GIT Lec 1: Intro Flashcards
Function of GIT
- transfer of nutrients, minerals, water from external to internal
(digestion - absorption - excretion)
-immune defense (host defense) - GIT is continuous with exterior
Digestion is
chemical changes of food to absorbable materials
Absorption is
transfer of digested food from intestine into blood and lymphatic vessels
Excretion is
removal of components not absorbed
Things that are excreted
bacteria, intestinal cells, drugs, cholesterol, steroids
Two parts of the GI system
tract and accessory organs
Tract in GIT is composed of
mouth, pharynx, esophagus, stomach, small intestine, large intestine
Accessory organs of GIT
pancreas, liver, gall bladder
composition of muscle from top of esophagus..
skeletal muscle
composition of muscle from mid-esophagus to anus..
smooth muscle
Layers of GIT (LUMEN TO EXTERIOR)
- Mucosa
- Submucosa
- Muscularis externa
- Serosa
Layers of Mucosa
- Epithelium
- Lamina propria
- Muscularis mucosa
Epithelial layer has..
- polarized layer (basolateral and apical side)
- villi and microvilli (cellular level)
basolateral
- also serosal, blood
- facing blood vessels
apical
- luminal,mucosal
- facing lumen
SA of GIT increased by
villi (finger-like projection in epithelial layer), microvilli, crypts (invaginations in epithelial layer)
Epithelial layer performs…
selective uptake of nutrients, electrolytes, water
polarized layer of epithelium caused by
different transport proteins at apical and basolateral surface and tight junctions that prevent movement of transport proteins to membrane regions
Crypts in epithelial layer..
have stem cells that divide and migrate up the villus (rapid cells turnover)
paracellular pathway through epithelium (GIT)
- between the cells
- limited by tight junction seal
- water, small ions pass through
transcellular pathway through epithelium (GIT)
- through the cells
- 2 step (transport on apical side then basolateral)
Lamina propria
- second layer of mucosa after epithelial layer
- connective tissue, small blood vessels, nerve fibers (end), lymphatic vessels, immune cells
Muscularis mucosa
- third layer of mucosa after epithelial layer and lamina propria
- thin layer of smooth muscle for villi movement not contraction of GIT
Submucosa
-second layer of GIT after mucosa
Submucosa has
- nerve cell bodies, that relay info from mucosa
- connective tissue, blood, lymphatic vessels
Muscularis externa
-third layer of GIT, after mucosa, submucosa before serosa
Muscularis externa has..(layers)
- thick inner layer of circular muscle
- myenteric nerve plexus
- thin outer layer of longitudinal muscle
myenteric nerve plexus
plexus of nerves from the sympathetic and parasympathetic systems between the two layers of muscle in the small intestine
Thick inner layer of circular muscle in small intestine is responsible for the..
narrowing of lumen
Thin outer layer of longitudinal muscle is responsible for the..
shortening of tube
Serosa
- last layer of GIT
- connective tissue, encasing intestine, connection to abdominal wall
Blood moves in GIT through
intestine then liver through via portal vein
portal vein drains..
blood from digestive tract into the liver
blood in the portal vein is
nutrient rich but oxygen poor