carbohydrate, protein, and fat digestion and absorption occur?

• What are proteins, lipids, carbohydrates, minerals and vitamins needed for?

• What is an essential vs. a nonessential nutrient?

• What are the three accessory organs of digestion?

• What is obesity and why is it a problem?

• What is LDL and HDL?

• What are the components of a healthy diet?

• Name and explain 4 eating disorders.

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What are the main steps in the

digestive process?• Ingestion –

• Digestion –

• Movement –

• Absorption –

• Elimination –

9.1 Overview of Digestion

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An overview of the digestive system

Figure 9.1 Organs of the GI tract and

accessory structures of digestion.

9.1 Overview of Digestion

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Livermajor metabolic organ ;

processes and stores nutrients;

produces bile for emulsification of fats

Gallbladderstores bile from liver; sends it to

the small intestine

Pancreasproduces pancreatic juice ; contains

digestive

enzymes, and sends it to the small intestine;

produces insulin and secretes it into the

blood after eating

Digestive tract organs

Esophaguspassageway where peristalsis pushes

food to stomach

Stomachsecretes acid and digestive enzyme

for protein; churns, mixing food with

secretions, and sends chyme to

small intestine

Small intestinemixes chyme with digestive enzymes

for final breakdown; absorbs nutrient

molecules into body; secretes

digestive hormones into blood

Large intestineabsorbs water and salt to form feces

Rectumstores and regulates elimination

of feces

Mouthteeth chew food; tongue tastes and

pushes food for chewing and swallowing

Pharynxpassageway where food is swallowed

Accessory organs

Salivary glandssecrete saliva which contains digestive

enzyme for carbohydrates

Anus

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What is the pathway that food

follows?

mouth

pharynx

esophagus

stomach

small intestine

large intestine

rectum

anus

9.1 Overview of Digestion

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Anatomy of the mouthCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

hard palate

soft palate

uvula

tonsil

incisors (2)

canine (1)

premolars (2)

molars (3)

Figure 9.3a The functions of the

different teeth.

9.2 The Mouth, Pharynx, and Esophagus

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Anatomy of a toothCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

root

crown

enamel

dentin

pulp

gum

jawbone

root canal

periodontal

membrane

cementum

9.2 The Mouth, Pharynx, and Esophagus

Figure 9.3b A cross section of a

tooth showing the crown and root.

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Soft palate closes

off nasopharynx.

Larynx rises and

epiglottis covers

glottis.

Lower gastroesophageal

sphincter relaxes and

food enters stomach.

hard palate food bolus

nasopharynx

soft

palate

a. Swallowing

trachea

(airway)

open

Esophagus

is closed.

epiglottis

esophagus

opensb. Peristalsis

esophagus

peristaltic

wave

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

glottis

bolus

stomach

Figure 9.4 The process of swallowing.

9.2 The Mouth, Pharynx, and Esophagus

How do we swallow food?

What’s heartburn?

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Anatomy of the stomachCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

mucosa layer

has rugae.

muscularis layer

has three layers

of muscle.

lower gastroesophageal

sphincter

cells that secrete

gastric juice

d. How the stomach empties

esophagus

lower gastroesophageal

sphincter

pyloric

sphincter

a. Stomach

gastric pit

gastric gland

b. Gastric glands

pyloric

sphincter

c: © Dr. Fred Hossler/Visuals Unlimited

Figure 9.5 The layers of the stomach.

9.3 The Stomach and Small Intestine

SEM 3,260xgastric pitc. Gastric pits in mucosa

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Small intestine

Figure 9.6 Absorption in the small intestine.

9.3 The Stomach and Small Intestine

Digestion & absorption of nutrients

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How are nutrients digested and

transported out of the small intestine?

+carbohydrate

pancreatic amylase

cell of

intestinal

villus

maltase

glucose

pH = basic

blood capillary

a. Carbohydrate digestion b. Protein digestion

blood capillary

pH = basic

protein

peptides

trypsin

peptidase

amino acids

bile salts fat globules

emulsification

droplets

lipase

monoglycerides

and free

fatty acids

chylomicron

c. Fat digestion

lymphatic

capillary

pH = basic

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Figure 9.7 Digestion and absorption of organic nutrients.

