Difference between revisions of "Control of Feeding - Anatomy & Physiology"
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| Line 87: | Line 87: | ||
==Control of GIT Secretions== | ==Control of GIT Secretions== | ||
| − | * | + | *Presence of food in the GIT is detected by open chemoreceptors |
| + | |||
| + | *Signals to the endocrine cells or via the ANS releases gastrointestinal peptide hormones | ||
| + | |||
| + | *These hormones act to promote secretion, provide negative feedback or affect motility | ||
| + | |||
| + | *Closed mechanoreceptors also act to alter secretions | ||
| + | |||
| + | *Conditioned (associative) and unconditiones responses act via the ANS | ||
| + | |||
| + | {| style="width:50%; height:200px" border="1" | ||
| + | |||
| + | !'''Conrtol Method''' | ||
| + | !'''Neural''' | ||
| + | !'''Endocrine''' | ||
| + | |- | ||
| + | | '''Saliva''' | ||
| + | | Yes | ||
| + | | No | ||
| + | |- | ||
| + | | '''Stomach''' | ||
| + | | Yes | ||
| + | | Yes | ||
| + | |- | ||
| + | | '''Small Intestine''' | ||
| + | | No | ||
| + | | Yes | ||
| + | |- | ||
| + | |} | ||
| + | |||
==Neuroendocrine Regulation of Feeding== | ==Neuroendocrine Regulation of Feeding== | ||
Revision as of 08:10, 16 July 2008
Feeding Methods
- Absorption over body surface
- Filter feeding
- Mucous trapping
- Fluid feeding
- Piercing and sucking
- Cutting and biting
- Seizing prey
- Jaws, teeth, beak
- Toxins
- Herbivores and grazing
- Invertebrates
- Vertebrates- bony plates or teeth
Functions of the GIT
- Secretion of enzymes and co-factors for digestion including water, ions and mucous
- Motility for forward propulsion, mechanical breakdown, mixing of ingesta and sphincter tone
- Migrating myoelectric complex to prevent debris accumulation
- Peristalsis
- Haustration
- Segmental motility
- Blood flow to muscles, submucosa and epithelial surfaces to sustain secretion, motility and the uptake of products of digestion
- Growth and repair
Control of the GIT
- Endocrine hormones released into the circulation by cells within the GIT or an accessory organ
- Paracrine mediators released by cells within the tract and diffuse locally to acton neighbouring target cells
- Neurotransmitters from nerves andother cells
- Autonomic nervous system superimposed over the local control
Control of Motility
- Intrinsic
- Muscle pacemaker cells (Cajal cells)
- Basic electric rhythm (BER) created of 3-20 per minute
- Passes through gap junctions
- Action potential created producing a slow wave of contraction
- Liklihood of an action potential is increased through the stretch of food in the lumen and chemical food stimulation
- Endocrine, paracrine or neural enter the enteric nervous system via sensory neurones
- Neurons interact with plexuses in the GIT wall
- Myenteric controls muscle movement
- Submucosa controls secretion and blood flow
- 2 plexuses connected by interneurones to co-ordinate control
- Autonomic nervous system superimposed
- Excitatory neurotransmitters are parasympathomimetic
- ACh (muscarinic M1 and M2)
- Serotonin
- Substance P
- Inhibitory neurotransmitters are sympathomimetic
- Vasoactive intestinal polypeptide (VIP)
- Nitroc oxide (NO)
- ATP
- Enkephalins
- Extrinsic nervous system (ANS)
- Sympathetic via norepinephrine (A1 and B2)
- Thoraco-lumbar innervation
- Parasympathetic via ACh (M1 and M2)
- Cranio-sacral innervation
- Sympathetic via norepinephrine (A1 and B2)
Control of GIT Secretions
- Presence of food in the GIT is detected by open chemoreceptors
- Signals to the endocrine cells or via the ANS releases gastrointestinal peptide hormones
- These hormones act to promote secretion, provide negative feedback or affect motility
- Closed mechanoreceptors also act to alter secretions
- Conditioned (associative) and unconditiones responses act via the ANS
| Conrtol Method | Neural | Endocrine |
|---|---|---|
| Saliva | Yes | No |
| Stomach | Yes | Yes |
| Small Intestine | No | Yes |