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What is the sympathetic nerve supply of the abdomen?
- Greater, lesser and least splanchnic nerves
- Lumbar splanchnic nerves
What does the somatic NS control?
External actions of skin and muscle
What does the autonomic NS control?
Internal activities of organs and glands
What is the spinal cord divided into?
31 segments which each segment giving rise to a pair of spinal nerves
- 8 pairs of cervical
- 12 pairs of thoracic
- 5 pairs of lumbar
- 5 pairs of sacral
- 1 pair of coccygeal
What is the dorsal horn of the spinal cord concerned with?
Receiving sensory information (afferent sensory fibres arrive)
What is the ventral horn of the spinal cord concerned with?
Sending motor information (efferent motor fibres leave)
When these efferent and afferent fibres come together, what does it make up?
A mixed spinal nerve –> enclosed by sheath
What are thoracic spinal nerves called?
Intercostal nerves supplying intercostal muscles, pleura, skin etc
What do intercostal muscles continue into the abdomen as?
Thoracoabdominal nerves suppling anterolateral muscles, peritoneum etc
Are intercostal/thoracoabdominal nerves somatic or autonomic?
Somatic nerves (e.g. consciously contract biceps or abdominal muscles)
Describe the autonomic sympathetic supply of the abdomen
- Greater, lesser and least splanchnic nerves
- Lumbar splanchnic nerves
N.B. splanchnic nerves generally refer to sympathetic nerves (one exception)
Where do greater, lesser and least splanchnic nerves begin?
Within thorax and then pierce diaphragm (emerge from the thoracic sympathetic chain)
What do the greater, lesser and least splanchnic nerves supply?
Foregut and midgut
What do the lumbar splanchnic nerves supply?
Hindgut
Describe the autonomic parasympathetic supply of the abdomen
- Vagus nerve (pierces diaphragm along with oesophagus)
- Pelvic splanchnic nerves (exception to sympathetic splanchnic)
What does the vagus nerve supply?
Foregut and midgut (all the way to the distal 1/3 of the TC)
What do pelvic splanchnic nerves supply?
Hindgut and pelvic organs
What are the only splanchnic nerves that are parasympathetic?
Pelvic splanchnic nerves
What do these autonomic nerve fibres form?
Autonomic plexuses –> around coeliac trunk, SMA, IMA then follow blood vessels to target organ
What do these autonomic nerve fibres form?
Autonomic plexuses –> around coeliac trunk, SMA, IMA then follow blood vessels to target organ
What happens if that sympathetic information needs to get to the body wall (e.g. for a sweat gland)?
It can re-enter the spinal nerve via the grey ramus communicans –> enter into the somatic spinal nerve
What happens if that sympathetic information needs to get to the body wall (e.g. for a sweat gland)?
It can re-enter the spinal nerve via the grey ramus communicans
Where does the sympathetic nervous system emerge?
From the spinal cord at the thoracic and lumbar segments (T1 down to around L2)
Where are preganglionic neurones of the sympathetic nervous system located?
In the lateral horns of spinal segments T1-L2
When preganglionic fibres leave the spinal cord and enter into the sympathetic chain, what happens?
They synapse (at the point of entry or could ascend or descend within chain)
Postganglionic then make way towards target organs via a plexus (braid of nerves)
Where are sympathetic ganglia located?
Near the spinal cord
What do preganglionic sympathetic fibres release?
ACh which is excitatory and stimulates ganglionic neurones
Within the abdomen, how is the sympathetic nerve supply different regarding synapsing?
Sympathetic fibres leave spinal cord, enter chain and pass straight through (without synapsing)
They course around the blood vessels of the GI tract (coeliac trunk, SMA, IMA) and it is here where they synapse
Within the abdomen, how is the sympathetic nerve supply different regarding synapsing?
Sympathetic fibres leave spinal cord, enter chain and pass straight through (without synapsing)
They course around the blood vessels of the GI tract (coeliac trunk, SMA, IMA) and it is here where they synapse
Where do synapses of sympathetic fibres occur in the abdomen?
