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| + | <big><center>[[Alimentary - Anatomy & Physiology|'''BACK TO ALIMENTARY - ANATOMY & PHYSIOLOGY''']]</center></big> |
| − | ==Introduction==
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| − | Different hormones, neurotransmitters and reflexes are involved in the complicated process of feeding in animals. Secretions and motility of the gastrointestinal tract are stimulated and carefully regulated by numerous factors, including environmental stimuli and the presence of food in different parts of the gastrointestinal tract from the [[Oral Cavity Overview - Anatomy & Physiology|oral cavity]] right through to the intestines.
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| − | When a harmful substance is ingested the body acts to eliminate it in different ways to prevent the animal becoming ill, for example, through [[Vomiting#The Vomit Reflex|vomiting]] and [[Diarrhoea|diarrhoea]]. If one or more of the pathways in controlling feeding is damaged or inhibited, then problems such as obesity occurs.
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| | ==Feeding Methods== | | ==Feeding Methods== |
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| − | There are a number of feeding methods, including absorption over the body surface, filter feeding, mucous trapping, fluid feeding, piercing and sucking, cutting and biting, seizing prey, the use of jaws, [[:Category:Teeth - Anatomy & Physiology|teeth]], [[Integument of Exotic Species - Anatomy & Physiology#The Beak|beaks]] and the use of toxins.
| + | *Absorption over body surface |
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| − | ==Functions of the GIT==
| + | *Filter feeding |
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| − | The main function of the GIT is to efficiently breakdown feed to the essential nutrients that can then be absorbed. The GIT then acts to propel the waste fed material out of the body. The following constitute this main function:
| + | *Mucous trapping |
| − | :The secretion of enzymes and co-factors for digestion including water, ions and mucous
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| − | :Motility for forward propulsion, mechanical breakdown, mixing of ingesta and sphincter tone
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| − | :Migrating myoelectric complex to prevent debris accumulation
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| − | :Peristalsis
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| − | :Haustration
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| − | :Segmental motility
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| − | :Blood flow to muscles, submucosa and epithelial surfaces to sustain secretion, motility and the uptake of products of digestion and growth and repair.
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| − | ==Control of the GIT==
| + | *Fluid feeding |
| | + | **Piercing and sucking |
| | + | **Cutting and biting |
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| − | Endocrine hormones are released into the circulation by cells within the GIT or an accessory organ; paracrine mediators are released by cells within the tract and diffuse locally to act on neighboring target cells; neurotransmitters from nerves and other cells can be used and the autonomic nervous system is superimposed over the local control.
| + | *Seizing prey |
| | + | **Jaws, teeth, beak |
| | + | **Toxins |
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| − | ==Control of Motility==
| + | *Herbivores and grazing |
| | + | **Invertebrates |
| | + | **Vertebrates- bony plates or teeth |
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| − | The control of motility is intrinsic. It uses muscle pacemaker cells (Cajal cells) to set a basic electric rhythm (BER) of 3-20 per minute. It passes through gap junctions and an action potential is created, producing a slow wave of contraction. The likelihood of an action potential is increased through the stretch of food in the lumen and chemical food stimulation.
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| − | Endocrine, paracrine or neural signals enter the enteric nervous system via sensory neurones. The neurons interact with plexuses in the GIT wall. The '''myenteric plexus''' controls muscle movement and the '''submucosa plexus''' controls secretion and blood flow. The two plexuses are connected by interneurones to co-ordinate control. The autonomic nervous system is superimposed.
| + | ==Functions of the GIT== |
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| − | '''Excitatory neurotransmitters''' are '''parasympathomimetic'''. They include: ACh (muscarinic M1 and M2), Serotonin and Substance P.
| + | *Secretion of enzymes and co-factors for digestion including water, ions and mucous |
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| − | '''Inhibitory neurotransmitters''' are '''sympathomimetic'''. They include: Vasoactive intestinal polypeptide (VIP), Nitric oxide (NO), ATP and Enkephalins.
