lecture 15- Intro to GI tract physiology

Question 1

list the layers of the gut tract will from outer to inner

Answer 1

serosa –> longitudinal smooth muscle layer –> myenteric plexus –> circular smooth muscle layer –> meissner’s plexus –> submocusa –> mucosa

Question 2

what is the serosa continuous with

Answer 2

mesentery (pathway for blood vessels to gut tube)

Question 3

what is the serosa replaced with when it is absent

Answer 3

replaced with adventitia connecting to abdominal wall

Question 4

what does the submucosa incorporate

Answer 4

blood vessels and submucosal plexus

Question 5

what does the mucosa support

Answer 5

supports simple columnar epithelium with goblet cells which lines entire gut tract

Question 6

what collectively forms the enteric nervous system of the gut tract

Answer 6

myenteric and meissner’s plexuses

Question 7

how does the enteric nervous system operate autonomously

Answer 7

via intrinsic regulation and sensory reflexes

Question 8

what do parasympathetics typically do to GI tract activity

Answer 8

increases it

Question 9

what do sympathetics typically do to GI tract activity

Answer 9

decreases it

Question 10

what are the neurons of the enteric nervous system supported by

Answer 10

intrinsic glial cells

Question 11

where is the myenteric plexus located

Answer 11

between longitudinal and smooth muscle layers

Question 12

what is the myenteric plexus primarily controlling

Answer 12

intestinal smooth muscle and participates in tonic and rhythmic contractions

Question 13

what does the meissner’s plexus mainly control

Answer 13

GI secretion, absorption and local blood flow

Question 14

what is meissners plexus concerned with

Answer 14

controlling function within inner wall of each minute segment of the intestine

Question 15

what is the usual stimulus for propulsive movements

Answer 15

distension

Question 16

what plexus is required for propulsive movements

Answer 16

myenteric

Question 17

what reflex is involved in receptive relaxation

Answer 17

vagovagal reflex

Question 18

what is the receptive relaxation initiated by

Answer 18

stomach distension

Question 19

what increases the distensibility of proximal end of stomach during receptive relaxation

Answer 19

CCK

Question 20

what is mixing and digestion in stomach stimulated by

Answer 20

vagus nerve increases gastric contractions; sympathetic decreases gastric contractions

Question 21

what is the gastroileal reflex mediated by

Answer 21

extrinsic ANS and gastrin

Question 22

what senses food and releases serotonin during peristaltic contractions

Answer 22

enterochromaffin cells in intestine

Question 23

where does most colonic water absorption occur

Answer 23

in proximal colon

Question 24

what does the valsalva maneuver result in

Answer 24

increased abdominal pressure

Question 25

where do slow waves originate

Answer 25

in interstitial cells of canal (pacemakers)

Question 26

what do spike potentials excite

Answer 26

muscle contraction

Question 27

what are spike potentials responsible for

Answer 27

opening calcium channels and smaller number of sodium channels in GI smooth muscle cells

Question 28

what factors cause depolarization

Answer 28

stretching of muscle; stimulation by acetylcholine (parasympathetic); stimulation by specific GI hormones

Question 29

what factors cause hyperpolarization

Answer 29

norepinephrine and epinephrine; stimulation of sympathetic nerves

Question 30

what are some causes of tonic contractions

Answer 30

continuous repetitive spike potentials, hormones and continuous entry of calcium ions

Question 31

what reflexes are integrated entirely within the gut wall enteric nervous system control

Answer 31

much of GI secretion, peristalsis, mixing contractions and local inhibitory effects

Question 32

what reflexes are from the gut to the pre vertebral sympathetic ganglia and then back to GI tract

Answer 32

transmit signals long distance to other areas of gut tract, cause evacuation of the colon (gastrocolic reflex), inhibit stomach motility and secretion (enterogastric reflex), and empty ileal contents into the colon (colonileal reflex)

Question 33

what reflexes are from the gut to the spinal cord or brain stem and then back to GI tract

Answer 33

reflexes from stomach and duodenum to brainstem and back to stomach control gastric motor and secretory activity, pain reflexes cause general inhibition of the entire GI tract, defecation reflex extend from the colon to the rectum to the spinal cord and back

Question 34

what are the 4 official GI hormones

Answer 34

gastrin, CCK, secretin, GIP

Question 35

where does all biologic activity of gastrin occur

Answer 35

in the 4 C-terminal aa

Question 36

what is stimulus for secretion of gastrin

Answer 36

small peptides and aa in stomach lumen, dissension of stomach, vagal stimulation mediated by GRP

Question 37

what inhibits secretion of gastrin

Answer 37

acid from stomach and somatostatin

Question 38

what are the actions of gastrin

Answer 38

stimulates gastric acid secretion by parietal cells and stimulates mucosal growth by stimulating synthesis of RNA and new protein

Question 39

when does Zollinger-Ellison syndrome occur

Answer 39

from gastrin secreting non-beta cell tumors of pancreas

Question 40

what is CCK homologous to

Answer 40

gastrin

Question 41

where is the biologic activity of CCK

Answer 41

C-terminal heptapeptide

Question 42

what is the stimulus for secretion of CCK

Answer 42

small peptides and aa, fatty acids and monoglycerides

Question 43

what is the site of secretion of CCK

Answer 43

I cells of duodenum, jejunum and ileum

Question 44

what is secretin homologous to

Answer 44

glucagon

Question 45

what is the stimulus for secretion of secretin

Answer 45

acid and fat in lumen of duodenum

Question 46

what is the site of secretion of secretin

Answer 46

S cells of duodenum, jejunum and ileum

Question 47

what stimulates pepsin secretion

Answer 47

secretin

Question 48

what is GIP homologous to

Answer 48

secretin and glucagon

Question 49

what is the stimulus for secretion of GIP

Answer 49

only GI hormone released in response to protein,fat and carb. released in response to orally administered glucose

Question 50

what is the site of secretion of GIP

Answer 50

K cells of duodenum and jejunum

Question 51

what are the actions of GIP

Answer 51

stimulates insulin release and inhibits gastric acid secretion by parietal cells

Question 52

what is the stimulus for secretion of motilin

Answer 52

fat, acid and nerve action

Question 53

what is the site of secretion of M cells

Answer 53

duodenum and jejunum

Question 54

what are the actions of motilin

Answer 54

stimulates gastric and intestinal motility. secreted during fasting

Question 55

what contributes to the slow emptying of cyme into the small intestine

Answer 55

stretching of stomach wall due to increased food volume promotes increased emptying of stomach due to local myenteric reflexes in the wall

Question 56

what factors are continually monitored in the duodenum and can initiate enterogastric inhibitory reflexes

Answer 56

degree of distension, presence of any degree of irritation of the duodenal mucosa, degree of acidity of duodenal chyme, presence of certain breakdown products in the chyme

Question 57

what is the most potent hormone in controlling the duodenum

Answer 57

CCK

Question 58

what are the 2 types of movement in the intestine

Answer 58

mixing and propulsive contractions

Question 59

irritation of _____ can cause powerful and rapid peristalsis

Answer 59

intestinal mucosa

Question 60

what intensifies peristalsis and emptying of ileal contents into cecum immediately after a meal

Answer 60

gastroileal reflex

Question 61

what are the principal functions of the colon

Answer 61

absorption of water and electrolytes from chyme. storage of fecal matter until it can be expelled

Question 62

what are haustrations produced by

Answer 62

produced by large circular constrictions plus contractions of the teniae coli