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Skeletal muscle deep layer –

longitudinal orientation

superficial layer – circular orientation superior, middle

and inferior pharyngeal constrictors

Straight muscular tube 25-30 cm long nonkeratinized stratified squamous epithelium esophageal glands in submucosa skeletal muscle in upper part and smooth in bottom

Extends from pharynx to cardiac stomach passing through esophageal hiatus in diaphragm inferior pharyngeal constrictor excludes air from it

Lower esophageal sphincter closes orifice to reflux

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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

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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

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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

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Notice: bulge of fundus, narrowing of pyloric region, thickness of pyloric sphincter and greater and lesser curvatures

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Cardia

Fundus

Body

Pylorus

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

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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

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Mucous cells secrete mucus

Regenerative cells divide rapidly to produce new cells

that migrate to surface Parietal cells

secrete HCl acid and intrinsic factor Chief cells

secrete pepsinogen chymosin and lipase in infancy

Enteroendocrine cells G cells

Make gastrin Others secrete hormones and

paracrine messengers

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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 )

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2 to 3 L of gastric juice/day (H2O, HCl and pepsin)

Activates pepsin and lingual lipase Breaks up connective tissues and plant cell walls

liquefies food to form chyme Converts ingested ferric ions (Fe3+) to ferrous ions (Fe2+)

absorbed and used for hemoglobin synthesis Destroys ingested bacteria and pathogens

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Intrinsic factor essential for B12 absorption by small intestine RBC production (lack causes pernicious anemia)

Pepsin - protein digestion 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

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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

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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

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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

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