| + | *Motility for forward propulsion, mechanical breakdown, mixing of ingesta and sphincter tone |
| | + | **Migrating myoelectric complex to prevent debris accumulation |
| | + | **Peristalsis |
| | + | **Haustration |
| | + | **Segmental motility |
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| − | ==Control of GIT Secretions==
| + | *Blood flow to muscles, submucosa and epithelial surfaces to sustain secretion, motility and the uptake of products of digestion |
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| − | The presence of food in the GIT is detected by open chemoreceptors. Signals to the endocrine cells or via the autonomic nervous system (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 unconditioned responses act via the ANS.
| + | *Growth and repair |
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| − | {| style="width:50%; height:200px" border="1"
| + | ==Control of the GIT== |
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| − | !'''Control Method'''
| + | *Endocrine hormones released into the circulation by cells within the GIT or an accessory organ |
| − | !'''Neural'''
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| − | !'''Endocrine'''
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| − | |-
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| − | | '''Saliva'''
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| − | | Yes
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| − | | No
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| − | |-
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| − | | '''Stomach'''
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| − | | Yes
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| − | | Yes
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| − | |-
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| − | | '''Small Intestine'''
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| − | | No
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| − | | Yes
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| − | |-
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| − | |}
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| − | ==Phases of Gastric Secretion==
| + | *Paracrine mediators released by cells within the tract and diffuse locally to acton neighbouring target cells |
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| − | ===Cephalic===
| + | *Neurotransmitters from nerves andother cells |
| − | [[Image:Cephalic phase of secretion diagram.jpg|thumb|right|250px|Cephalic phase of secretion - Copyright RVC 2008]]
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| − | This phase is an unconditioned reflex. It is stimulated by the sight, smell and taste of food. It involves the vagus nerve ([[Cranial Nerves - Anatomy & Physiology|CN X]]) and parasympathetic fibres that synapse in the submucosal plexus. [[Gut Endocrine Function - Anatomy & Physiology|Gastrin]] is secreted from the endocrine cells in the pyloric mucosa. Postganglionic fibres activate chief, parietal, mucous and G cells. Histamine is secreted due to paracrine action. There is an increase in [[Monogastric Stomach - Anatomy & Physiology|stomach]] motility by release of hydrochloric acid and pepsinogen. It is a short phase and overlaps with the gastric phase of secretion. It is inhibited by stress and increased by aggression.
| + | *Autonomic nervous system superimposed over the local control |
| − | [[Image:gastric control of secretion diagram.jpg|thumb|right|250px|Gastric control of secretion - Copyright RVC 2008]]
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| − | ===Gastric===
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| − | Chemical and mechanical receptors in the [[Monogastric Stomach - Anatomy & Physiology|stomach]] respond to stretch and chemical stimulation by an increase in the pH of gastric contents. It is a response to undigested materials, especially proteins. Histamine and [[Gut Endocrine Function - Anatomy & Physiology|gastrin]] are released. It is a negative feedback loop by sympathomimetic somatostatin released by paracrine method to inhibit gastrin secretion (when pH falls below 3). The submucosal and myenteric plexuses are activated in vagus reflex arcs causing the postganglionic release of ACh at parietal cells. The neural response and presence of peptides in chyme stimulates gastrin release. Parietal and chief cells stimulate via gastrin acting in the bloodstream. It is a long response.
| + | ==Control of Motility== |
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| − | [[Image:Intestinal control of secretion diagram.jpg|thumb|right|250px|Intestinal control of secretion - Copyright RVC 2008]]
| + | *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 |
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| − | ===Intestinal===
| + | *Endocrine, paracrine or neural enter the enteric nervous system via sensory neurones |
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| − | Chyme in the [[Duodenum - Anatomy & Physiology|duodenum]] inhibits acid secretion and motility by decreasing the [[Monogastric Stomach - Anatomy & Physiology|stomach]] distension and increasing the stretch of the [[Duodenum - Anatomy & Physiology|duodenum]] leading to the enterogastric reflex. A drop in pH below 4.5 causes release of secretin which inhibits parietal and chief cells and stimulates buffer release from the [[Pancreas - Anatomy & Physiology|pancreas]]. Chyme causes the release of secretin, [[Gut Endocrine Function - Anatomy & Physiology|GIP]] and [[Gut Endocrine Function - Anatomy & Physiology|CCK]] decreasing gastric secretions and motility.
