Download Human Anatomy & Physiology II

Chapter 19
The Digestive System
Copyright 2010, John Wiley & Sons, Inc.

In 1822, a Canadian was accidently wounded
by gunshot. An army surgeon began
immediate work on the wound. The wound
healed, but a small opening leading into his
stomach covered by a fold of flesh allowed
direct observation of the inside of his
stomach. The doctor extracted gastric juices
and stomach contents at various stages of
digestion and noted the stomach muscle
contractions. The results of his experiments
and observations formed the basis of our
modern knowledge of digestion.
Functions of the Digestive System
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Ingestion: eating
Secretion: release of water, enzymes, buffers
Mixing and propulsion: movement along GI
tract
Digestion: breakdown of foods
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Mechanically: by movements of digestive organs
Chemically: by enzymes
Absorption: moving products of digestion into
the body
Defecation: dumping waste products
Copyright 2010, John Wiley & Sons, Inc.
Organs of the Digestive System
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Gastrointestinal (GI) tract
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A tube through which foods pass and where
digestion and absorption occur.
Includes: mouth, pharynx, esophagus, stomach,
small intestine, large intestine
Accessory organs:
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Organs that help in digestion but through which
food never passes.
Includes: teeth, tongue, salivary glands, liver,
gallbladder, and pancreas
Copyright 2010, John Wiley & Sons, Inc.
Organs of the Digestive System
Copyright 2010, John Wiley & Sons, Inc.
Mouth (Oral Cavity)
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Formed by
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Uvula
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U-shaped extension of soft palate posteriorly
During swallowing, uvula blocks entry of food or
drink into nasal cavity
Tongue: muscular accessory organ
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Cheeks and tongue
Hard palate anteriorly, soft palate posteriorly
Maneuvers food for chewing
Adjusts shape for speech and swallowing
Lingual tonsils at base of tongue
Copyright 2010, John Wiley & Sons, Inc.
Teeth
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Accessory organs in bony sockets of
mandible and maxilla
Three external regions
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Crown: above gums
Neck: between crown and root near gum line
Root: part(s) embedded in socket
Three layers of material
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Enamel: hardest substance in body; over crown
Dentin: majority of interior of tooth
Pulp cavity: nerve, blood vessel, and lymphatics
Copyright 2010, John Wiley & Sons, Inc.
Teeth
Copyright 2010, John Wiley & Sons, Inc.
Teeth
Humans have two sets of teeth
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The 20 deciduous teeth are replaced by the
permanent teeth between ages 6 and 12 years.
The 32 permanent teeth appear between 6 years
and adulthood.
Four types of teeth
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Incisors (8): used to bite, slice, cut food
Cuspids (Canines) (4): used to tear/rip food
Premolars (bicuspids) (8): for crushing and
grinding food
Molars (tricuspids) (12): used for crushing and
grinding food
Copyright 2010, John Wiley & Sons, Inc.
Teeth
Copyright 2010, John Wiley & Sons, Inc.
Salivary Glands
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Exocrine glands with ducts that empty into
oral cavity
Three pairs of salivary glands
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Parotid
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Submandibular
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In floor of mouth; medial and inferior to mandible
Sublingual
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Largest; inferior and anterior to ears
Inferior to tongue and superior to submandibular
Saliva: 99.5% water, salivary amylase,
mucus and other solutes
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Dissolves food and starts digestion of starches
Copyright 2010, John Wiley & Sons, Inc.
Digestion in the Mouth
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Mechanical digestion
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Chewing mixes food with saliva
Rounds up food into a soft bolus for swallowing
Chemical digestion
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Salivary amylase (enzyme) breaks down
polysaccharides (starch)  maltose and larger
fragments
Continues in the stomach for about an hour until
acid inactivates amylase
Copyright 2010, John Wiley & Sons, Inc.
