Difference between revisions of "Control of Feeding - Anatomy & Physiology"
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− | + | <big><center>[[Alimentary - Anatomy & Physiology|'''BACK TO ALIMENTARY - ANATOMY & PHYSIOLOGY''']]</center></big> | |
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==Feeding Methods== | ==Feeding Methods== | ||
− | + | *Absorption over body surface | |
+ | |||
+ | *Filter feeding | ||
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+ | *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== | ==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== | ==Control of the GIT== | ||
− | Endocrine hormones | + | *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== | ==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 | + | *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 | ||
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==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 | ||
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===Cephalic=== | ===Cephalic=== | ||
− | [[Image:Cephalic phase of secretion diagram.jpg|thumb|right| | + | [[Image:Cephalic phase of secretion diagram.jpg|thumb|right|150px|Cephalic phase of secretion - Copyright RVC 2008]] |
+ | *Unconditioned reflex | ||
− | + | *Sight, smell, taste of food | |
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− | + | *Vagus nerve (CN X) | |
− | + | *[[Endocrine System - Gut - Anatomy & Physiology|Gastrin]] secreted from endocrine cells in pyloric mucosa | |
− | + | *Histamine secreted from paracrine action | |
− | + | *Increase stomach motility by release of hydrochloric acid and pepsinogen | |
− | + | ===Gastric=== | |
− | [[Image: | + | [[Image:gastric control of secretion diagram.jpg|thumb|right|150px|Gastric control of secretion - Copyright RVC 2008]] |
+ | *Chemical and mechanical receptors in stomach | ||
− | + | *Histamine and gastrin released | |
− | + | *Negative feedback loop by sympathomimetic somatostatin released by paracrine method to inhibit gastrin secretion (when pH falls below 3) | |
− | === | + | ===Intestinal=== |
+ | [[Image:Intestinal control of secretion diagram.jpg|thumb|right|150px|Intestinal control of secretion - Copyright RVC 2008]] | ||
+ | *Chyme in the duodenum inhibits acid secretion and motility | ||
− | [[Gut | + | *Chyme causes release of secretin, [[Endocrine System - Gut - Anatomy & Physiology|GIP]] and [[Endocrine System - Gut - Anatomy & Physiology|CCK]] |
− | === | + | ===Pancreatic=== |
+ | [[Image:Pancreatic control of secretion diagram.jpg|thumb|right|150px|Pancretic control of secretion - Copyright RVC 2008]] | ||
+ | *[[Endocrine System - Gut - Anatomy & Physiology|CCK]], secretin and [[Endocrine System - Gut - Anatomy & Physiology|Gastrin]] | ||
− | + | *Parasympathetic stimulation during cephalic and gastric phases | |
− | + | *Negative feedback from paracrine sympathomimetics (somatostatin and enkephalins) | |
− | + | ===Biliary=== | |
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− | === | ||
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− | + | *[[Endocrine System - Gut - Anatomy & Physiology|CCK]] empties [[Gall Bladder - Anatomy & Physiology|gall bladder]] | |
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− | + | *Secretin stimulates hydrogencarbonate ions from bile duct | |
− | + | ===Small Intestinal=== | |
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− | + | *Succus entericus | |
− | + | *Secretin, [[Endocrine System - Gut - Anatomy & Physiology|GIP]] and [[Endocrine System - Gut - Anatomy & Physiology|Gastrin]] | |
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− | + | *Vagal tone and parasympathomimetic reflex | |
− | + | ==Neuroendocrine Regulation of Feeding== | |
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Revision as of 09:12, 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
Control Method | Neural | Endocrine |
---|---|---|
Saliva | Yes | No |
Stomach | Yes | Yes |
Small Intestine | No | Yes |
Phases of Gastric Secretion
Cephalic
- Unconditioned reflex
- Sight, smell, taste of food
- Vagus nerve (CN X)
- Gastrin secreted from endocrine cells in pyloric mucosa
- Histamine secreted from paracrine action
- Increase stomach motility by release of hydrochloric acid and pepsinogen
Gastric
- Chemical and mechanical receptors in stomach
- Histamine and gastrin released
- Negative feedback loop by sympathomimetic somatostatin released by paracrine method to inhibit gastrin secretion (when pH falls below 3)
Intestinal
- Chyme in the duodenum inhibits acid secretion and motility
Pancreatic
- Parasympathetic stimulation during cephalic and gastric phases
- Negative feedback from paracrine sympathomimetics (somatostatin and enkephalins)
Biliary
- CCK empties gall bladder
- Secretin stimulates hydrogencarbonate ions from bile duct
Small Intestinal
- Succus entericus
- Vagal tone and parasympathomimetic reflex