packet 19 Flashcards
Funnel-shaped tube extending from internal nares to the esophagus (posteriorly) and larynx (anteriorly)
Skeletal muscle lined by mucous membrane
Deglutition or swallowing is facilitated by saliva and mucus
starts when bolus is pushed into the oropharynx
sensory nerves send signals to deglutition center in brainstem
soft palate is lifted to close nasopharynx
larynx is lifted as epiglottis is bent to cover glottis
pharynx
Collapsed muscular tube In front of vertebrae Posterior to trachea Posterior to the heart Pierces the diaphragm at hiatus hiatal hernia or diaphragmatic hernia
esophagus
histology of esophagus
mucosa
submucosa
muscularis
adventitia
stratified squamous
mucosa
large mucous gland
submucosa
upper 1/3 is skeletal, middle is mixed, lower 1/3 is smooth
upper & lower esophageal sphincters are prominent circular muscle
muscularis
connective tissue blending with surrounding connective tissue–no peritoneum
adventitia
esophagus swallowing
voluntary and involuntary phase
tongue pushes food to back of oral cavity
voluntary phase
pharyngeal stage
breathing stops & airways are closed
soft palate & uvula are lifted to close off nasopharynx
vocal cords close
epiglottis is bent over airway as larynx is lifted
involuntary phase
Upper sphincter relaxes when larynx is lifted
Peristalsis pushes food down
circular fibers behind bolus
longitudinal fibers in front of bolus shorten the distance of travel
Travel time is 4-8 seconds for solids and 1 sec for liquids
Lower sphincter relaxes as food approaches
swallowing
If lower sphincter fails to open
distension of esophagus feels like chest pain or heart attack
If lower esophageal sphincter fails to close
stomach acids enter esophagus & cause heartburn (GERD)
for a weak sphincter—don’t eat a large meal and lay down in front of TV
smoking and alcohol make the sphincter relax worsening the situation
Control the symptoms by avoiding
coffee, chocolate, tomatoes, fatty foods, onions & mint
take Tagamet HB or Pepcid AC 60 minutes before eating
neutralize existing stomach acids with Tums
Gastroesophageal Reflex Disease
large sausage stretches due to rugae Parts of stomach cardia fundus---air in x-ray body pylorus---starts to narrow as approaches pyloric sphincter Empties as small squirts of chyme leave the stomach through the pyloric valve
stomach
Hydrochloric acid converts pepsinogen from chief cell to pepsin
Intrinsic factor
absorption of vitamin B12 for RBC production
Gastrin hormone (g cell)
“get it out of here”
release more gastric juice
increase gastric motility
relax pyloric sphincter
constrict esophageal sphincter preventing entry
Mucosa & Gastric Glands
Three layers of smooth muscle–outer longitudinal, circular & inner oblique
Permits greater churning & mixing of food with gastric juice
muscularis
Gentle mixing waves
every 15 to 25 seconds
mixes bolus with 2 quarts/day of gastric juice to turn it into chyme (a thin liquid)
More vigorous waves
travel from body of stomach to pyloric region
Intense waves near the pylorus
open it and squirt out 1-2 teaspoons full with each wave
mechanical digestion
Protein digestion begins
HCl denatures (unfolds) protein molecules
HCl transforms pepsinogen into pepsin that breaks peptides bonds between certain amino acids
Fat digestion continues
gastric lipase splits the triglycerides in milk fat
most effective at pH 5 to 6 (infant stomach)
HCl kills microbes in food
Mucous cells protect stomach walls from being digested with 1-3mm thick layer of mucous
chemical digestion in stomach
Regulation of Gastric Secretion and Motility
Cephalic phase
Gastric phase
Intestinal phase
***note on test as micro essay–describe 3 phases
preperation
Cerebral cortex =sight, smell, taste & thought
stimulate parasympathetic nervous system
Vagus nerve
increases stomach muscle and glandular activity
Thinking of tonight’s dinner, perhaps????
cephalic phase
Working
Nervous control keeps stomach active
stretch receptors & chemoreceptors provide information
vigorous peristalsis and glandular secretions continue
chyme is released into the duodenum
Endocrine influences over stomach activity
distention and presence of caffeine or protein cause G cells secretion of gastrin into bloodstream
gastrin hormone increases stomach glandular secretion
gastrin hormone increases stomach churning and sphincter relaxation
gastric phase
emptying
Stretch receptors in duodenum slow stomach activity & increase intestinal activity
Distension, fatty acids or sugar signals medulla
sympathetic nerves slow stomach activity
Hormonal influences
secretin hormone decreases stomach secretions
cholecystokinin(CCK) decreases stomach emptying
gastric inhibitory peptide(GIP) decreases stomach secretions, motility & emptying
intestinal phase
