01:377:213 Lecture Notes - Lecture 18: Esophagus, Muscularis Mucosae, Smooth Muscle Tissue
13 May 2018
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I. The Pharynx (throat)
A. Muscular tube that starts as nose and goes to neck
B. Serves as a common passageway for food, liquids, and air
C. Pharyngeal muscles cooperate with oral cavity and esophagus to initiate
swallowing process called deglutition
1. Nasopharynx
2. Oropharynx
3. Laryngopharynx (hypopharynx)
D. Three phases of swallowing
1. Buccal phase: starts when bolus is compressed against hard palate.
Tongue retracts which forces bolus into pharynx, helps palatal muscles
elevate soft palate and isolates nasopharynx. voluntary
2. Pharyngeal phase: bolus comes with contacts with posterior pharyngeal
wall. Muscles elevate larynx and folding of epiglottis directs the bolus past
the closed glottis . only takes a second. Goes to esophagus. As it goes to
esophagus breathing ceases
3. Esophageal phase: starts when upper esophageal sphincter opens
a) After passing peristaltic waves push bolus through esophagus. As
it goes towards stomach it goes through lower esophageal
sphincter
II. The Esophagus
A. Hollow muscular tube that transports foods and liquids to the stomach
1. Contains upper and lower esophageal sphincters
2. Posterior to trachea slightly left of midline
3. Empties into stomach
4. Upper and lower aren't distinct by sphincter
a) Upper and lower sphincters are just locations
B. Histology of the Esophageal Wall
1. Wall of the esophagus has mucosa, submucosa, and muscular layers
a) Esophageal wall has several distinctive features
(1) Epithelium is abrasive resistant
(2) Mucosa and submucosa form large folds that run down
esophagus
(a) These folds allow expansion for large bolus
(3) Muscle tone keeps esophagus closed except during
swallowing
(4) Smooth layer of muscularis mucosae is thin or absent near
pharynx, inferiorly it thickens near the junction of stomach
(a) Muscularis mucosae Of esophagus composed of
single layer of longitudinal smooth muscle (diff
than rest of digestive tract)
(5) Submucosa contains scattered esophageal glands
(a) Only One of two regions of digestive tract that has
submucosal glands
(i) Mucus secretion that lubricates bolus and
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protects the epithelial surface
(6) Muscular layer has inner circular and outer longitudinal
layers
(a) Superior 3rd of esophagus, both layers contain
skeletal muscle fibers and some isolated smooth
muscle cells
(b) Middle 3rd even mixture of skeletal and smooth
muscle tissue
(c) Inferior 3rd only smooth muscle cells
(d) Visceral reflexes over contractions
2. Adventitia of connective tissue outside muscle layer anchors esophagus to
the posterior body wall
III. The Stomach
A. The stomach performs three major functions:
1. Temporarily store ingested food
2. Mechanically digest food
3. Chemically digest food through acids and enzymes
a) The end result is the production of chyme
(1) Viscus, acidic, soupy mixture
B. Size varies from person to person
1. Increases at meal, decreases as chyme leaves stomach
C. The muscularis mucosae and muscular layer of the stomach contain extra layers
of smooth muscle cells in addition to usual circular and longitudinal layers
1. Extra layers strengthen wall and assist in mixing and churning
D. The lining of the stomach does not directly absorb any nutrients
1. Some salts, water and lipid soluble substances are indirectly absorbed in
stomach
a) Alcohol and drugs enter the region of mucosa after damaging the
epithelium
b) Enter bloodstream within capillaries
c) EGD- endoscopy of upper gastrointestinal tract
IV. The Small Intestine
A. 90% of nutrient absorption
1. Rest take place in proximal portion of large intestine
B. Averages 20 feet in length, 1.6inches diameter at junction with stomach, 1in at
junction with large intestine
C. Anatomy of the small intestine is specialized to increase its surface area for
absorption and secretion
1. Intestinal lining has series ringed shaped projections called circular folds
a) Each circular fold is a permanent feature as the small intestine fills
b) Around 800 folds
D. Regions of the small intestine
1. Duodenum: shortest and widest. Approx 10 inches long. Mixing bowl
that receives chyme from stomach and digestive secretions from pancreas
and liver. Sharp bend: duodenojejunal flexure
2. Jejunum: 8ft long. Bulk of chemical digestions and nutrient absorption
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Document Summary
Tongue retracts which forces bolus into pharynx, helps palatal muscles elevate soft palate and isolates nasopharynx. voluntary: pharyngeal phase: bolus comes with contacts with posterior pharyngeal wall. Muscles elevate larynx and folding of epiglottis directs the bolus past the closed glottis . only takes a second. As it goes to esophagus breathing ceases: esophageal phase: starts when upper esophageal sphincter opens, after passing peristaltic waves push bolus through esophagus. As it goes towards stomach it goes through lower esophageal sphincter. Mixing bowl that receives chyme from stomach and digestive secretions from pancreas and liver. Sharp bend: duodenojejunal flexure: jejunum: 8ft long. Bulk of chemical digestions and nutrient absorption: ileum: longest 12ft long. Cecum collects and stores materials from ilium and begins process of compaction. Appendix is attached to cecum (3. 6 inches long): organ of lymphatic system. Inflammation of appendix: appendicitis: colon: larger diameter and thinner wall than small intestines, ascending colon, transverse colon, descending colon, sigmoid colon: 6 inches long.
