Lecom - Physiology 62: General Principles Of Gi Function - Motility, Nervous Control, And Blood Circulation

Front 1

Layers of the intestinal wall

Back 1

(1) serosa (2) outer longitudinal (3) inner circular (4) submucosa (5) mucosa

Front 2

Types of electrical activity of the GI smooth muscle (2)

Back 2

(1) slow waves (2) spikes

Front 3

Slow waves

Back 3

slow, undulating changes in the resting membrane potential that sets GI rhythmic contractions; this is NOT an action potential

Front 4

intensity of slow waves

Back 4

5-15 mV

Front 5

Rhythm of contraction for (1) stomach (2) duodenum (3) ileum

Back 5

(1) stomach = 3/mintute (2) duodenum = 12/min (3) ileum = 8-9/minute

Front 6

Interstitial cells of Cajal

Back 6

electrical pacemakers for smooth muscle and undergo cyclic changes in membrane potential due to unique ion channells that periodically open and produce inward currents; believed to be cause of slow waves

Front 7

Where do the slow waves cause contraction of smooth muscle?

Back 7

stomach; they do not themselves "cause" muscle contraction---they instead excite the appearance of intermittent spike potentials, and the spike potentials excite the muscle contraction

Front 8

Spike potentials

Back 8

true action potentials

Front 9

When do spike potentials occur automatically?

Back 9

when the resting membrane potential of the GI smooth muscle becomes more positive than abour -40mV

Front 10

How are action potential fibers generated in GI smooth muscle?

Back 10

the channels allow large number of calcium ions along with smaller number of sodium ions -- contain calcium-sodium channels ; longer duration of action potentials

Front 11

Calcium-sodium ions

Back 11

Slower to open and close then the rapid sodium channels

Front 12

Resting membrane potential GI smooth muscle (normal conditions)

Back 12

56mV

Front 13

Factors that depolarize the membrane

Back 13

(1) stretching of the muscle (2) stimulation by ACh released from parasympathetics (3) stimualtion by several specific GI hormones

Front 14

Factors that hyperpolarize the membrane

Back 14

(1) epinephrine and NE (2) stimulation of sympathetics

Front 15

Tonic contraction

Back 15

continuous, not associated with the basic electrical rhythm of the slow waves but often lasting several minutes or even hours

Front 16

Causes of tonic contraction

Back 16

(1) continuous repetitive spike potentials (2) hormones or other factors that bring about continuous partial depolarization of smooth muscle membrane without causing action potentials (3) continuous entry of calcium ions into the interior of the cell brought about in ways not associated with changes in membrane potential

Front 17

Enteric nervous system plexi

Back 17

(1) myenteric (Auerbach's) plexus (2) Meissner's plexus

Front 18

Auerbach's plexus location

Back 18

outer plexus lying between the longitudinal and circular muscle layers

Front 19

Meissner's plexus location

Back 19

inner plexus; submucosa

Front 20

Myenteric (Auerbach's Plexus) function

Back 20

controls the GI movements; (1) increased tonic contraction (2) increased intensity rhythmical contractions (3) slightly increased rate of rhythm of contraction (4) increased velocity of conduction of excitatory waves along the gut wall (more rapid peristalsis)

Front 21

Meisser's plexus stimulation

Back 21

controls mainly GI secretion and local blood flow

Front 22

Neural control of gut wall

Back 22

(1) myenteric and submucosal plexuses (2) extrinsic control of these by sympathetic and parasympathetic fibers (3) sensory fibers passing from the luminal epithelium and gut wall to the enteric plexuses, then to the prevertebral ganglia of the spinal cord and directly to the spinal cord and brain stem

Front 23

Meissner's plexus inhibition

Back 23

vasoactive intestinal polypeptide; useful for inhibiting some of the intestinal sphincters (pyloric and ileocecal)

Front 24

Where are the postganglionic parasympathetics located in the GI tract?

Back 24

mainly in the myenteric and submucosal plexuses

Front 25

Sympathetic levels GI system

Back 25

T5-L2

Front 26

Stimulation of sympathetics in GI tract

Back 26

(1) direct effect of secreted NE to inhibit intestinal tract smooth muscle (except for the mucosal muscle, which is excites) and (2) inhibitory effect of NE on the neurons of the entire enteric system

Front 27

GI Reflexes

Back 27

(1) reflexes that are integrated entirely within the gut wall enteric nervous system (2) Reflexes from the gut to the prevertebral sympathetic ganglia and then back to the GI tract (3) Reflexes from the gut to the spinal cord or brain stem and then back to the GI tract

Front 28

Gastrocolic reflex

Back 28

signals from the stomach to cause evacuation of the colon

Front 29

Enterogastric reflex

Back 29

signs from the colon and small intestine to inhibit stomach motility and stomach secretion

Front 30

colonoileal reflex

Back 30

reflexes from the colon to inhibit emptying of ileal contents into the colon

Front 31

Reflexes from the gut to the spinal cord or brain steam and then back to the GI tract

