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Lecture 19
Digestive System
General Anatomy
 Divisions
o Digestive ________________
 Muscular tube extending from the mouth to the anus
 Includes the oral cavity, pharynx, esophagus, stomach, small
intestine, and large intestine
o Accessory organs
 The teeth, tongue, salivary glands, ____________, gallbladder, and
pancreas
 Walls of the digestive tract
o Layers
 __________________ – innermost layer that lines the lumen
 Epithelium – simple columnar in most of the tract
 Lamina propria – loose connective tissue layer
 Muscularis mucosa – thin layer of smooth muscle
 Submucosa – loose connective tissue
 Contains blood vessels, lymphatic vessels, a nerve plexus,
and __________________ glands
 Muscularis externa – Consists of two layers of smooth muscle near
the outer surface
 _____________________ layer – consists of the inner
layer which encircles the tract
 Longitudinal layer – consists of the outer layer which runs
the length of the intestine
 Serosa – consists of a thin layer of areolar tissue topped by a
simple squamous mesothelium
Relationship to the Peritoneum
 The peritoneum is a __________________ membrane that lines the peritoneal
cavity of the abdomen and covers the mesenteries and viscera
o Organs that are within the peritoneal cavity are intraperitoneal
o Organs dorsal to the peritoneum are _________________________
 The mesenteries are serous membranes the bind the intestines together and
suspend them from the abdominal wall
 The lesser omentum is a membrane that extends from the stomach to the liver
 The ______________________ omentum is a membrane that extends from the
stomach and loosely covers the intestines like an apron
o It extends down the abdomen and then turns back on itself and passes
upward, forming a pouch
The Mouth through the Esophagus
 The oral cavity – the mouth
o The cheeks –the ______________________ limits of the mouth
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o The tongue – the muscular organ that aids in food intake, detects food,
manipulates food, and initiates swallowing
o The __________________ – the wall that separates the oral cavity from
the nasal cavity (it allows us to breathe through the nose while chewing)
 Hard palate – supported by palatine process of the maxillae and
palatine bones
 Soft palate – posterior to the hard palate, composed of muscle, but
no bone
o The teeth –
 _______________________ dentition – Our teeth don’t all have
the same shape
 Incisors – chisel-like cutting teeth used to bite off a piece of
food
 Canines – pointed teeth that act to puncture and shred food
o Act as weapons in many mammals
 Premolars and Molars – have broad surfaces for
___________________ and grinding
 Diphyodont dentition – We have ____________ sets of teeth in a
lifetime
 Deciduous teeth – baby teeth erupt from the age of 6 to 30
months
 Permanent teeth – replace deciduous teeth between 6 and
25 years of age
 Teeth layers –
 Alveolus – tooth socket
 Periodontal ligament – ____________________ fibers that
anchor the tooth
 Cementum – outermost layer of the root
 Dentin – hard yellowish tissue deep in the tooth
 _____________________- – outermost layer of the crown
(above the root)
 Pulp cavity – space within the tooth containing loose
connective tissue, blood vessels, and nerves
The salivary glands
o Parotid gland – anterior and inferior to the ear
 Over the ____________________ muscle
 Largest of the salivary glands
o Submandibular gland – medial to the margin of the mandible
o Sublingual gland – located in the __________________ of the mouth
The pharynx
o Regions covered in lecture 17
o Has constrictors that push food to the _________________________
The esophagus
o Straight muscular tube dorsal to the trachea, leading to the stomach
o Mucosa has esophageal glands that secrete lubricating mucus
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The Stomach
 Muscular sac in the upper left region of the abdominal cavity just below the
______________________
 Functions
o It stores food (expanding from 50 ml to up to 4 L)
o It mechanically breaks up food particles
o It begins ___________________ digestion, producing a mixture of semidigested food called chyme
 Curvatures:
o Lesser curvature – short distance between esophagus and intestines
o _______________________ curvature – longest distance between
esophagus and intestines
 Regions:
o Cardia– small area within about 3 cm of the esophagus
o Fundus – dome-shaped portion superior to the esophageal attachment
o _________________ – the largest portion of the stomach
o Pylorus –funnel-shaped portion that connects to the intestines
 Microscopic anatomy:
o Innermost layer (mucosa) has simple columnar glandular epithelium
o The mucosa has depressions called gastric ___________
o Surrounding the gastric pits are gastric ______________ of various types
 Mucous cells secrete mucus
 _________________ cells secrete hydrochloric acid
 Chief cells secrete pepsinogen
The small intestine
 Gross anatomy
o Regions:
 Duodenum – first 10 inches