Near the blood vessels of the GI tract
Where do synapses of sympathetic fibres occur in the abdomen?
Near the blood vessels of the GI tract
Describe route of motor efferent sympathetic nerves in the thorax
• Motor efferent fibres leave the spinal cord via the ventral root that then contribute to the mixed spinal nerve
• Sympathetic so then jump into sympathetic chain via the white ramus communicans
o Then synapses and postganglionic fibre go towards target organ
o Or, ascends or descends before it synapses then head out to target organ
• If fibre needs to make its way to body wall, it jumps back into spinal nerve via the grey ramus communicans which then heads to body wall
What are sympathetic ganglia in the thorax also referred to as?
Paravertebral (as next to vertebral column)
Describe route of motor efferent sympathetic nerves in the abdomen
• Motor efferent fibres leave spinal cord via the ventral root the contribute to mixed spinal nerve
• Jump into sympathetic chain via white ramus communicans
o Passes straight through chain (without synapsing) towards blood vessels (coeliac, SMA, IMA) and synapses there
o Postganglionic fibre then goes on to supply target organs
What are sympathetic ganglia in the abdomen also referred to as?
Prevertebral ganglia
What sensory route does pain (e.g. ischaemia) take?
Afferent fibres for pain use the sympathetic system to go back to the CNS
What sensory route does general sensation from the organs (e.g. how full the stomach is) take?
The parasympathetic system
Describe route during appendicitis
- Appendix becomes inflamed
- Sends afferent fibres back to the sympathetic chain
- Enters mixed spinal nerve via white ramus communicans
- Mixed nerve splits and afferent information enters spinal cord via dorsal root
Where are the preganglionic neurones of the parasympathetic system located? (i.e. origin)
Brainstem or sacral spinal cord (S2-S4)
What is the parasympathetic supply of the foregut and midgut via?
Vagus nerve
What is the parasympathetic supply of the hindgut via?
Pelvic splanchnic
Describe the length of pre/post ganglionic fibres in parasympathetic system?
Long preganglionic, short postganglionic fibre
Where are prevertebral ganglia found? What do they contain? Where are they found?
Abdomen
Cell bodies for sympathetic nervous system
Around the three unpaired visceral arteries (CT, SMA, IMA)
What are prevertebral ganglia?
Synapse between pre-synaptic and post-synaptic sympathetic fibres
What do prevertebral ganglia contain?
- Synapse between pre-synaptic and post-synaptic sympathetic fibres
- Presynaptic parasympathetic fibres
- Afferent (visceral) fibres (going back to CNS)
Why do only presynaptic parasympathetic fibres pass through prevertebral ganglia?
As these are very long and synapse nearly at target organ –> only presynaptic passes through ganglia)
Where are the autonomic plexuses of the abdomen found?
Parasympathetic and sympathetic nerve networks that surround the 3 unpaired visceral arteries
All interconnected
What is found at the bifurcation of the aorta?
Superior hypogastric plexus (plexus of fibres mainly from sympathetic chain)
How does the superior hypogastric plexus join the inferior hypogastric plexus?
Via hypogastric nerve
What does the inferior hypogastric plexus receive?
Receives pelvic splanchnic nerves (parasympathetic)
What do the hypogastric nerves contain?
Sympathetic fibres
How does pain sensation go back to the CNS?
Via sympathetic motor fibres to the posterior root of spinal cord segments
How does referred pain occur?
At these same vertebral levels, there is also afferent information coming from body wall (somatic nervous system)
Where does pain from the foregut go to?
T6-T9 (same as dermatomes) –> can be referred to skin
From the midpoint of the sigmoid colon, where does pain pass?
What is this known as?
Takes a different route –> passes to S2-S4 via parasympathetic fibres
Pelvic pain line
Where does pain from the midgut go to?
T8-T12
Where does pain from the hindgut go to?
T12-L2
What is the cardiac / lower oesophageal sphincter known as a physiological sphincter?
No thickening of circular muscle
What is the pyloric sphincter?
Anatomical sphincter –> thickening of the circular muscle in muscularis externa
Dictates gastric emptying
What is a hiatal hernia?
