Download Chapter 2: Chemistry, Matter, and Life

Chapter 19
The Digestive System
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Key Terms
absorption
esophagus
pancreas
bile
gallbladder
peptic ulcer
chyle
hydrolysis
peristalsis
chyme
ingestion
peritoneum
defecation
intestine
saliva
deglutition
lacteal
sphincter
digestion
liver
stomach
duodenum
mastication
villi
emulsify
mesentery
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General Structure and Function of the
Digestive System
General Functions
• Digestion
• Absorption
• Elimination
Divisions
• Digestive tract
• Accessory organs
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Figure 19-1 The digestive system.
Which accessory organs of digestion secrete into the
mouth?
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General Structure and Function of the
Digestive System (cont.)
Peritoneum
• Lines the abdominopelvic
cavity; covers abdominal
organs
• Layers of the peritoneum
– Parietal
– Visceral
• Subdivisions
– Mesentery
– Mesocolon
– Greater omentum
– Lesser omentum
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General Structure and Function of the
Digestive System (cont.)
The Wall of the Digestive Tract
• Mucosal membrane, or mucosa
• Submucosa
• Smooth muscle, the muscularis externa
• Serous membrane, or serosa
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Figure 19-3 Wall of the digestive tract.
What type of tissue is between the submucosa and the
serous membrane in the digestive tract wall?
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General Structure and Function of the
Digestive System (cont.)
Pop Quiz
19.1
Which of the following is the correct order from the
outermost to innermost layer?
A) Submucosa, serous membrane, smooth muscle,
mucous membrane
B) Smooth muscle, serous membrane, mucous
membrane, submucosa
C) Serous membrane, smooth muscle, submucosa,
mucosa
D) Mucous membrane, submucosa, smooth muscle,
serous membrane
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General Structure and Function of the
Digestive System (cont.)
Pop Quiz Answer
19.1
Which of the following is the correct order from the
outermost to innermost layer?
A) Submucosa, serous membrane, smooth muscle,
mucous membrane
B) Smooth muscle, serous membrane, mucous
membrane, submucosa
C) Serous membrane, smooth muscle, submucosa,
mucosa
D) Mucous membrane, submucosa, smooth muscle,
serous membrane
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Organs of the Digestive Tract (cont.)
• Mouth
• Pharynx
• Esophagus
• Stomach
• Small intestine
• Large intestine
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Organs of the Digestive Tract (cont.)
The Mouth
• Also called oral cavity, processes food by:
– Ingestion
– Mastication
– Mixing with saliva
– Deglutition
• Tongue
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Figure 19-4 Gastrointestinal motility.
Which type of motility would be most useful in the
esophagus, where the contents should move quickly?
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Organs of the Digestive Tract (cont.)
The Teeth
• Sets of teeth
– Deciduous
– Permanent
• Types of teeth
– Incisors
– Cuspids
– Molars
• Six-year molars
• Premolars
• Third molars or wisdom teeth
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Organs of the Digestive Tract (cont.)
The Teeth (cont.)
• Parts of a tooth
– Dentin
– Crown
– Enamel
– Root
• The gum
– Gingiva
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Figure 19-5 The mouth and teeth.
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Organs of the Digestive Tract (cont.)
The Pharynx
• Also called the throat
• Divisions
– Oropharynx
– Nasopharynx
– Laryngopharynx
• Soft palate
• Uvula
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Organs of the Digestive Tract (cont.)
The Esophagus
• Muscular tube.
• Food is lubricated with mucus.
• Peristalsis.
• No digestion occurs here.
• Passes through esophageal hiatus of the diaphragm to
join stomach.
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Organs of the Digestive Tract (cont.)
The Stomach
• Structure
– Greater curvature
– Lesser curvature
– Fundus
– Body
– Pylorus
• Sphincters
– Lower esophageal
sphincter (LES)
– Pyloric
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Organs of the Digestive Tract (cont.)
The Stomach (cont.)
• Functions
– Storage pouch
• Rugae
– Secrete substances to form gastric juice
• Hydrochloric acid prepares proteins for digestion.
• Pepsin digests proteins.
– Delivery of chyme to the small intestine
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Organs of the Digestive Tract (cont.)
The Small Intestine
• Subdivisions of the small intestine
– Duodenum
– Jejunum
– Ileum
• Functions of the small intestine
– Secretion
– Motility
– Digestion
– Absorption
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Figure 19-7 The intestines.
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Organs of the Digestive Tract (cont.)
The Large Intestine
• Subdivisions of the large intestine
– Cecum
• Ileocecal valve
• Appendix
– Ascending colon
– Transverse colon
– Descending colon
– Sigmoid colon
– Rectum
– Anal canal
– Anus
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Organs of the Digestive Tract (cont.)
• Functions of the large intestine
– Production of mucus
– Reabsorb some water
– Form feces (stool)
– Defecation
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Organs of the Digestive Tract (cont.)
Pop Quiz
19.2
Which organ receives food flowing through the
pyloric sphincter?
A) Stomach
B) Jejunum
C) Duodenum
D) Esophagus
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Organs of the Digestive Tract (cont.)
