Appetite regulation Flashcards
3 methods of regulation of function
1) Nervous sytem:
a) Intrinsic (enteric)
b) Extrinsic (autonomic)- interfaces with CNS through this
2) Paracrine
3) Endocrine
Enteric (intrinsic) nervous system description
Rich plexus (network) of ganglia (nerve cells + glial cells) interconnected by tracts of fine, unmyelinated nerve fibres.
Enteric (intrinsic) nervous system function
If the sympathetic and parasympathetic nerves to the gut are cut?
Integrates the motor and secretory activities of the GI system.
Can function independently of central control.
If SNS/ PNS cut, many motor and secretory activities continue as controlled by the enteric nervous system.
Enteric Neural Dysfunction/Degeneration caused by?
Inflammation (ulcerative colitis; Crohn’s disease)
Post-operative injury
Irritable bowel syndrome
Ageing (constipation)
Enteric nervous system regulates
Motility Blood flow Water and electrolyte transport Secretion Absorption
Types of neurones in enteric nervous sytem
Feature of all of them?
Sensory: respond to mechanical (stretch), thermal, osmotic and chemical stimuli.
Motor: axons terminate on smooth muscle cells of the circular or longitudinal layers, secretory cells of the gastrointestinal tract, or gastrointestinal blood vessels.
Interneurons: neurons between neurons integrate the sensory input and effector output
Most are multipolar (one axon, multiple dendrites)
Nervous plexuses in gut
Location
What does it control?
Major plexuses: Myenteric+ Submucosal;
1) Myenteric plexus: located between the circular and longitudinal smooth muscle layers. Controls activity of muscularis externa. Controls gut motor function.
2) Submucosal plexus: Sensing environment within lumen, Blood flow, epithelial and endocrine cell function.
Minor plexuses
including deep muscular plexus (inside circular muscle), and the ganglia supplying biliary system and pancreas
Autonomic nervous system regulates?
Description?
Branches?
Regulates smooth muscle, cardiac muscle and glands. Not accessible to voluntary control. Two branches: i) Sympathetic ii) Parasympathetic
Sympathetic nervous system anatomy in relation to gut
Final effect
Cell bodies of preganglionic neurons in the thoracic and lumbar spinal cord.
Cell bodies of postganglionic neurons in the pre- and para- vertebral ganglia.
Lumbar splanchnic nerves carry sympathetic innervation to the remainder of the gut.
Thoracic splanchnic nerves carry innervation to fore and midgut.
Neurotransmitter= Norepinephrine
Activation of the sympathetic nerves usually inhibit the activities of the GI system.
Parasympathetic nervous system anatomy in relation to gut
Final effect
Cell bodies of preganglionic neurons in the brainstem and sacral spinal cord (cranio-sacral)
Cell bodies of postganglionic neurons close to target organs.
Preganglionic neurons synapse on ganglia close to gut wall or directly with enteric plexi
Most of the GI tract via branches of the vagus nerve (down to the level of the transverse colon).
Remainder of the colon, the rectum and the anus receive parasympathetic fibers from the pelvic nerves.
Neurotransmitter =Acetyl Choline
Excitation usually stimulates the activities of the GI tract. (mostly stomach+ duodenum)
Autonomic nervous system overall action diagram
slide 16, lecture 11
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Interaction of gut with central nervous system diagram
slide 17, lecture 11
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GI tract is innervated by?
Intrinsic innervation:
Neurons of the enteric nervous system.
Extrinsic innervation:
Afferents (pain, nausea, fullness)
Efferents (coordination - sympathetic and parasympathetic nervous systems).
Complexity allows fine control of the GI tract.
Innervation of Autonomic Nervous System (PNS, SNS)
The parasympathetic nervous system innervates the gut via long preganglionic neurones (mostly via the vagus nerve) and short postganglionic neurones to promote gut motility, secretion and digestion
The sympathetic nervous system innervates the gut via short preganglionic and long post ganglionic fibres to inhibit gut motility and secretion, and cause constriction of blood vessels and contraction of sphincters.
Function of the gastrointestinal endocrine system
Hormones released by?
Produced by endocrine cells in the mucosa or submucosa of the stomach, intestine and pancreas.
Can act as paracrine or neurocrine (hormones released from neurone e.g. hypothalamus) factors as well as endocrine.
Functions:
1) Regulation of the mechanical processes of digestion (e.g. smooth muscle of GI tract and sphincters, gall bladder).
2) Regulation of the chemical and enzymatic processes of digestion (e.g. secretory cells located in the wall of the GI tract, pancreas and liver).
