GI Tract Part 1 Flashcards
Alimentary canal extends from
oral cavity to anus
Breakdown of food occurs in 5 phases—
ingestion, fragmentation, digestion, absorption, & elimination
— occurs in oral cavity, accompanied by —; results in — formation
Ingestion
fragmentation
bolus
Stomach completes fragmentation & initiates —
digestion
Contractions of smooth Mm
peristalsis
peristalsis is under — control
autonomic
In duodenum, pancreatic & biliary secretions results in
emulsificationof fat
In jejunum & ileum, 1’ absorption of
nutrients
In colon, resorption of — & elimination of —
water
waste
GI tract is a muscular tube lined by
mucus membrane
Large #’s of — associated with GI tract
glands
e.g., liver, pancreas & intestinal glands; embryological outgrowths of GI tract
— scattered throughout GI tract
Diffuse lymphoid tissue (MALT, GALT)
4 distinct layers of GI tract:
mucosa, submucosa, muscularis externa& adventitia(=serosa)
Mucosa has 3 overall functions:
protection, secretion & absorption
GI tract is subdivided into 3 layers:
epithelium, lamina propria, & muscularis mucosae
epithelium—
secretory & absorptive functions; different modifications at different levels of GI tract
lamina propria—
underlying connective tissue; contains lymphoid nodules, glands, blood vessels & lymphatics
muscularis mucosae—
thin layer of smooth Mm; boundary between mucosa & submucosa
Submucosa—
loose to dense irregular connective tissue layer beneath muscularis mucosae
submucosa supports —, and contains (3)
mucosa
larger blood vessels, nerves, lymphatics
Muscularis externa(= propria)—
usually inner circular & outer longitudinal smooth Mm layers
Muscularis externa mm fibers oriented at —
right angles
Segmentation—
local contractions
local contractions results in
mixing of food
how does segmentation occur? both…
proximally and distally, in either direction
Peristalsis—propels food — only
distally
aborally
Adventitia—
outer loose connective tissue layer, contains major Nn, vessels, & adipose tissue
Within abdominal cavity, referred to as
serosa(= visceral peritoneum)
Continuous with supporting —
mesentery
Lined by simple squamous epithelium (= —)
mesothelium
In other areas, adventitia merges with — tissue
retroperitoneal
Smooth Mm of gut controlled by
autonomic nervous sys
parasympathetic stimulation —
excitatory
sympathetic stimulation is —
inhibitory
Parasympathetic motor Nn synapse with ganglia located
near effector organ
in GI tract, ganglia located
within wall of gut, within submucosa & muscularis externa
Clusters of parasympathetic ganglia within submucosa; called
Meissner’s plexus(= submucosal plexus)
Larger clusters located between inner circular & outer longitudinal Mm layers called
myenteric or Auerbach’s plexus
Short, muscular tube, lined
by stratified squamous
nonkeratinized epithelium
esophagus
In upper third, muscularis
externa composed of
voluntary skeletalMm
Middle third is made of
skeletalMm &
smoothMm
Lower third is made of
smooth Mm only
Gastro-esophageal
junction between
esophagus & stomach
contains
gastroesophageal
sphincter
Pyrosis
“heartburn”
heartburn is due to
regurgitation of stomach
acid into distal
esophagus from cardia of
stomach
Regions of stomach: (3)
cardia, fundus, & pylorus
cardia—surrounded by
smooth Mm cardiac sphincter
cardiac sphincter
gastroesophageal sphincter
cardiac spinchter is located adjacent to
esophagus
cardia contains predominately
mucous secreting glands
glandular portion of stomach
fundus
what does fundus secrete (3)
acid, pepsin, & some mucus
Some texts differentiate fundus from corpus (body); both
glandular (fundus closer to cardia, corpus closer to pylorus)
pylorus contains 1’
mucus (& gastrin) secreting glands
— controls outflow from stomach into duodenum
Smooth Mm pyloric sphincter
Peptic/gastric ulcer
loss of
stomach/duodenal
epithelium/ mucosa
Ulcer
damage extends below
level of basement membrane
(=> bleeding)
Erosion
partial loss of
epithelium (no bleeding)
Tx of peptic/gastric ulcer with
antacids (e.g.,
tagamet, cimetidine)
Ulcers frequently associated
with chronic infection with
Helicobacter pylori
stomach produces
urease
urease
increases gastric pH
secondarily increases acid production
Tx of ulcers with
“triple therapy”—2
long-term abx & proton
pump inhibitor (prevents H+
secretion)
stomach
distensible organ used for food storage
how many chambers in the stomach
single in most animals
Food undergoes mechanical breakdown via — & chemical breakdown via
muscular activity
gastric secretions to form chyme
In addition to inner circular & outer longitudinal Mm layers of stomach, also third inner — layer in muscularis externa
oblique
Little absorption occurs in stomach, except for (3)
water, alcohol, & some drugs (e.g., aspirin)
Stomach lining contains prominent longitudinal folds, —
rugae
In glandular body of stomach, mucosa contains prominent
gastric pits (= foveolae)
what do gastric pits form?
entrance to gastric glands (straight, tubular glands)
gastic glands secrete ~– liters watery gastric juice/ day
2
what does gastric juice contain (5)
HCl (pH ~1) pepsinogen (inactive precursor of pepsin, hydrolyzes protein) gastrin rennin lipase
Pepsinogen converted to pepsin by action of —
HCl
Mucosa itself protected by thick layer of —
mucus
Gastric glands contain several types of cells—5 different classes:
mucous secreting cells acid secreting cells pepsin secreting cells enteroendocrine cells undifferentiated stem cells
acid secreting cells =
= parietal cells= oxyntic cells
what do acid secreting cells secrete (2)
HCl & intrinsic factor
HCl & intrinsic factor are necessary for
absorption of Vit B12 from ileum
Most numerous in middle third of gland, stain pinkto purple
acid secreting cells
pepsin secreting cells = (3)
chief cells, pepticcells, or zymogeniccells
what do pepsin secreting cells secrete?
inactive pepsinogen
where are pepsin secreting cells located
base of gland (bottom third)
how do pepsin secreting cells stain? why?
stain purple due to large #’s of ribosomes
Parietal & chief cells have long life spans; replaced every..
1 yr
Parietal & chief cells controlled by — & hormones from —
autonomic nervous system
endocrine cells in region of pylorus
enteroendocrine cells =
APUDcells (amine precursor uptake & decarboxylation)
paracrine cells target cells within — vicinity
local
what do paracrine cells secrete
variety of peptide hormones in response to local factors; control GI motility, gastric secretion
gastrin
secreted by “G” cells
stimulates secretion of HCl & pepsin
somatostatin
sec by “D” cells
inhibits secretion of gastrin
secretin(secreted by “S” cells), inhibits — & stimulates —
gastric secretion
smooth Mm contraction
Undifferentiated stem cells—mainly in — of gland
neck
undifferentiated stem cells continuously divide to
replace lost or damaged epithelial cells
As undifferentiated stem cells mature, migrate
up or down gland