Difference between revisions of "Control of Feeding - Anatomy & Physiology"
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==Neuroendocrine Regulation of Feeding== | ==Neuroendocrine Regulation of Feeding== | ||
+ | |||
+ | ===Gut Peptides=== | ||
+ | |||
+ | {| style="width:75%; height:300px" border="1" | ||
+ | |||
+ | !'''Peptide''' | ||
+ | !'''Site of Release''' | ||
+ | !'''Effect on Feeding''' | ||
+ | |- | ||
+ | | '''CCK''' | ||
+ | | Duodenum | ||
+ | | Reduces food intake | ||
+ | |- | ||
+ | | '''Ghrelin''' | ||
+ | | Gastric fundus | ||
+ | | Increases food intake | ||
+ | |- | ||
+ | | '''GLP-2''' | ||
+ | | Intestine | ||
+ | | Reduces food intake | ||
+ | |- | ||
+ | | '''Motilin''' | ||
+ | | Small intestine | ||
+ | | Indirectly inhibits food intake | ||
+ | |- | ||
+ | | '''Oxyntomodulin''' | ||
+ | | Large intestine | ||
+ | | Inhibits food intake | ||
+ | |- | ||
+ | | '''Pancreatic Polypeptide''' | ||
+ | | Pancreas | ||
+ | | Inhibits food intake | ||
+ | |- | ||
+ | | '''PYY3-36''' | ||
+ | | Intestine | ||
+ | | Inhibits food intake | ||
+ | |- | ||
+ | | '''Somatostatin''' | ||
+ | | Pancreas | ||
+ | | Inhibits food intake | ||
+ | |- | ||
+ | |} | ||
+ | |||
+ | |||
+ | ===Other Peptides=== | ||
+ | |||
+ | {| style="width:75%; height:200px" border="1" | ||
+ | |||
+ | !'''Peptide''' | ||
+ | !'''Site of Release''' | ||
+ | !'''Effect on Feeding''' | ||
+ | |- | ||
+ | | '''Leptin''' | ||
+ | | Adipocyte | ||
+ | | Reduces food intake | ||
+ | |- | ||
+ | | '''NPY''' | ||
+ | | Arcuate nucleus | ||
+ | | Increases food intake | ||
+ | |- | ||
+ | | '''Agrp''' | ||
+ | | Arcuate nucleus | ||
+ | | Increases food intake | ||
+ | |- | ||
+ | | '''MCH''' | ||
+ | | Lateral hypothalamus | ||
+ | | Increases food intake | ||
+ | |- | ||
+ | | '''Orexins''' | ||
+ | | Lateral hypothalamus | ||
+ | | Increases food intake | ||
+ | |- | ||
+ | | '''CART''' | ||
+ | | Arcuate nucleus | ||
+ | | Inhibits food intake | ||
+ | |- | ||
+ | | '''α MSH''' | ||
+ | | Arcuate nucleus | ||
+ | | Inhibits food intake | ||
+ | |- | ||
+ | | '''Bdnf''' | ||
+ | | Ventromedial nucleus | ||
+ | | Inhibits food intake | ||
+ | |- | ||
+ | | '''Serotonin''' | ||
+ | | Brainstem | ||
+ | | Inhibits food intake | ||
+ | |- | ||
+ | | '''Cannabinoids''' | ||
+ | | CNS | ||
+ | | Increases food intake | ||
+ | |- | ||
+ | |} |
Revision as of 09:23, 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
Neuroendocrine Regulation of Feeding
Gut Peptides
Peptide | Site of Release | Effect on Feeding |
---|---|---|
CCK | Duodenum | Reduces food intake |
Ghrelin | Gastric fundus | Increases food intake |
GLP-2 | Intestine | Reduces food intake |
Motilin | Small intestine | Indirectly inhibits food intake |
Oxyntomodulin | Large intestine | Inhibits food intake |
Pancreatic Polypeptide | Pancreas | Inhibits food intake |
PYY3-36 | Intestine | Inhibits food intake |
Somatostatin | Pancreas | Inhibits food intake |
Other Peptides
Peptide | Site of Release | Effect on Feeding |
---|---|---|
Leptin | Adipocyte | Reduces food intake |
NPY | Arcuate nucleus | Increases food intake |
Agrp | Arcuate nucleus | Increases food intake |
MCH | Lateral hypothalamus | Increases food intake |
Orexins | Lateral hypothalamus | Increases food intake |
CART | Arcuate nucleus | Inhibits food intake |
α MSH | Arcuate nucleus | Inhibits food intake |
Bdnf | Ventromedial nucleus | Inhibits food intake |
Serotonin | Brainstem | Inhibits food intake |
Cannabinoids | CNS | Increases food intake |