Regulation of Gut Function Flashcards
What 2 branches is the gut NS divided into?
What is the Autonomic NS further divided into?
NS divided into:
Autonomic = extrinsic
Enteric = intrinsic
ANS = SNS + PNS
SNS = sympathetic NS; ‘fight or flight’
PNS = parasympathetic NS; ‘rest and digest’
Where do the sympathetic preganglionic neurons that supply the gut arise from?
What is the sympathetic NS supplying the gut composed of?
The thoracic and lumbar spinal cord - stomach = T6-T9; colon = L2-L5
Short pre-ganglionic neuron that terminates at the ganglions (collection of nerve bodies), from which the long post-ganglionic neurons arise and terminate at the target organ
What are the names of the ganglions from which the post-ganglionic neurons innervating the stomach, small intestine and colon arise?
What is the neurotransmitter responsible for the affects of the SNS?
What is the overall affect of the SNS?
Stomach = coeliac ganglion; Small intestine + first part of the colon = superior mesenteric ganglion; Distal portion of the colon + rectum = inferior mesenteric and pelvic ganglion
Norepinephrin
Inhibition of GI tract activity
Which parasympathetic nerve supplies the GI tract?
Where do the pre-ganglionic neurons arise from?
What is the parasympathetic NS supplying the gut composed of?
What is the neurotransmitter responsible for the affects of the PNS?
What is the overall of the PNS on the GI tract?
Vagus nerve
Dorsal vagal complex within the brainstem from the sacral spinal cord
Long pre-ganglionic neurons that synapse quite close to the target organ, following on with a short post-ganglionic neuron
Acetylcholine
Stimulates GI tract activity
Describe the diagram below of the SNS and PNS innervation of the GI tract:
Sympathetic = short, myelinated pre-ganglionic neurons originate from the CNS and terminate at the ganglions close to the spinal cord. Long, unmyelinated post-ganglionic neurons originate from the ganglions and innervate the target organ, causing a ‘fight or flight’ response via norepinephrine
Parasympathetic = long, myelinated pre-ganglionic neurons originate form the CNS and terminate at a ganglion near the target organ. Short, unmyelinated post-ganglionic neurons originate from the ganglion and innervate the target organ, causing a ‘rest and digest’ response via acetylcholine
What is the enteric (intrinsic) NS innervation of the GI tract?
Fill in the missing labels in the pic below and describe each of the layers:
Functions autonomously (can still function even if nerve supply from the spinal cord is cut off) - acts like a ‘2nd brain’. It resides within the gut itself
From the inside of the GI tract travelling outside:
Lumen (white central bit) = where the food bolus comes through
Mucosa = divided into the epithelium, lamina propria and muscularis mucosa
Submucosa = in which there is lymph drainage and blood supply, and the Meissner (submucosal) plexus
Muscularis propria (inner circular and outer longitudinal) = contains the myenteric plexus between the 2 muscle layers
Serosa =
What is the function of the myenteric and meissner plexi?
What are the 3 ways muscle contraction can be changed / affected?
Myenteric = controls the motility and contractility of the muscle layer of the gut. Senses stretch and responds with contraction - responsible for peristalsis
Submucosal = senses the local environment e.g. lipids, proteins etc. This then increases secretion of enzymes, hormones and acid to aid digestion. Also plays a small role in the motility of the gut
Contraction is controlled by tone, velocity and intensity.
What is the local reflex action when having ingested a meal?
Food enters the gut lumen and stretches the inestinal smooth muscles
Distension of the gut causes stimulation of the sensory neurons in the myenteric plexus - cause peristalsis
Chemicals in the food stimulate sensory neurons in the submucosal plexus - release of hormones, enzymes and acid
Food is digested, absorbed and moves along the GI tract
What is the mechanism for peristalsis in terms of the muscle contractions and relaxations?
When the gut senses a food bolus, the circular muscles behind contract to propel the food bolus foward, whilst the longitudinal muscles ahead relax to receive the food bolus
And then vice versa occurs - i.e. the longitudinal muscles contract whilst the circular muscles relax
Sequential contractions - moves food/chyme from mouoth to anus
So overall, what are the affects of the SNS and PNS on the GI tract in terms of peristalsis, absorption, secretion, blood flow, etc.?
The myenteric and submucosal plexi cause a local response when they detect the food bolus, but they also feedback to the CNS
SNS feedback = reduced peristalsis, absorption, secretion, and blood flow
PNS feedback = increased peristalsis, absorption, secretion, and blood flow
What is Hirschprung’s disease?
What do they present with?
How is it treated?
Mainly diagnosed in pediatrics, but sometimes in adults too. A congenital condition - born without the ganglions of the myenteric and submucosal plexi. Therefore, characterised by an enlarged colon
Usually present with constipation - as there is tonal contraction in the rectum but without reciprocal relaxation
Initially, laxatives, enema etc. to treat symptoms such as constipation. But eventually require surgery (colectomy)
What are the 3 categories of gut hormones and what are their characteristics? Give examples of hormones that fall into each category:
Endocrine - hormones such as gastrin, CCK, secretin, GIP, motilin etc. are secreted by enteroendocrine cells into the bloodstream
Paracrine - hormones such as somatostatin, histamine etc. are also secreted by enteroendocrine cells, but have a more local effect as they not secreted into the bloodstream, instead move via the paracellular pathway e.g. somatostatin
Neurocrine - hormones such as vasoactive intestinal peptide (VIP), gastrin release peptide (GRP), and enkephalins etc. that are secreted by nerve cells and act on nerve cells
What are enteroendocrine cells?
Where are they found?
Specialised epithelial cells - possess hormone containing granules, stimulated by chemical changes e.g. lipids, amino acids, etc. to release the hormones within the granules
The small intestine contains brush borders (villi) and the enterocytes are found in the crypts (grooves between the villi)
Place these list of enzymes to where they would be found in the GI tract on the image below:
Secretin, CCK, Somatostatin, Gastrin, Ghrelin, Histamine, Insulin, Glucagon, Pancreatic Polypeptide, PYY, GIP, GLP-1, GLP-2, Oxyntomodulin, Neurotensin
Why is gastrin an important gut hormone?
Where is it synthesised, what stimulates its release and what is it’s function?
Important to maintain stomach pH below 3
Synthesised in the gastric antrum mainly
Its release is stimulated by amino acids and peptides in the lumen of the stomach, gastric distension, and vagus nerve stimulation
It works by stimulating gastric acid secretion by parietal cells in stomach and also have some trophic (growth) effects on the mucosa of the small bowel, colon and stomach
