Introduction to G.I. tract

Question 0

What is the serosa? It is made up of what kind of epithelium? What is it continuous with?

Answer 0

Outer layer of connective tissue made up of simple squamous epithelium. It is continuous with mesentary (double layer of tissue in posterior abdominal wall and serves as a pathway for blood vessels to gut tube)

Question 1

What are the layers of the gut tract wall from outside to inside?

Answer 1

Serosa (adventitia)–>Longitudinal smooth muscle layer–>Myenteric plexus (of Auerbach)–>Circular smooth muscle layer–>Meissner’s plexus (submucosal plexus)–>mucosa

Question 2

In which areas of the gut tube is the mesentary missing? What is it replaced with?

Answer 2

Mesentary is missing in the esophagus in thoracic cavity and ascending and descending colon in abdominal cavity. It is replaced with adventitia connecting to abdominal wall.

Question 3

The enteric nervous system is made up of what two plexuses?

Answer 3

Myenteric and Meissner’s plexuses

Question 4

Myenteric and Meissner’s plexuses can operate autonomously via _______ and ______. It works with ______ and _____ systems. _____ generally increases GI activity, ____ generally decreases GI activity. Neurons are supported by _____

Answer 4

intrinsic regulation and sensory reflexes; sympathetic and parasympathetic (vagus nerve); parasympathetic, sympathetic; intrinsic glial cells

Question 5

1. Myeteric (Auerbach’s) plexus is located between _____ and ____ layers.
2. It controls ______ and participates in ____ and _____ contractions.
3. It consists of a _______chain of ______ neurons
4. It extends the ____ length of the G.I. tract
5. Its mostly _____(inhibitory/excitatory?) and uses _____ as the NT
6. Some inhibitory signals may inhibit _______ muscles like the NT ____

Answer 5

1. longitudinal and smooth muscle
2. intestinal smooth muscle, tonic and rhythmic
3. linear, interconnecting
4. entire
5. excitatory, Ach/NO
6. intestinal sphincter muscles, VIP

Question 6

1. The myenteric (Aurbach’s) plexus increases _______ of gut wall
2. It also increases intensity of ________
3. It slightly increases the rate of ______ contraction
4. It increases velocity of _______

Answer 6

1. tonic contraction
2. rhythmical contractions
3. rhythmical contractions
4. excitatory waves

Question 7

1. Meissner’s (Submucosal) plexus controls _____, _____ and _____
2. It is mainly concerned with controlling function within ____ of each minute segment of the intestine
3. It helps in control of ____, _____, and ______ of submucosal muscle

Answer 7

1. GI secretion, absorption, and local blood flow
2. inner wall
3. local secretion, local absorption, and local contraction

Question 8

1. The submucosa is similar to ____ but ____

2. The submucosa incorporates ______ and ______

Answer 8

1. lamina propria, thicker

2. blood vessels and submucosal plexus

Question 9

1. The mucosa is a ____ cell layer
2. The mucosa forms a _____ lining the entire G.I tract.
3. The mucosa includes the ______ and _____.

Answer 9

1. single
2. continuous
3. lamina propria and muscularis mucosa

Question 10

What is the lamina propria? What is the muscularis mucosa?

Answer 10

Lamina propria=loose CT with sensory nerves, blood vessels and glands
Muscularis mucosa=thin layer of smooth muscle, creates mucosal ridges and folds

Question 11

1. Propulsive movements are created by ______ at any point in the gut which can cause a ____ to occur.
2. Contractile ring moves ____ after it appears
3. The usual stimulus that causes contractile ring is ____. But it may also occur due to _____ or _____ irritation or strong ______signals
4. Propulsive movements requires the presence of functional _____
5. Propulsive movements can occur in ____ direction but dies out when traveling in ____ direction

Answer 11

1. stimulation, contractile ring
2. forward
3. distension, chemical, physical, parasympathetic
4. myenteric plexus
5. any, oral

Question 12

1. Mixing movements may be caused by ______ (in other words, propulsive movements may result in mixing)
2. At other times, ______ contractions occur every few centimeters in the gut wall (so material can’t move forward in oral direction)

