regulation of gut function Flashcards
- What are the divisions of the gut nervous system
Autonomic (extrinsic)
- Sympathetic
- Parasympathetic
Enteric (intrinsic)
- Where do sympathetic preganglionic neurons arise from?
Thoracic and Lumbar spinal cord
Stomach (T6-9) Colon (L2-5)
- What are the sympathetic postganglionic neurons innervating the stomach called?
- What are the sympathetic postganglionic neurons innervating the small intestine called?
- What are the sympathetic postganglionic neurons innervating the distal colon and rectum called?
Coeliac ganglion
Superior mesenteric ganglion Inferior mesenteric and pelvic ganglion
- What effect does the activation of the sympathetic nervous system have on the activities of the gastrointestinal tract?
- What is parasympathetic innervation to the stomach, small intestine and proximal colon supplied by?
Inhibitory
Vagus nerve
- Where do the preganglionic neurons originate from?
- What effect does the activation of the parasympathetic nervous system have on the activities of the gastrointestinal tract?
Dorsal vagal complex within brainstem from sacral spinal cord
Stimulatory
- What neurotransmitter is used in the sympathetic nervous system?
- What neurotransmitter is used in the parasympathetic nervous system?
Noradrenaline
Acetylcholine
- How are the neurones arranged in the enteric nervous system?
Myenteric (Auerbach’s) plexus- Between longitudinal and circular muscles
Submucosal (Meissner's) plexus- Inside of the circular muscles
- What is the overall function of the myenteric plexus?
To control the activity of the muscularis propria
Controls gut motility Tone velocity of contraction and intensity of contraction
- What are the functions of the submucosal plexus?
Senses local environment (gut lumen)
Controls secretion, blood flow, epithelial and endocrine cell function
- How do the myenteric and submucosal plexus work when food enters the gut?
Food stretches the intestinal smooth muscles
Distension of gut causes stimulation of sensory neurons in myenteric plexus Chemicals in food stimulates sensory neurons in submucosal plexus Sequential contraction/relaxation of circular and longitudinal muscles by inhibitory/excitatory neurotransmitter causes peristalsis, which allows food to move along GI tract
- Describe the contraction of muscle groups during peristalsis
Circular muscles behind the bolus of food contract
Longitudinal muscles ahead of the bolus of food contract causing it to shorten and widen to receive bolus
- Where do the sensory neurons from the epithelium send signals to?
Prevertebral ganglia, spinal cord and brainstem
Submucosal plexus Myenteric plexus
- Are the sympathetic neurons supplying the myenteric and submucosal plexuses, mainly pre or postganglionic?
- Are the parasympathetic neurons supplying the myenteric and submucosal plexuses, mainly pre or postganglionic?
postganglionic
all pre ganglionic
- Does sympathetic stimulation of the enteric nervous system have a stimulatory or inhibitory effect?
- Does parasympathetic stimulation of the enteric nervous system have a stimulatory or inhibitory effect?
Inhibitory, Reduces peristalsis, absorption, secretion and blood flow (via enteric nervous system and directly)
Stimulatory, Increases peristalsis, absorption, secretion and blood flow
- What disease is the most common cause of neonatal bowel obstruction?
- What happens in Hirschsprung’s diseases?
Hirschsprung’s disease
Congenital absence of ganglion of myenteric and submucosal plexuses
Tonal contraction without reciprocal relaxation Intestinal distension proximal to aganglionic segment of bowel
- What cells are the endocrine and paracrine hormones secreted from?
- Where are the neurocrine hormones secreted from?
Enteroendocrine cells
Postganglionic non-cholinergic neurons of the enteric nervous system
- Where are enteroendocrine cells found?
- What are examples of stimuli for the release of the hormone-containing granules?
Located at the base of intestinal crypts throughout the GI tract, from stomach to colon
Small peptides, amino acids, fatty acids, oral glucose, distension of an organ, and vagal stimulation
- Where are the K- and I-cells found?
- Where are the L-cells found?
In the proximal small intestine (duodenum nd jejenum)
Distal small intestine (ileum)
- Where are secretin, CCK and somatostatin all released from?
- Where are PYY, GIP, GLP-1, GLP-2, Oxyntomodulin, Neurotensin, Somatostatin all released from?
Duodenum
Distal small intestine
- What are some of the hormones that are secreted by the colon?
PYY, GLP-1, Oxyntomodulin, Neurotensin and Somatostatin
- What cells are Gastrin secreted from?
