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Gastrointestinal sys

Gastrointestinal system.

What is the primary function of the gastrointestinal system? Absorption of dietary nutrients.
How are the processes of the GI system maximised? By secretions added along the tube that convert large molecules to smaller ones i.e. digestion.
What is motility? Contents, including secretions, are mixed and moved along tube by co-ordinated contraction and relaxation.
What are secondary processes of the GI? Storage and excretion.
What constitutes the mucosa? Epithelium, lamina propria and muscularis mucosa.
How often is the epithelium replaced in the GI? Every 2-3 days.
Which way does the apical side of the GI face? It faces the GI lumen.
Which way does the basolateral side face? It faces the interstitium and vasculature.
What two features of the epithelium increase GI surface area? Villi and crypts.
What is the structure of the epithelium in the GI? Single cell layer forming continuous lining of GI tract.
What is the lamina propria? Loose connective tissue made up of elastin and collagen fibres.
What does the lamina propria contain? Sensory nerves, blood and lymph vessels and secretory glands.
What is the structure of the muscularis mucosa? Thin layer of smooth muscle.
What is the function of the muscularis mucosa? Further increases surface area by creating ridges and folds.
What is the submucosa? A thicker layer with similar composition to the lamina propria
What is the function of the submucosa? Incorporates blood vessels and nerve bundles that form submucosal plexus (meissner plexus)- an integral part of the enteric nervous system.
What is the meissner plexus? Lies in the submucosa of the intestinal wall- the nerves of this are derived from the myenteric plexus which is derived from the plexus of the PNS.
What constitutes the muscularis externa? Circular muscle, myenteric plexus and longitudinal muscle.
What is the role of the ENS? Co-ordinates contractions to mix and move contents between compartments.
What is the function of sphincters? To regulate flow from compartment to the next.
What is the serosa? Outermost layer of connective tissue and layer of squamous epithelial cells.
What are the 3 divisions of the autonomic nervous system that regulate the GI? Parasympathetic, sympathetic and enteric.
Where does the parasympathetic nervous system derive its innervation from? Vagus (medulla oblongata) and pelvic-splanchnic nerves.
What does the parasympathetic nervous system respond to? Stretch, pressure, temperature and osmolarity.
What primary neurotransmitters are used? Acetylcholine, gasric-releasing peptide and substance P.
What does the PSNS in general do to the GI? The PSNS signals stimulate GI secretions and motility facilitating digestion and absorption of nutrients.
Where do nerves of the sympathetic nervous system originate? In thoracic (T5-T12) and lumbar (L1-L3) regions, then synapse in 1 of 3 ganglia.
What innervates the upper GI tract? Innervated by nerves that synapse in superior cervical ganglion.
In general what does the SNS do to the GI? Generally decreases GI secretions and motility.
How are the PSNS and SNS linked to the ENS? They usually synapse with ENS components.
Can the ENS act independently? ENS can operate autonomously via intrinsic regulation and sensory reflexes.
How are ENS nerves organised? Into myenteric and submucosal plexuses.
What is the structure of the myenteric plexus? A dense parallel neuronal configuration.
What are the functions of the myenteric plexus? Primary role of regulating intestinal smooth muscle. Participates in tonic and rhythmic contractions.
What is the main function of the submucosal plexus? Primarily regulates intestinal secretions and local absorptive environment.
What is another function of the submucosal plexus? Can also synapse on blood vessels, circular and longitudinal muscle, muscularis mucosa.
What supports the ENS neurons? Enteric glial cells (resemble brain astrocytes).
What regulates many GI reflex actions? Neural circuits involving mechanoreceptor or chemoreceptor stimulation in the mucosa.
How is the GI reflex transported back? Signal transmitted back to neurons in submucosal plexus, which stimulate other neurons in submucosal or myenteric plexus that regulate endocrine or secretory cells.
What does the neurotransmitter enkephalins do? Constrict muscle around sphincters and decrease intestinal secretions.
What are other examples of ENS neurotransmitters? VIP, substance P, ACh, nitric oxide and serotonin.
What is the function of acetylcholine in the ENS? Contracts wall muscle, relaxes sphincters and increases salivary, gastric and pancreatic secretion.
What is the function of vasoactive intestinal peptide? Relaxes sphincters, increases pancreatic and intestinal secretion.
What is the function in norepinephrine? Relaxes wall muscle, contracts sphincters and decreases salivary secretions.
