14 Regulation of Gut Function Flashcards
Q: What are the 3 regulatory systems? 2 subs of 1.
A: Nervous stimulation: neurotransmitters released from neurones innervate target cells. -> intrinsic (enteric) and extrinsic (autonomic)
Paracrine : hormones released by cells in the vicinity of the target cell and reach target cell by diffusion.
Endocrine : hormones produced by endocrine cells, released into the blood where they reach their targets via the circulation.
Q: How many neurons do we have in the GIT wall? What do they communicate with? What system do they make and why is it referred to as the second brain? Independence?
A: totalling somewhere between 10 and 100 million nerve cells (compared with 300 billion in the brain)
cells in the autonomic nervous system (combined function)
enteric nervous system = integrating centre for coordinating function = similar to how the brain receives signals from different parts of the body (afferent signals), integrates them, and produces a response (efferent signals)
ENT can do so independent of the central nervous system
In experimental animal models, the independence of the enteric nervous system can be demonstrated by severing the sympathetic and parasympathetic nerves innervation to the gut. Afterwards, many motor and secretory activities continue unaffected.
Q: How are nerves in the GIT arranged? (3)
A: in rich plexuses (a dense local network of nerves and supporting cells)
of ganglia (nerve cells which carry signals, and glial cells which provide ((insulate, protective, nutritional and structural)) support)
These ganglia are interconnected by tracts of fine, unmyelinated nerve fibres
Q: What can cause dysfunction of the ENS? (4)
A: Inflammation (ulcerative colitis; Crohn’s disease)
Following invasive abdominal surgery
Irritable bowel syndrome
Ageing (constipation)
Q: What are the 2 main structures of the ENS? Where are they? Afferent/efferent functions? What does it allow/function?
A: gut wall has two main plexuses (plexi) - the myenteric plexus and the submucosal plexus -> both communicate
Myenteric plexus (also known as Auerbach’s plexus) = located between the circular and longitudinal smooth muscle layers =has efferent innervation of both =careful control of the entire activity of muscularis externa =allows for coordinated control of motor function, and hence, motility
Submucosal plexus (also known as Meissner’s plexus) =in submucosa =has both afferent and efferent functions. =Afferent: Senses the environment within lumen using mechanoreceptors, chemoreceptors and osmoreceptors. =Efferent: Can fine tune local blood flow, epithelial transport and secretory/paracrine/endocrine cell function.
Q: What are the 5 key efferent functions of the ENS?
A: SPAMW
Secretion - Perfusion - blood flow Absorption - Motility - Water and electrolyte transport
Q: Describe secretion as a role of the ENS.
A: controlling the secretion of enzymes, paracrine signals and endocrine hormones to regulate local and non-local gut functions.
Q: Describe perfusion as a role of the ENS.
A: blood flow needs to be carefully controlled to ensure high perfusion in regions of the gut that are working (vascular smooth muscle cells [VSMC], submucosal glands) and/or absorbing (enterocytes)
Q: Describe absorption as a role of the ENS.
A: carefully controlling the absorption of nutrients, vitamins, minerals and ions by adjusting expression of luminal transport proteins
Q: Describe motility as a role of the ENS.
A: smooth muscle cells [SMCs] in the circular and longitudinal muscle layers can contract and relax to cause effective gut transit. It may be desirable to accelerate this (e.g. following a large meal) or stop it completely (e.g. during exercise)
Q: What are the 3 neuronal populations of the ENS? (describe) Most neurons are?
A: Most are neurons are multipolar (one axon, one cell body, multiple dendrites)
Sensory: respond to mechanical, 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
Q: What is the third plexus of the GIT? Where? (2)
A: Minor plexuses
including deep muscular plexus (inside circular muscle), and the ganglia supplying biliary system and pancreas
Q: What does the ANS regulate? (3) Control? (2) 2 branches? (what are they associated with) How do they differ?
What does central control interact with? why?
