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> | |
+ | |||
==Introduction== | ==Introduction== | ||
− | + | ==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== | ==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 act on neighbouring target cells | ||
+ | |||
+ | *Neurotransmitters from nerves and other 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 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 | ||
− | |||
==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 | ||
Line 63: | Line 120: | ||
===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 | ||
+ | |||
+ | *Vagus nerve (CN X) | ||
+ | **Parasympathetic fibres | ||
+ | **Synapse in submucosal plexus | ||
+ | |||
+ | *[[Endocrine System - Gut - Anatomy & Physiology|Gastrin]] secreted from endocrine cells in pyloric mucosa | ||
+ | |||
+ | *Postganglionic fibres activate chief, parietal, mucous and G cells | ||
+ | |||
+ | *Histamine secreted from paracrine action | ||
+ | |||
+ | *Increase stomach motility by release of hydrochloric acid and pepsinogen | ||
+ | |||
+ | *Short phase | ||
− | + | *Overlaps with gastric phase of secretion | |
− | |||
+ | *Inhibited by stress, increased by aggression | ||
+ | [[Image:gastric control of secretion diagram.jpg|thumb|right|150px|Gastric control of secretion - Copyright RVC 2008]] | ||
===Gastric=== | ===Gastric=== | ||
− | Chemical and mechanical receptors in | + | *Chemical and mechanical receptors in stomach respond to stretch and chemical stimulation |
+ | |||
+ | *Increase in pH of gastric contents | ||
+ | |||
+ | *Response to undigested materials, especially proteins | ||
+ | |||
+ | *Histamine and gastrin released | ||
+ | |||
+ | *Negative feedback loop by sympathomimetic somatostatin released by paracrine method to inhibit gastrin secretion (when pH falls below 3) | ||
+ | |||
+ | *Submucosal and myenteric plexuses activated in vagus reflex arcs | ||
+ | |||
+ | *Postganglionic release of ACh at parietal cells | ||
+ | |||
+ | *Neural response and presence of peptides in chyme stimulate gastrin release | ||
− | + | *Parietal and chief cells stimulate via gastrin acting in the bloodstream | |
+ | *Long response | ||
+ | [[Image:Intestinal control of secretion diagram.jpg|thumb|right|150px|Intestinal control of secretion - Copyright RVC 2008]] | ||
===Intestinal=== | ===Intestinal=== | ||
− | Chyme in the [[Duodenum - Anatomy & Physiology|duodenum]] inhibits acid secretion and motility by decreasing the | + | *Chyme in the [[Duodenum - Anatomy & Physiology|duodenum]] inhibits acid secretion and motility by decreasing the 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 stimulate buffer release from the [[Pancreas - Anatomy & Physiology|pancreas]] | ||
+ | *Chyme causes release of secretin, [[Endocrine System - Gut - Anatomy & Physiology|GIP]] and [[Endocrine System - Gut - Anatomy & Physiology|CCK]] decreasing gastric sectreions and motility | ||
+ | [[Image:Pancreatic control of secretion diagram.jpg|thumb|right|150px|Pancretic control of secretion - Copyright RVC 2008]] | ||
===Pancreatic=== | ===Pancreatic=== | ||
− | + | *[[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=== | ===Biliary=== | ||
− | [[Gut | + | *[[Endocrine System - Gut - Anatomy & Physiology|CCK]] empties [[Gall Bladder - Anatomy & Physiology|gall bladder]] |
+ | |||
+ | *Secretin stimulates hydrogencarbonate ions from bile duct | ||
===Small Intestinal=== | ===Small Intestinal=== | ||
− | + | *Succus entericus | |
+ | |||
+ | *Secretin, [[Endocrine System - Gut - Anatomy & Physiology|GIP]] and [[Endocrine System - Gut - Anatomy & Physiology|Gastrin]] | ||
+ | |||
+ | *Vagal tone and parasympathomimetic reflex | ||
==Neuroendocrine Regulation of Feeding== | ==Neuroendocrine Regulation of Feeding== | ||
− | + | *[[Endocrine System - Hypothalamus - Anatomy & Physiology|Hypothalamus]] is the critical region of feeding control | |
+ | |||
+ | *Major hypothalamic nuclei involved: | ||
+ | **[[Endocrine System - Hypothalamus - Anatomy & Physiology#Nuclei|Arcuate]] | ||
+ | **[[Endocrine System - Hypothalamus - Anatomy & Physiology#Nuclei|Ventromedial hypothalamus]] | ||
+ | **[[Endocrine System - Hypothalamus - Anatomy & Physiology#Nuclei|Dorsomedial hypothalamus]] | ||
+ | **[[Endocrine System - Hypothalamus - Anatomy & Physiology#Nuclei|Lateral hypothalamus]] | ||
+ | **[[Endocrine System - Hypothalamus - Anatomy & Physiology#Nuclei|Paraventricular hypothalamus]] | ||
===Gut Peptides=== | ===Gut Peptides=== | ||
+ | |||
{| style="width:75%; height:300px" border="1" | {| style="width:75%; height:300px" border="1" | ||
Line 103: | Line 215: | ||
|- | |- | ||
| '''CCK''' | | '''CCK''' | ||
− | | | + | | Duodenum |
| Reduces food intake | | Reduces food intake | ||
|- | |- | ||
Line 115: | Line 227: | ||
|- | |- | ||
| '''Motilin''' | | '''Motilin''' | ||
− | + | | Small intestine | |
| Indirectly inhibits food intake | | Indirectly inhibits food intake | ||
|- | |- | ||
| '''Oxyntomodulin''' | | '''Oxyntomodulin''' | ||
− | | | + | | Large intestine |
| Inhibits food intake | | Inhibits food intake | ||
|- | |- | ||
