Gastrointestinal Physiology 11-14

Question 1

Characteristics of smooth muscle cells in the GI tract

Answer 1

• function as a synctitium
• cells are arranged in bundles of fibers
• muscle fibers are electrically connected to eachother by gap junctions

Question 2

Components of extrinsic and intrinsic control systems that regulate GI tract functions

Answer 2

• systems located in the wall of the GI tract (intrinsic systems)
  
  • nerves- enteric nervous system
  • endocrine secretions- secretin, gastrin, CCK, GIP, and motilin
• systems located outside the wall of the GI tract (extrinsic systems)
  
  • nerves- vagus and splanchnic nerves
  • endocrine secretions- aldosterone

Question 3

Functions of the enteric nervous system (ENS)

Answer 3

a component of the autonomic nervous system, located within the GI wall–> autonomic regulation of GI elementary functions

Question 4

Plexus Myentericus

Answer 4

in the muscularis externa, between longitudinal and circular muscle–> control of the muscular activity, muscle tone and contraction rhythm

Question 5

Plexus submucosus

Answer 5

between submucosa and circular muscle–> mucus secretion and reabsorption

Question 6

enteric neurons

Answer 6

secrete their neurotransmitter from varicosities or bulge-like structures located on often lengthy axonal collaterals or branches. the effect of an enteric neuron is spread to affect a wide area

Question 7

dogiel type 1 enteric neuron

Answer 7

small cell body with short dendrites. motor neurons

Question 8

dogiel type 2 enteric neuron

Answer 8

large cell bodies with one or 2 long dendrites. sensory neurons

Question 9

dogiel type 3 enteric neuron

Answer 9

multiple shapes and functions

Question 10

sensory nerve cells

Answer 10

detect changes or stimulus and regulates function

axons go to other enteric nerve cells and to the CNS

Question 11

mechanoreceptors

Answer 11

recognize stretching of intestinal wall or volume changes by intraluminal pressure

Question 12

chemoreceptors

Answer 12

detect nutrients, osmolarity, pH

neurites–> decodification of the stimulus–> sensibilization of the endocrine cell

Question 13

interneuron

Answer 13

process signals coming from other nerve cells or from the CNS

Question 14

muscle motor neurons

Answer 14

primarily located in the plexus myentericus

stimulatory: Ach–> M3–> increase motility
inhibitory: NO, ATP, VIP, NANC

Question 15

secretomotor neurons

Answer 15

primarily located in the plexus submucosus

stimulatory: Ach, Substance P and VIP–> increase secretion
inhibitory: SOMA and NPY

Question 16

vasomotor neurons

Answer 16

in both plexuses

ach and VIP–> increase vasodilation

Question 17

under physiological conditions, is the GI tract under inhibition or stimulation?

Answer 17

inhibition

Question 18

GI motility disorders

Answer 18

hypoganglionosis

hirschsprung’s disease (congenital megacolon)

Question 19

ATP

Answer 19

non-peptide, in postganglionic sympathetic neurons, function is to contract muscle cells

Question 20

NO

Answer 20

non-peptide, in gastric nerves, function is to reduce motility

Question 21

vasoactive intestinal polypeptde

Answer 21

peptide, in parasympathetic ganglia, function is vasodilation, relaxation of smooth muscle and sphincters

Question 22

substance P

Answer 22

peptide, in sympathetic ganglia, function is to increase secretion and motility

Question 23

neuropeptide Y

Answer 23

peptide, in postganglionic sympathetic neurons, function is to inhibit secretion

Question 24

slow wave

Answer 24

rhythm of GI contraction frequency controlled by these slow waves of smooth muscle membrane potential
not action potentials, slow, undulating changes in the resting membrane potential
origin not completely understood, may come from interstitial cells of Cajal

Question 25

spike potentials

Answer 25

true action potentials occur automatically when the resting membrane potential of the GI smooth muscle becomes more positive than about 40mV the higher the slow wave potential rises, the greater the frequency of the spike potentials

Question 26

three types of GI reflexes essential to GI control

Answer 26

1. reflexes integrated entirely within the gut wall enteric nervous system--> control GI secretion, peristalsis, mixing contractions, local inhibitory effects 2. reflexes form the gut to the prevertebral sympathetic ganglia and then back to the GI tract--> transmit signals long distances to other areas of the GI tract - ---gastrocolic reflex: signal form the stomach that causes evacuation of the colon - ---enterogastric reflex: signal from the colon and small intestine to inhibit stomach motility and secretion - ---colonoileal reflex: signal from the colon to inhibit emptying of ileal contents into the colon 3. reflexes from the gut to the spinal cord or brain stem and then back to the GI tract - ---reflexes from the stomach and duodenum to the brain stem and back to the stomach to control gastric motor and secretory activity - ---pain reflexes that cause general inhibition of the entire GI tract - ---defecation reflexes that travel from the colon and rectum to the spinal cord and back again to produce the colonic, rectal, and abdominal contractions required for defecation

Question 27

peristaltic reflex

Answer 27

stretching of the intestinal wall during the passage of a bolus triggers a reflex that constricts the lumen behind the bolus and dilated the lumen ahead of it--> coordination of longitudinal and circular musculature--> propulsive movement of the GI content a property of many syncytial smooth muscle cells proximal to the site of distention: excitatory motor neurons are stimulated--> Ach and Sp--> smooth muscle contraction distal to the site of distention: inhibitory motor neurons are stimulated--> NO, ATP, VIP--> smooth muscle relaxation

