
Skeletal muscle


deep layer –
longitudinal
orientation
superficial layer –
circular
orientation
 superior, middle
and inferior
pharyngeal
constrictors
25-1

Straight muscular tube 25-30 cm long




Extends from pharynx to cardiac stomach passing
through esophageal hiatus in diaphragm


nonkeratinized stratified squamous epithelium
esophageal glands in submucosa
skeletal muscle in upper part and smooth in bottom
inferior pharyngeal constrictor excludes air from it
Lower esophageal sphincter closes orifice to reflux
25-2
25-3
25-4


Series of muscular contractions coordinated by
centers in the brain
Buccal phase


tongue collects food and pushes it back into oropharynx
Pharyngeal-esophageal phase



soft palate rises and blocks nasopharynx
infrahyoid muscles lift larynx; epiglottis folded back
pharyngeal constrictors push bolus down esophagus
 liquids in 2 seconds -- food bolus may take 8 seconds
 lower esophageal sphincter relaxes
25-5
25-6

Mechanically breaks up food, liquifies food and begins
chemical digestion of protein and fat


resulting soupy mixture is called chyme
Does not absorb significant amount of nutrients

absorbs aspirin and some lipid-soluble drugs
25-7

Muscular sac (internal volume from 50ml to 4L)
J - shaped organ with lesser and greater curvatures
 regional differences






cardiac region just inside cardiac orifice
fundus - domed portion superior to esophageal opening
body - main portion of organ
pyloric region - narrow inferior end
 antrum and pyloric canal
Pylorus - opening to duodenum

thick ring of smooth muscle forms a sphincter
25-8
Cardia
Fundus
Body
Pylorus

Notice: bulge of fundus, narrowing of pyloric region, thickness
of pyloric sphincter and greater and lesser curvatures
25-9

Innervation by
parasympathetic fibers from vagus
 sympathetic fibers from celiac plexus


All blood from stomach enters hepatic portal
circulation and is filtered through liver before
returning to heart
25-10
25-11

Mucosa



simple columnar glandular epithelium
lamina propria is filled with tubular glands (gastric pits)
Muscularis externa has 3 layers

outer longitudinal, middle circular and inner oblique layers
25-12
25-13

Mucous cells


Regenerative cells


secrete HCl acid and intrinsic factor
Chief cells



divide rapidly to produce new cells
that migrate to surface
Parietal cells


secrete mucus
secrete pepsinogen
chymosin and lipase in infancy
Enteroendocrine cells

G cells
 Make gastrin

Others secrete hormones and
paracrine messengers
25-14
25-15

Parietal cells contain carbonic anhydrase (CAH)
CO2 + H2O  H2CO3  HCO3- + H+
 H+ is pumped into stomach lumen by H+K+ATPase
  HCO3- in blood causes alkaline tide (blood pH )

2 to 3 L of gastric juice/day
(H2O, HCl and pepsin)
25-16


Activates pepsin and lingual lipase
Breaks up connective tissues and plant cell walls


Converts ingested ferric ions (Fe3+) to ferrous ions (Fe2+)


liquefies food to form chyme
absorbed and used for hemoglobin synthesis
Destroys ingested bacteria and pathogens
25-17

Intrinsic factor



Pepsin - protein digestion



essential for B12 absorption by small intestine
RBC production (lack causes pernicious anemia)
secreted as pepsinogen (inactive)
HCl converts it to pepsin (active)
Gastric lipase and chymosin
lipase digests butterfat of milk in infant
 chymosin curdles milk by coagulating proteins

25-18
25-19

Many produced by enteroendocrine cells
hormones enter blood  distant cells
 paracrine secretions  neighboring cells


Gut-brain peptides

signaling molecules produced in digestive tract and
CNS
25-20


Swallowing center signals stomach to relax
Food stretches stomach activating a receptive-relaxation
response


resists stretching briefly, but relaxes to hold more food
Rhythm of peristalsis controlled by pacemaker cells in
longitudinal muscle layer
gentle ripple of contraction every 20 seconds churns and mixes
food with gastric juice
 stronger contraction at pyloric region; ejects 3 ml
 typical meal emptied from stomach in 4 hours

25-21

Induced by


excessive stretching of stomach, psychological
stimuli or chemical irritants (bacterial toxins)
Emetic center in medulla causes

retching
 lower esophageal sphincter to relax
 stomach and duodenum to contract spasmodically

vomiting
 when abdominal contraction forces upper esophageal
sphincter to open
25-22
25-23