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47 Cards in this Set
- Front
- Back
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What normally happens when the intraabdominal P increases?
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As it increase,
the pressure increases equally on the stomach and intraabdominal LES |
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What happens in hiatus hernia?
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Entire LES moves upward into the thoracic cavity and person is more likely to reflux
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What happens when the intraabdominal P increases in hiatus hernia?
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This increase does NOT inc LES pressure
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What segments does the LES have?
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Intrathoracic segment: subject to negative P
Intraabdominal segment: subject to positive P ->These P in these segments vary with phases of respiration |
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What does the presence of the intraabdominal segment of the LES help the sphincter with?
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Helps sphincter maintain an effective barrier btw the stomach and esophagus
->If intraabdominal P is raised, the P of both the terminal segment and the intragastric contents is equally raised (.: there is no effective change in the gradient of P btw the stomach and the esophagus) |
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What are the characteristics of the LES?
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**1) Intrinsic physiological sphincter: this region remains tonically contracted at rest. Offers resistance to flow from below and prevents reflux.
2) Assisted by the presence of an Intraabdominal Segment |
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What happens if you have an incompetent LES?
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Sphincters fail to close
->gives rise to heartburn |
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What happens in heartburn (Pyrosis)?
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Burning sensation, radiating upwards in the chest towards the neck, ue to the acid reflux into esophagus
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Who is heartburn a particular problem for?
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Women in their last trimester of prgenancy
Repeated exposure to acid reflux may risk cancer |
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What affect does progsterone have on the LES?
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Relaxes musculature of the sphincter
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What effect does gastrin have?
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At physiological levels, no effect
->at very high levels, gastrin acts on the LES to tighten it |
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Does the stomach do any digestion?
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Yes, but very little
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What are the motor functions of the stomach?
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1) Temporary storage: 1-2L, has to be stored cuz the Small intestine needs time to digest and absorb
2) Physical disruption and mixing of contents: bolus becomes a semi-liquid consistency= CHYME (meal transported up to the colon in this form) 3) Propulsion into duodenum: highly regulated, requires only small amount of chyme to be released |
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Wha is the structure of the stomach?
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Starts wih Cardia
3 sections of stomach: 1-fundus (bulges above) 2-corpus: main portion (body) 3- antrum: distant region Pyloric sphincter at the end of the antrum |
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What are the functions of teh stomach?
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Proximal stomach: storage
Distal stomach: mixing and propulsion |
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What does the proximal stomach consist of?
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Cardia, fundus and 1/3 of corpus
Thin-walled (musculature is less developed) |
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What does the distal stomach encompass?
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Half of corpus, antrum and pyloric sphincter
Thick-walled |
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What is the intragastric pressure?
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~5 mmHg
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What happens with the intake of a meal?
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Normal empty stomach: has small lumen, ~50mL
Intake of meal: increaes from 50mL to 1500mL ONLY Proximal region of stomach expands with the intake of a meal |
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What is receptive relaxation?
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One of the degglutition reflexes
keeps intragastric P low |
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What happens if the vagi to the proximal stomach is cut?
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Receptive relaxation is limited
Get a great increase in intragastric pressure |
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What do the vagal efferents do?
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Go from degglutition centre to proximal stomach
Activate inhibitoru enteric neurons in proximal stomach Act on NANC (inhibitory neurons |
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What do the vagal afferents do?
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Enhance the response
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What is the vago-vagal reflex?
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Both afferent and efferent effector fibres are mediated by vagus nerves
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What is the local reflex?
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Not as important as the vagal reflexes for receptor relaxation
Can also activate inhibitory enteric neurons (enhances receptive relaxation) |
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What is receptive relaxation?
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The ability of the stomach to accomadate a large meal without significant increase in intragastric P
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What is receptive relaxation restricted to?
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Proximal part of stomach
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What is receptive relaxation due to?
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Vagalyy mediated reflex, initiated by swallowing and resulting in the inhibition of muscle tone and increase in intragastric volume
->Transmitter released by the inhibitory enteric neurons activated by the vagus is NANC |
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What does an entering meal do?
