GI 2

Question 1

what are the fluid secretions in the digestive system?

Answer 1

-water
-digestive enzymes
-mucus

Question 2

what is the fluid secretion of water?

Answer 2

-ions are transported from ECF into the lumen
-creates osmotic gradient for water movement

Question 3

what is the fluid secretion of digestive enzymes?

Answer 3

-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)

Question 4

what is the fluid secretion of mucus?

Answer 4

viscous glycoprotein (mucins) secretions that protect GI cells and lubricate the contents
-mucus cells in stomach and salivary glands, goblet cells in intestines

Question 5

most __________ facilitate digestion

Answer 5

FLUIDS

Question 6

what is motility?

Answer 6

-movement of material through the GI tract as a result of muscle contraction

Question 7

what are the two purposes of motility?

Answer 7

-moves food from mouth to anus
-mechanically mixing food breaks it into uniformly small particles

Question 8

what is motility determined by?

Answer 8

-by properties of smooth muscle and modified by chemical/mechanical input from nerves, hormones and paracrine signals

Question 9

what are the graphs of motility?

Answer 9

Question 10

where do slow waves likely originate?

Answer 10

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

Question 11

where do slow waves spontaneously begin?

Answer 11

-in ICC and spread to adjacent smooth muscle through gap junctions
-different regions controlled by different ICC groups

Question 12

what are the three basic patterns of contraction that occur in the Gi system bringing about different types of movement?

Answer 12

1. migrating motor complex (motilin) (between meals)
2. peristaltic contractions (during or following a meal)
3. segmental contractions (during or following a meal)

Question 13

what is the migrating motor complex (motilin)?

Answer 13

-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

Question 14

what are peristaltic contractions?

Answer 14

-progressive wave of contraction of circular muscle behind a mass (bolus) of food (2-2.25cm/s)

Question 15

what are segmental contractions?

Answer 15

-small segments alternatively contract and relax circular and longitudinal (churns and mixes)

Question 16

what are primarily regulated functions in the GI system?

Answer 16

-motility and secretion by neural and GI peptides

Question 17

what is the neural regulation?

Answer 17

-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

Question 18

what is the GI peptide regulation?

Answer 18

-hormones, neuropeptides and cytokines

Question 19

what are the similarities between the ENS and CNS?

Answer 19

-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

Question 20

what are the ENS short reflexes?

Answer 20

-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

Question 21

what are the ENS long reflexes?

Answer 21

-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)