Phgy 210: Digestion 2

Front 1

Does muscularis mucosa participate in propulsion?

Back 1

No

Front 2

What is propulsion in the GIT a result of?

Back 2

Gradients of P: results from coordinated contractions of muscular elements in wall off GIT (most of the tract= smooth muscle)
Variations in resistance: normally, little/no resistance (sphincters, under normal circumstances, don't offer any resistance, open as a one-way valve)

Front 3

What kind of flow is there normally?

Back 3

Slow
Aboral
Little/no resistance

Front 4

What is segmentation?

Back 4

Series of rings of contractions (divides gut into segments)

Front 5

What is peristalsis?

Back 5

Propagated wave of contraction which moves along wall of region of GIT, narrowing lumen and moving towards aboral regions

Front 6

What is degglutition?

Back 6

Swallowing
Very complex set of activities that take place very rapidly

Front 7

What are the 3 phases of degglutition?

Back 7

1) Oral: transport from anterior to posterior part of mouth
2) Pharyngeal: crossing of food over pharynx
3) Esophageal: carries food to stomach
**There are 3 separate phases, but when we swallow, it is a continuum

Front 8

How does degglutition occur?

Back 8

Series of highly coordinated muscular movements aimed a tbuilding up pressure, emporarily sealing off of compartments to prevent dissipation of pressure and decreasing resistance

Front 9

Which is the only phase that is under voluntary control?

Back 9

Oral phase

Front 10

What happens in the oral phase?

Back 10

Transport of bolus, which is a masticated, insalivated mass of food, from the anterior to posterior portion of the mouth

Front 11

Where are the reflexes involved in the oral phase coordinated?

Back 11

Degglutition center in the Medulla Oblongata
(the action of swallowing or njot is voluntary, but everything that follows depends on the medulla oblongata)

Front 12

What role does the cortex play in degglutition?

Back 12

Facilitates involuntary reflexes coordinated by the medulla

Front 13

What does the egglutition centre do?

Back 13

Involuntary
reflexes coordinate movement

Front 14

What are the functions of the oral phase?

Back 14

1) Ability to initiate: voluntary (cortex)

2) Coordinated movements: reflex, involuntary (medulla)

Front 15

Whst if the medullar centre is removed?

Back 15

Can't swallow

Front 16

What happens in the pharynx?

Back 16

The digestive and respiratory tracts cross

Front 17

What does the epiglottis do?

Back 17

Blocks opening of trachea

Front 18

What happens in the pharyngeal phase?

Back 18

Very rapid sequence of events to ensure the passage of the bolus into the esophagus and nowhere else
->Vocal cords come together to close trachea
->Larynx moves up and forward to fit under the tongue

Front 19

What is the order of passage in the pharyngeal phase?

Back 19

Passage into the nose/mouth and trachea are blocked
Pharynx
Upper Esophageal Sphincter

Front 20

Describe the Pharyngeal phase.

Back 20

Under involuntary control
a) A series of protective reflexes, initiated by stimulation of afferent fibres in the pharynx, organized in the Degglution centre, closing the nasal, oral and laryngeal cavities, so the bolus only goes one way. At thesame time, respiration is briefly inhibited (apnea)
b) Transfer to esophagus: pharyngeal muscles contract and UES relaxes

Front 21

What happens if the pharyngeal receptors are blocked?

Back 21

Can't swallow

Front 22

Whatkind of fibres link to degglutition centre and the pharyngeal receptors?

Back 22

Afferent fibres

Front 23

What kind of fibres jointhe degglutition centre and its action?

Back 23

Efferent fibres

Front 24

What are the actions of the degglutition centre?

Back 24

-Protectice reactions: various closures of tract and preventing bolus from going back into mouth
-Degglutition apnea: direct influence on respiratory center, inhibiting it
-Relax UES
-Contract pharyngeal constrictor muscles

Front 25

What does the vagus do?

Back 25

Has somatic fibers that innervates striated muscle

Front 26

Which muscles do the UES corespond to?

Back 26

Cricopharyngeus muscle
(needs to be neurally activated)

Front 27

What happens in Cricopharyngeus muscle closure?

Back 27

Impulses originate in CNS,meduated by vagus
Vgus releases ACh, which causes muscle contraction (when it acts on nicotinic receptors)

Front 28

What happens when the vagus is inactivated?

Back 28

Relax sphincter, can't get any contractions

Front 29

What happens in Cricopharyngeus muscle relaxation?

Back 29

Cessation of impulses, results in muscle relaxation

Front 30

Summarize pharyngeal phase. (4 points)

Back 30

1) Involuntary
2) Rapid: 1/5 of a second for a bolus to pass through pharynx to esophagus (stop breathing/speaking as blous travels through the pharynx)
3) Stereotyped: once initiated, all the series of events will occur
4) Temporalspatial coordination: if abnormality of this, very serious problem, can get a stroke

Front 31

What is the main function of the esophageal phase?

