Gi Physiology 2010

Front 1

Myenteric plexus

Back 1

-Auerbach's plexus
-larger of the two plexuses
-located betweenlongitudinal m layer from esophagus to rectum
-concerned with control of motility

Front 2

Submucosal plexus

Back 2

-Meissner's plexus
-lies in submucosa of the small and large intestine
-concerned primarily with control of secretion from glands of the GI tract

Front 3

Activation of symp. nervous system in GI?

Back 3

-inhibit secretion and produce vasoconstriction
-inhibit conctraction in muscluaris externa
-stimulates contraction of sphincters and the muscularis externa

Front 4

Where do the Parasymp innervation of GI come from?

Back 4

-cholinergic fibers from vagus (GI tract to level of transverse colon) and pelvic nerves (descending colon to rectum)
-

Front 5

Where do parasymp fibers terminate? what is there function?

Back 5

-Myenteric and submucosal plexus
-increases contraction and secretion

Front 6

local reflex arc

Back 6

-cell bodies of afferent neurons that lie in the submucosal and myenteric plexus

Front 7

central reflex arc

Back 7

-cell bodies of the other sensory neurons are located in the dorsal root ganglia or cranial ganglia (nodose)

Front 8

visceral Nociceptive fibers and non-nociceptive fibers of the thorax and abdomen travel to CNS via what nerves?

Back 8

-nociceptive = sympathetic
-non-nociceptive = parasympathetic

Front 9

What type of smooth muscle is in the GI? what does this mean?

Back 9

-single unit type
-neighboring cells are connected by gap junctions
-electrical activity spreads easily from cell to cell

Front 10

Is Na conductance higher or lower in smooth m vs. skeletal? What is the significance of this?

Back 10

Na conductance is higher in smooth m making resting potential less neg than that of skeletal

Front 11

Where are the pacemaker cells of the GI located?

Back 11

-between the longitudinal and circular smooth muscle of muscularis externa

Front 12

In the stomach and small intestine what do the frequency of slow waves represent?

Back 12

the max frequency that contractions can occur

Front 13

Describe the neuromusclular junctions in the smooth m of the GI?

Back 13

-No postjunctional specialization
-circular smooth layer: lots of innervation, small gaps btwn nerve and m. (20 nm)
-longitudinal m. layer: less dense innervation and gaps btwn n and m are large (80 nm)

Front 14

Length-tension curve of smooth m

Back 14

-broader in smooth m. vs skeletal so force is effective over wide range of m lengths

Front 15

Contraction time of smooth m

Back 15

-contraction time for smooth is slower than skeletal
-smooth increasing tension instead of twitches

Front 16

Tone of smooth m

Back 16

-smooth m has higher levels of Ca2+ so has a resting tension
-tone can be modified by neurotransmitters, hormones and drugs

Front 17

Two nuclei that sensory input from oral cavity terminates at to modify chewing?

Back 17

-trigeminal sensory
-mesencephalic nuclei

Front 18

Where is the swallowing center located?

Back 18

Medulla and lower pons

Front 19

How long does it take for food to move from the upper esophagus to the stomach? What is this mainly controlled by?

Back 19

-10 s
-swallowing center through the vagus

Front 20

What is the secondary peristalsis controlled by?

Back 20

-intrinsic nervous system

Front 21

What does intensity of perstalsis depend on?

Back 21

-size of bolus and peristalsis is not required for liquid bolus in upright position

Front 22

Why is the lower esophageal sphincter tone high during quiescent periods? How can it be increased?

Back 22

-myogenic mechanisms (remainder of esophagus is flaccid)
-Can be increased by neural (ACh) and hormonal (gastrin) influences)

Front 23

What is relaxation of the lower esophageal sphincter mediated by?

Back 23

-the vagus through vasoactive intestinal peptide (VIP) and nitric oxide (NO)

Front 24

Achalasia

Back 24

-insufficient relaxation of lower esophageal sphincter to allow food into stomach.
-Is attributed to abnormal enteric nervous function

Front 25

Gastroesophageal reflux disease (GERD)

Back 25

-normally LES transiently relaxes and closes (permits belching)
-in GERD the relaxations occur more frequently or are prolonged allow reflux of gastric contents (acid and pepsin) into esophagus which can produce ulceration

Front 26

diffuse esophageal spasm

Back 26

-prolonged painful contraction of esophagus instead of normal perstalsis after awallowing

Front 27

What organ acts like a homogenizer?

