Chapter 14
Digestive System
Anatomy and Physiology II
Ms. Harborth
PART I:
Digestive System
Takes in food (ingests)
 Breaks it down physically (digests)
 Absorbs nutrients
 Rids body of indigestible remains
(defecates)

Anatomy of the Digestive System

Alimentary
canal (GI tract)
◦ Ingests, digests,
absorbs,
defecates

Accessory
digestive organs
◦ Teeth, tongue,
large digestive
glands
Alimentary Canal
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Continuous, hollow muscular tube
Submucosal and myenteric nerve plexuses
30 feet long in cadaver
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Mouth
Pharynx
Esophagus
Stomach
Small intestine
Large intestine
Anus
Mouth
Labia
 Cheeks
 Hard and soft
palate
 Uvula
 Vestibule
 Oral cavity
proper
 Tongue
 Lingual frenulum

Pharynx
Oropharynx
 Laryngopharynx
 2 skeletal muscle
layers

◦ Inner layer
longitudinal
◦ Outer layer circular
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Peristalsis
Esophagus
10 inches long
 4 tissue layers
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Mucosa – innermost
Submucosa
Muscularis externa
Serosa
 Visceral peritoneum
 Parietal peritoneum
 Mesentery
Stomach
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10 inches long, can
hold 1 gallon
Diameter changes
Cardiac region
◦ Cardioesphageal
sphincter
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Fundus
Body
Pylorus
◦ Pyloric sphincter
Stomach
Rugae
 Greater curvature
 Lesser curvature
 Lesser omentum
 Greater omentum
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Stomach

Gastric pits
◦ Gastric glands
◦ Gastric juice
Ex: Intrinsic factor
 Chief cells
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◦ pepsinogens
Parietal cells
 Mucous neck cells
 Chyme

Small Intestine
6-13 ft long
 Ileocecal valve
 Duodenum
 Jejunum
 Ileum
 Pancreatic ducts
 Bile duct
 Peyer’s patches

Food Absorption
Microvilli
 Villi
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◦ Lacteal lymphatic
capillary
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Circular folds
Large Intestine
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5 ft
Cecum
Appendix
Colon
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Ascending colon
Transverse colon
Descending colon
Sigmoid colon
Rectum
Anal canal
Accessory Digestive Organs

Salivary glands
◦ Parotid glands
◦ Submandibular glands
◦ Sublingual glands

Saliva
◦ Bolus
◦ Salivary amylase
◦ Lysozyme and IgA antibodies
Accessory Digestive Organs
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Teeth
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Masticate
Deciduous teeth
Permanent teeth
Incisors
Canines
Premolars (bicuspids)
Molars
Teeth Continued
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Crown and Root
Gingiva
Enamel
Neck
Cementum
Periodontal membrane (ligament)
Dentin
Pulp cavity
Pulp
Root canal
Accessory Digestive Organs
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Pancreas
◦ Retroperitoneal
◦ Digestive
enzymes in
alkaline fluid
◦ Endocrine organ
Accessory Digestive Organs
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Liver and Gallbladder
◦ Liver
 4 lobes
 Bile
 Common hepatic duct
◦ Gallbladder
 Cystic duct
 Stores and concentrates bile
Functions of Digestive System
1. Ingestion
 2. Propulsion
 3. Food breakdown: mechanical digestion
 4. Food breakdown: chemical digestion
 5. Absorption
 6. Defecation
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digestion animation
Digestion Reflexes

Mechano/Chemoreceptors triggered by:
◦ Stretch of organ by food
◦ pH of contents
◦ Presence of certain breakdown products
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Activate or Inhibit:
◦ Glands that secrete digestive juices or
hormones
◦ Smooth muscles that mix and propel food
Activities of Mouth, Pharynx, and
Esophagus
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Mouth – mechanical and
chemical digestion
Deglutition (tongue, soft palate,
pharynx, and esophagus)
◦ Buccal phase
◦ Pharyngeal-esophageal phase
FYI: Swallowing can occur while
standing on your head!
Activities of Stomach

