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Chapter 15
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1
15.1
Anatomy of the digestive
system
2
A. Introduction
1.
Also called the alimentary canal or
gastrointestinal (GI) tract
2. Digestion includes both physical and
chemical processes that reduce food into
soluble molecules that can be absorbed
into the blood stream
3. Functions of the digestive system:
a. Ingest food
b. Break food down into small molecules
c. Absorb nutrient molecules
d. Eliminate non-digestible wastes
3
Structures of the digestive system
4
B. The mouth (oral cavity)
1.
Tongue
a. Composed of skeletal muscle
b. Papillae
1) Help it handle food
2) Contain taste buds
c. Lingual frenulum attaches it to the floor
of the mouth
2. Roof separates the oral cavity from the
nasal cavities
a. Hard palate
b. Soft palate
5
C. Teeth and salivary glands
1.
Teeth
a. 20 deciduous (baby) teeth
b. 32 adult teeth embedded in the maxilla
and mandible
1) 4 incisors per jaw
2) 2 cuspids (canines) per jaw
3) 4 bicuspids per jaw
4) 6 molars per jaw
6
Teeth, cont.
c.
Tooth structure
1) Crown – layers of enamel, dentin, and
pulp
2) Root – layers of cementum, dentin, and
pulp
d. Diseases
1) Caries occur when bacteria break down
sugars and produce acids that erode the
enamel
2) Gum diseases are more likely as we age
– gingivitis and periodontitis
7
Human teeth
8
2. Salivary glands
a.
Salivary glands
1) Parotid
2) Sublingual
3) Submandibular
b. Saliva – solution of mucus and water
1) Salivary amylase – begins the process
of digesting carbohydrates
2) Moistens food and prepares it for
swallowing
3) Antibacterial lysozyme and secretory
antibodies
9
D. The pharynx
1.
2.
Passageway for food and air
Three parts
a. Nasopharynx - air
b. Oropharynx – food and air
c. Laryngopharynx - food
3. Tonsils
a. Palatine tonsils
b. Lingual tonsils
c. Pharyngeal tonsil (adenoids)
10
E. Swallowing
1.
2.
3.
Begins with the voluntary phase
Reflex action – once food or drink is
pushed back to the oropharynx
Bolus – chewed and swallowed food or
drink
11
Swallowing
12
F. The Wall of the Digestive Tract
1.
Mucosa (mucous membrane layer)
a. Layer of epithelium that lines the lumen
b. Glandular epithelial cells secrete
digestive enzymes
c. Goblet cells secrete mucus
2. Submucosa (submucosal layer)
a. Loose connective tissue
b. Contains blood vessels, lymphatic
vessels, and nerves
c. Peyer’s patches are scattered throughout
the submucosa of the small intestine
13
Wall layers, cont
3.
Muscularis (smooth muscle layer)
a. Inner, circular layer
b. Outer, longitudinal layer
c. The stomach has an extra oblique layer
4. Serosa (serous membrane layer)
a. Thin, outermost layer of squamous
epithelium
b. Secretes serous fluid
c. Adventitia – outer connective tissue layer
of the esophagus
14
Wall of the alimentary canal
15
G. The esophagus
1.
2.
3.
4.
5.
Muscular tube from the pharynx to the
stomach
Peristalsis pushes food along the
alimentary canal
Function is to transport food to the
stomach; no chemical digestion
Esophageal sphincter marks the entrance
to the stomach
Heartburn occurs when some of the
stomach contents escapes into the
esophagus; GERD – chronic reflux disorder
16
Peristalsis
17
H. The stomach
1.
Thick-walled, J-shaped organ on the left
side of the abdominal cavity
2. Continuous with the esophagus and
duodenum of the small intestine
3. Rugae – deep folds in its wall
4. Functions
a. Stores and liquefies food
b. Starts the digestion of proteins
c. Moves food into the small intestine
18
5. Regions of the stomach
a.
b.
c.
d.