Organ
Enzymes secreted
Substance digested
Resulting products
Salivary Glands
amylase
carbohydrates
Stomach
Protease
proteins
HCl
proteins
maltose
partially digested
proteins
partially digested
proteins
Protease
proteins
peptides, amino acids
Lipase
fats
fatty acids and glycerol
Amylase
carbohydrates
simple sugars
Peptidase
proteins
amino acids
sucrase
sucrose (table sugar)
simple sugars
lactase
lactose (milk sugar)
simple sugars
maltase
maltose
simple sugars
Pancreas
Small Intestines
Pharynx and Esophagus
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Food passages from mouth  stomach
Swallowing: 3 stages
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Voluntary stage: bolus of food  oropharynx
Pharyngeal stage: oropharynx  esophagus
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Soft palate moves up and epiglottis moves down;
prevent food from entering nasopharynx and larynx
Esophageal: food  stomach by peristalsis
Esophageal sphincters:
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Upper: controls entry  esophagus
Lower: controls entry  stomach
Copyright 2010, John Wiley & Sons, Inc.
Pharynx and Esophagus
Copyright 2010, John Wiley & Sons, Inc.
Pharynx and Esophagus
Copyright 2010, John Wiley & Sons, Inc.
Stomach
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J- shaped enlargement of GI tract
Mixing chamber and holding reservoir
Very elastic/expandable and muscular –
usually holds 2.6 pints. When fully stretched,
can hold up to 7 pints.
Four regions
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Cardia: surrounds upper opening
Fundus: superior and to left of cardia
Body: large central portion
Pylorus: lower part leading to pyloric sphincter
and duodenum
Copyright 2010, John Wiley & Sons, Inc.
Stomach
Copyright 2010, John Wiley & Sons, Inc.
Stomach Wall: Four Layers
1. Mucosa
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Empty stomach lies in folds called rugae
2. Secretory cells
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Mucous cells  mucus
Parietal cells  HCl and intrinsic factor
 These secretions collectively called gastric juice
3. Muscularis: Three layers
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Outer: longitudinal
Middle: circular
Inner: oblique (extra layer not in other organs) provides for
efficient gastric contractions
4. Serous membrane (serosa)
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Visceral peritoneum: covers organs
Copyright 2010, John Wiley & Sons, Inc.
Stomach Wall: Four Layers
Copyright 2010, John Wiley & Sons, Inc.
Pancreas
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Location: behind stomach
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Secretions that help digestion
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Produces pancreatic juice
Sodium bicarbonate (NaHCO3): pH 7.1-8.2) –
neutralizes the HCl from the stomach
Empties into the small intestine
Produces insulin to bind with and break down
sugar in the blood (glucose)
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The production of insulin is what keeps sugar from freely moving
through the blood
Normal blood glucose before eating = 80-100mg
Normal blood glucose 30 min after eating = 120-150mg
Blood glucose returns to normal 1 hour after eating
Copyright 2010, John Wiley & Sons, Inc.
Liver and Gallbladder
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Weighs 1.4 kg (3 lb): 2nd largest organ in the
body; large right lobe + 3 smaller parts
In right upper quadrant, below diaphragm
Makes 1.7 pints of bile per day delivered to
the small intestine
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Bile gives feces its characteristic color. Without it,
feces would be grey-white.
The liver is the only organ capable of
regenerating itself.
The gallbladder also produces excess bile in
between meals
Copyright 2010, John Wiley & Sons, Inc.
Bile
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Functions of bile
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Emulsification: breaking apart clusters of fats so
they are more digestible
Absorption of fats
Gallstones may form from bile
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Obstruct bile ducts from gallbladder  pain
Copyright 2010, John Wiley & Sons, Inc.
Liver, Gallbladder, Duodenum
Copyright 2010, John Wiley & Sons, Inc.
Liver
Copyright 2010, John Wiley & Sons, Inc.
Liver Functions
1. Carbohydrate metabolism
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Polysaccharide stored in liver as glycogen
Converts glycogen, fructose, galactose, lactic
acid, amino acids  glucose to  blood glucose
2. Lipid metabolism
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Produces cholesterol, triglycerides; makes bile
Makes lipoproteins for lipid transport
3. Protein metabolism
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Remove NH2 from amino acids  ammonia (NH3)
 urea  to kidneys (urine)
Synthesize most plasma proteins: albumin
Copyright 2010, John Wiley & Sons, Inc.
Liver Functions
4. Removes many harmful substances from
blood
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Detoxifies alcohol
Inactivates steroid and thyroid hormones
Eliminates some drugs (like penicillin) into bile
5. Excretion of bilirubin
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From heme (in RBCs) to bile  feces
6. Stores fat-soluble vitamins (A,D,E,K) and
minerals (Fe, Cu)
7. Activates vitamin D
Copyright 2010, John Wiley & Sons, Inc.
