Download Lecture 19

Lecture 19
General Anatomy
 Divisions
o Digestive tract
 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, liver, gallbladder, and pancreas
 Walls of the digestive tract
o Layers
 Mucosa – 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 mucous glands
 Muscularis externa – Consists of two layers of smooth muscle near
the outer surface
 Circular 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 serous 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 retroperitoneal
 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 greater 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 lateral limits of the mouth
o The tongue – the muscular organ that aids in food intake, detects food,
manipulates food, and initiates swallowing
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o The palate – 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 –
 Heterodont 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 crushing
and grinding
 Diphyodont dentition – We have two 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 – collagen fibers that anchor the tooth
 Cementum – outermost layer of the root
 Dentin – hard yellowish tissue deep in the tooth
 Enamel – 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 masseter muscle
 Largest of the salivary glands
o Submandibular gland – medial to the margin of the mandible
o Sublingual gland – located in the floor of the mouth
The pharynx
o Regions covered in lecture 17
o Has constrictors that push food to the esophagus
The esophagus
o Straight muscular tube dorsal to the trachea, leading to the stomach
o Mucosa has esophageal glands that secrete lubricating mucus
The Stomach
 Muscular sac in the upper left region of the abdominal cavity just below the
diaphragm
 Functions
o It stores food (expanding from 50 ml to up to 4 L)
o It mechanically breaks up food particles
o It begins chemical digestion, producing a mixture of semi-digested food
called chyme
 Curvatures:
o Lesser curvature – short distance between esophagus and intestines
o Greater 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 Body – 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 pits
o Surrounding the gastric pits are gastric glands of various types
 Mucous cells secrete mucus
 Parietal 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 pancreas
 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 bile (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 thick and muscular walls and a rich blood
supply
 Ileum – last 12 feet of small intestine (note the spelling - not
“ilium”)
 It has thinner, less-muscular walls than the jejunum
 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
 Circular folds - spiral ridges that slow the path of food and
increase surface area by a factor of 2 or 3
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Villi – finger-shaped projections about .5 to 1 mm high that give
the mucosa a fuzzy appearance (like a terrycloth towel)
 They 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 20
The Large intestine
 The large intestine is about 6 feet long and 2.5 inches in diameter (it’s larger in
diameter than the small intestine)
 Regions:
o Cecum
 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 bacteria 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
 Descending 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 Rectum
 Sends waste downward through the pelvic cavity (about 15 cm)
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
 Bile is a fluid containing minerals, cholesterol, neutral fats,
phospholipids, and bile acids
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 Bile emulsifies fat to improve fat digestion
o Gross Anatomy
 It has four lobes
 Right lobe – Superior and largest lobe
 Left lobe – Superior lobe; smaller than right lobe
 Caudate lobe – Inferior lobe, posterior (near vena cava)
 Quadrate 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 hepatocytes 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 portal 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
central 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 cystic 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
 The smaller ducts converge on a main pancreatic duct
 The pancreatic duct runs lengthwise through the pancreas and joins
the bile duct at the duodenum