Sight, smell, and taste of
food stimulates
parasympathetic reflexes
◦ Gastric juices secreted
◦ Hormone gastrin released
 Makes stomach glands produce
pepsinogens, mucus, and HCl
FYI:You make 2-3 Liters of gastric
juice a day!
Chemistry in the Stomach
HCl makes pepsinogen
pepsin
 Rennin: works on milk protein (only in
infants)
 Hardly any chemical digestion occurs

◦ Aspirin and alcohol are absorbed through
stomach wall
Food Propulsion from Stomach
Chyme is end product
Pylorus only allows liquid and
small particles to pass through
sphincter
 Each contraction squirts 3 ml
of chyme
 Rest is squeezed back into
stomach
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◦ Causing enterogastric reflex
FYI: It usually takes 4 hours for
your stomach to empty, or 6 hours
if meal was high in fat
Activities of Small Intestine
Carb and protein digestion had begun in stomach,
but no fat digestion
 Microvilli make few enzymes
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◦ Brush border enzymes
◦ Hormones:
 Secretin
 Cholecystokinin (CCK)
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Pancreatic juices are enzyme and bicarbonate rich
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Complete digestion of starch
Carry out ½ of protein digestion
Responsible for fat digestoin
Digest nucleic acids
Absorption in Small Intestine

Water and end products absorbed
through intestinal cell plasma membranes
via active transport
◦ Except lipids – absorbed through diffusion
Then to the hepatic portal vein
 By the end of ileum, only water and
indigestible food materials and LOTS of
bacteria
FYI: Takes about 3-6 hours for food to go
through small intestine
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Activities of Large Intestine
Bacteria metabolize and
release gases (methane and
hydrogen sulfide) and some
vitamins
 These gases make feces
smell
 Peristalsis and mass
movements
 Defecation reflex
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PART II:
Nutrition and Metabolism

Major nutrients
◦ Carbohydrates
◦ Lipids
◦ Proteins
Vitamins and minerals
 Water
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Metabolism
Catabolism and
anabolism
 Carbohydrate
metabolism
 Fat metabolism
 Protein metabolism
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Carbohydrate Metabolism
Glucose
ATP
 Cellular
respiration
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◦ Glycolysis, Krebs
cycle, electron
transport chain
Fat Metabolism
Liver
 Fat is broken down
to acetic acid
 Acetic acid is
broken down in
mitochondria to
make ATP, CO2, and
water
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Protein Metabolism
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Proteins are broken down
into amino acids
Cellular uptake
20 amino acids are needed,
8 can’t be made by our cells
(“essential amino acids”)
IF no other energy source is
available, amine groups are
removed as ammonia, and
rest is used by mitochondria
for ATP
Liver’s Role in Metabolism
Used in digestion, detoxifying drugs &
alcohol, degrades hormones, makes
cholesterol, albumin, clotting proteins and
lipoproteins, and METABOLISM
 Blood circulates through, liver grabs
nutrients and macrophages kill pathogens
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Liver
Glycogenesis
 Glycogenolysis
 Gluconeogenesis

Cholesterol

HDL and LDL
Body Energy Balance
Energy intake = heat + work + energy
source
 Rising or falling blood levels of nutrients,
hormones, or body temperature affect
eating behavior
 Psychological factors influence as well
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Metabolic Rate
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Basal metabolic rate
◦ Amount of heat produced when at rest
◦ Influenced by:
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Surface area
Sex
Age
Emotions
Amount of thyroxine
Total metabolic rate
◦ Amount of kilocalories body needs to fuel all
activities
◦ Stays elevated well after exercise
Body Temperature Regulation

Hypothalamus
◦ Heat-promoting mechanisms
 Vasoconstriction
 Shivering
◦ Heat loss mechanisms
 Radiation through skin