Back 31

Propulsion of bolus fromm upper portion through lower portion of esophagus to the stomach

Front 32

Where does the body of the esophagus lie?

Back 32

Thoracic cavity

Front 33

What protects the esophagus?

Back 33

Sphincters (upper and lower)

Front 34

Describe the GIT pressures.

Back 34

UES: high P zone
Body of esophagus: Intrathoracic -> negative P (due to this neg P, food willl tend to reflux back into pharynx)
LES: Intragastric positive P, also a high P zone, .: gastric content doesn't reflux back into esophagus

Front 35

What does the vagus innervate?

Back 35

Somatic
-Entire esophagus innervated

Front 36

What autonomic fct does the vagus have?

Back 36

Synapses with enteric neurons, which innervates the muscle
(doesn't directly activate muscles, can also have NANC receptors)

Front 37

What are the 2 esophageal forces?

Back 37

1) Gravity: helps, but is not essential. Only plays a role in esophagus, especially for liquids
2) Peristalsis: major mechanism that propels bolus. Very prominent in the esophagus, propagative wave of contraction

Front 38

What is peristalsis?

Back 38

Wave of contraction moving over the wall of the oorgan, narrowing the lumen and setting up a gradiemt of pressure favouring abhoral movement

Front 39

What happens when we swallow?

Back 39

Primary peristaltic wave is generated
Takes 8-10 seconds tobe propagated the length of the esopagus
-> primary peristalsis is part of degglutition reflexes

Front 40

What does the frequency of primaryperistalsis depend on?

Back 40

How much we swallow

Front 41

Where do the vagus somatic fibres go?

Back 41

To the striated proximal region of the esophagus
->Somatic: progressivle activated the striated muscles .: generating a wave

Front 42

What happens in the vagus autonomic fibres?

Back 42

Simultaneous signal along the entire length of the esophagus

Front 43

What happens if vagus is cut? (cut high in the neck)

Back 43

no innervation therefore no primary peristalsis

Front 44

What happens if the cut is transthoracic?

Back 44

Primary peristalsis continues because the distal esophaugus has the enteric circuitry necessary for the propagation of the peristaltic wave
->as long as some enteric neurons are activated, it will propagate a wave

Front 45

Where does the peristaltic wave move?

Back 45

Across the entire esophagus, despite the fact that 1/3 of the esophagues is striated muscle
->get smooth propagated contraction

Front 46

What does peristalsis result from in the striated portion of the esophagus?

Back 46

Sequential firing of the vagal motor neurons, activating the progressivley more distal regions of the musculature

Front 47

What happens in the smooth muscle region?

Back 47

Once some enteric neurons are activated, they can relay and activate other enteric neurons, and prpagate muscle cointraction in the aboral direction, independent of the extrinsic nerves.
->integrity of enteric innervation is critical to the propagaion of the peristaltic wave in the distal esophagus

Front 48

What is required for continuation and propagation of the primary peristalsis in the distal esophagus?

Back 48

Intactness of the ENS

Front 49

What is the vagus important for initiating peristalsis in?

Back 49

Proximal esophagus

Front 50

Describe secondary peristalsis/

Back 50

Initiated y local distension
Can be mediated by enteric reflexes or long (vagal) reflexes

Front 51

How many secondary peristaltic waves are there?

Back 51

Several waves, until the bolus has been displaced

Front 52

What initiates primary and secondary waves?

Back 52

1ry: stimulation of pharyngeal
2ry: local distention

Front 53

What is the LES?

Back 53

Last 4 cm of the esophagus
Half is above the diaphragm, the other half is below

Front 54

What does the LES d?

Back 54

Normally prevents acidic content of stomach to reflux in esophagus (remains tonically contracted)

Front 55

What kind nof receptor is present in the musculature between the esophagus and the stomach?

Back 55

an NANC

Front 56

Why must this musculature be tonically contracted at rest?

Back 56

To maintain the 5 pH difference, prevents reflux of gastrointestinal tract)
pH esophagus= 7
pH stomach= 2

Front 57

What is the closure of LES?

Back 57

Mygenic (property of the muscle itself)

Front 58

What is the relaxation of LES?

Back 58

mediated by nerves. Sphincter opens when we swallow and muscle relaxes
Local release of NANC (NT that goes to enteric neurons)(inhibitory, inhibits muscle tone at this site)

Front 59

What happens when youre not swallowing?

Back 59

The LES is in a state of tone and its walls are in firm apposition

Front 60

Is the tone under neural and hormonal influences?

Back 60

Yes, through the tone is largely myogenic

Front 61

What is relaxation of the LES?

Back 61

a degglutition reflex
Initiated during swallowing and mediated by vagal efferent fibres, releasing ACh, which aactivate inhibitory enteric neurons which release a NANC transmitter, causing muscle tone decrease