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Small Intestine - Anatomy & Physiology (view source)
Revision as of 13:27, 10 July 2008
, 13:27, 10 July 2008→Regulation & Control
==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
*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==