Back 31

(1) reflexes from the stomach and duodenum to the brainstem and back to the stomach - vagus nerve - to control gastric motor and secretory processes (2) pain reflexes that cause inhibition of GI tract (3) defection reflexes that travel from the colon and rectum to spinal cord and back to produce abdominal contractions

Front 32

Gastrin stimuli

Back 32

protein, distension, nerves (acid INHIBITS release)

Front 33

Gastrin site of secretion

Back 33

G cells of the antrum, duodenum, and jejunum

Front 34

Gastrin action

Back 34

stimulates gastric acid secretion and mucosal growth

Front 35

Cholecystokinin stimuli

Back 35

protein, fat, acid

Front 36

Cholecystokinin site of secretion

Back 36

I cells of duodenum, jejunum, and ileum

Front 37

Cholecytoskinin actions

Back 37

Stimulates pancreatic enzyme secretion. Pancreatic bicarb secretion, gallbladder contraction, and growth of exocrine pancreas; inhibits gastric emptying

Front 38

Secretin stimuli

Back 38

acid and fat

Front 39

Secretin site of secretion

Back 39

S cells of duodenum, jejunum, and ileum

Front 40

secretin actions

Back 40

Stimulates pepsin secretion, pancreatic bicarb secretion, biliary bicard secretion, and growth of exocrine pancrease; Inhibits gastric acid secretion

Front 41

Gastric inhibitory peptide stimuli

Back 41

protein, fat, carbs

Front 42

Gastric inhibitory peptide site of secretion

Back 42

K cells of duodenum and jejunum

Front 43

Gastric inhibitory peptide actions

Back 43

stimulates insulin increase and inhibitis gastric acid secretion

Front 44

Motilin stimuli

Back 44

fat, acid, and nerve

Front 45

motilin site of secretion

Back 45

M cells of the duodenum and jejunum

Front 46

Motilin action

Back 46

stimulates gastric motility and intestinal motility

Front 47

_____ inhibits appetite to prevent overeatinf during meals by stimulating sensory afferent nerve fibers of the duodenum

Back 47

CCK

Front 48

glucose-dependent insulinotropic peptide

Back 48

gastric inhibitory peptide (stimulates insulin secretion)

Front 49

interdigestive myoelectric complexes

Back 49

waves of gastroinestinal motility stimulated by motilin; move through the stomach every 90 minutes in a fasted person

Front 50

Two types of movement in the GI tract

Back 50

(1) propulsive movements, which caused food to move forward (2) mixing movements, which keep the intestinal contents thoroughly mixed at all times

Front 51

Major stimulus for intestinal peristalsis

Back 51

distention of the gut; to a lesser extent chemical and physical irritation of the epithelial lining of the gut; parasympathetic stimulation

Front 52

Effectual peristalsis requires

Back 52

an active myenteric plexus (peristalsis only occurs weakly or not at all in any portion of the GI tract that has a congenital absence of the myenteric plexus)

Front 53

Receptive relaxation

Back 53

Relaxation of the gut several cm downstream from the food (toward the anus), which allows food to be propelled more easily toward the anus than toward the mouth (this does not occur in the absence of the myenteric plexus)

Front 54

Law of the gut

Back 54

the peristaltic reflex plus the anal direction of movement of the peristalsis

Front 55

Mechanisms of mixing in the gut

Back 55

(1) peristalsis, especially when the sphincters are closed (2) local intermittent constrictive contractions

Front 56

reticuloendothelial cells

Back 56

line the liver sinusoids; remove bacteria and other particulate matter that may enter the blood from the GI tract

Front 57

Non-fat, water soluble nutrients in the splanchnic ciruclation

Back 57

proteins and carbs are absorbed from the gut, transported to the venous blood; both the reticuloendothelial cells and hepatic cells absorb and temporarily store from 1/2 to 3/4 of the nutrients

Front 58

Fate of fats absorbed from the intestinal tract

Back 58

NOT carried to portal blood; they are absorbed in the intestinal lymph and conducted to the systemic circulating blood by way of the thoracic duct (bypass liver)

Front 59

Blood flow in each area of the GI tract and in each layer of the gut wall is directly related to _____

Back 59

the level of activity in that area

Front 60

Causes of increased blood flow during GI activity

Back 60

(1) vasodilator substances are released from the mucosa of the intestinal tract during the digestive process (CCK, vasoactive intestinal peptide, gastrin, and secretin) (2) Gastrointestinal glands secrete kalldin and bradykinin (3) decreased oxygen concentration in the gut wall can increase intestinal blood flow which causes vasodilation

Front 61

Consequences of circulatory shock on the GI tract

Back 61

blood flow to the gut becomes curtailed and there is an oxygen deficit in the tips of the villi -- diminishes intestinal absorptive capacity

Front 62

Autoregulatory escape

Back 62

local metabolic vasodilators override sympathetic vasoconstriction

Front 63

Sympathetic stimulation GI tract

Back 63

causes strong vasoconstriction of the intestinal and mesenteric veins