| '''Pancreatic Polypeptide''' | | '''Pancreatic Polypeptide''' | ||
− | | | + | | Pancreas |
| Inhibits food intake | | Inhibits food intake | ||
|- | |- | ||
Line 131: | Line 243: | ||
|- | |- | ||
| '''Somatostatin''' | | '''Somatostatin''' | ||
− | | | + | | Pancreas |
| Inhibits food intake | | Inhibits food intake | ||
|- | |- | ||
|} | |} | ||
+ | |||
===Other Peptides=== | ===Other Peptides=== | ||
Line 149: | Line 262: | ||
|- | |- | ||
| '''NPY''' | | '''NPY''' | ||
− | + | | Arcuate nucleus | |
| Increases food intake | | Increases food intake | ||
|- | |- | ||
| '''Agrp''' | | '''Agrp''' | ||
− | + | | Arcuate nucleus | |
| Increases food intake | | Increases food intake | ||
|- | |- | ||
| '''MCH''' | | '''MCH''' | ||
− | + | | Lateral hypothalamus | |
| Increases food intake | | Increases food intake | ||
|- | |- | ||
| '''Orexins''' | | '''Orexins''' | ||
− | + | | Lateral hypothalamus | |
| Increases food intake | | Increases food intake | ||
|- | |- | ||
| '''CART''' | | '''CART''' | ||
− | + | | Arcuate nucleus | |
| Inhibits food intake | | Inhibits food intake | ||
|- | |- | ||
| '''α MSH''' | | '''α MSH''' | ||
− | + | | Arcuate nucleus | |
| Inhibits food intake | | Inhibits food intake | ||
|- | |- | ||
| '''Bdnf''' | | '''Bdnf''' | ||
− | + | | Ventromedial nucleus | |
| Inhibits food intake | | Inhibits food intake | ||
|- | |- | ||
Line 181: | Line 294: | ||
|- | |- | ||
| '''Cannabinoids''' | | '''Cannabinoids''' | ||
− | | | + | | CNS |
| Increases food intake | | Increases food intake | ||
|- | |- | ||
|} | |} | ||
+ | |||
+ | ==The Vomit Reflex== | ||
+ | |||
+ | *Emesis is the process of vomiting | ||
+ | |||
+ | *Retching involves the abdominal and chest walls contracting | ||
+ | |||
+ | *Vomiting includes retching and the action of the diaphragm | ||
+ | |||
+ | *Diaphragm moves caudal to open the cardia | ||
+ | |||
+ | *Gastrointestinal tract have protective stimuli to recognise harmful products ingested. The mechanoreceptors and chemoreceptors respond using viscerent afferent pathways. | ||
+ | |||
+ | *Medulla co-ordinates process | ||
+ | |||
+ | *Chemoreceptive trigger zone in the 4th ventricle responds to blood and CSF | ||
+ | |||
+ | *Inputs also from inner ear and higher centres | ||
+ | |||
+ | *Emetic agents | ||
+ | **Histamine | ||
+ | **ACh | ||
+ | **Dopamine | ||
+ | **Catecholamines | ||
+ | **5-hydroxytryptamine | ||
+ | |||
+ | *Anti-emetic agents | ||
+ | (INCLUDE HERE) | ||
==Species Differences== | ==Species Differences== | ||
===Equine=== | ===Equine=== | ||
− | The | + | *The horse cannot vomit |
− | |||
− | |||
− | + | ==Links== | |
− | |||
− |
Revision as of 09:08, 22 July 2008
Introduction
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 act on neighbouring target cells
- Neurotransmitters from nerves and other 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)
- Parasympathetic fibres
- Synapse in submucosal plexus
- Gastrin secreted from endocrine cells in pyloric mucosa
- Postganglionic fibres activate chief, parietal, mucous and G cells
- Histamine secreted from paracrine action
- Increase stomach motility by release of hydrochloric acid and pepsinogen
- Short phase
- Overlaps with gastric phase of secretion
- Inhibited by stress, increased by aggression
Gastric
- Chemical and mechanical receptors in stomach respond to stretch and chemical stimulation
- Increase in pH of gastric contents
- Response to undigested materials, especially proteins
- Histamine and gastrin released
- Negative feedback loop by sympathomimetic somatostatin released by paracrine method to inhibit gastrin secretion (when pH falls below 3)
- Submucosal and myenteric plexuses activated in vagus reflex arcs
- Postganglionic release of ACh at parietal cells
- Neural response and presence of peptides in chyme stimulate gastrin release
- Parietal and chief cells stimulate via gastrin acting in the bloodstream
- Long response
Intestinal
- Chyme in the duodenum inhibits acid secretion and motility by decreasing the stomach distension and increasing the stretch of the duodenum leading to the enterogastric reflex
- A drop in pH below 4.5 causes release of secretin which inhibits parietal and chief cells and stimulate buffer release from the pancreas
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
- Hypothalamus is the critical region of feeding control
- Major hypothalamic nuclei involved:
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 |
The Vomit Reflex
- Emesis is the process of vomiting
- Retching involves the abdominal and chest walls contracting
- Vomiting includes retching and the action of the diaphragm
- Diaphragm moves caudal to open the cardia
- Gastrointestinal tract have protective stimuli to recognise harmful products ingested. The mechanoreceptors and chemoreceptors respond using viscerent afferent pathways.
- Medulla co-ordinates process
- Chemoreceptive trigger zone in the 4th ventricle responds to blood and CSF
- Inputs also from inner ear and higher centres
- Emetic agents
- Histamine
- ACh
- Dopamine
- Catecholamines
- 5-hydroxytryptamine
- Anti-emetic agents
(INCLUDE HERE)
Species Differences
Equine
- The horse cannot vomit