Digestive System - Upper Flashcards
contents of digestive system
oral cavity and alimentary canal:
- esophagus
- stomach
- small and large intestines
- extrinsic glands
describe digestive tract and name the 4 layers
layered hollow tube:
- mucosa
- submucosa
- muscularis externa
- serosa (where continuous w/ mesentery) or adventitia (where fixed to wall of cavity)
function of digestive system
secrete enzymes and hormones that function in digestive process
epithelium of esophagus
stratified squamous nonkeratinized epithelium
glands of esophagus
- esophageal cardiac glands
- esophageal glands proper
esophageal cardiac gland secretion
mucus-secreting
esophageal cardiac gland location
in lamina propria, at top and bottom of esophagus (mainly top), but not super abundant
what are esophageal cardiac glands similar to?
cardiac glands in stomach
esophageal glands proper secretion
primarily mucus secreting, but also some serous cells that secrete lysozyme
esophageal glands proper location
in submucosa
muscularis mucosae
single longitudinal layer of smooth muscle
how does the muscularis externa change as you move proximal to distal in the esophagus?
- upper third = striated, skeletal muscle
- middle third = outer layer of smooth muscle, inner layer of skeletal muscle
- lower third = smooth muscle
function of esophagus
conveys food (bolus) from pharynx to stomach by the peristaltic activity of the muscularis externa
what are the two sphincters in the muscularis externa?
- upper = pharyngoesophageal
- lower = gastroesophageal
overall function of the two sphincters of esophagus
ensures bolus transported in one direction only - toward stomach
function of the upper esophageal sphincter (UES)
initiates swallowing
function of the lower esophageal sphincter (LES)
prevents acid reflux from stomach into esophagus
GERD and cause
gastroesophageal reflux disease - caused by persistent acid reflux
what can acid reflux from stomach into esophagus lead to?
ulceration and dysphagia - ultimately can lead to fibrosis and stricture of the lower esophagus
Barrett’s esophagus
- abnormal growth growth of intestinal-type cells (simple columnar) in the lower esophagus
- more easily injured by stomach acid
what is Barrett’s esophagus a risk factor for?
adenocarcinoma of esophagus
what sex does Barrett’s esophagus present in more?
3x more incidence in males
hiatal hernia
portion of stomach that can move into thoracic cavity
what causes hiatal hernia?
if esophageal hiatus in diaphragm does not close entirely during development
what can result from hiatal hernia?
reflux esophagitis and ulceration - difficulty swallowing and a feeling of a lump in the throat
function of the stomach
acidifies and converts food into viscous fluid called chyme
what does the stomach produce?
digestive enzymes and hormones
rugae
longitudinal folds of the mucosa and submucosa that disappear in distended stomach
describe gastric pits in the different parts of the stomach
deepest in pylorus and shallowest in cardia
what are gastric pits?
entrance to gastric glands
regions of stomach
- cardia
- fundus
- body
- pylorus
cardia
- tubular glands with coiled end
- mucus secreting
fundus
- simple tubular glands
- shallow gastric gland pits
- abundant parietal and chief cells
what section of stomach is the primary contributor to gastric juice?
fundus
body of stomach
similar to fundus
pylorus
- deep gastric pits
- branched glands
- primarily mucus secreting
- occasional parietal cell
- gastrin secreting G cells
lining of gastric mucosa
mucus-producing simple columnar surface lining cells (NOT goblet cells)
lamina propria of gastric mucosa
loose CT containing:
- smooth muscle cells
- lymphocytes
- plasma cells
- mast cells
- fibroblasts
what type of glands does the gastric mucosa contain?
gastric glands
muscularis mucosae of gastric mucosa
- poorly defined inner circular layer
- outer longitudinal layer of smooth muscle
- occasionally an outermost circular layer
contents of gastric mucosa
- epithelium
- lamina propria
- gastric glands
- muscularis mucosae
composition of gastric submucosa
- dense irregular collagenous CT
- fibroblasts
- mast cells
- lymphoid elements
- Meissner’s plexus
composition of gastric muscularis externa
3 layers of smooth muscle:
- incomplete inner oblique
- thick middle circular
- outer longitudinal
which layer of gastric muscularis externa forms the pyloric sphincter?
thick middle circular layer
function of gastric muscularis externa
mixing gastric contents and stomach emptying
what influences rate of stomach emptying?
chyme characteristics:
- viscosity
- pH
- lipid content
- osmolality
- caloric density
gastric serosa
covers the external surface of the stomach
epithelium of fundus and body region
mucus-secreting surface lining cells
parts of gastric glands
isthmus, neck, and base
isthmus of gastric glands
connects gland to the base of a gastric pit
what types of cells do gastric glands have?
parietal, chief. mucous neck, enteroendocrine
-also have regenerative cells
regenerative cells
replace all other cells in the gland, pit and luminal surface - located primarily in neckand isthmus
what do surface-lining simple columnar cells contain?
apically located mucinogen granules
what do surface-lining simple columnar cells secrete?
cloudy, thick, viscous mucus with high bicarbonate content (acid protection) - coats surface epithelium (~100 um thick)
how often are surface lining cells renewed?
every 3-5 days
mucous neck cells location
neck of gastric glands
can mucous neck cells divide?
maybe
mucous neck cell description
- short microvilli
- apical mucous granules
- prominent golgi
- shorter columnar cell than surface lining cells
what do mucous neck cells secrete?