| + | *Neurons interact with plexuses in the GIT wall |
| − | [[Image:Pancreatic control of secretion diagram.jpg|thumb|right|250px|Pancretic control of secretion - Copyright RVC 2008]]
| + | **Myenteric controls muscle movement |
| | + | **Submucosa controls secretion and blood flow |
| | + | **2 plexuses connected by interneurones to co-ordinate control |
| | + | **Autonomic nervous system superimposed |
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| − | ===Pancreatic===
| + | *Excitatory neurotransmitters are parasympathomimetic |
| | + | **ACh (muscarinic M1 and M2) |
| | + | **Serotonin |
| | + | **Substance P |
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| − | Involves [[Gut Endocrine Function - Anatomy & Physiology|CCK]], secretin and [[Gut Endocrine Function - Anatomy & Physiology|Gastrin]]. Parasympathetic stimulation during cephalic and gastric phases. Negative feedback occurs from paracrine sympathomimetics (somatostatin and enkephalins).
| + | *Inhibitory neurotransmitters are sympathomimetic |
| | + | **Vasoactive intestinal polypeptide (VIP) |
| | + | **Nitroc oxide (NO) |
| | + | **ATP |
| | + | **Enkephalins |
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| − | ===Biliary===
| + | *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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| − | [[Gut Endocrine Function - Anatomy & Physiology|CCK]] empties the [[Gall Bladder - Anatomy & Physiology|gall bladder]] and secretin stimulates hydrogencarbonate ions from the bile duct.
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| − | ===Small Intestinal=== | + | ==Control of GIT Secretions== |
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| − | Involves secretin, [[Gut Endocrine Function - Anatomy & Physiology|GIP]] and [[Gut Endocrine Function - Anatomy & Physiology|gastrin]]. Controlled by vagal tone and the parasympathomimetic reflex.
| + | *Presence of food in the GIT is detected by open chemoreceptors |
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| − | ==Neuroendocrine Regulation of Feeding==
| + | *Signals to the endocrine cells or via the ANS releases gastrointestinal peptide hormones |
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| − | The [[Hypothalamus - Anatomy & Physiology|hypothalamus]] is the critical region of feeding control. The major hypothalamic nuclei involved are; [[Hypothalamus - Anatomy & Physiology#Nuclei|arcuate]], [[Hypothalamus - Anatomy & Physiology#Nuclei|ventromedial hypothalamus]], [[Hypothalamus - Anatomy & Physiology#Nuclei|dorsomedial hypothalamus]], [[Hypothalamus - Anatomy & Physiology#Nuclei|lateral hypothalamus]] and [[Hypothalamus - Anatomy & Physiology#Nuclei|paraventricular hypothalamus]].
