GI 2 Flashcards
what are the fluid secretions in the digestive system?
-water
-digestive enzymes
-mucus
what is the fluid secretion of water?
-ions are transported from ECF into the lumen
-creates osmotic gradient for water movement
what is the fluid secretion of digestive enzymes?
-exocrine glands (salivary and pancreas)
epithelial cells in stomach and small intestine
-proteins synthesized on rough ER and packaged in secretory vesicles until needed
-once released some remain bound to apical membrane by lipid anchors
-some are released in inactive form: zygomen (stock pile without cellular damage)
what is the fluid secretion of mucus?
viscous glycoprotein (mucins) secretions that protect GI cells and lubricate the contents
-mucus cells in stomach and salivary glands, goblet cells in intestines
most __________ facilitate digestion
FLUIDS
what is motility?
-movement of material through the GI tract as a result of muscle contraction
what are the two purposes of motility?
-moves food from mouth to anus
-mechanically mixing food breaks it into uniformly small particles
what is motility determined by?
-by properties of smooth muscle and modified by chemical/mechanical input from nerves, hormones and paracrine signals
what are the graphs of motility?
where do slow waves likely originate?
in a network of cells known as the interstitial cells of cajal (ICC)
-modified smooth muscle cells serving as the pacemaker for slow wave activity
where do slow waves spontaneously begin?
-in ICC and spread to adjacent smooth muscle through gap junctions
-different regions controlled by different ICC groups
what are the three basic patterns of contraction that occur in the Gi system bringing about different types of movement?
- migrating motor complex (motilin) (between meals)
- peristaltic contractions (during or following a meal)
- segmental contractions (during or following a meal)
what is the migrating motor complex (motilin)?
-usually begins in the stomach and passes from section to section, terminating at the ileum
-90-120 minutes (first 45-60 mins quiescent)
-20-30 min period of infrequent peristaltic contractions
-sweeps food remnants and bacteria out of the upper Gi tract and into the large intestine
what are peristaltic contractions?
-progressive wave of contraction of circular muscle behind a mass (bolus) of food (2-2.25cm/s)
what are segmental contractions?
-small segments alternatively contract and relax circular and longitudinal (churns and mixes)
what are primarily regulated functions in the GI system?
-motility and secretion by neural and GI peptides
what is the neural regulation?
-submucosal and myenteric plexuses from the ENS: 100-500 million neurons
-neurons synapses with each other, smooth muscles, glands and epithelial cells
-short reflexes in integrated entirely within the ENS
-long reflexes integrated within the CNS
what is the GI peptide regulation?
-hormones, neuropeptides and cytokines
what are the similarities between the ENS and CNS?
-intrinsic neurons: entirely within the Gi tract
-neurotransmitters and neuromodulators: 30 neurotransmitters many identical to CNS (serotonin, ACh, VIP, NO)
-glial support cells: similar to astrocytes
-diffusion barrier: like BBB
-integrating center: can function autonomously
what are the ENS short reflexes?
-short reflexes: originate in the enteric nervous system and are carried out entirely within the wall of the gut
-myenteric plexus: motility
-submucosal plexus: secretion from GI secretory cells
what are the ENS long reflexes?
-are integrated in the CNS. Some originate outside the GI tract, but others originate in the enteric nervous system
-if a long reflex begins in the brain, it is a cephalic reflex (feedforward and emotional)
