1. Skeletal muscle deep layer – longitudinal orientation
superficial layer – circular orientation
superior, middle and inferior pharyngeal constrictors

2. Esophagus 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

3. Swallowing

4. Swallowing

5. Swallowing (Deglutition)
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

6. X-ray: Swallowing in Esophagus

7. Stomach
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

8. Gross Anatomy of Stomach
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

9. Gross Anatomy of Stomach
Cardia
Fundus
Body
Pylorus
Notice: bulge of fundus, narrowing of pyloric region, thickness of pyloric sphincter and greater and lesser curvatures

10. Innervation and Circulation
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

11. Gross Anatomy of Stomach

12. Unique Features of Stomach Wall
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

13. Gastric Gland

14. Cells of Gastric Glands
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

15. Opening of Gastric Pit

16. 2 to 3 L of gastric juice/day (H2O, HCl and pepsin)
Gastric Secretions
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)

17. Functions of Hydrochloric Acid
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

18. Gastric Enzymes and 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

19. Production and Action of Pepsin
Zymogen

20. Chemical Messengers 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

21. Gastric Motility 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

22. Vomiting Induced by Emetic center in medulla causes
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