9.3 The Stomach and Small Intestine

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The 3 accessory organs

9.4 The Accessory Organs and Regulation of Secretions

• Pancreas Digestive enzymes

Bicarbonate

Insulin/glucagon

• Liver Filters blood (detox)

Removes:

Iron

Stores Vit A, D, E, K & B12

Bile

Glucose glycogen

• Gallbladder Store bile

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

gallbladder

common bile duct

duodenum

a.

bile

common hepatic duct

pancreatic ductpancreas

pancreatic

juice

central

vein

bile canals

branch of

hepatic

artery

branch of

hepatic

portal veinbile ductb.

Figure 9.8 Accessory organs of the digestive system.

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Liver disorders

• Hepatitis

• Cirrhosis

9.4 The Accessory Organs and Regulation of Secretions

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GI Hormones

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

gallbladder liver

stomach

pancreas

blood vessel

duodenum

gastrin

CCK

secretin

Figure 9.9 Hormonal control

and regulation of digestion.

9.4 The Accessory Organs and Regulation of Secretions

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Figure 41.19a

Liver

Gallbladder

Food

Stomach

Duodenumof small intestine

Gastricjuices

Pancreas

1

Gastrin

Key

Stimulation

Inhibition

GI Hormones

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Bile

Chyme

CCK

HCO3, enzymes

Secretin

Key

Stimulation

Inhibition

2

CCK

GI Hormones

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Figure 41.19c

Secretinand CCK

Gastricjuices

3

Key

Stimulation

Inhibition

GI Hormones

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The large intestine

• Includes the cecum, colon, rectum, and anal

canal.

• Diameter

• Cecum = appendix:

9.5 The Large Intestine and Defecation

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The large intestine

• Functions to

9.5 The Large Intestine and Defecation

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The large intestine

9.5 The Large Intestine and Defecation

Figure 9.10 The regions of the large intestine.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

vermiform

appendix

orifice of

appendix

transverse colon

ascending

colon descending

colon

small

intestine

cecum

anal canal

internal anal sphincter external anal sphincter

anus

sigmoid colonrectum

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Disorders of the colon and rectum

• Diarrhea

• Constipation

• Hemorrhoids

• Diverticulosis

• Irritable bowel syndrome (IBS

• Inflammatory bowel disease/colitis (IBD)

• Polyps and cancer

9.5 The Large Intestine and Defecation

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An overview of the digestive system

Figure 9.1 Organs of the GI tract and

accessory structures of digestion.

9.1 Overview of Digestion

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Livermajor metabolic organ ;

processes and stores nutrients;

produces bile for emulsification of fats

Gallbladderstores bile from liver; sends it to

the small intestine

Pancreasproduces pancreatic juice ; contains

digestive

enzymes, and sends it to the small intestine;

produces insulin and secretes it into the

blood after eating

Digestive tract organs

Esophaguspassageway where peristalsis pushes

food to stomach

Stomachsecretes acid and digestive enzyme

for protein; churns, mixing food with

secretions, and sends chyme to

small intestine

Small intestinemixes chyme with digestive enzymes

for final breakdown; absorbs nutrient

molecules into body; secretes

digestive hormones into blood

Large intestineabsorbs water and salt to form feces

Rectumstores and regulates elimination

of feces

Mouthteeth chew food; tongue tastes and

pushes food for chewing and swallowing

Pharynxpassageway where food is swallowed

Accessory organs

Salivary glandssecrete saliva which contains digestive

enzyme for carbohydrates

Anus

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Figure 41.20

Transport ofglucose intobody cellsand storageof glucoseas glycogen

Breakdownof glycogenand releaseof glucoseinto blood

Homeostasis:70–110 mg glucose/100 mL blood

Stimulus:Blood glucose

level dropsbelow set point.

Pancreassecretesglucagon.

Stimulus:Blood glucose

level risesafter eating.

Pancreassecretesinsulin.