When stomach protrudes from the abdomen back into the thorax through the oesophageal opening in the diaphragm
What are the different types of hiatal hernias?
What are these hernias known as?
Type I –> ‘sliding’
Type II –> ‘paraoesophageal’ (rolling)
Acquired
What happens in a ‘sliding’ hiatal hernia?
Cardia of stomach protrudes through opening
What happens in a ‘rolling’/paraoesophageal?
Part of fundus of stomach protrudes through opening alongside cardia
What is a congenital hernia?
Defect of diaphragm development (failure of formation or failure of fusion)
Abdominal organs (intestines) protrude through hole in diaphragm into thorax due to lack of space around week 10
What is a congenital hernia associated with?
Pulmonary hypoplasia –> reduced space in which lung can develop
What is pulmonary hypoplasia?
Incomplete development of the lungs, resulting in an abnormally low number or size of bronchopulmonary segments or alveoli.
Most often occurs secondary to other foetal abnormalities that interfere with normal development of the lungs.
Where is the most common area for congenital hernia?
Posterolateral
Where does the blood supply to the foregut come from?
Coeliac trunk (T12)
What is Meckel’s diverticulum?
Most common congenital malformation of the GI tract
An outpouching in the distal ileum
Is a leftover of the vitelline duct
What are the dangers with Meckel’s diverticulum?
May contain ectopic gastric or pancreatic tissue
Food may also become trapped
May bleed, become inflamed, cause obstruction
Inflamed = diverticulitis
What was the vitelline duct a connection between?
Yolk sac and gut tube
How can Meckel’s diverticulum present?
Similar to appendicitis
What is an abdominal aortic aneurysm (AAA)?
Bulge or swelling in aorta
Ballooning of blood vessel, walls become weak and pressure of blood running through it makes it balloon
What happens if AAA occurs around a major branch of the abdominal aorta?
If occurs around main vessel (e.g. IMA) it can occlude it
Can cut off blood supply to hindgut
What are the branches of the IMA?
Left colic (has ascending and descending branch)
Sigmoidal
Superior rectal
If the IMA is occluded, how can blood still reach hindgut?
Collateral route
What vessels courses alongside the colon, from middle colic artery (SMA) to the hindgut?
Marginal artery
What does marginal artery act as?
Branch between midgut (SMA) and hindgut (IMA)
Route for collateral blood supply to hindgut if IMA is occluded
What is the sigmoid volvulus?
Sigmoid volvulus is a cause of large bowel obstruction and occurs when the sigmoid colon twists on its mesentery, the sigmoid mesocolon.
What does volvulus mean?
Twisting
How do volvuluses happen?
Due to mobility of mesentery
What can a sigmoid volvulus lead to?
Constipation, ischaemia, necrosis, infection, rupture
How is blood drained from the GI tract?
IMV drains hindgut which meets splenic vein
These then meet SMV to form the hepatic portal vein
(This is most common configuration)
What else does hepatic portal vein have contribution from?
Left gastric vein
What is another configuration for vein from GI tract?
IMV joins to SMV, splenic vein then joins
Why is the blood supply of the liver unique?
Receives 2x blood supplies (hepatic artery proper, hepatic portal vein)
How is the liver drained?
Blood from hepatic artery and portal vein flows through sinusoids in liver to hepatic veins
What do the hepatic veins drain into?
IVC
Where is the IVC?
Against the posterior abdominal wall
Close relation to posterior aspect of liver
How is the liver anchored to the anterior abdominal wall?
Falciform ligament
How is the liver anchored to the diaphragm?
Coronary ligaments
What is the falciform ligament a remnant of?
Ventral mesentery
What is the bare area of the liver?
Devoid of any peritoneum as pushed against diaphragm
What are the 4 anatomical segments of the liver?
Visceral surface
- Right
- Left
- Caudate (close to IVC)
- Quadrate (square shaped, close to gall bladder)
What is the porta hepatis?
Where portal triad enters liver
How many functional subdivisions of the liver are there?
Why is this important?
8
Each receives its own arterial blood supply, own contribution from hepatic portal system, own biliary system
