Lecture 43 - Small Intestine Flashcards
Describe the small intestines
large surface area of villous mucosa
where does digestion occur in the small intestines
- intra-luminal (pancreatic enzymes & bile acids)
- surface (brush border enzymes)
what is the job of amylase
break down carbs
what is the job of lipase
break down fats
what is the job of protease
break down protein
T/F: to fully digest and absorb nutrients, luminal digestion, brush border digestion, and nutrient transporters are needed
TRUE
what are the mucosal folds
inner surface of small intestines that form circular folds to increase surface area and regulate flow
what are the villi
tiny projections that stick into the lumen covered with cells for absorption
what are the microvilli
tiny hairlike structures on villi to increase the surface area of each cell
what cells line the villi
- Columnar absorptive cells
- mucus-secreting goblet cells
- Intraepithelial lymphocytes
- enterendocrine cells
- tuft cells
what cells line the crypt
- Undifferentiated stem cells that secrete Cl-/water
- Paneth cells that secrete anti-microbial peptides and help maintain stem cells
anoikis
programmed cell death that occurs after loss of adhesion/contact with cell membrane
what transporters are present in the villus
- Na-K pump (sodium in)
what transporters are present in the crypt
- Na-K pump (sodium out)
- Na/K/Cl channel (sodium in)
- cystic fibrosis transmembrane conductance regulator (Cl- secretion)
describe a defective CFTR
accumulation of Cl- in epithelial cells and lack of hydration of extracellular mucus secretions
describe an activated CFTR
secretion»_space;> absoprtion
Overactivity releases too many Cl- ions and increases water flow in guts
what is D+
- increase in frequency or volume
- occurs w mismatch between secretion and absorption
what are the 4 categories of D+
- osmotic
- secretory
- malabsorptive
- other
describe osmotic D+
occurs when there are non-absorbable susbtances in the gut that draw water
describe malabsorptive D+
loss of epithelial cells and inefficient fluid and electrolyte absorption
describe secretory D+
intestinal cells release more fluid/electrolytes into the lumen
what do injuries in the villous epithelium cause
severe maldigestion and malabsorption
T/F: recovery in villous damage is not possible
FALSE - crypt spars stem cells
what do injuries in the crypt epithelium cause
prevents ability to regenerate raoud turnover rate
what are the two types of motility patterns
- interdigestive (fasting; housekeeping)
- Digestive (after meal)
what are the 3 functions of intesting motility
- propulsion
- mixing
- reservoir
describe interdigestive motility
- strong peristaltic contractions
- “housekeeper” (clean GI)
- controlled by enteric system
what are the 3 phases of interdigestive motility
phase I - no contractions
Phase II - intermittent
Phase III - continuous
the migrating myoelectirc complex is driven by
motilin
describe digestive motility
- helps promote digestion and absorption of meal
- short, peristaltic bursts
- activation of vagus nerve and hormones
what types of contractions are present in digestive motility
- tonic - sustained, characteristic of sphincters
- peristalsis - aboral wave of contraction
- segmental - stationary rings of contraction that delay transit
in carnivores/omnivores, disgestive motility is stimulated by _____ and is ____
vagus nerve; slower
T/F: in ruminants, there is no digestive motility pattern
TRUE