Answer 12

1. peristaltic contractions

2. local intermittent constrictive

Question 13

1. slow waves within neurons ______(are/are not) action potentials
2. Slow waves are ___, undulating changes in ________ potential.
3. Intensity of slow waves varies between ___ and ___ mv.
4. Frequency ranges from ____ to ___ waves per minute (increases from ____ to ___)

Answer 13

1. are not
2. slow, resting membrane
3. 5, 15
4. 3, 12, stomach, duodenum

Question 14

1. Slow waves may be caused by complex interactions among the ____ and the _____ cells of ____ (smooth muscle cell electrical pacemakers).
2. ____ undergo cyclic changes that periodically open and produce inward (pacemaker) currents that may generate slow wave activity
3. Slow waves excite the appearance of _____ which excite ____

Answer 14

1. smooth muscle cells, interstitial cells of Cajal
2. Cells of Cajal
3. intermittent spike potentials, muscle contraction

Question 15

1. Spike potentials are _____ action potentials. They occur automatically when resting membrane potential of GI smooth muscle is above ____ (threshold)
2. The higher the slow wave potential, the ____ the frequency of the spike potential
3. A spike potential lasts ___ times as long as a typical AP in a large nerve fiber (10-20ms)
4. Spike potentials are responsible for opening _____ channels and smaller number of ____ channels in GI _____ cells
5. Channels open ____ and close ____.

Answer 15

1. true, -40mv
2. greater
3. 10-40
4. calcium, sodium, smooth muscle
5. slowly, rapidly

Question 16

Which NTs makes it difficult to reach spike potentials (hyperpolarization)? Which NTs makes it easier to reach spike potential (depolarization)?

Answer 16

Stimulation by norepinephrine and sympathetics causes hyperpolarization (harder to reach spike potential); stimulation by stretch, acetylcholine and parasympathetics makes it more likely to reach spike potential (depolarization)

Question 17

Look at figure 62-4 and notes from class on that slide

Answer 17

Slide 21

Question 18

What are 3 factors that cause depolarization?

Answer 18

1. Stretching of muscle
2. Stimulation by acetylcholine (parasympathetic)
3. Stimulation by specific GI hormones

Question 19

Factors that cause hyperpolarization

Answer 19

1. Norepinephrine and epinephrine

2. Stimulation of sympathetic nerves

Question 20

Causes of Tonic contractions (contractions that increase the muscle tone within the wall of the gut tube)

Answer 20

1. Continuous and repetitive spike potentials
2. Hormones
3. Continuous entry of calcium ions

Question 21

1. GI reflexes are reflexes that are integrated entirely within the ______
2. GI reflexes are responsible for what 4 things?

Answer 21

1. gut wall enteric nervous system control
2. GI reflexes are responsible for much of GI secretion, peristalsis, mixing contractions and cause local inhibitory effects

Question 22

1. Reflexes can travel from the gut to the _____ and then back to the ____.
2. These reflexes transmit signals ____ to other areas of the gut tract
3. What is the gastrocolic reflex? Enterogastric reflex? Colonoileal reflex?

Answer 22

1. prevertebral sympathetic ganglia, GI tract
2. long distances
3. Gastrocolic reflex=causes evacuation of the colon
   Enterogastric reflex=inhibits motility and secretion
   Colonoileal reflex=empty ileal contents into the colon

Question 23

Reflexes can also from from the gut to the spinal cord or brain stem and then back to the GI tract.

1. These include reflexes that travel from the ____ and ___ to ___ and back to the ___. They control ____ and ____ activity.
2. Pain reflexes cause ____ of the entire GI tract.
3. ____ reflexes extend from the colon to the rectum to the spinal cord and back.

Answer 23

1. stomach, duodenum, brainstem, stomach; gastric motor and secretory
2. general inhibition
3. Defecation

Question 24

Gastrin

1. Stimulus for secretion:
2. Site of secretion:
3. Actions:

Answer 24

1. Protein, distension, nerve action (acid inhibits release)
2. Gastrin cells of antrum, duodenum, jejunum (in response to stimuli associated with ingestion of a meal (i.e., stomach distention or gastrin releasing peptide)
3. Stimulates gastric acid secretion and mucosal growth

