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Describe the anatomy and histology of the muscular layers to the extent they are discussed in your text.
longitudinal and concentric
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Indicate the role of the Interstitial Cells of Cajal in generating the slow wave or basic electrical rhythm (BER).
- couple the longitudinal and circular muscles
- determines: max frequency, direction of propagation, speed of propagation
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Discuss the conditions that permit a slow wave to produce a contraction or generate action (spike) potentials.
the depolarization is strong enough to reach the threshold
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Compare the functional differences between tonic and phasic smooth muscle. Compare the frequency of the BER in stomach, small and large intestine and sphincters.
tonic can provide sustained contraction - segmentation
phasic is on and off, repetitive and slow - peristalsis
stomach < large intestine < small intestine < sphincters
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Explain the role of neurocrines or endocrines in modulating slow wave activity
ACh, CCK, gastrin: excitatory, depolarize, stim contraction, make the contraction longer and stronger
Epi, GIP, VIP, secretin: inhibitory, hyperpolarize, inhibit contraction, make the contraction weaker and shorter
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The functions of motility are:
- agitate the lumenal contents
- mix the contents with secretions from the various GI organs
- optimize the time necessary for digestion and absorption and promote the orderly movement of contents from mouth to anus
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Each section of the GI tract expresses a unique electrical activity that normally moves the contents in an _______ direction.
orthograde
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The resting membrane potential in smooth muscle is not constant but _______, which is termed, ________, an inherent property of the smooth muscle cell that occurs without neurochemical mediation.
- depolarizes and repolarizes with time
- myogenic
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The oscillations are known as _______ or _________ and originate in the ______.
- slow waves
- the basic
- electrical rhythm (BER)
- Interstitial Cells of Cajal (ICC)
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Interstitial Cells of Cajal (ICC) are specialized ________ cells that determine _____________.
- pacemaker
- the maximal contractile frequency or how often contractions can develop, the propagation velocity and direction of propagation
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ICCs have properties of ______ and ________. The branched processes of the cells form _______ with _________ and thus _________.
- fibroblasts
- smooth muscle cells
- gap junctions
- smooth muscle cells
- couple the electrical activity of the longitudinal and circular layers
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Two distinct types of motility: segmentation and peristalsis.
- sphincter, proximal stomach
- contraction: long, tonic
- spike rate: high
- esophagus, gastric antrum, small intestine
- contraction: phasic
- spike rate: low
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Neurocrine regulation on smooth muscle activity
- ACh, gastrin and CCK
- depolarize
- stimulate contraction
- increase the amplitude of the slow wave and the frequency of spike -> longer and stronger contractions
- epinephrine, VIP, secretin and GIP
- hyperpolarize
- inhibit contraction
- decrease slow wave amplitude and decrease or abolish spike potential -> decrease the force and frequency of action potentials
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In the stomach, the slow frequency promotes _______.
The fast frequency in the small intestine is instrumental in ________.
The slow frequency in the colon promotes _________.
- slow mixing
- rapidly removing acid contents and preventing ulcers
- net water absorption and controlled emptying of waste products
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