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.
