Nervous + Homonal Control Of Gut Flashcards
What are the 3 mechanisms that control the gut
- Autonomic nervous system
- Enteric nervous system
- Hormones and Paracrine substances
Each nervous pathway has 2 neurons: Pre and Post ganglionic.
Compare their synapses and what substances they release
Pre:
- Synapse with ganglia outside CNS (In walls of effector organ)
- All release ACh
Pos:
- Synapse with peripheral effector
- Release ACh, NA or Neuropeptides
What are 2 nervous structures of the Parasympathetic System (the ‘on’ button of the gut)
- Vagus Nerve (Very important)
- Pelvic Splanchnic Nerves (S2-S4)
Outline the pathway of Sympathetic Innervation to Gut in 4 steps
(acts as an ‘off’ button, mainly to contract blood vessels)
- T5-L2 nerves (Thoracolumbar) pass through Sympathetic chain WITHOUT synapsing.
- They then coalesce to form the following Presynaptic Splanchnic Nerves;
- Greater (T5-T9)
- Lesser (T10-T11)
- Least (T12) - These then synapse with Prevertebral (In front of spine) Ganglia
- Post ganglionic fibres synapse with effector organ
Name 4 Prevertebral Ganglia that the Sympathetic Presynaptic Splanchnic Nerves synapse with
- Coeliac
- Renal
- Superior Mesenteric
- Inferior Mesenteric
What is the Enteric Nervous System? (ENS)
A completely autonomous nervous system that exists throughout the entire GI Tract
(Can operate independently, but extensively connected to main ANS)
Parasympathetic PRE-ganglionic fibres and Sympathetic POST-ganglionic fibres both extend to the 2 main plexuses where the ENS exists.
Compare the 2 plexuses in;
- Location
- Function
Submucosal/ Meissner’s Plexus:
- Lies in Submucosa
- Majorly involved with Secretions and Blood Flow
Mynteric/ Auerbach’s Plexus (Deeper):
- Lies between Circular and Longitudinal muscle layers
- Majorly involved in Motility
Gut hormones can be Endocrine, Paracrine or Neurocrine
Name 3 Endo, 1 Para and 1 Neuro
Endo;
- Gastrin
- Cholecystokinin
- Secretin
Paracrine;
- Somatostatin (GHIH)
Neurocrine;
- Gastrin Releasing Peptide
Endocrine and Paracrine gut hormones are all released from what kind of cells?
Where are they found?
When do the cells release hormones?
- Enteroendocrine cells
- Between epithelial cells in gut mucosa
- Release hormones in response to food intake OR stretch
There are 2 main families of gut hormones.
Name them and the hormones in each family
Gastrin family;
- Gastrin
- Cholecystokinin
Secretin family;
- Secretin
- Gastric Inhibitory Peptide (GIP)
Where is Gastrin released from?
What else do these cells do?
- G cells in antrum of stomach
- Increases gastric acid secretion (G cells stimulate parietal cells when releasing gastrin)
What are 3 stimulants for Gastrin release
- Protein breakdown in stomach
- Vagus nerve
- Stretch receptors
What cells are Cholecystokinin (CCK) released from?
What stimulates CCK release?
- I cells in Duodenum and Jejunum
- Protein and fat breakdown + Acid detection
State 3 actions of CCK
- Stimulates pancreas to release digestive enzymes
- Contracts gall bladder to release more bile into Duodenum
- Relaxes Sphincter of Oddi (to let P/ GB secretions enter duodenum)
What are 2 actions of Secretin
- Increases HCO3 secretions from Pancreas and Gallbladder
- Decreases gastric acid secretion