soluble mucous - not as thick as mucus produced by surface lining cells
what induces mucous neck cell secretion?
vagal stimulation
parietal/oxyntic cells description
- pyramidal-shaped cells in upper half of gastric glands
- eosinophilic w/ H&E
- intracellular tubulovesicular system
- many mitochondria
- secretory intracellular canaliculi
function of parietal/oxyntic cells
seecrete HCl and gastric intrinsic factor
what is gastric intrinsic factor and why is it needed?
glycoprotein needed for vitamin B12 absorption in small intestine
intracellular canaliculi of parietal cells
deep invaginations of the apical plasma membrane lined by microvilli
changes to parietal cell when stimulated to secrete HCl
- number of microvilli increase
- complexity of the tubulovesicular system decreases
what stimulates HCl secretion?
ACh and gastrin (APUD cells of pylorus)
how is HCl formed by parietal cells?
H+, K+, and Cl- are pumped into canaliculus and then HCl is formed extracellularly
what event increases effects of ACh and gastrin on parietal cell secretion?
histamine binding to histamine H2 receptor
what cells produce histamine?
enterochromaffin-like cells in lamina propria around gastric glands
what drugs inhibit histamine-dependent acid secretion?
anti-acid drugs like cimetidine (1st generation)
what drugs inactivate acid secretion?
2nd generation drugs - omeprazole - bind to H+, K+-dependent ATPase
describe series of reactions mediated by CA that affects blood and mucous pH on surface
- CO2 absorbed from blood or formed in parietal cells (metabolism) combines w/ OH- to form carbonic acid (requires CA)
- carbonic acid -> HCO3- and H+
- HCO3- diffuses out of cell and is picked up by capillaries
what happens to the HCO3- once it exits the parietal cells?
enters a fenestrated capillary in lamina propria, w/ blood flowing toward surface epithelium -> diffuses into the mucus blanket to increase the pH
chief/zymogenic cells
- pyramidal-shaped cells in lower half of fundic glands
- basophilic w/ H&E
what do chief/zymogenic cells secrete?
- pepsinogen
- rennin and lipase precursors
pepsinogen
precursor of pepsin enzyme
chief/zymogenic cell description
- abundant basally located rER
- supranuclear golgi
- apical secretory granules (zymogen)
enteroendocrine cells
- DNES = diffuse neuroendocrine cells
- also called APUD cells = amine precursor uptake and decarboxylation cells
do all enteroendocrine cells take up amine precursors?
no
number of enteroendocrine cell types
> 12 different cell types that contain small hormone-containing granules
how many hormones does any given enteroendocrine cell secrete?
only one hormone
where are enteroendocrine cells located?
down near base of crypts
what is typical of all cells of the diffuse endocrine system?
numerous small, electron dense granules
gastric juices
- water
- HCl
- mucus
- pepsin
- lipase
- rennin
- electrolytes
what facilitates activation of pepsinogen to pepsin?
very acidic conditions (pH 2.0) - catalyzes partial hydrolysis of proteins
regulation of gastric secretion, in general
affected by neural (vagus n.) and hormonal activity
secretin
- released by cells in duodenum when pH < 4.5
- stimulates pancreatic HCO3- and fluid section
- stimulates chief cells to secrete pepsinogen
gastrin
- G cells in pylorus and duodenal mucosa
- 2 forms: small G17 in pylorus + large G34 in duodenum
- stimulates HCl secretion
somatostatin
- D cells of pylorus and duodenum
- inhibits gastrin release
- indirectly inhibits HCl secretion
gastric inhibitory peptide/ urogastrone
- cells in duodenum and jejunum
- directly inhibit HCl secretion
- stimulate insulin release
what are the two gastric hormones?
cholescystekinin (CCK) and motilin
cholescystekinin
- produced in duodenum and jejunum
- stimulates gallbladder contraction when fat is in small intestine
motilin
-released cyclically (every 90 min) during fasting from cells in upper GI tract
gastritis
gastric mucosal inflammation common in middle-aged and older individuals - may be superficial or affect entire thickness, causing mucosal atrophy
what causes gastritis
often unknown etiology
zollinger-ellison syndrome
patients w/ gastrin secreting tumors have hyperplasia and hypertrophy of fundus + high acid secretion -> stomach ulcers, diarrhea
gastric/peptic ulcers
areas of gastric or duodenal mucosa destroyed by gastric secretions
where are gastric/peptic ulcers commonly found?
in cardiac and pyloric regions and first part of duodenum
causes of gastric/peptic ulcers
- excess HCl secretion
- nervous irritation
- reduced vascular supply
- reduced mucus secretion
- infection (H. pylori)
- NSAIDS
treatment of gastric/peptic ulcers
- antibiotics
- stress management
- elimination of alcohol, aspirin/NSAIDS, and cigarette use
- antacids and/or drugs that inhibit gastric secretions
how do NSAIDS cause ulcers?
shut down prostaglandin synthesis, which is important in protecting the GI tract
phases of H. pylori infection
- active phase
- stationary phase
- colonization phase
active phase of H. pylori infection
H. pylori increases gastric pH by producing ammonia via urease
stationary phase of H. pylori infection
bacteria attach to fucose containing receptors on surface of mucus cells in pylorus - bacteria releases proteases that kill surface cells
colonization phase of H. pylori infection
bacteria detach and replicate in mucus blanket
