GI Tract Part 1 Flashcards
what does the alimentary canal extend from
oral cavity to anus
what are the 5 phases that breakdown of food occurs in
ingestion, fragmentation, digestion, absorption, elimination
what phases of food breakdown occurs in the oral cavity
ingestion and fragmentation resulting in bolus formation
what phases of food breakdown occurs in the stomach
fragmentation and initiates digestion
what is peristalsis and what type of innervation is it
contractions of smooth muscle under autonomic control
what do duodenum, pancreatic and biliary secretions do
emulsification of fat
where does the primary absorption of nutrients occur
jejunum and ileum
what phases of food breakdown occur in the colon
resorption of water and elimination of waste
what is the gut
a muscular tube lined by mucus membrane
what are the 4 distinct layers of the GI tract
mucosa, submucosa, muscularis externa and adventitia
what are the 3 functions of the mucosa
protection, secretion and absorption
what are. the 3 layers of the mucosa
epithelium, lamina propria and muscularis mucosae
what are the functions of the epithelium in the mucosa
secretory and absorptive functions
what is the lamina propria and what does it contain
underlying CT, contains lymphoid nodules, glands, blood vessels and lymphatics
what is the muscularis mucosae
-thin layer of smooth muscle, boundary between mucosa and submucosa
what is the submucosa
loose to dense irregular CT layer beneath muscularis mucosae
what does the submucosa contain
larger blood vessels, nerves and lymphatics
what are the 2 layers of the muscularis externa
inner circular layer and outer longitudinal smooth muscle layers
describe how the muscle fibers of the inner circular layer and the outer longitudinal layer are oriented to each other
at right angles
what does segmentation do
local contractions that result in mixing of food occurring proximally and distally
what does peristalsis do
propels food distally only (aborally)
what is the adventitia and what does it contain
outer loose CT layer, contains major nerves, vessels, and adipose tissue
what is the adventitia referred to within the abdominal cavity
serosa or visceral peritoneum
what is the adventitia continuous with
the supporting mesentary
what is the adventitia lined with
simple squamous epithelium (mesothelium)
what does the adventitia merge with in some areas
retroperitoneal tissue
what is the result of parasympathetic stimulation in the gut
excitatory
what is the result of sympathetic stimulation in the gut
inhibitory
where do parasympathetic motor nerves synapse in the GI tract
with ganglia located within submucosa and muscularis externa
what are clusters of parasympathetic ganglia within submucosa called
Meissner’s plexus or submucosal plexus
what are large clusters located between inner circular and outer longitudinal muscle layers called
myenteric or Auerbach’s plexus
describe the esophagus
short muscular tube lined by stratified squamous nonkeratinized epithelium
in the upper third of the esophagus what is the muscularis externa composed of
voluntary skeletal muscle
in the middle third of the esophagus what is the muscularis externa composed of
skeletal muscle and smooth muscle
in the lower third of the esophagus what is the muscularis externa composed of
smooth muscle only
what does the gastro-esophageal junction between the esophagus and the stomach contain
gastroesophageal sphincter
what is pyrosis and what is its cause
heartburn, due to regurgitation of stomach acid into distal esophagus from cardia of stomach
what are the regions of the stomach
cardia, fundus, and pylorus
what is the cardia surrounded by
smooth muscle cardiac sphincter
what does the cardiac sphincter contain
mucus secreting glands
what is another name for the cardiac sphincter
gastroesophageal sphincter
what is the fundus and what does it secrete
glandular portion of stomach; secretes acid, pepsin and some mucus
what is another name for the body of the stomach
corpus
what does the pylorus contain
primarily mucus and gastrin secreting glands
what is the pyloric sphincter made of and what does it control
made of smooth muscle and controls the outflow from stomach into duodenum
what happens in peptic/gastric ulcer
loss of stomach/duodenal epithelium/mucosa
where does damage extend to in an ulcer
below level of basement membrane which results in bleeding
where does damage extend to in erosion
partial loss of epithelium which does not result in bleeding
how are peptic/gastric ulcers treated
with antacids
what are ulcers frequently associated with
