Term
| What is the main function of the GI tract and what processes does it utilize to accomplish this? |
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Definition
Supply the body with essential compounds (pretty much everything from biochem)
It does this by using contraction, secretion, digestion, and absorption |
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Term
| What determines what is absorbed in the GI tract? |
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Definition
| Pretty much anything that is fat or water soluble with the exception of Fe and Ca, which are regulated |
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Term
| What is the main difference between the excretion products of the kidney and GI tract |
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Definition
| Kidneys secrete water soluble materials, whereas the GI tract secretes water insoluble materials |
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Term
| What is the cephalic phase of digestion and what controls it? |
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Definition
| It is a phase of digestion that begins before food enters the body (primed through sight, smell, etc.) and prompts the initial release of gastric juices. The vagus nerve controls this. |
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Term
| What is the gastric phase of digestion? |
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Definition
The 2nd phase in digestion, triggered by distension in the stomach, presence of food, and a drop in pH.
It is characterized by gastrin-histamine stimulation which causes parietal cells to release gastric acid |
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Term
| What governs the contraction of muscles as well as secretions in the GI tract? |
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Definition
| Nerve plexuses located in the submucosal layer |
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Term
| What are the 2 nervous systems that control regulation of the GI tract? |
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Definition
1. CNS via the ANS
2. Enteric nervous system ("minibrain" in the GI tract) |
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Term
| What are the two nerve plexuses in the enteric nervous system? What does each control? |
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Definition
Submucosal and Myenteric
Submucosal controls secretions
Myenteric controls motility |
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Term
| Which parts of the ANS are stimulatory to the EP and which are inhibitory? |
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Definition
Sympathetic is inhibitory
Parasympathetic is stimulatory |
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Term
| Are GI smooth muscle cells single unit, or multi unit? What does this mean? |
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Definition
1. Single unit
2. Electrical coupling between cells allows long lengths of muscle to contract and behave as a single unit |
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Term
| What controls contraction in smooth muscles? |
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Definition
1. Free calcium concentration in the cell controls the activity of Smooth muscle myosin phosphorylation
2. Phosphorylation of myoson activates ATPase activity, leading to contraction
3. Dephosphorylation by myosin phosphatases leads to relaxation
NOTE: Myosin phosphatases can be inhibit or stimulated by neural or hormonal inputs |
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Term
| What is the difference between tonic and phasic smooth muscle |
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Definition
1. Tonic smooth muscle is located in places requiring steady contraction (sphincters)
2. Phasic smooth muscle requiring rhymthic changes (caudal stomach) |
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Term
| Explain the contraction of phasic smooth muscle in terms of electrical waves |
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Definition
| There is the smooth wave (a low frequency wave that the membrane fluctuates with). When this fluctuation crosses a threshold, a spike potential occurs. The strength of contraction is proportional to the frequency of the spikes. |
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Term
| How is the slow wave generated in smooth muscle? |
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Definition
| Pacemaker cells in the interstitial cell network are coupled to the smooth muscle and provide the slow wave |
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