Cardiac stomach
Fundic stomach
Body of the stomach
Pyloric stomach
19
Anatomy & histology of the stomach
20
6. Digestive functions of the stomach
a. Acts on food both chemically and physically
b. Muscular wall churns and mixes food with
gastric juice
c. Gastric pits lead to gastric glands that
produce gastric juice
d. Alcohol and water are absorbed through the
stomach wall
e. Churned food and gastric juice mixture is
called chyme which leaves the stomach in 2
to 6 hours
f. Ulcer – open sore, mainly caused by the
bacterium, Helicobacter pylori
21
g. Makeup of gastric juice
1)
Chief cells
a) Secrete pepsinogen
b) Pepsinogen becomes the proteindigesting enzyme pepsin when activated
by HCl
2) Parietal cells
a) Produce hydrochloric acid – kills bacteria
and activates pepsin
b) Produces intrinsic factor – binds to
vitamin B12 and prevents it from being
destroyed in the acidic environment
22
Gastric juice, cont
3)
4)
5)
Enteroendocrine cells produce gastrin that
regulates muscular contractions and
secretions of the stomach
Mucous cells secrete protective mucus
ECL cells release histamine to enhance the
action of gastrin
23
I. Peritoneum
1. Serous membrane of the abdominal cavity
2. Parietal peritoneum lines the abdominal wall
3. Visceral peritoneum covers the organs
a. Lesser omentum – mesentery that runs
between the stomach and liver
b. Greater omentum – mesentery that hangs
down in front of the intestines
1) Cushions and insulates the abdominal
cavity
2) Contains macrophages
3) Can wall off portions of the alimentary
wall that may be infected
24
Function of the mesentery
25
J. The small intestine
1.
Extends from the pyloric valve of the
stomach to the ileocecal valve where it
joins the large intestine (about 18 ft in a
cadaver)
2. Regions of the Small Intestine
a. Duodenum – many folds and villi
1) Glands secrete mucus
2) Receives pancreatic secretions and bile
b. Jejunum
c. Ileum contains Peyer’s patches with few
folds and villi
26
Regions of the small intestine
27
3. Wall of the small intestine
a.
b.
c.
d.
Wall is modified to greatly increase
surface area
Circular folds – permanent transverse
folds
Villi – finger-like projections containing
blood capillaries and a lacteal (lymphatic
capillary)
Microvilli – microscopic extensions of the
columnar cells; called the brush border
28
Anatomy of the small intestine
29
4. Functions of the small intestine
a.
Digestion of fats, proteins, and carbohydrates into
soluble molecules
1) Bile and pancreatic enzymes enter the
duodenum for chemical digestion
2) Intestinal enzymes complete chemical digestion
b.
Absorption of nutrients
1) Sugars and amino acids enter the blood
2) Glycerol and fatty acids enter the lacteal
c.
Movement of nondigested remains to the large
intestine
1) Segmentation
2) Peristalsis
30
5. Regulation of contraction and secretion
a.
The central nervous system allows a
response to hunger signals
b. Enteric nervous system - a network of
nerves within the walls of the GI tract that
controls its own movements and secretions
c. Autonomic nervous system
1) Parasympathetic division is the major
controller of digestive activities
2) Sympathetic division slows digestive
activities
31
d. Nervous control
1) Cephalic phase - Sight or smell of food
causes parasympathetic stimulation of
gastric secretion
2) Gastric phase – stretch of the stomach
causes gastric contraction and secretion
by gastric glands including gastrin
3) Intestinal phase – stretch of the
duodenum causes contraction and
secretion in the small intestine and feeds
back to the stomach
32
e. Hormonal control
1)
2)
3)
4)
5)
6)
Gastrin - causes gastric contraction and
secretion by gastric glands
Secretin – causes bicarbonate release from
pancreas & liver production of bile
Gastric inhibitory peptide (GIP) – inhibits
gastric action & slows contractions
Cholecystokinin (CCK) – causes enzyme
release from pancreas & gall bladder
release of bile
Leptin – from adipocytes, causes full
feeling
Ghrelin – from stomach, triggers hunger
33
Hormonal control of secretion
34
K. The large intestine
1.
Has a larger diameter but is shorter than the small
intestine
2.
Functions
a. Absorbs water, salts, and some vitamins
b. Stores indigestible material until it is eliminated
3.
