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THE
DIGESTIVE
SYSTEM

These notes will help you demonstrate your ability to microscopically and macroscopic identify,
recognize, illustrate and label correctly the different tissue types of the digestive system
...
I will link the textbook and you can have a
look at it to get a more detailed explanation of everything 

FUNCTIONS OF THE DIGESTIVE SYSTEM
•Ingestion—taking in food
•Digestion—breaking food down both physically and chemically
•Absorption—movement of nutrients into the bloodstream
•Defecation—rids the body of indigestible waste

ORGANS OF THE DIGESTIVE SYSTEM
•Two main groups of organs
•Alimentary canal (gastrointestinal tract)—continuous coiled hollow tube
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The organs of the alimentary canal are:
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Mouth
Pharynx
Oesophagus/Esophagus
Stomach
Small intestine

 Large intestine
 Anus
•Accessory digestive organs which includes the teeth, tongue, and other large
digestive organs
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•Tonsils
•Palatine tonsils—located at posterior end of oral cavity
•Lingual tonsils—located at the base of the tongue

The mouth is responsible for:

•Mastication (chewing) of food
•Mixing masticated food with saliva
•Initiation of swallowing by the tongue
•Allows for the sense of taste

PHARYNX ANATOMY
•Nasopharynx—not part of the digestive system
•Oropharynx—posterior to oral cavity
•Laryngopharynx—below the oropharynx and connected to the esophagus
 The pharynx serves as a passageway for air and food
 Food is propelled to the esophagus by two muscle layers:
•Longitudinal inner layer
•Circular outer layer
 Food movement is by alternating contractions of the muscle layers (peristalsis)

ANATOMY AND PHYSIOLOGY OF THE PHARYNX
Anatomy
•About 10 inches long
•Runs from the pharynx to stomach through the diaphragm
Physiology
•Conducts food by peristalsis (slow rhythmic squeezing)
•Passageway for food only (respiratory system branches off after the pharynx)

Layers of Tissue in the Alimentary Canal Organs
Four layers from deep to superficial:
•Mucosa
•Submucosa
•Muscularis externa
•Serosa

MESENTERY
•double layer of peritoneum,
•a sheet of two serous membranes fused back to back that extends to the digestive organs from the
body wall; connecting organs to the dorsal and ventral part of the body wall

PERITONEUM
Functions:
•Hold organs in place,
•sites of fat storages
•provide a route by which circulatory vessels and nerves reach organs in peritoneal cavity
Types:
•visceral peritoneum-covers an organ or viscera
•Parietal peritoneum – lines the body cavities
Peritoneal cavity•slit like potential space
•containing lubrication serous fluid that is secreted by peritoneum
•allows the organs to glide easily along another and along the body walls as they move during
digestion

SPECIALIZED MESENTERIES
 Ligaments:
•ligamentum venosum which is found on the superior part fissure liver and is a cordlike remnant of
ductus venosus of foetus
•The falciform ligament attaches the anterior part of the liver to the anterior abdominal wall and
diaphragm

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

Vertical/ventral mesentery – falciform ligament binds liver to anterior abdominal wall
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Greater omentum – from the greater curvature of the stomach anterior, reflexes backwards
and consists of 4 layers
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It continues to run upwards to the
transvers colon

ANATOMY OF THE STOMACH
•Regions of the stomach

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Cardiac region—near the heart
Fundus—expanded portion lateral to the cardiac region
Body—middle portion
Pylorus—funnel-shaped terminal end

•Rugae—internal folds of the mucosa
•Stomach can stretch and hold 4 L (1 gallon) of food when full
•External regions:
 Lesser curvature—concave medial surface
 Greater curvature—convex lateral surface

LAYERS OF TISSUE IN THE STOMACH
1
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Mucous neck cells—produce a sticky alkaline mucus
Gastric glands—situated in gastric pits and secrete gastric juice
Chief cells—produce protein-digesting enzymes (pepsinogens)
Parietal cells—produce hydrochloric acid
Enteroendocrine cells—produce gastrin
Submucosa
•Just beneath the mucosa
•Soft connective tissue with blood vessels, nerve endings, mucosa-associated lymphoid
tissue, and lymphatics
3
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Serosa
 This is the outermost layer of the wall which contains fluid producing cells
 Visceral peritoneum—outermost layer that is continuous with the innermost layer
 Parietal peritoneum—innermost layer that lines the abdominopelvic cavity

Small Intestine
•The body’s major digestive organ

•Site of nutrient absorption into the blood
•Muscular tube extending from the pyloric sphincter to the ileocecal valve
•Suspended from the posterior abdominal wall by the mesentery
Subdivisions of the Small Intestine
 Duodenum
 Attached to the stomach
 Curves around the head of the pancreas

 Jejunum
 Attaches anteriorly to the duodenum

 Ileum
 Extends from jejunum to large intestine
Three structural modifications that increase surface area:
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


Microvilli—tiny projections of the plasma membrane (create a brush border appearance)
Villi—finger like structures formed by the mucosa
Circular folds (plicae circulares)—deep folds of mucosa and submucosa

Large intestine
Larger in diameter, but shorter in length, than the small intestine

•Extends from the ileocecal valve to the anus
•No villi present
•Goblet cells produce alkaline mucus which lubricates the passage of faeces
•Muscularis externa layer is reduced to three bands of muscle called tineae coli
•These bands cause the wall to pucker into haustra (pocket like sacs)
•Subdivisions:
 Cecum: saclike first part of the large intestine
 Appendix: hangs from the cecum
 Colon:
•Ascending—travels up right side of abdomen
•Transverse—travels across the abdominal cavity
•Descending—travels down the left side
•Sigmoid—S-shaped region; enters the pelvis
 Rectum
 Anal canal

Accessory Digestive Organs
•Teeth
•Salivary glands
•Pancreas
•Liver

•Gallbladder

Teeth
•Function is to masticate (chew) food
•Humans have two sets of teeth
•Deciduous (baby or “milk”) teeth
•A baby has 20 teeth by age two
•First teeth to appear are the lower central incisors
Teeth
•Permanent teeth replace deciduous teeth between the ages
of 6 and 12
•A full set is 32 teeth, but some people do not have wisdom teeth (third molars)
•If they do emerge, the wisdom teeth appear between ages of 17 and 25
Classification of Teeth
•Incisors—cutting
•Canines (eyeteeth)—tearing or piercing
•Premolars (bicuspids)—grinding
•Molars—grinding
Regions of a Tooth
•Crown—exposed part
•Enamel—hardest substance in the body
•Dentin—found deep to the enamel and forms the bulk of the tooth
•Pulp cavity—contains connective tissue, blood vessels, and nerve fibres
•Root canal—where the pulp cavity extends into the root
•Neck- Region in contact with the gum
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Saliva is a mixture of mucus and serous fluids
...
Contains salivary
amylase to begin starch digestion

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