Question 25

CCK

1. Stimulus for secretion:
2. Site of secretion:
3. Actions:

Answer 25

1. Protein, fat, acid
2. I cell of duodenum, jejunum, ileum
3. Stimulates pacreatic enzyme secretion, pancreatic bicarbonate secretion, stimulates growth of exocrine pancreas, inhibits gastric emptying, inhibits apetite

Question 26

Secretin

1. Stimulus for secretion:
2. Site of secretion:
3. Actions:

Answer 26

1. Acid and fat
2. S cells of the duodenum, jejunum, and ileum
3. Stimulates pepsin secretion, stimulates pancreatic bicarbonate secretion, stimulates biliary bicarbonate secretion, stimulates growth of exocrine pancreas, and inhibits gastric acid secretion

Question 27

GIP (Gastric Intestinal peptide)

1. Stimulus for secretion:
2. Site of secretion:
3. Actions:

Answer 27

1. Protein, fat, carbohydrates
2. K cells of duodenum and jejunum
3. Stimulates insulin release, inhibits gastric acid secretion

Question 28

Motilin

1. Stimulus for secretion
2. Site of secretion
3. Actions

Answer 28

1. Fat, acid, nerve action
2. M cells of duodenum and jejunum
3. Stimulates gastric and intestinal motility, secreted during fasting

Question 29

At what point do we enter the stage of no return for food material? (voluntary, pharyngeal and esophageal)

Answer 29

Pharangeal

Question 30

Describe the neurological and mechanical elements of swallowing

Answer 30

Look in text book

Question 31

What are the motor functions of the stomach?

Answer 31

1. Storage of large amounts of food
2. Mixing food with gastric secretions (mixing waves in upper portion of stomach occur every 15-20 sec and move towards antrum, mixing waves are replaced by peristaltic waves that drive food toward the pylorus, thickness of circular muscle layer in pylorus is 50-100% greater than elsewhere in stomach=pyloric sphincter
3. Slow emptying of chyme into small intestine (stretching of stomach wall due to increased food volume promotes increased emptying of stomach due to local myenteric reflexes in the wall)

Question 32

In duodenum, the inhibitory effects of enterogastric nervous reflexes:

1. Reflexes occur directly from the ___ through the ___ of the gut wall
2. Reflexes occur through ____ nerves that go to ___ ganglia and then back through ____ to the ____
3. Reflexes may occur via ___ back to the____

Answer 32

1. duodenum, enteric nervous system
2. extrinsic, prevertebral, inhibitory sympathetic nerve fibers, stomach
3. vagus nerve, brainstem

Question 33

What are the factors that are continually monitored in the duodenum and that can initiate Enterogastric inhibitory reflexes?

Answer 33

1. Degree of distension of the duodenum
2. Presence of any degree of irritation of the duodenal mucosa
3. Degree of acidity of duodenal chyme
4. Presence of certain breakdown products in the chyme (especially proteins)

Question 34

What are the hormonal factors that control feedback from the duodenum:

Answer 34

1. CCK =most potent

2. Other inhibitors include secretin and GIP

Question 35

1. The 2 types of movement in intestine are ___ and ___ contractions
2. Localized contractions cause ____. It chops the chyme 2-3 times per minute and mixes the foods with secretions.
3. ____ contractions (Propulsive) can occur in any part of the SI and move towards the anus (0.5-2.0 cm/sec); travels only __to __ cm before dissipating so ___ hours are required for passage of chyme through SI.

Answer 35

1. Propulsive and mixing
2. segmentation
3. Peristaltic

Question 36

Mechansims that control intestinal movement:

1. ____ is initiated by stomach distenstion and conducted via ____
2. Hormones including ___, ___, ___, ____
3. Irritation of the intestinal mucosa can cause powerful and rapid ___
4. Right after meal, ___ intensifies perstalsis and emptying of ___ into__

Answer 36

1. Gastroenteric reflex, myenteric plexus
2. gastrin, CCK, insulin, motilin, serotonin
3. peristalsis (peristaltic rush)
4. gastroileal, ileal, cecum

Question 37

1. What are the principal functions of the colon?

2. What are Haustrations?

Answer 37

1. Functions: absorption of water and electrolytes from chyme and storage of fecal matter until it can be expelled
2. Haustrations: produced by large circular constrictions plus contractions of the teniae coli

Question 38

Describe the processes involved with defecation

Answer 38

Look in text