Regions
a. Cecum - blind sac below ileocecal valve;
vermiform appendix is attached
b. Colon - ascending colon, transverse colon,
descending colon, sigmoid colon
1) Haustra
2) Taenia coli
c. Rectum
d. Anal canal
35
The large intestine
36
Large intestine, cont
4. Feces
a. 75% water
b. 25% solids
1) Bacteria
2) Fiber and other indigestible remains
c. Color comes from a breakdown product
of bilirubin
5. Colon bacteria feed on cellulose and produce
fatty acids, B-complex vitamins, vitamin K,
and gases that contribute to flatus
37
6. Defecation reflex
a.
b.
c.
d.
Rectal muscles contract and relax the
internal anal sphincter
Feces move into the anal canal
Voluntary relaxation of the external anal
sphincter and a pushing movement,
propels the feces from the body
There is much variation in the frequency of
defecation
38
7. Irregular bowel movements
a.
Constipation
1) Slow movement with more absorption
of water
2) Feces are dry and hard
3) Chronic constipation is associated with
hemorrhoids
b. Diarrhea
1) Fast movement with not enough water
reabsorbed
2) Caused by infection of the lower
intestinal tract or irregular nervous
stimulation
39
8. Other disorders of the large intestine
a. Polyps
1) Small growths arising from the epithelial
lining of the colon
2) Can be benign or cancerous (colon
cancer)
b. Diverticulosis
1) Presence of saclike pouches
2) Diverticulitis – inflammation occurs
a) Cramps or steady pain
b) Fever
c) Loss of appetite, nausea, and vomiting
40
15.2 Accessory organs of digestion
Teeth and salivary glands were
covered with the oral cavity
41
A. Pancreas
1.
Endocrine function – pancreatic islets secrete
insulin, glucagon, and somatostatin
2.
Exocrine function acinar cells produce pancreatic
juice
a. Sodium bicarbonate to neutralize acidic chyme
b. Digestive enzymes for all types of foods
1) Amylase digests starch
2) Three protein-digesting enzymes – released
in inactive forms
a) Trypsin – activated by enterokinase
b) Chymotrypsin and Carboxypeptidase –
activated by trypsin
3) Lipase digests fat
4) Nucleases break down nucleic acids
42
The pancreas
43
B. The liver
1.
Liver Structure
a. Two main lobes
b. Each lobe is divided into many hepatic
lobules
1) Hepatic cells
2) Hepatic sinusoids
3) Kupffer cells – phagocytic macrophages
c. Portal triads are located between the
lobules
1) Bile duct
2) A branch of the hepatic artery
3) A branch of the hepatic portal vein
44
Liver structure, cont
d.
e.
Bile ducts merge to form the common
hepatic duct
Central veins from each lobule enters a
hepatic vein
45
Liver anatomy
46
2. Liver functions
a.
b.
c.
d.
e.
Detoxifies blood
Removes and stores nutrients
Stores iron and vitamins A, D, E, and K
Makes plasma proteins
Maintains blood glucose concentrations
1) Insulin stores glucose as glycogen
(glycogenesis)
2) Glucagon breaks down glycogen to
glucose (glycogenolysis)
3) New glucose made from other molecules
(gluconeogenesis)
47
Liver functions, cont
f.
g.
h.
Produces urea after breaking down amino
acids
Forms and secretes bile
Helps regulate the blood cholesterol level
48
3. Liver disorders
a.
Jaundice – yellow tint to the whites of
the eyes and skin due to bilirubin
deposits
1) Hemolytic jaundice
2) Obstructive jaundice
3) Hepatitis
b. Cirrhosis – liver becomes fatty and then
liver tissue is replaced by fibrous scar
tissue
49
C. The gallbladder
1.
Sac on the inferior surface of the liver that
stores and concentrates excess bile
2. When needed, bile leaves the gallbladder
via the cystic duct
3. The cystic duct joins the common hepatic
duct to form the common bile duct that
enters the duodenum with the pancreatic
duct
4. Function of bile salts
a. Emulsification of fats
b. Enhance absorption of fatty acids,
cholesterol, and fat soluble vitamins
50
15.3 Chemical Digestion
51
A. Digestive enzymes
1.
2.
3.
Digestive enzymes are hydrolytic enzymes
Break down substances with the addition of
water at specific bonds
Have an optimum pH to function at
52
B. Carbohydrates
1.
2.
3.
4.
5.