chronic infection with helicobacter pylori
what does helicobacter pylori produce
urease which increases gastric pH which increases acid production
how are ulcers associated with helicobacter pylori treated
with triple therapy- 2 long term antibiotics and proton pump inhibitor
how does food undergo mechanical breakdown in the stomach
via muscular activity
how does food undergo chemical breakdown in the stomach
via gastric secretions to form chyme
what is the third layer of the muscularis externa in the stomach called
inner oblique
what is absorbed in the stomach
little absorption occurs except water, alcohol and some drugs such as aspirin
what are the prominent longitudinal folds in the stomach lining called
rugae
what does the mucosa in the glandular body of the stomach contain
gastric pits
what do gastric pits form the entrance to
gastric glands
describe gastric glands
straight, tubular glands
what does gastric juice contain
HCl, pepsinogen, gastrin, rennin, lipase
what is pepsinogen and what does it do
inactive precursor of pepsin that hydrolyzes protein
what is pepsinogen converted to pepsin by
action of HCl
what is the mucosa of the stomach protected by
thick layer of mucus
what are the 5 types of cells in gastric glands
mucus secreting cells, surface mucus cells, mucus neck cells, acid secreting cells, pepsin secreting cells
where are mucus secreting cells found
cover luminal surface and upper third of pit
what do surface mucus cells secrete and where are they located
secrete thick, insoluble mucus and bicarbonate ions; located on surface
what do mucus neck cells secrete and where are they located
secrete soluble mucus, located in upper third of pit, at neck of gastric gland
what is another name for acid secreting cells
parietal cells
what do acid secreting cells do
secrete HCl and intrinsic factor
what is intrinsic factor necessary for
absorption of Vitamin B12 from ileum
where are acid secreting cells most numerous and what color do they stain
in middle third of gland and stain pink to purple
what is another name for pepsin secreting cells
chief cells
what do pepsin secreting cells secrete and where are they located
secrete inactive pepsinogen and located at the base of gland (bottom third)
what color do pepsin secreting cells stain and why
purple due to large numbers of ribosomes
what color do mucus secreting cells stain on H and E
clear
how often are mucus secreting cells renewed
3-7 days
how often are parietal and chief cells replaced
every year
what are parietal and chief cells controlled by
autonomic nervous system and hormones from endocrine cells in region of pylorus
what does APUD cells stand for
amine precursor uptake and decarboxylation
what are enteroendocrine cells
paracrine cells
what do enteroendocrine cells do
secrete variety of peptide hormones such as gastrin and secretin in response to local factors
- control GI motility and gastric secretion
what secretes gastrin and what does it do
secreted by G cells, stimulates secretion of HCl and pepsin
what secretes somatostatin and what does it do
secreted by D cells and inhibits secretion of gastrin
what secretes secretin and what does it do
secreted by S cells and inhibits gastric secretion and stimulates smooth muscle contraction
where are undifferentiated stem cells located
in the neck of gland
what is the main function of the small intestine
primary site of absorption and digestion
what are the relative lengths of small intestine
ileum> jejunum> duodenum
what are plica circulares and where are they located
valve like folds/rings in the mucosa and submucosa throughout the small intestine
what is the function of plica circulares
increase surface area and contain submucosal core
what is the mucosal surface made up of and what is its core
made of villi that have a core of lamina propria
what are between the villi
crypts of lieberkuhn
what is coeliac disease and what happens
gluten enteropathy that causes villus blunting and atrophy resulting in malabsorption and weight loss
what is the epithelium supported by and what does it contain
supported by connective tissue lamina propria, containing capillaries and lymphatics for absorption of nutrients
what are intestinal villi lined by
simple columnar epithelium
what are mucosal cells of the small intestine called
enterocytes
what is the brush border
apical/luminal surface highly folded, modified into microvilli
what is the function of the brush border
increased surface area for absorption coated with protected glycocalyx of disaccharides
what is the site of membrane digestion at the brush border
glycocalyx of disaccharides