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Induces local distension, which sets up local (enteric) and long (vagal-vagal) reflexes which sustain the receptive relaxation
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What is the wave of "appropriate" activity in the upper GIT?
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1) Generate P to transport pharynx
2) Reflexes protecting airways 3) Relax UES 4) Contract pharyngeal constrictors *squeeze bolus through) 5) Primary peristalsis propagated along esophagus (push bolus ahead) 6) Relax LES (relaxes long before bolus actually reaches there) 7) Accomodate through gastric receptive relaxation in proximal stomach |
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Is there peristalsis in the proximal stomach?
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No, it is only the main form of contractile activity in the DISTAL stomach
Peristalsis= wave if movement over distal portion of the stomach |
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What does gastointestinal peristalsis result in?
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Propagated contraction that results from a series of local enteric reflexes in response to local distension
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What happens if the magnitude of the stimulus increases?
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Interaction of neural and hormonal factors also increase
It is directly related to the amplitude of contraction ->Greater degree of distension, greater amplitude of contraction |
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What are the electrical characteristices of smooth muscle?
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FREQUENCY
Direction Velocity |
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What is the membrane potential in the stomach?
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unstable mb potential wavs: 10-15 mV lasting 1-4 sec, but recurring at regular intervals
->these are SLOW waves (BER waves) they occur in every muscle fiber |
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Describe the waves.
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Peaks occur synchronously aroun the circumference of propagation
Depol/repol are synchronous circumferentially, but "migrate" along longitudinal axis -Lag in the appearance of the peak as you move along the long axis |
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What is the second electrical signal?
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ERA
Appears sequentially along the long axis, but ynchronously around the circumference |
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Which wave is ALWAYS associated with a contraction
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ERA always ass't with a contraction
(BER not always ass't with a contraction) |
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What are the number of spike of the ERA associated with?
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The amplitude of contraction
->Contraction is propagated along the long axis |
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What is the resting mb potential of the GI smooth muscle cell?
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~60mV (outside is positive)
**This resting mb potential is unstable, showing rhythmic depolaizations of 10-15mV** (at regular intervals, with uniform time course) which are propagated to adjacent cells ->these spontaneous waves are the BER (basic electrical rhythm) and are independent of innervation Spikes sometimes occur, these are ERA (electrical respomse activity) |
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What is the BER (ECA)?
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Constantly present (NOT initiative of contractions)
Propagated from cell to cell Frequency constant for a given region Detectable in longitudinal and circular muscle Origin is non-neuronal |
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Describe the ERA spikes.
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Intermittent
Phase-locked to the BER (can't happen btw waves, only occur at the peak of a depol) Stimulus: ACh or stretch receptors Ca2+ dependent in longitudinal and circular fibers Cell to cell propagation: MYOGENIC #spike/burst is proportional to the magnitude of the stimuls |
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Describe the contractions
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Ass't with spikes (ERA)
Amplitude of contractions is proportional to the #spikes/burst (proportional to magnitude of stimulus) MAXIMAL frequency of contractions is limited tby f of BER (no faster than every 20sec) |
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What determines the max f of the contractile activity?
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Determined by the f of the BER
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Describe the propagation of contractile activity.
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Though it has built-in the abililty of smooth muscle to propagate electrical signals from cell to cell (myogenic response)
**Peristaltic contraction still requires integrity of ENS** |
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What determine the amplitude of the contractile activity?
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Magintue of stimulus (stretch, ACh)
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Describe the waves of depol in the stomach?
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Begin in the pacemaker cells in the musculature in the upper corpus
Spread towards the pylorus with a frequency of 3/min -a velocity increases from 1cm/s in the corpus to 3-4cm/sec in the antrum Spkie potential (initiate contractions) only occur intermittently, but always related to BER .: When gastric contractions occur, they occur at 20sec interval (or a multiple therof) Higher conduction velocity in the antrum results in the whole terminal antrum synchronously contracting: ANTRAL SYSTOLE |
