GI 2 Flashcards
What is avoiding autodigesting
breaking food down into small enough molecules to be absorbed without digesting the cells of the GI tract
what are 3 challenges of digestive system
autodigestion, maintaining mass balance, defense
why is it hard to maintain mass balance
we secrete a lot more than we ingest (have to reabsorb most)
what is defense in the digestive system
absorbing water and nutrients while preventing bacteria, viruses and other pathogens from entering body
what are defense mechanisms
mucus, digestive enzymes, acid and lymphoid tissue
where are 80% of lymphocytes
in small intestine
how is water secreted
ions are transported from ECF into lumen
created osmotic gradient for water to follow
what secretes digestive enzymes
- exocrine glands (salivary and pancreas)
- epithelial cells in stomach and small int
how does secretion work in epithelial cells
proteins synthesized on rough ER and packaged in secretory vesicles until needed
what are mucus secretions
viscous glycoprotein (mucins) secretions that protect GI cells and lubricate the contents
what type of cell secretes mucus in stomach and salivary glands
mucus cells
what type of cell secretes mucus in intestines
goblet cells
what do most fluid secretions facilitate
digestion, soften and moisten
in stomach what kind of enzymes are there
enzymes preferring acidic conditions
in small intestine what kind of enzymes are there
enzymes preferring alkaline conditions
two purposes of motility
- moves food from mouth to anus
- mechanically mixing food breaks it into uniformly small particles
what part of digestive tract is skeletal muscle
mouth, pharynx, 1st part of esophagus
what is type of muscle is the digestive tract from 2nd part of esophagus on
smooth muscle
what is GI motility determined by
properties of smooth muscle and modified chemical/mechanical input from nerves, hormones, and paracrine signals
What type of smooth muscle cells are in digestive tract
single unit smooth muscle cells
what are single unit smooth muscle cells
gap junction slink them electrically and mechanically meaning uniform contraction
tonic smooth muscle that is usually contracted
sphincters
relaxes to allow material to pass
phasic smooth muscle that cycles between contraction and relaxation
2/3 esophagus, posterior region of stomach, small, large intestines
what are slow waves
spontaneous depolarizations in GI smooth muscle
what are slow waves modified by
chemical input from neurons, hormones, and paracrine signals
where do slow waves originate
network of cells: interstitial cells of cajal (ICC)
next to myenteric plexus
what are the ICC cells
modified smooth muscle cells serving as the pacemaker for slow wave activity
how does slow waves spread through the smooth muscle
gap junctions of adjacent smooth muscle
why does stomach have waves 3times/min but small int 12 times/min
different regions controlled by different ICC groups
what are 3 basic patterns of contraction occurring in the GI bringing different types of movement
- migrating motor complex (motilin)
- peristatic
- segmental
when does migrating motor complex begin
between meals
where does migrating motor complex start
progressive wave of contraction begins in stomach and passes from section to section, terminating in ileum
what are the parts of the migrating motor complex
45-60 minutes quiescent
20-30 min of infrequent peristaltic contractions
5-15 mins cycle rapid forceful contractions
how long is MMC
90-120 mins
what does the MMC do
sweeps food remnants and bacteria out of the upper GI tract and into large intestine
what kind of movement are peristaltic contractions responsible for
forward movement (esophagus and less frequently in small int.)
what is peristaltic contractions
progressive wave of contraction of circular muscle behind a mass (bolus) of food (2-25cm/s)
what are segmental contractions responsible for
mixing (intestines)
what are segmental contractions
small segments alternatively contact and relax circular and longitudinal (churns and mixes)
what are the regulated functions in the GI system
motility and secretion
what forms the ENS
100-500 million neurons of submucosal and myenteric plexuses
what do neurons synapse with to regulate GI function
with eachother, smooth muscles, glands and epithelial cells
where are short reflexes integrated
originate in ENS and carried out entirely within wall of gut
where are long reflexes integrated
within CNS, some originate outside GI tract but some in ENS
what GI peptides alter motility and secretion to regulate GI function
hormones, neuropeptides, and cytokines
what similarities does the ENS share with CNS
- intrinsic neurons: within GI
- neurotransmitters (many similar to CNS) and neuromodulators
- glial support cells
- diffusion barrier (blood gut barrier)
- integrating center (can function autonomously)
what does myenteric plexus add input
motility
what does submucosal plexus add input
secretion from GI secretory cells
what stimuli causes short reflexes from ENS
distension, presence of food, osmolarity, acid
If a long reflex begins in brain what is it
cephalic reflex (feedforward and emotional)
what other type of info is sent to CNS
Sensory info
ENS receives info from CNS via autonomic nerves
what does parasympathetic and sympathetic input do for digestion
parasympathetic enhances GI function (vagus) sympathetic inhibits
what can GI peptides act as
hormones or paracrine signals
what do GI peptides do
excite or inhibit motility and secretion
where are GI peptides secreted
secreted into lumen to act on apical membrane receptors or ECF to act on neighbouring cells
- some act outside GI (brain)
how many peptides have been identified and how many are hormones
over 30
only a handful