| + | *These hormones act to promote secretion, provide negative feedback or affect motility |
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| − | ===Gut Peptides===
| + | *Closed mechanoreceptors also act to alter secretions |
| − | {| style="width:75%; height:300px" border="1"
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| − | !'''Peptide'''
| + | *Conditioned (associative) and unconditiones responses act via the ANS |
| − | !'''Site of Release'''
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| − | !'''Effect on Feeding'''
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| − | |-
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| − | | '''CCK'''
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| − | | [[Duodenum - Anatomy & Physiology|Duodenum]]
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| − | | Reduces food intake
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| − | |-
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| − | | '''Ghrelin'''
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| − | | Gastric fundus
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| − | | Increases food intake
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| − | |-
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| − | | '''GLP-2'''
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| − | | Intestine
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| − | | Reduces food intake
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| − | |-
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| − | | '''Motilin'''
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| − | | [[Small Intestine Overview - Anatomy & Physiology|Small intestine]]
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| − | | Indirectly inhibits food intake
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| − | |-
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| − | | '''Oxyntomodulin'''
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| − | | [[Large Intestine - Anatomy & Physiology|large intestine]]
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| − | | Inhibits food intake
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| − | |-
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| − | | '''Pancreatic Polypeptide'''
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| − | | [[Pancreas - Anatomy & Physiology|Pancreas]]
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| − | | Inhibits food intake
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| − | |-
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| − | | '''PYY3-36'''
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| − | | Intestine
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| − | | Inhibits food intake
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| − | |-
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| − | | '''Somatostatin'''
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| − | | [[Pancreas - Anatomy & Physiology|Pancreas]]
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| − | | Inhibits food intake
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| − | |-
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| − | |}
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| − | ===Other Peptides=== | + | {| style="width:50%; height:200px" border="1" |
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| − | {| style="width:75%; height:200px" border="1"
| + | !'''Conrtol Method''' |
| − | | + | !'''Neural''' |
| − | !'''Peptide''' | + | !'''Endocrine''' |
| − | !'''Site of Release''' | |
| − | !'''Effect on Feeding''' | |
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| − | | '''Leptin''' | + | | '''Saliva''' |
| − | | Adipocyte | + | | Yes |
| − | | Reduces food intake | + | | No |
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| − | | '''NPY''' | + | | '''Stomach''' |
| − | | [[Hypothalamus - Anatomy & Physiology#Nuclei|Arcuate nucleus]] | + | | Yes |
| − | | Increases food intake | + | | Yes |
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| − | | '''Agrp''' | + | | '''Small Intestine''' |
| − | | [[Hypothalamus - Anatomy & Physiology#Nuclei|Arcuate nucleus]] | + | | No |
| − | | Increases food intake
| + | | Yes |
| − | |-
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| − | | '''MCH'''
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| − | | [[Hypothalamus - Anatomy & Physiology#Nuclei|Lateral hypothalamus]]
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| − | | Increases food intake
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| − | |-
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| − | | '''Orexins'''
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| − | | [[Hypothalamus - Anatomy & Physiology#Nuclei|Lateral hypothalamus]]
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| − | | Increases food intake
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| − | |-
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| − | | '''CART'''
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| − | | [[Hypothalamus - Anatomy & Physiology#Nuclei|Arcuate nucleus]]
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| − | | Inhibits food intake
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| − | |-
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| − | | '''α MSH'''
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| − | | [[Hypothalamus - Anatomy & Physiology#Nuclei|Arcuate nucleus]]
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| − | | Inhibits food intake
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| − | |-
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| − | | '''Bdnf'''
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| − | | [[Hypothalamus - Anatomy & Physiology#Nuclei|Ventromedial nucleus]]
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| − | | Inhibits food intake
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| − | |-
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| − | | '''Serotonin'''
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| − | | Brainstem
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| − | | Inhibits food intake
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| − | |-
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| − | | '''Cannabinoids'''
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| − | | [[Nervous and Special Senses - Anatomy & Physiology#Central Nervous System (CNS)|CNS]]
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| − | | Increases food intake | |
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| − | ==Species Differences==
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| − | ===Equine===
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| − | The anatomy of the equine stomach, the close proximity of the exiting duodenum and the entering oesophagus along with the well developed cardiac sphincter, make it difficult for the horse to vomit. However on rare occasions it does occur.
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| − | '''Click here for more information on [[Vomiting#The Vomit Reflex|The Vomit Reflex]]'''.
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| − | {{OpenPages}}
| + | ==Neuroendocrine Regulation of Feeding== |
| − | [[Category:Feeding Control]]
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| − | [[Category:A&P Done]]
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