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| ==Regulation & Control== | | ==Regulation & Control== |
| | | |
− | *The functions of the small (and large) intestine are regulated by three elements: | + | *The functions of the small (and large) intestine are regulated by three mechanisms: |
| **Endocrine hormones | | **Endocrine hormones |
| **Paracrine hormones | | **Paracrine hormones |
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| *Control is mainly local, with superimposed co-ordination through the ANS. | | *Control is mainly local, with superimposed co-ordination through the ANS. |
| *All signals affect the small intestine via sensory neurones. | | *All signals affect the small intestine via sensory neurones. |
− | **The sensory neurones interact with the two plexuses in the intestinal wall. | + | **Neurones interact with the two plexuses in the intestinal wall. |
− | **Sensory neurones in the myenteric plexus produce changes in muscle contractility | + | **Neurones in the ''myenteric plexus'' produce changes in muscle ''contractility'' |
− | **Sensory neurones in the submucosal plexus produce changes in secretion and blood flow to the small intestine | + | **Neurones in the ''submucosal plexus'' produce changes in ''secretion'' and ''blood flow'' to the small intestine |
− | **Plexuses are connected via interneurones | + | **Plexuses are connected via interneurones. |
| + | **Excitatory neurotransmitters of the parasympathetic nervous system include: |
| + | ***substance P |
| + | ***acetylcholine (via muscarinic M1 and M2 receptors) |
| + | ***serotonin (5-HT) |
| + | **Inhibitory (sympathomimetic) neurotransmitters include: |
| + | ***vasoactive intestinal polypeptide (VIP) |
| + | ***nitric oxide (NO) |
| + | ***ATP |
| + | ***enkephalins |
| + | *The autonomic nervous system (ANS) control is superimposed over local control. |
| + | **The ANS acts via the same two plexuses. |
| + | **Parasympathetic innervation stimulates motility and secretion |
| + | **Sympathetic innervation antagonises the parasympathetic nervous system and inhibits motility and secretion. |
| + | *Generation of action potentials is intrinsic to the smooth muscle in the intestine. |
| + | **'''Interstitial cells of Cajal''' act as muscle pacemakers and generate a ''basic electrical rhythm''(BER). |
| + | **The BER is able to pass between cells due to the presence of gap junctions. The muscle therefore acts as a syncytium. |
| + | **Some BER are sufficient to generate an action potential. |
| + | ** |
| | | |
| ==Lymphatics== | | ==Lymphatics== |