Question 28

vagovagal reflex

Answer 28

afferent and efferent fibers of the vagus nerve coordinate responses to gut stimuli via the dorsal vagal complex in the brain stimulation of mechanical receptors located in the gastric mucosa stimulates vagus afferents controls contraction of the GI muscle layers in response to distention of the tract by the chymus active during the receptive relaxation of the stomach in response to swallowing food when food enters the stomach, this reflex goes from the stomach to the brain, then back again to the stomach causing active relaxation of the smooth muscle in the stomach wall

Question 29

motility of the stomach

Answer 29

1. the gastric store- tonic relaxation and tonic contraction 2. the gastric pump- strong peristaltic wave in the antrum 3. passage into the grinder and then into the pylorus 4. emptying of fluid and pre-digested particles into the duodenum increased pressure after stomach filling induces a reflectory relaxation of the stomach 1. receptive relaxation-- vagovagal reflexes 2. adaptive relaxation-- gastro-gastric reflexes 3. feedback relaxation

Question 30

intestinal motility functions

Answer 30

- mixing of food with digestive juices - enhancing contact between intestinal wall and food - peristalsis, the propulsive movement of the chymus distally

Question 31

digestive period of intestinal motiility

Answer 31

propulsive pattern: peristaltic wave--> fast aboral migrating contractions nonpropulsive pattern: segmentation--> localized contractions of circular muscle, small segments of the intestine contract tightly, dividing the gut into 2 segments of constricted and dilated lumen

Question 32

interdigestive period of intestinal motility

Answer 32

time in which stomach and small intestine are empty between meals--> migrating motoric complex, typically lasts 80-120 minutes phase 1: motoric rest, no contractions phase 2: intermittent and irregular contractions, sometimes isolated stronger ones phase 3: strong peristaltic contractions starting from the stomach and migrating distally to reach the colon

Question 33

migrating motoric complex

Answer 33

helps push indigested material out of the intestine | control of the bacterial population

Question 34

motility of the large intestine

Answer 34

mixing activity is prominent in horses and pigs, colonic segmentation is more pronounced and results in the formation of sacculations or haustra antiperistaltic waves: oral migrating contractions that impeded the movement of ingesta, causing a more intense mixing activity

Question 35

pathologic contractions

Answer 35

giant contractions with high amplitude and long lasting contraction oral migrating: vomitting aboral migrating: diarrhea

Question 36

vomitting

Answer 36

defense mechanism and important clinical sign activated in order to eliminate GI content complex reflex involving many striated muscle groups and other structures outside the GI tract coordinated in the brainstem

Question 37

vomiting stimuli

Answer 37

before food intake after food intake--> visceral afferents to vomiting center after absorption--> stimulate chemoreceptor trigger zone in the area postrema

Question 38

vomiting sequence of events

Answer 38

antiperistaltic wave originates in duodenum propulsion of ingesta toward stomach contraction of abdominal musculature increasing intra-abdominal pressure expansion of chest cavity while glottis remains closed in order to lower intrathoracic pressure relaxation of lower esophageal sphincter opening of upper esophageal sphincter

Question 39

Concerning GI smooth muscle cells, which one is true? A. their contraction cannot be extrinsically influenced B. spike potentials do not conduce to a contraction C. they show spontaneous undulations in the membrane potential

Answer 39

C

Question 40

Which kinds of sensory neurons will be stimulated during the peristaltic reflex? A. chemosensitive neurons B. mechanosensitive neurons

Answer 40

B

Question 41

Inhibitory muscle motor neurons use: A. acetylcholine B. substance P C. NO, ATP, VIP

Answer 41

C

Question 42

The proximal stomach serves a storage function in retaining food A. True B. False

Answer 42

A

Question 43

Vomiting contains only ingesta of gastric origin A. True B. False

Answer 43

B

Question 44

Diarrhea

Answer 44

increase in frequency of defecation or fecal volume volume increase is often due to increased water content water in the gut results from ingested water, water secreted by glands of the GI tract, or water secreted or lost directly through mucosal epithelium diarrhea occurs when there is a mismatch between secretion and absorption

Question 45

malabsorptive diarrhea

Answer 45

absorption is inadequate to recover all secreted water viral, bacterial, protozoan infections destruction of the villi and reduced length shortened villi cause a loss of absorptive intestinal surface area more affected are mature enterocytes that possess the enzymes of the brush border and transport proteins

Question 46

secretory diarrhea

Answer 46

rate of intestinal secretion increases and overwhelms the absorptive capacity some pathogenic bacteria produce enterotoxins which bind to enterocytes and stimulate the adenylyl cyclase activity and the production of cAMP--> opening of chloride channels, water and other electrolytes follow

Question 47

defectation

Answer 47

internal and external anal sphincters internal is normally tonically contracted--> anal continence internal is parasympathetically innervated by the sacral spinal segment and sympathetically innervated by the lumbar segment in most species: sympathetic stimulation--> constriction of the sphincter; parasympathetic stimulation--> relaxation voluntary constriction of the external anal sphincter will block the reflector activation of defecation

Question 48

retrosphincteric reflex

Answer 48

feces accumulates in the rectum peristaltic movement of feces into the rectum and relaxation of internal sphincter urge to defecate