 Begins at the pyloric valve, forms an arc around the head of
the ________________________
 Internally, it has spiral ridges called circular folds that
cause the chyme to move slowly and cause more contact
with the mucosa
 It receives and mixes the stomach contents, pancreatic juice
(from the pancreas), and _______________ (from the gall
bladder and liver)
 Jejunum – next 8 feet
 Begins at the dudenojejunal flexure
 Has large, tall, closely-spaced circular folds
 It has relatively __________________ and muscular walls
and a rich blood supply
 Ileum – last 12 feet of small intestine (note the spelling - not
“ilium”)
 It has __________________, less-muscular walls than the
jejunum
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It has prominent lymphatic nodules in clusters called Peyer
patches
It is connected to the first part of the large intestine (the
cecum) at the ileocecal valve
Microscopic anatomy
o To increase surface area there are three kinds of folds or projections
 ____________________ folds - spiral ridges that slow the path of
food and increase surface area by a factor of 2 or 3
 Villi – finger-shaped projections about .5 to 1 mm high that give
the mucosa a ___________________ appearance (like a terrycloth
towel)
 The increase surface area by a factor of 10
 Microvilli – Each cell of a villus has a fuzzy brush border of
microvilli and 1 m high
 This wrinkling of the cell membrane increases the surface
area by a factor of ___________
The Large Intestine
 The large intestine is about 6 feet long and 2.5 inches in __________________
(it’s larger in diameter than the small intestine)
 Regions:
o ___________________
 Blind pouch at the beginning of the large intestine that connects to
the ileum (at the ileocecal valve)
 Attached to the cecum is the appendix – a blind tube about 5 cm
long
 It contains lymphocytes and plays an important role in the
immune system
 In herbivorous vertebrates, the cecum and appendix are
filled with _________________ that digest plant fiber
o Colon
 Ascending Colon – extends up on the right side of the abdominal
cavity
 Transverse Colon – extends from right to left
 ___________________ Colon – extends down the left side of the
abdominal cavity
 Sigmoid Colon – S-shaped portion that directs waste medially and
downward
 Other Structures –
 Taneae coli are distinct muscle bands that run the length of
the large intestine
 Haustra are a series of bulges in the walls of the intestine
 Epiploic appendages are small but numerous fat-filled
pouches that are attached superficially to the taeniae coli
o ____________________
 Sends waste downward through the pelvic cavity (about 15 cm)
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o Anal Canal
 The last 3 cm of the rectum
 Secretes extra mucus which lubricates the canal during defecation
Accessory Glands of Digestion
 The liver
o Reddish brown organ under the diaphragm
o In addition to performing other functions, it produces _____________
 Bile is a fluid containing minerals, cholesterol, neutral fats,
phospholipids, and bile acids
 Bile emulsifies fat to improve fat digestion
o Gross Anatomy
 It has four lobes
 _______________ lobe – Superior and largest lobe
 Left lobe – Superior lobe; smaller than right lobe
 Caudate lobe – Inferior lobe, posterior (near vena cava)
 ________________ lobe – Inferior lobe, anterior, 4-sided
(near gall bladder)
o Microscopic Anatomy
 The interior of the liver contains hepatic lobules
 Each lobule contains a central vein passing through its core
 The lobule consists of plates of cells called hepatocytes
 The plates have blood-filled chambers called hepatic sinusoids
 The ______________________ secrete bile into bile canaliculi
 Bile canaliculi lead to bile ductules
 Bile ductules lead to hepatic ducts
 Bile moves towards the periphery of the lobule
 Blood flows into the liver from two sources:
 Hepatic _______________ vein
 Hepatic artery
 Blood flows from these sources from the periphery into the hepatic
sinusoids
 The hepatocytes process the blood, and the blood collects in the
_______________ vein in the center of the lobule
 Blood from the central veins converges in the hepatic veins
which empty into the inferior vena cava
 The gallbladder and bile passages
o The liver produces bile, which then travels to the gallbladder
o The gallbladder is a pear-shaped sac on the underside of the liver
 It stores and concentrates bile
o The neck of the gallbladder leads to the _________________ duct
o The cystic duct combines with the common bile duct to carry bile to the
duodenum through the common bile duct
 The Pancreas
o Ninety percent of the pancreas is exocrine tissue
o This tissue has a system of branching ducts
 The finest branches end in sacs of secretory cells called acini
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The smaller ducts converge on a main _______________________
duct
The pancreatic duct runs lengthwise through the pancreas and joins
the bile duct at the duodenum
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