Pop Quiz Answer
19.2
Which organ receives food flowing through the
pyloric sphincter?
A) Stomach
B) Jejunum
C) Duodenum
D) Esophagus
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The Accessory Organs (cont.)
• Release secretions through ducts into the digestive
tract.
• Salivary glands open to mouth.
• Other organs release secretions into the duodenum:
– Liver
– Gallbladder
– Pancreas
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The Accessory Organs (cont.)
Salivary Glands
• Functions -Secrete saliva
• Moistens food
• Facilitates mastication
and deglutition
• Helps keep teeth and
mouth clean
• Three pairs:
– Parotid glands
– Submandibular glands
– Sublingual glands
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The Accessory Organs (cont.)
The Liver
• Structure of the liver
– Largest accessory organ
– Right, left lobes
– Portal vein
– Hepatic artery
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The Accessory Organs (cont.)
The Liver (cont.)
• Functions of the liver
– Manufactures bile
– Controls blood glucose levels
– Modifies fats
– Stores some vitamins, iron
– Forms blood plasma proteins
– Destroys old red blood cells
– Synthesizes urea
– Detoxifies harmful substances
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The Accessory Organs (cont.)
The Liver (cont.)
• Bile
– Manufactured in the liver.
– Bile leaves the liver by ducts.
• Common hepatic duct
• Cystic duct
• Common bile duct
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Figure 19-9 Accessory organs of digestion.
Into which part of the small intestine do these accessory
organs secrete?
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The Accessory Organs (cont.)
The Gallbladder
• Muscular sac
• Located on inferior surface of the liver
• Stores bile
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The Accessory Organs (cont.)
The Pancreas
• Gland that produces enzymes
• Releases large amounts of sodium bicarbonate
(NaHCO3)
• Also functions as an endocrine gland
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Enzymes and the Digestive Process
(cont.)
• Fundamental chemical process of digestion
• Enzymes
– Required for digestion
– Catalysts
– Highly specific proteins
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Enzymes and the Digestive Process
(cont.)
Role of Water
• Hydrolysis
• Seven liters of water secreted into the digestive tract
daily
• Produces digestive juices
• Dilutes food
• Used in the chemical process of digestion
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Figure 19-10 Hydrolysis.
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Digestion, Step by Step
Digestion in the Mouth
• Chews food, mixes with saliva
• Some starches changed to sugars via salivary amylase
Digestion in the Stomach
• Secretes HCl, enzymes
– Denatures proteins
• Secretes mucus
• Forms chyme
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Digestion, Step by Step (cont.)
Digestion in the Small Intestine
Most digestion occurs in the duodenum.
• Fats
• Carbohydrates
• Proteins
• Nucleic acids
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Absorption (cont.)
• Villi in mucosa of the small intestine:
– Arteriole and venule bridged with capillaries
• Capillaries absorb:
– Simple sugars
– Small proteins
– Amino acids
– Simple fatty acids
– Water
• Portal system transports nutrients to the liver.
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Absorption (cont.)
• Absorption of fats
– Lacteals absorb fat.
– Fat/lymph mixture (chyle) drains from the small
intestine.
– Chyle merges with lymphatic circulation, enters
blood in veins near the heart.
– The liver further processes absorbed fats.
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Absorption (cont.)
• Absorption of vitamins and minerals
– Vitamins and minerals are absorbed from the small
intestine.
– Minerals and some vitamins mix with water and are
absorbed directly into the blood.
– Other vitamins are incorporated in fats and
absorbed along with fats.
– Vitamin K and some B vitamins are produced by
bacterial action in the colon and are absorbed from
the large intestine.
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Figure 19-11 Carbohydrates.
Name the two monosaccharide components of sucrose.
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Enzymes and the Digestive Process
(cont.)
Pop Quiz
19.3
Which enzyme digests carbohydrates?
A) Amylase
B) Pepsin
C) Lipase
D) Trypsin
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Enzymes and the Digestive Process
(cont.)
Pop Quiz Answer
19.3
Which enzyme digests carbohydrates?
A) Amylase
B) Pepsin
C) Lipase
D) Trypsin
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Control of Digestion and Eating (cont.)
Control of Digestion
Two types of control over digestion—nervous and hormonal
• Nervous control of digestion
– Parasympathetic stimulation increases activity
– Sympathetic stimulation decreases activity
• Hormonal control of digestion
– Digestive organs produce hormones
• Gastrin
• Gastric inhibitory peptide (GIP)
• Secretin
• Cholecystokinin (CCK)
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Control of Digestion and Eating (cont.)
Control of Hunger and Appetite
• Hunger
– Desire for food
– Regulated by hypothalamic centers
– Respond to nutrient levels
– Satisfied by adequate meal
• Appetite
– No relationship to need for food
– May not be satisfied by adequate meal
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Control of Digestion and Eating (cont.)
• Short-term regulation of hunger
– Hypothalamus induces hunger sensations
– Ghrelin hormone
– Food consumption
• Long-term regulation of body weight
– Leptin hormone produced by adipocytes
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Figure 19-12 Regulation of food intake.
