What is the upper esophageal sphincter made of
Striated muscle, not smooth
What innervates the upper esophageal sphincter
The vagal somatic division, so even if vagus nerve is usually autonomic, this isnt because were talking about striated muscle
How is the upper esophageal sphincter kept in its resting state
Vagal somatic nerve releases Ach onto nicotinic receptors in the sphincter constantly, this maintaining a constant contraction of the striated muscle
So for it to relax we have to stop this Ach flow
How is teh upper esophageal sphincter opened
We need to inhibit the vagal somatic nerve to prevent it from releasing Ach onto the sphincter, because when that flow stops the contraction will stop and well get relaxation such that food can pass through in a low resistance way
This is part of the deglutition reflex
Characteristics of the pharyngeal phase
Rapid (0.2 seconds)
Involuntary
Stereotyped, as in must be identical every time
Temporal-spatial coordination: coordination such that food does not enter airway
What’s the pressure situation in the esophagus
Negative relative to atmospheric pressure, liek -5 to -10 mmHg
This is due to teh fact that the esophagus is in the thoracic cavity, which has a bunch of stupid pressures going on
What are the forces than affect bolus movement in esophagus
Gravity: minor effect, not huge for liquids and none for solids
Peristalsis: main one, bolus moved by muscle contraction
Primary peristaltic wave
Basically every time you swallow theres a primary peristaltic wave, a wave of circular muscle contraction that propels the bolus down the esophagus, this is part of the deglutition reflex, so driven by teh deglutition center in the medulla
What ensures that primary peristalsis is a smooth wave
The fact that all the signals originate in the deglutition centre of the medulla, so when the reflex is starts, stretch receptors of the pharynx get triggered, tells the deglutition centre, the medulla then activates first the vagal somatic nerve to trigger the relaxation of the upper esophageal sphincter, it does so by activating the striated muscle cells in a sequential way, first one then 2, etc
Then just after it activates the vagal autonomic nerve so activate the ENS neurons so they can cause smooth muscle contraction in a coordinated way down the esophagus, but these smooth muscle cells arent activated sequentially but rather all at once, but they dont contract all at once because theres a built in delay the lower down the tube you go, increased latency
What’s latency and where do we see it in deglutition
Latency is the time between stimulus detection and response
We see it in the contraction of esophageal smooth muscle cells, theyre all stimulated at the same time by the vagal autonomous nerve but the contraction does not occur simultaneously, they occur just after one another to make a smooth wave
If we cut the vagus nerve, can we still get primary peristalsis
No, since the activity of the vagus nerve is required to initiate the reflex, we need at least enough nerve to activate that first ENS neuron, after that it can self activate, but until then vagus nerve is required
In what scenario would you get secondary peristalsis and how do you fix it
In the event that the bolus gets stuck, like the primary peristalsis isnt enough to propel the bolus all the way down, so we need to trigger a second wave
It’s triggered specifically by the local distension caused by the stuck bolus, this will signal to the enteric neurons directly, basically telling it to have a wave of propagated contractions to push it down further, this would be a short reflex
The local distension can also communicate with the deglutition centre, causing a long reflex, the medulla will in turn activate a vagal autonomic neuron to activate the ENS to have more contraction waves
Vagal vagal réflexes
Another name for teh long reflexes because it involves communicating via sensory neurons to the medulla (goes through the vagus) and eliciting a vagal response, vagus used twice, vagal -vagal, and this will continue until the bolus has moved
Lowe esophageal sphincter
Basically the last 4 cm of the esophagus, 2 of which are above the level of the diaphragm, the other two below
Its important that the sphincter remains closed until bolus is passing through due to the very acidic nature of the stomach
It’s an intrinsic physiological sphincter, meaning it keeps itself closed, producing an anti reflux mechanism
How does the LES stay closed
The UES had a constant flow of Ach to keep the muscle contracted, not the case here, here its kept closed by a property intrinsic to the muscle itself
The muscle has residual resistance, like muscle tone, that just at rest keeps it in a closed state, this is myogenic closure, contraction at rest
How does the LES open
At rest and under neither ANS or ENS control its contracted, myogenic closure, but when we want to open it well need intervention, neurogenic control, where basically the vagal autonomous fibres stimulates inhibitory ENS neurons that will release NANC peptides onto the muscle cells to cause them to relax
This relaxation is also a part of the deglutition reflex
Why is it important for half the LES to be below the diaphragm
Since its below the diaphragm its also subject to any intrabdominal pressure changes that teh stomach undergoes, which can literally be caused by anything, like bending over, which is important because if the stomach pressure were higher than the LES pressure then the stomach acidic content would go down its pressure gradient and up the esophagus, quite damaging
Note that the LES in a rest position is 20mmHg higher than the stomach, so if you bend over and increase the intraabdominal pressure by 100, the LES pressure below the diaphragm will rise to 120mmHg, still keeping the peace
What causes heart burn
A failure in teh closer of teh LES that allows some of the stomach content aka acid to reach the esophagus, burns cuz its acid
What hormones can modulate the contractility of the LES
Progesterone, it can decrease its contraction, making it looser so to speak, a less tight seal, explains why pregnant women get heart burn, that combined with the presence of the fetus increasing intrabdominal pressure
3 motor functions of the stomach
Storage for one, can store up to 2L of food, proximal (top) half of stomach)
Physical mixing and disruption of content, done with gastric juices, becomes chyme (semi-liquid consistency), distal (bottom) half of stomach
Propulsion into duodenum: its regulated and slow
What are the regions of the stomach
Teh fundus (top), the body and the antrum, theres also a small region at the exit, the pylorus, with the famous pyloric sphincter leading to the duodenum
Musculature in proximal vs distal parts of the stomach
Proximal: main function is storage so musculature is thinner
Distal: mains functions are mixing and propulsion, so musculature is thicker
What’s different about the mucosa of the stomach
Has rugae, folds, as well as many different niche cell type specific to its function
Rugae allows for increase in surface area
What’s different about the muscularis externa of the stomach
Differs in that it has an extra layer, the oblique layer, this is the most internal
So longitudinal-> circular-> oblique
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Respiration 132
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Respiration 235
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Respiration 325
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Respiration 427
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Respiration 542
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Respiration 620
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Respiration 715
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Cardio 119
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Cardio 216
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Cardio 314
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Cardio 422
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Cardio 519
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Cardio 621
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Cardio 77
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Cardio 820
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Cardio 917
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Cardio 1012
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Endocrinology 116
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Endocrinology 224
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Endocrinology 323
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Endocrinology 432
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Endocrinology 532
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Renal 118
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Renal 231
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Renal 323
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Renal 419
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Renal 527
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Renal 617
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GI 127
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GI 222
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GI 326
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GI 422
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GI 528
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GI 633
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GI 723