Small Intestine
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Length
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Three major regions: duodenum, jejunum,
ileum
Functions
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10-20 feet long in living person – coiled to fill
abdominal cavity
Extends from pylorus of stomach to cecum of
large intestine
Site of most of digestion
Essentially all nutrient absorption occurs here
Ends in ileocecal sphincter (in RLQ)
Copyright 2010, John Wiley & Sons, Inc.
Small Intestine
Copyright 2010, John Wiley & Sons, Inc.
Small Intestine
Copyright 2010, John Wiley & Sons, Inc.
Intestinal Wall Structure
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Contains 1000’s of intestinal glands that
secrete intestinal juices
Lining is in folds called plicae
Plicae is covered with fingers called villi
Purpose of villi – to increase the surface area
for contact between capillaries and intestinal
lining for faster absorption of food into blood
stream.
Each villi is covered with microvilli, which
further increase surface area.
Copyright 2010, John Wiley & Sons, Inc.
Intestinal Wall Structure
Copyright 2010, John Wiley & Sons, Inc.
Digestion in Small Intestine
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Mechanical digestion
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Segmentation activity: for mixing
Peristalsis for movement of intestinal contents
after most absorption completed: slow waves
Chemical digestion: 2 L/d of secretions
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Alkaline chyme due to bicarbonate
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From pancreas and alkaline mucus from small intestine
Enzymes produced by cells on villi
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Peptidases: breaks small peptides
Disaccharidases: sucrase, lactase, and galactase
Copyright 2010, John Wiley & Sons, Inc.
Absorption in the Small Intestine
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Chyme enters small intestine carrying
partially digested carbohydrates and proteins
Intestinal juice (composed of bile, pancreatic
juice, intestinal juice) completes digestion
90% of absorption of products of digestion
occurs in the small intestine
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Monosaccharides; amino acids
Fatty acids and monoglycerides
Phosphate sugar, and bases of DNA, RNA
Copyright 2010, John Wiley & Sons, Inc.
Absorption of Products of Digestion
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Water and salt
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Primarily osmotic movement that accompanies
other nutrients
Vitamins
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Fat-soluble (A, D, E, K) absorbed with fat
Water-soluble (B’s, C) with simple diffusion
B12
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Combines with intrinsic factor for transport through
duodenum and jejunum
Finally can be absorbed by active transport in ileum
Copyright 2010, John Wiley & Sons, Inc.
Large Intestine
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Structure: 4 regions – all total about 5 feet
long.
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Cecum – tube connecting small to large intestine
 Ileocecal sphincter – valve between the 2
 Appendix attached – it has no digestive function
but does play a role in immunologic defense
mechanism
Colon: ascending, transverse, descending and
sigmoid
Rectum
Anal canal with sphincters
Copyright 2010, John Wiley & Sons, Inc.
Large Intestine
Copyright 2010, John Wiley & Sons, Inc.
Digestion and Absorption
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Ileocecal sphincter limits rate of emptying of
ileum
Slow peristalsis
Mass peristalsis
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Triggered by presence of food in stomach
Wastes move from mid-colon  rectum
Bacterial digestion
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Produce some B-vitamins + vitamin K
Produce gases: flatus
Colon absorbs salt + water
Copyright 2010, John Wiley & Sons, Inc.
Defecation
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1/3 pound of feces is a normal daily defecation.
Fecal matter is made of:
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Water
Rubbed off digestive track lining cells
Millions of dead intestinal bacteria
Fiber and remnants of food
Intestinal bacteria (esp. E. Coli) live in symbiosis
with the intestines to break down food remnants
to produce vitamins B6 and K
Food can take 3-5 days to make the full journey
Control: Phases of Digestion
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Rule: activate forward and inhibit behind
Three phases: cephalic, gastric, intestinal
1. Cephalic: smell, sight, thought of food 
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Cranial nerves VII + IX stimulate salivary glands
Cranial nerve X (vagus) stimulates gastric glands
2. Gastric: stretching, pH of stomach 
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Gastrin activates stomach and relaxes pyloric sphincter
3. Intestinal phase: intestinal hormones play key
roles
Copyright 2010, John Wiley & Sons, Inc.
Conditions/Disorders
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1. Tooth decay – bacteria in mouth thrives on sugars in
food. They produce acids as wastes which eat at tooth
enamel.
