15. GI Tract Introduction

Question 1

What are the layers of the gut tract wall from outer to inner?

Answer 1

1. serosa
2. longitudinal smooth muscle
3. myenteric plexus
4. circular smooth muscles
5. meissner’s corpuscle
6. submucosa
7. mucosa

Question 2

What is the serosa layer?

Answer 2

1. outer layer of connective tissue and simple squamous epithelium
2. continuous with the mesentery (pathway for blood to gut tube)

Question 3

Where is the serosa layer missing in the GI tract?

Answer 3

1. esophagus, where it is replaced with adventitia to connect to abd wall

Question 4

What is the submucosa?

Answer 4

1. lamina propria but thicker

2. incorporates the blood vessels and submucosal plexus

Question 5

What layers does the mucosa include in order to form a continuous sheet that lines the entire GI tract?

Answer 5

1. lamina propria: loose CT with nerve, blood vessel, glands

2. muscularis mucosa: thin smooth muscles, form mucosal ridge

Question 6

What type of cells help form the mucosa layer of gut?

Answer 6

1. simple columnar epithelium with goblet cells

2. line entire gut tract

Question 7

What forms the enteric nervous system?

Answer 7

1. myenteric and meissners plexuses

2. neurons are supported by intrinsic glial cells

Question 8

How does the enteric nervous system operate?

Answer 8

1. intrinsic regulation and sensory reflexes
2. parasympathetic increase GI activity
3. sympathetic decrease GI activity

Question 9

Where are myenteric plexus and what does it control?

Answer 9

1. in between longitudinal and smooth muscles
2. tonic and rhythmic contraction of smooth intestinal muscles
3. excitatory (Ach, NO)
4. inhibitory (VIP)

Question 10

Activation of the myenteric plexus will lead to what effects?

Answer 10

1. increased tonic contraction of gut wall
2. more intense rhythmic contractions
3. increased rate of contractions
4. increased velocity

Question 11

What does the Meissner’s plexus mostly control?

Answer 11

1. GI secretion, absorption, and local blood flow

2. mostly local effects not long distant.

Question 12

What is peristalsis?

Answer 12

1. propulsion of food along the gut tract forcing bolus from one direction to the other

Question 13

How does peristalsis work?

Answer 13

1. circular muscles contract to prevent backflow
2. longitudinal muscle will propel the bolus forward, causing distension of the tube
3. distension will cause contraction of next circular ring, and the next segment of longitudinal muscle

Question 14

What is receptive relaxation?

Answer 14

1. vagovagal reflex, which activated by food and casues distension of the proximal region of stomach
2. CCK is then released causing distal distention of stomach

Question 15

What is the role of the distal stomach with mixing food and beginning digestion?

Answer 15

1. contraction of distal region mixes food with gastric secretions
2. contraction seals off distal end and propels food back into the “body” of stomach for mixing

Question 16

What will increase gastric contractions, to improve mixing?

Answer 16

1. stimulation of vagus nerve (parasympathetic)

Question 17

Stimulation of what nervous system leads to decreased gastric mixing?

Answer 17

1. stimulation of sympathetic nervous system, and inhibition of signals to vagus nerve

Question 18

When is gastric emptying the fastest?

Answer 18

with isotonic solutions, occur with contraction of distal end of stomach to duodenum

Question 19

What will slow the emptying of the stomach contents into the duodenum?

Answer 19

1. hypo-/hypertonic solutions

2. fat (increases CCK that slows emptying)

Question 20

Why would acid in the duodenum slow gastric emptying?

Answer 20

1. the duodenum is a basic environment, that can be damaged by too low a pH, therefore gastric secretions will be reduced to protect the duodenal lining

Question 21

What does food in the stomach continue to activate?

Answer 21

1. the gastroileal reflex

2. mediated by extrinsic ANS and gastrin

Question 22

What increases mixing and digestion in the small intestine?

Answer 22

1. vagus nerve (parasympathetic) increases digestion

2. sympathetic NS, inhibits vagus nerve signaling. decreasing digestion

Question 23

What is the role of enterochromaffin cells?

Answer 23

1. sense food in intestine
2. release serotonin
3. serotonin activate primary afferent neurons for peristalsis

Question 24

What system is in control of the peristalsis in the small intestine?

Answer 24

1. enteric nervous system

Question 25

What causes the ileocecal sphincter to close, and prevent fecal backflow into the small intestine?

Answer 25

1. distension of the proximal colon | 2. site of mass colonic water absorption

Question 26

What creates haustra?

Answer 26

segmented contraction in proximal colon

Question 27

What occurs in the distal colon?

Answer 27

1. semisolid, slow moving fecal material | 2. fecal material propelled into rectum in mass movement

Question 28

Defecation

Answer 28

1. internal anal sphincter must relax allowing movement into rectum, and urge begins with 25% filling of rectum

Question 29

What prevents defecation?

Answer 29

external anal sphincter under voluntary control

Question 30

What maneuver will increase the ability to defecate?

Answer 30

1. valsalva maneuver which increase intra-abdominal pressure

Question 31

What is the gastrocolic reflex?

Answer 31

1. stretching of stomach increases parasympathetic stimulation and frequency of mass movements along the GI tract. 2. CCK and gastrin react but at slower rate.

Question 32

What are slow waves?

Answer 32

1. slow oscillating potentials inherent to smooth muscles of GI tract

Question 33

Where do slow waves originate from?

Answer 33

1. interstitial Cajal cells 2. can vary intensity from 5-15mV 3. frequency from 3-12/min

Question 34

What cause muscle contraction of the smooth muscles in the GI tract?

Answer 34

1. spike potentials

Question 35

What do spike potentials generate?

Answer 35

1. open Ca channels, and Na channels in GI smooth muscles | 2. have a longer time of activation than normal action potential

Question 36

What is a spike potential?

Answer 36

1. action potential of smooth muscle GI 2. frequency= the amplitude of the signal 3. last 10-40x longer than normal action potential

Question 37

What factors cause depolarization of GI smooth muscles cells?

Answer 37

1. muscle stretching 2. Ach stimulation (parasympathetic) 3. GI specific hormone stimulation

Question 38

What factors cause hyperpolarization of smooth muscles of GI tract?

Answer 38

1. norepi/epi | 2. sympathetic nerve stimulation

Question 39

What cause tonic contractions of GI tract?

Answer 39

1. continuous repetitive spike potential 2. hormones 3. continuous entry of Ca ion

Question 40

What are the major three different types of GI reflexes?

Answer 40

1. reflex integrated within gut wall enteric nervous system 2. from gut to prevertebral sympathetic ganglia and back to GI 3. from gut to spinal cord/brainstem and back to GI

Question 41

What are the different type of reflexes that are associated with the enteric nervous system?

Answer 41

1. GI secretions 2. peristalsis 3. mixing contractions 4. local inhibitory effects

Question 42

What reflexes send signals from the gut to the prevertebral sympathetic ganglia and back to the GI?

Answer 42

1. gastrocolic (evacuation of colon) 2. enterogastric (inhibit stomach motility/secretion) 3. colonoileal (empty ileal content into colon)