Exam 4: Digestive System Flashcards
functions of the digestive system
5 primary, 2 associated
primary:
-ingestion, movement of food, digestion (mechanical and chemical), absorption, and excretion
associated:
-immune defense, endocrine secretions
composition of the digestive system
alimentary canal (digestive tract) - tube within a tube accessory organs: tongue, teeth, salivary glands, liver, gallbladder, pancreas
lumen of alimentary canal considered functionally external to the body
histology layers (4)
mucosal
submucosa
muscularis externa
serosa/adventitia
mucosal layer
-mainly epithelium - changes
depending on where you are
-basement membrane supporting it: lamina propria
-muscularis mucosa: muscle layer around, shape and secretions in layer
epithelium in stomach, esophagus, intestine, rectum
stomach: columnar cells
esophagus: non keratinized stratified squamous
intestine: villi in columnar
rectum: nonkeratinized stratified squamous
submucosa layer
dense, irregular connective tissue that supports the glands and blood vessels
muscularis externa layer
circular muscle and longitudinal muscle
work together to give peristalsis waves
-circular would constrict and longiudinal would push it along
serosa/adventitia layers
serosa: stomach and intestines, serous membranes that lubricate and protect, secretes fluid to avoid rubbing
adventitia: pharynx, esophagus, rectum
protective CT layer - no serous secretions, in places where no rubbing should occur
enteric plexus - autonomic nervous system
parasympathetic: inc muscle activity, tone, gland secretions
sympathetic: dec all activity - directs blood flow to skeletal muscle
stress can cause GI distress
enteric plexus is formed by 2 separate plexuses
submucosa and myenteric
submucosa plexus
contains stretch and chemical receptors
controls shape of mucosa ad degree of secretion
-closer to the lumen, sensitive to what moves through lumen
myenteric plexus
located between circular and longitudinal muscle layers
controls paristalsis
-faster if higher motility, slower if you want to process food slowly
oral cavity components and functions
components: tongue, teeth, gingiva, tonsils
receives secretions from salivary glands
site of mastication (chewing)
beginning of chemical digestion
dentition - adult
adult: 2,1,2,3/2,1,2,3 x2
2 incisors, 1 canine, 2 premolars, 3 molars
long roots
dentition-deciduous/baby teeth
2,1,2/2,1,2 x 2
short roots
only 3 types of teeth - no premolars
tooth anatomy - regions
root: embedded in bone
- well into alveolar process of mandible or maxilla
neck: protected by gum tissue
- sensitive to decay since not well protected by crown
crown: external surface
- strong and protective, enamel
root canal
contains pulp (blood vessels and nerve)
- of decay in this you can get abscess bacteria in bloodstream
- if infected may have to get a root canal - they remove the pulp
dentin
- secretory cells in channels
- cells secrete cementin to attach to socket
- produce periodontal ligaments
- matrix similar to bone by higher % of hydroxyapatite
- if lose a tooth you lose the stimulation to alveolar process area and can lose bone mass
enamel
hardest substance in body (97% hydroxyapatite)
cells degenerate after production
-important to keep enamel healthy, if it wears away you get access to dentin and can get cavities
why is saliva produced? (3)
chemical digestion
lubrication of food
defense of oral cavity
saliva composition
water electrolytes and buffer mucins- lubrication of food antibodies (IgA) enzymes
types of salivary enzymes (2)
salivary amylases: begins carbohydrate digestion
lingual lipase: begins lipid digestion
both inactived in stomach acid environment
functions of tongue and ulva
tongue: positions food, aids in forming bolus, contains taste buds
ulva: prevents food from entering nasopharynx
3 phases of deglutition
both voluntary and involuntary reflex
buccal phase, pharyngeal phase, esophageal phase
buccal phase of deglutition
1st phase
tongue compresses bolus against hard palate and begins to move bolus back (voluntary!!)
pharyngeal phase of deglutition
2nd phase
tongue depresses and moves bolus into oropharynx contacting pharyngeal arches (now INVOLUNTARY action begins!!)
larynx lifts as epiglottis closes glottis
upper esophageal sphincter opens
esophageal phase of deglutition
3rd phase
bolus enters esophagus and peristalsis takes over
upper esophageal sphincter closes
larynx returns to position with glottis open
breathing can resume
esophagus
moves bolus though peristalsis
nonkeratinized startified squamous of mucosa does not have goblet cells
2 extra layers of lubrication and protection for esophagus
submucosal glands: secrete mucus in upper part of esophagus, lubricates esophageal lining
cardiac glands: in lamina propria of esophogastric junction
- protects lower esophagus from reguritated acidic gastric secretions
- pyrosis (heart burn, acid reflux) occurs when secretions overwhelmed
regions of the stomach
4 or 5
-cardac
-fundus (collects gas)
-body: most digestion in stomach here, rugae
-pyloric region: where chyme getting ready to leave stomach
can be divided in 2: antrum: till mixing wih gastric secretion and pyloric canal: getting ready to go into SI
the environment of the adult stomach is maintained at a pH between
1.5 and 2
digestive action of the stomach
- bolus enters, subjected to peristaltic waves that mix the food with mucous secretions in fundus forming chyme. salivary digestion continues
- stretch receptors stimulate G-cells to release gastrin
- gastrin activates chief and parietal cell secretions
- chief cells release pepsinogen
- HCl from parietal cells activates pepsinogen to form pepsin pH 2
- Parietal cells release intrinsic factor to bind V B12
- inc gastrin results in inc stomach motility
- chyme mixes with gastric secretions
what do stretch receptors stimulate
G cells to release gastrin
what does gastrin activate
chief and parietal cells
chief cells release
pepsinogen
what does HCl from parietal cells activate
pepsinogen to pepsin pH2
what to parietal cells release
intrinsic factor to vitamin B12
what enters the bloodstream during a large meal due to inc stimulation of parietal cells
alkaline tide
chloride shift, bicarb going out , makes you tired
stomach action in an infant
can only get a pH of 5
modified chief cell secretions:
- renin released- in presence of Ca, acts on casein protein in milk to form curds
alpha and beta stay soluble due to kappa
renin breaks kappa - not soluble, curds
- gastric lipase: digests milk fat
- both secretions optimal at pH 5
3 phases in stomach response
cephalic, gastric, intestinal
cephalic phase - stomach response
gastric secretions begin in response to thinking, smelling or seeing food - have not ingested yet
gastric phase- stomach response
- stretch receptors directly trigger G cells and indirectly trigger parietal and chief cells
- chemoreceptors monitor pH level (can be stimulated by anxiety, caffeine)
intestinal phase - stomach response
- regulation of stomach emptying
- stretch receptors result in CCK and GIP release
CCK
stimulates pancreatic and gallbladder secretions
GIP
stimulates pancreas and slows motility of stomach in response to high fat meals