Back 27

stomach

Front 28

Three layers of smooth muscle of the stomach?

Back 28

outer-longitudinal
middle-circular
inner-oblique

Front 29

Where's the sympathetic innervation from for the stomach?

Back 29

the splanchnic

Front 30

Whats the intrinsic motor innervation from for the stomach?

Back 30

submucosal and myenteric plexus

Front 31

Cardia

Back 31

region of stomach surrounding the superior opening (LES sometimes called cardiac sphincter)

Front 32

antrum

Back 32

inferior region of the stomach, has two parts:
1) antrum (pyloric antrum)-continuous with body of stomach
2)pyloric canal-leads to duodenum

Front 33

vagovagal reflex

Back 33

relaxation of body or fundus of stomach which can be induced by directly filling stomach with gas or liquid

Front 34

receptive relaxation of stomach for the body and fundus of the stomach

Back 34

-can be initiated as part of the reflex relaxation of lower esophageal sphincter induced by primary esophageal peristalsis

Front 35

what is the receptive relaxation reflex dependent on?

Back 35

Vagal innervation

Front 36

the receptive relaxation reflex allows accommodation of ______ without significant increase in _______.

Back 36

-1L-2L
-intragastric pressure

Front 37

Why is there only a little bit of mixing in the fundus and body of the stomach?

Back 37

-muscle layers are thin and contractions are weak
-contents from layers based on their densities

Front 38

When are fats emptied from the stomach?

Back 38

-fats from an upper oily layer and are thus emptied last

Front 39

What substances leave the stomach rapidly?

Back 39

inert, isotonic solutions (glucose)

Front 40

which substances leave the stomach slowly?

Back 40

-solutions containing nutrients (amino acids) empty more slowly reflecting feedback from receptors in the small intestine (rate of emptying depends on calorie density)

Front 41

What happens in the antrum of the stomach?

Back 41

-site where most mixing occurs
-produces vigorous peristaltic contractions
-food broken down and mixed with gastric juice

Front 42

Where do contractions produced by gastric slow waves orignate from? where do they move towards?

Back 42

-Originate from the middle of the body of the stomach and move towards the pyloris

Front 43

Pyloric pump

Back 43

- A small fraction of the chyme containing particles (<2 mm) is pushed into the duodenum.
-The peristaltic contractions that eject this chyme into the duodenum is called the pyloric pump

Front 44

retropulsion

Back 44

the pyloric sphincter closes and this forces the rest of the antral contents back into the proximal antrum

Front 45

What is the frequency and duration of gastric contractions?

Back 45

-3/min (same frequency as slow waves)
-duration ranges from 2 to 20 sec

Front 46

Duodenal factors that delay emptying gastric emptying

Back 46

1)hypertonicity of duodenal contents
2)decrease in duodenal pH (normally pH in d. is kept near 5 and pH <3.5 inhibits gastric emptying
3)Fatty acids or mono- or diglycerides in duodenum
4) peptides and amino acids (especialy tryptophan)
5)Duodenal distention

Front 47

neural pathways for gastric emptying?

Back 47

-ENS working in concert with vagus is crucial for normal emptying
-vagtomy delays gastric emptying

Front 48

Where are the hormones released from that may be involved in controlling gastric emptying?

Back 48

duodenum and jejunum

Front 49

What hormone is released in response to acid?

Back 49

secretin

Front 50

What hormone is released in response to fats?

Back 50

cholecystokinin (CCK) and glucose dependent insulinotropic peptides (GIP, formerly gastric inhibitory peptide)

Front 51

What hormone is released in response to amino acids?

Back 51

gastrin

Front 52

What hormone is released in response to hypertonicity?

Back 52

unknown

Front 53

two non-duodenal factors affecting gastric contraction

Back 53

-Ileal break
-colonic distention causes relaxation of gastric muscle

Front 54

ileal break

Back 54

glucose or fats in the ileum reduces gastric contractions

Front 55

colonic distention

Back 55

causes relaxation of gastric muscle

Front 56

When does Migrating myoeletric complex (MMC) occur?

Back 56

-occurs during fasting
-antrum quiescent for 1-2 hrs

Front 57

What happens during MMC?

Back 57

-After antrum in quiescent, there is a period of intense electrical and motor activity lasting 10-20 min
-strong antral contractions occur but pylorus is relaxed

Front 58

What is the point of MMC?

Back 58

-allows for emptying large chunks of undigested material from stomach