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Control of Digestion and Eating (cont.)
Pop Quiz
19.4
Which portion of the autonomic nervous system
inhibits digestion?
A) Somatic
B) Parasympathetic
C) Sympathetic
D) Visceral
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Control of Digestion and Eating (cont.)
Pop Quiz Answer
19.4
Which portion of the autonomic nervous system
inhibits digestion?
A) Somatic
B) Parasympathetic
C) Sympathetic
D) Visceral
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Disorders of the Digestive System (cont.)
Peritonitis
• Inflammation of the peritoneum following infection of an
organ covered by peritoneum
– Localized
– Generalized
• Examples of causative factors: ruptured appendix,
perforated ulcer, penetrating wound
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Disorders of the Digestive System (cont.)
Diseases of the Mouth and Teeth
• Dental caries
• Gingivitis
• Periodontitis
• Vincent disease
• Oral thrush
• Parotitis
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Disorders of the Digestive System (cont.)
Disorders of the Esophagus and Stomach
• Hiatal hernia and gastric reflux
– Heartburn
– Chronic reflux or gastroesophageal reflux disease
(GERD)
• Nausea and vomiting (emesis)
• Stomach cancer
• Gastritis and peptic ulcer
• Pyloric stenosis
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Figure 19-13 Disorders involving the esophagus and stomach.
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Disorders of the Digestive System (cont.)
Intestinal Disorders
• Inflammatory disorders
– Appendicitis
– Inflammatory bowel disease
• Crohn disease
• Ulcerative colitis
– Celiac disease
– Irritable bowel syndrome (IBS)
– Enteritis and gastroenteritis
– Diverticulitis
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Disorders of the Digestive System (cont.)
Intestinal Disorders (cont.)
• Diarrhea
• Constipation
– Spastic constipation
– Flaccid constipation
• Intestinal obstruction
– Intussusception
– Volvulus
• Colon and rectal cancer
– Sigmoidoscope
– Colonoscope
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Figure 19-14 Intestinal obstructions.
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Figure 19-15 Imaging of the colon.
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Disorders of the Digestive System (cont.)
Cirrhosis and Other Liver Diseases
• Cirrhosis
– Active liver cells replaced by inactive connective
(scar) tissue.
– Alcoholic (portal) cirrhosis is most common type.
– Varicose veins (varices) of the digestive tract.
• Jaundice
• Hepatitis
– Types of hepatitis virus: A, B, C, D, E
• Liver cancer
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Disorders of the Digestive System (cont.)
Gallstones
• Cholelithiasis
• Cholecystitis
Pancreatic Disorders
• Pancreatitis
• Pancreatic cancer
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Figure 19-16 Gallstones.
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Effects of Aging and the Digestive System
• Decreased digestive organ activity
– Decrease in saliva
– Tooth loss
– Poor nutrient absorption
– Slowing of peristalsis
• Decreased tissue replacement
• Increased risk of cancer
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Case Study
Learning Objective
16. Using the case study,
describe the
colonoscopy procedure
and its role in
diagnosing certain
colon disorders.
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Case Study (cont.)
Colonoscopy
 Recommended for people over the age of 50 years as
baseline; every 10 years thereafter for low-risk persons
 Used to detect colorectal cancers
 Preparation:
− Nothing to eat from the evening prior to the
examination
− Bowel cleansing

Types of colonoscopies:
− Flexible lighted endoscope

− Virtual colonoscopy using computerized x-rays
May remove polyps and abnormal tissue with
endoscope
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Word Anatomy (cont.)
Word Part
Meaning
Example
General Structure and Function of the Digestive System
ab-
away from
In absorption, digested materials are taken
from the digestive tract into the circulation.
enter/o
intestine
The mesentery is the portion of the
peritoneum around the intestine.
mes/o-
middle
The mesocolon, like the mesentery, comes
from the middle layer of cells in the
embryo, the mesoderm.
Organs of the Digestive Tract
gastr/o
stomach
The gastrointestinal tract consists mainly of
the stomach and intestine.
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Word Anatomy (cont.)
Word Part
Meaning
Example
The Accessory Organs
amyl/o
starch
The starch-digesting enzyme in saliva is
salivary amylase.
bil/i
bile
Bilirubin is a pigment found in bile.
cyst/o
bladder, sac
The cystic duct carries bile into and out of
the gallbladder.
hepat/o
liver
The hepatic portal system carries blood to
the liver.
lingu/o
tongue
The sublingual salivary glands are under
the tongue.
Control of Digestion
chole-
bile, gall
Cholecystokinin is a hormone that activates
the gallbladder (cholecyst/o).
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Word Anatomy (cont.)
Word Part
Meaning
Example
Disorders of the Digestive System
lith-
stone
A fecalith is a hardened piece of fecal
material.
odont/o
tooth
Periodontitis is a disease of the gums and
the tissue around a tooth.
-rhea (the
flow,
“r” is
discharge
doubled
when added
to a word)
Diarrhea is a flow of watery bowel
movements through (dia-) the digestive
tract.
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