2. Gingivitis – inflammation of the gums; most common
oral disease; slight bleeding when brushing teeth… best
thing to do it keep brushing. Can lead to necrotizing
gingivitis = “trench mouth”
3. Peridontal disease – inflammation of the gums, bones
and supporting structures.
4. Oral Cancers – malignancy of the oral cavity; can be
lips, tongue, salivary glands, floor of mouth, pharynx
5. Halitosis – chronic bad breath; odor can come from
stomach or sinus infections – brushing teeth is
ineffective.
Copyright 2010, John Wiley & Sons, Inc.
Progression of Gingivitis
Conditions/Disorders
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6. Malocclusion – faulty relationship between teeth when
jaws are closed
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Overbite – protrusion of upper teeth causing them to hang over
lower teeth
Underbite – positioning lower front teeth outside of upper front
teeth. Can only be fixed by breaking and moving the mandible in
extreme cases.
Copyright 2010, John Wiley & Sons, Inc.
Conditions/Disorders
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7. Mumps – infection of the parotid gland; common
symptom is dysphagia; can cause sterility on males
because the virus can spread to the testes.
8. Eating disorders
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Overeating – causes the stomach to stretch and not feel full, so
extra consumption of calories leads to overweight
Anorexia Nervosa – starving oneself – makes the body go into
survival mode and turn any food consumed to fat for
preservation.
Bulimia – eating then purging – has the same effect on the body
as Anorexia Nervosa, but also erodes the enamel off of the teeth
due to the stomach acid always being regurgitated.
Conditions/Disorders
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9. Acid reflx – backward movement of stomach contents
into lower portion of esophagus (AKA: heart burn). If
sever and untreated, it can cause asthma attacks,
bleeding, chronic irritation, leading to precancerous cells
and ulcers.
10. Hiatal hernia – weakness of diaphragm, which allows
part of the upper stomach or small intestines to push
through to the lower portion of the thorax
11. Peptic Ulcers – excavation (erosion) of the mucosal
wall
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Gastric – ulcers of the stomach (symptoms relieved by vomiting)
Duodenal – stress related (symptoms relieved by eating)
Conditions/Disorders
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11. Gallstones – solid clumps of material (cholesterol)
that form in the gallbladder; if no symptoms then it is
called silent gallstones. Symptoms = pain following
eating.
12. Jaundice – yellowish skin or eyes. Discoloration
due to bile not draining out of the liver. Common in
babies where the liver is not fully developed. Immediate
symptom of all liver problems (including Hepatitis C).
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13. Cirrhosis of the liver – destroyed liver cells replaced
by scar tissue. Often thought of as an alcoholics
disease.
Conditions/Diseases
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14. Appendicitis – inflammation of the appendix due to
foreign body in blind pouch; could be a seed
(watermelon, lemon), fecal matter (due to constipation),
etc.
15. Lactose intolerant – intolerance to milk products;
causes stomach cramping and diarrhea
16. Constipation – abnormal infrequency of defecation.
There is excessive water absorption in the large intestine
causing hard stool.
17. Obstipation – no bowel movement indicates
obstruction. Back up of the system can cause patient to
vomit feces.
Conditions/Diseases
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18. Diarrhea – unusual frequency of bowel movements
– as well as extreme change in consistency. Often is a
symptom of a problem with the intestines.
19. Avitaminosis – deficiency in viamins
20. Hypervitaminosis – too much of a vitamin – causes
toxicity.
21. Colitis – inflammation of the colon and rectum;
diarrhea, abdominal pain, rectal bleeding
22. Colic – leading theory believes that abdominal pain
leading to flatulence. Occurs in infants around 1-4
months of age. Signs and Symptoms: high pitch cry for
long periods of time, drawing legs up to abdomen.
Procedures
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1. ileostomy – excretory orifice from ileum to outside
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2. colostomy – excretory orifice is from colon to outside
Procedures
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3. sigmoidoscopy – illumination of the lower bowel to
inspect sigmoid for ulcers, tumors, etc.
4. cholecystectomy – surgical proceedure to remove
gallbladder
5. colonoscopy – procedure where cameras are inserted
into the colon (large bowel and distal end of small bowel)
to check for ulcers or polyps. It is advised that men and
women over 50 have one done every 5 years.