3) Control of post absorptive processes involved in the assimilation of digested food and CNS feedback regulating intake (e.g. GIP stimulates insulin release from pancreatic beta cells, PYY3-36 acts on the CNS to suppress appetite)
4) Effects on the growth and development of the GI tract (long term effect) (e.g. GLP-2 promotes small intestinal growth).
Enteroendocrine cells general structure
General trend= fingers of cytoplasm into lumen with lots of receptors (e.g. fatty acids, amino acids) which can cause appropriate hormone release at basolateral end which is near a capillary
Examples of paracrine actions
Histamine released from stomach wall cells is a key physiological stimulus to HCl secretion by gastric parietal cells.
Somatostatin from the stomach can inhibit acid secretion by paracrine mechanisms.
Gut hormones
Gastrin Somatostatin Secretin CCK (Cholecystokinin) GIP (gastric inhibitory peptide)/ (glucose dependent insulinotropic peptide) PYY (Peptide YY)
Gastrin synthesised?
Synthesised in gastric antrum and upper small intestine
Gastrin release stimulated by?
Amino acids and peptides in the lumen of the stomach.
Gastric distension.
Vagus nerve directly
Gastrin stimulates?
Gastrin stimulates gastric acid secretion.
When is gastrin inhibited?
Release inhibited when pH of stomach falls below pH 3.
Where is somatostatin produced?
Synthesized in endocrine D cells of the gastric and duodenal mucosa, pancreas (also hypothalamus)
Also in small and large intestine
Function of somatostatin in gut?
Somatostatin is a universal inhibitor
(Endocrine Cyanide) (lots of hormones are suppressed by it)
Release in response to a mixed meal.
Inhibition of: gastric secretion, motility, intestinal and pancreatic secretions, release of gut hormones, intestinal nutrient and electrolyte transport, growth and proliferation.
Analogues used to treat neuroendocrine tumours, e.g. Octreotide which has a longer half life than SS which is very short
Secretin produced by?
-Secreted by the S cells of the upper duodenum and jejunum.
Secretin stimulus?
- Major stimulus is the presence of acid in the duodenum (pH falls below 4.5).
Secretin stimulates?
Potentiated by?
- Stimulates pancreatic bicarbonate secretion (effect potentiated by CCK).
High levels of secretin=?
- High concentrations: inhibition of gastric acid and gastric emptying.
CCK produced in?
Secreted by cells most densely located in the small intestine.
CCK release stimulated by?
Release stimulated by fat and peptides in the upper small intestine.
Independent of vagus nerve
CCK action
- stimulates pancreatic enzyme release
- delays gastric emptying
- stimulates gallbladder contraction.
- decreases food intake and meal size.
GIP secreted by?
Secreted by mucosal K cells (predominant in the duodenum and jejunum).
When is GIP released?
- GIP released following ingestion of a mixed meal.
GIP action
What happens without it?
- Stimulates insulin secretion.
- GIP receptor antagonists reduce postprandial insulin release. (injecting glucose into blood directly without ingestion= less insulin release)
PYY production?
- Cells found throughout the mucosa of the terminal ileum, colon and rectum.
- Released from L cells post prandially (particularly protein).
PYY action?
- PYY reduces intestinal motility, gallbladder contraction and pancreatic exocrine secretion.
- Inhibitor of intestinal fluid and electrolyte secretion.
- PYY3-36 inhibits food intake (makes you think you’re fuller than you are)
SBA:
Regarding the nervous control of the gastrointestinal tract:
a) Thoracic sphlanchic nerves carry sympathetic innervation to the internal anal sphincter
b) Enteric nervous system nerve fibres are myelinated
c) Cell bodies of parasympathetic preganglionic neurons are found in the brainstem
d) The pelvic nerves carry parasympathetic innervation to the ascending colon
e) Acetyl choline is the major neurotransmitter of the sympathetic nervous system
a- those are the lumbar sphlanchic nerves that carry sympathetic innervation to internal anal sphincter
b- dont need speed of response so unmyleinate
c- correct, where vagus nerve cell bodies are, for e.g.
d- ascending colon innervated by vagus nerve
e- Ach is major neurotransmitter of PNS
SBA;
Regarding the control of gut function:
a) The myenteric plexus is located between the circular muscle layer and submucosa
b) Somatostatin acts solely as a paracrine signal
c) The sympathetic nervous system acts directly on the vascular system to increase blood flow to the gut
d) The vagus nerve stimulates gastrin release
e) The parasympathetic nervous system innervates the gut via short preganglionic and long preganglionic neurones
a- located between longitudinal and circular muscle layers
b-SS can act systemically, not purely paracrine
c- decreases blood flow instead of increase
d- correct
e-SNS innervates gut by long pre-ganglionic rather than short, synapses to post ganglionic close to organs