A: smooth muscle, cardiac muscle and glands
not under conscious control and cannot be activated voluntarily
- Sympathetic – associated with stress and the fight or flight response
- Parasympathetic – associated with sedate activities, including rest, repair and recuperation
structure and function of these braches is very different, as are the neurotransmitters they release.
enteric nervous system to control gut function.
Q: How do the PNS and SNS of the ANS differ in terms of neuronal cell bodies? (2,2)
A: SNS
- Preganglionic cell bodies are located in the spinal cord in the lower thoracic and upper lumbar spinal cord
- Postganglionic cell bodies are in the pre- and paravertebral ganglia
PNS
- Preganglionic cell bodies are located in the brainstem and sacral spinal cord
- Postganglionic cell bodies are located very close to the target organs.
Q: How do the PNS and SNS of the ANS differ in terms of neuron length? (2,2) Relate one to the neurons of the ENS.
A: SNS - Preganglionic nerves synapse with the postganglionic nerves close to the spine, which makes the preganglionic neurons relatively SHORT compared to the postganglionic neurons which extend from the sympathetic chain to the target organ and are relatively LONG.
PNS - Preganglionic nerves synapse with the postganglionic nerves close to the target organs, which could be as far from the brain as the rectal muscle wall. This makes the preganglionic neurons relatively LONG compared to the postganglionic neurons which are relatively SHORT, extending from ganglia outside of, or inside, the directly with gut plexus of the ENS.
Q: How do the PNS and SNS of the ANS differ in terms of innervation? (3,2) What does this reflect?
Q: SNS - Pre-ganglionic neurons are in the splanchnic nerves arising from the thoracic and lumbar regions. Thoracic branches innervate the foregut and associated organs, and the lumbar branches innervate the hindgut.
-> some post ganglionic N from sympathetic ganglia can directly act of blood vessels (while the rest go through ENS)
PNS - Most GI tract innervation in the branch of the ANS arises from the vagus nerve (CNX). Structures from the descending colon onwards receive innervation from the pelvic splanchnic nerves.
embryological origins of the gut
Q: How do the PNS and SNS of the ANS differ in terms of neurotransmitter? Between pre and post?
A: SNS - The major neurotransmitter of the SNS is NOREPINEPHRINE/noradrenaline (NE). Although synapses in the sympathetic chain use acetylcholine (ACh) to communicate, most synapses between the SNS and the enteric nervous system use NE.
PNS - The major neurotransmitter of this branch of the ANS is acetylcholine.
always ACh
Q: How do the PNS and SNS of the ANS differ in terms of gut function?
A: SNS - The general impact of the SNS on the gut function is to REDUCE ACTIVITY.
PNS - The general impact of the PNS on the gut function is to INCREASE ACTIVITY.
Q: Majority sympathetic fibres… but… 3 examples.
A: do not directly innervate structures in the GI tract- terminate on neurons in the intramural plexuses.
BUT: Vasoconstrictor sympathetic fibers do directly innervate the blood vessels of the GI tract- coeliac, superior and inferior mesenteric.
Q: Afferent signals? (2) Directly to ENS? To CNS (->PNS and ANS -> ENS)?
A: Chemo and mechanoreceptors in wall of GI tract
local afferents
Splanchnic and vagal afferents
Q: What are the 2 types of innervation of the GIT? (2-1,2 examples) What does this allow?
A: 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.
Q: What produces the gastrointestinal endocrine system? Can act as?
A: by (entero)endocrine cells in the mucosa or submucosa of the stomach, intestine and pancreas
paracrine or neurocrine factors
Q: Name 3 hormones released by the duodenum.
A: Secretin
CCK
Somatostatin
Q: Name 3 hormones released by the stomach. Effect of 2?
A: Gastrin*
Ghrelin
Somatostatin*
Histamine***
paracrine signalling:
- D-cells secrete somatostatin -> inhibits secretion of acid from parietal cells in the gastric pits.
- enterochromaffin-like (ECL) cells secrete histamine -> binds to H2 receptors on the parietal cells, stimulating acid secretion.