- What is the release of Gastrin stimulated by?
Produced from the G cells of the stomach antrum
Amino acids and peptides in the lumen of the stomach Gastric distension Vagus nerve
- What does gastrin do and what does it’s trophic effects affect?
- Below what pH is the release of gastrin inhibited?
Stimulates gastric acid secretion by parietal cells in the stomach
Trophic effects on the mucosa of the small intestine, colon and stomach
pH of 3
- What cells is secretin released from and where are these cells found?
- What stimulates the release of secretin?
S cells of the upper duodenum and jejunum
Presence of acid in the duodenum (pH falls below 4.5)
- What are the functions of secretin?
Stimulates pancreatic bicarbonate secretion (effect potentiated by CCK)
Inhibition of gastric acid and gastric emptying Inhibits gastrin and growth of stomach mucosa Stimulates biliary secretion of bicarbonate and fluid Trophic effect on the exocrine pancreas
- What cells release Cholecystokinin and what stimulates this release?
I-cells of the duodenum and the jejunum
Fat and peptides in the upper small intestine
- What are the functions of Cholecystokinin?
Stimulates pancreatic enzyme release
Stimulates gallbladder contraction and relaxation of the sphincter of Oddi Delays gastric emptying Decreases food intake and meal size Trophic effects on the exocrine pancreas and gallbladder
- What cells secrete Glucose-dependent insulinotropic peptide (GIP)?
- What stimulates the secretion of GIP?
Mucosal K-cells predominant in the duodenum and jejunum
In response to fatty acids, amino acids and glucose in the duodenal lumen (only one with response to all three types of macronutrient)
- Does GIP stimulate or inhibit insulin secretion and gastric acid release respectively?
- As well as the 3 macronutrient types, what is GIP secretion also stimulated by?
Stimulates insulin secretion, Inhibits gastric acid release
Change in intraluminal osmolarity
- Where is motilin secreted from and what does it do?
Released in the proximal small bowel
Stimulates gastric acid and small bowel motility This causes undigested food in these regions to move into the large intestine
- Where is somatostatin synthesised?
- What is somatostatin released in response to?
Endocrine D cells of the gastric and duodenal mucosa and pancreas
Fat, bile salts and glucose
- What is the function of somatostatin?
Inhibition of:
Gastric secretion Motility Intestinal and pancreatic secretions Release of gut hormones Intestinal nutrient and electrolyte transport Growth and proliferation
- Where is Glucagon-like peptide-1 (GLP-1) produced and what cells secrete it?
- What is the release of GLP-1 stimulated by?
- What is the function of GLP-1?
Produced in small intestine and secreted from L cells of the small intestine
Presence of hexose and fat Induces satiety Increases sensitivity of pancreatic beta-cells to glucose
- What cells secrete pancreatic polypeptide?
- What is the secretion of pancreatic polypeptide stimulated by?
- What function might pancreatic polypeptide have?
Pancreatic polypeptide cells in the pancreas
Fat Potential role in satiety
- Where is peptide YY secreted from and what stimulates this secretion?
- What is the function of peptide YY?
Secreted from L-cells found throughout the mucosa of the terminal ileum, colon and rectum and it is released post-prandially (particularly protein)
Reduces intestinal motility, gallbladder contraction and pancreatic exocrine secretion
- What is the function of the Vasoactive Intestinal Peptide (VIP)?
- What is the function of the Gastrin-Releasing Peptide (GRP)?
- What do the Enkephalins do?
Relaxation of gut smooth muscle and stimulates pancreatic secretions
To induce gastrin release Act on opioid receptors in the gut and inhibit peristalsis by increasing smooth muscle tone in the gut
- What happens in Zollinger Ellison syndrome?
- What are the 2 possible treatments for this syndrome
Tumour of gastric cells causes overproduction of gastrin and acid resulting in stomach and intestinal ulceration
Treatment with proton pump inhibitor (Omeprazole) to inhibit acid secretion Role for somatostatin analogues to halt tumor growth and reduce secretion
- What happens in the cephalic phase?
Parasympathetic nervous system via vagus nerve stimulates the enteric plexus
Postganglionic neurons stimulate secretion of gastrin, acid (parietal cells) and digestive enzymes (chief cells - pepsinogen) Gastrin released into bloodstream and induces secretion by parietal and chief cells
- How is the cephalic phase initiated?
Smell, thought, sight and taste of food and tactile stimulations of food in the mouth stimulate the brainstem