Salivary amylase breaks carbohydrates into
maltose
Action stops in the stomach (too acidic)
Pancreatic amylase continues the hydrolysis to
maltose
Brush border enzymes of the small intestine break
down disaccharides to monosaccharides (mainly
glucose)
a. Sucrose broken down by sucrase
b. Lactose broken down by lactase
c. Maltose broken down by maltase
Monosaccharides are absorbed by intestinal cells
into blood capillaries
53
Carbohydrate digestion & absorption
54
C. Proteins
1.
2.
3.
4.
Pepsin in the stomach hydrolyzes proteins
into short polypeptides
Three pancreatic proteinases – trypsin,
chymotrypsin, and carboxypeptidase
break down polypeptides to peptides and
some amino acids
Peptidases (brush border enzymes)
complete the digestion of peptides into
amino acids in the small intestine
Amino acids are absorbed by intestinal
cells into blood capillaries
55
Protein digestion & absorption
56
D. Fats
1.
2.
3.
First emulsified by bile in the duodenum
Digested by pancreatic lipase to glycerol
and fatty acids
Enter intestinal cells where the fatty acids
are packaged as lipoproteins and then
enter the lacteals
57
Fat digestion & absorption
58
E. Nucleic acids
1.
2.
3.
Pancreatic nucleases break down DNA and
RNA into nucleotides
Brush border nucleotidases break down the
nucleotides to sugar, phosphate, and
nitrogenous base
These chemicals enter intestinal cells into
the blood capillaries
59
Major digestive enzymes
60
15.4 Effects of aging
61
A. Effects of Aging
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
Incidence of gastrointestinal disorders increases
Periodontitis
Esophageal hiatal hernia
Heartburn & GERD
Peristalsis slows
Peptic ulcers may occur more frequently
Diverticulosis and constipation – not enough fiber
The liver shrinks
Gallbladder difficulties occur – gallstones
Cancer
Hemorrhoids
Fecal incontinence
62
15.5 Homeostasis
63
A. Homeostasis
1.
2.
3.
4.
Alimentary canal is also part of the
endocrine system
Nutrients absorbed by the alimentary canal
are used for energy, growth, and repair
Vitamins needed for normal growth and
development
Minerals assist in many body processes
64
Human Systems Working Together
65
15.6 Nutrition
66
A. Nutrition
1.
2.
3.
4.
Nutrition – interaction between food and
the living organism
Nutrient – substance the body uses to
maintain health
A balanced diet contains all the essential
nutrients in correct proportions
Nutrients enter the blood and are
distributed to the tissues
67
Nutrition, cont
5.
Essential molecules must be present in
food because the body is unable to produce
them
a. Two essential fatty acids
b. Nine essential amino acids
6. Glucose is the body’s immediate energy
source
7. Fats are a long-term energy source
8. Amino acids used by the cells to construct
proteins and can be used for energy is
needed
68
Newest dietary guidelines
Go to www.choosemyplate.gov to personalize
69
B. Vitamins
1.
2.
3.
4.
Vital to life
Play essential roles in cellular metabolism
Fat-soluble - vitamins A, D, E, and K
Water-soluble
a. B-complex vitamins and vitamin C
b. Most are coenzymes
70
Vitamins
71
C. Minerals
1.
2.
Inorganic elements
Macronutrients
a. Sodium
b. Magnesium
c. Phosphorus
d. Chlorine
e. Potassium
f. Calcium
3. Micronutrients – trace elements needed in
very small amounts
72
Minerals
73
D. Eating disorders
1.
Obesity
a. Body weight 20% or more above the
ideal weight for a person’s height
b. 36% of women and 32% of men in the
U.S. are overweight
c. Caused by a combination of factors –
hormonal, metabolic, and social
74
2. Bulimia nervosa
a.
b.
c.
d.
e.
Can coexist with either obesity or
anorexia nervosa
Binge eating, then purging
Alters blood composition, leading to
abnormal heart rhythm, kidney failure
and even death
Stomach acids can cause teeth to erode
Esophagus and stomach may rupture
75
3. Anorexia nervosa
a. Morbid fear of gaining weight
b. Individuals have a distorted self-image
c. Individuals have all the symptoms of starvation
1) Low blood pressure
2) Irregular heartbeat
3) Constipation
4) Constant chilliness
5) Bone density decreases
6) Menstruation stops in females
7) Internal organs do not function well
8) Skin dries up
76
Anorexia Nervosa & Bulimia Nervosa
77