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Satietycenter

Ghrelin

Insulin

Leptin

PYY

Other hormones

associated with

eating

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Veins to heart

Mouth Stomach

Esophagus

Lymphatic system

Lipids

Absorbed food(except lipids)

Hepatic portal vein

Absorbedwater

Liver

Secretionsfrom salivaryglands

Secretionsfrom gastricglands

Small intestine

Secretions from liver

Secretions from pancreasRectum

Anus

Largeintestine

Digestive system secretion & nutrient absorption

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What is obesity? What is BMI?

9.6 Nutrition and Weight Control

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To understand weight and nutrition, we first

have to understand nutrients

• Nutrients are components of food that are

needed to perform physiological body functions.

• Nutrients include

– carbohydrates.

– proteins.

– lipids.

– minerals.

– vitamins.

9.6 Nutrition and Weight Control

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Carbohydrates• Simple sugars primary energy source

• Refined grains fiber and vitamins are removed

white bread, cake, and cookies

• Complex carbohydrates beans, whole-grain products, nuts, and fruits

• Refined sugars & fructose sweeteners may contribute to obesity. Increases insulin secretion insulin resistance

Type 2 diabetes and increased fat metabolism.

Increase fat deposition may increase the risk of coronary heart disease, liver diseases, and certain cancers

9.6 Nutrition and Weight Control

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How can you reduce high-glycemic

index carbohydrates?

9.6 Nutrition and Weight Control

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Proteins

• 8 essential amino acids

• Complete proteins have: animals such as meat and dairy

Nonanimal sources: tofu, soymilk, and other processed food from soybeans

• Incomplete proteins lack: legumes, nuts, grains

9.6 Nutrition and Weight Control

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Can proteins be harmful?

9.6 Nutrition and Weight Control

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Lipids

• Lipids include fats, oils, and cholesterol.

• Saturated fats

• Essential fatty acids

9.6 Nutrition and Weight Control

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Choosing the most healthy fat and oil

Figure 9.14

Saturated and

unsaturated fatty

acids.

9.6 Nutrition and Weight Control

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Can lipids be harmful?

9.6 Nutrition and Weight Control

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How can you reduce “bad” fats and

cholesterol in your diet?

9.6 Nutrition and Weight Control

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A summary of minerals

9.6 Nutrition and Weight Control

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Vitamins

9.6 Nutrition and Weight Control

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Fat-soluble vitamins

9.6 Nutrition and Weight Control

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Water-soluble vitamins

9.6 Nutrition and Weight Control

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Antioxidants

9.6 Nutrition and Weight Control

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What is your BMI?

Figure 9.11 The body mass index chart.

9.6 Nutrition and Weight Control

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Source: U.S. Department of Agriculture: Dietary Guidelines for Americans, 2005

Body Mass Index (BMI)

6’6”

6’4”

6’2”

6’0”

5’10”

5’8”

5’6”

5’4”

5’2”

5’0”

4’10”

underweight

healthy weight

overweight

obese

19 25 30

Heig

ht

50 75 100 125

Weight (lb)

275250225200175150

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Why should we be concerned

with obesity?

9.6 Nutrition and Weight Control

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Why should we be concerned

with obesity?

• It is associated with:

an increased risk of premature death

type 2 diabetes

Hypertension

CVD

Stroke

gallbladder disease

respiratory dysfunction

Osteoarthritis

certain cancers.

9.6 Nutrition and Weight Control

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Searching for the magic

weight-loss bullet• Trendy diet programs

Pritikin diet:

Atkins:

Zone and South beach diets:

Caveman, or Paleo Diet

• Prescription drugs

9.6 Nutrition and Weight Control

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Searching for the magic

weight-loss bullet• Surgical procedures

Gastroplasty:

Gastric bypass:

Gastric banding:

Liposuction:

9.6 Nutrition and Weight Control

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Eating disorders are associated with body image

Figure 9.16 The characteristics of different eating disorders.

9.6 Nutrition and Weight Control

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

a. Anorexia nervosa b. Bulimia nervosa c. Muscle dysmorphia

a: © Ted Foxx/Alamy RF; b: © Donna Day/Stone/Getty Images; c: © Corbis RF

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Eating disorders

• Anorexia nervosa:

• Bulimia nervosa:

9.6 Nutrition and Weight Control

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Eating disorders

• Binge-eating disorder:

• Muscle dysmorphia:

9.6 Nutrition and Weight Control