What is the function of neuropeptide Y? Relaxes wall muscle and decreases intestinal secretions.
What is the function of gastric-releasing peptide? Increases gastrin secretion.
What is the function of substance P? Contracts wall muscle and increases salivary secretions.
Which type of cell releases cholecystokinin, glucose-dependent insulinotropic peptide, gastrin, motilin and secretin? I, K, G, M and S.
What is the function of cholecystokinin? Increases enzyme secretion; contracts gall-bladder; increases gastric emptying.
What is the function of glucose-dependent insulinotropic peptide? Releases insulin; inhibits acid secretion.
What is the function of gastrin? Increases gastric acid secretion.
What is the function of motilin? Increases contractions and migrating motor complexes.
What is the function of secretin? Releases HCO3- and pepsin.
What are paracrines? A form of cell-cell communication in which a cell produces a signal to induce changes in nearby cells, altering the behavior of those cells.
What is the distribution of the GI paracrines? Prostaglandins and somatostatin are more widespread in their release and actions than histamine.
What cells release histamine? Enterchromaffin-like cells and mast cells.
What cells release prostaglandins? Cells lining GI tract.
What cells release somatostatin? D cells.
What is the function of histamine? Increases gastric acid secretion.
What is the function of prostaglandins? Increase blood flow and mucus and HCO3- secretion.
What is the function of somatostatin? Inhibits peptide hormones and gastric acid.
What triggers the cephalic phase? The thought of food, conditions suggestive of previous food intake.
What effects does the cephalic phase have? Primarily neural and causes ACh and VIP release.
Where are the hormones released in the cephalic phase? Salivary glands, stomach, pancreas and intestines.
When does the gastric phase occur? Begins when food and oral secretions enter the stomach. Coincides with distension.
What occurs as a result of the gastric phase? Elicits neural, hormonal and paracrine GI responses.
When does the intestinal phase occur? Begins when stomach contents reach the duodenum.
What occurs as a result of the gastric phase? Initiates primarily hormonal, but also paracrine and neural responses.
Define absorption. The process of transporting dietary contents across the gastrointestinal barrier of the body.
What is the function of the upper GI tract? Transports and prepares food to be absorbed.
What is included in the upper GI tract? Mouth, oesophagus and stomach.
What is the technical name for chewing? Mastication.
Where is most of the saliva produced? 1-1.5l of saliva/day mainly by sublingual, submandibular and parotid glands.
What is the composition of the saliva? Hypotonic to plasma: composition determined by ductal modification of secretion.
Is swallowing voluntary or involuntary? Initiated voluntarily, then involuntary once initiated.
What happens at the back of the mouth during swallowing? The larynx and hyoid bone move upward, and the epiglottis closes off access to the larynx.
How does the food enter the oesophagus? The upper esophageal sphincter relaxes, allowing the bolus to enter the esophagus.
What is peristalsis? A series of co-ordinated muscle contractions/relaxations usually taking 6-10 seconds (a wave).
When does peristalsis commence? After upper oesopheageal sphincter.
Where are secretions in the stomach derived from? From pits i.e. gastric invaginations. The pits contain multiple cell types.
What are the three motility functions of the stomach? Accomodation via receptive relaxation, mixing via slow wave-initiated contractions and retropulsion and gastric emptying.
What is included in gastric secretions? Include ions and water, mucus from mucous neck cells, pepsinogen from chief cells and intrinsic factor and H+ parietal cells.
What and where are the sections of the small intestine? Duodenum (first 0.3m), jejunum (next 2.3m) and ileum (final 3.4m).
What occurs in the small intestine? Most macronutrient, vitamin and mineral absorption occurs here.
How is the small intestine adapted to absorption? Facilitated by huge increase in surface area created by villi (10-fold) and microvilli (20-fold).
What are the structures of the large intestine? Caecum, ascending, transverse and descending sigmoid colon, rectum and anus.
What are the functions of the large intestine? Significant water and ion absorption. Motility of contents: mixing and propulsion.
What is involved in motility in the small intestine? It involves both mixing via segmentation and propulsion via peristalsis.
What happens in the small intestine between meals? Migrating motor complexes sweep the intestinal lumen free of residual particles between meals.
What is the function of the ileocecal sphincter? It regulates the amount of chyme entering the large intestine.
What is chyme? The pulpy acidic fluid which passes from the small intestine, consisting of gastric juices and partly digested food.
What is the function of the internal and external sphincters? Regulate the feces exiting the GI system.
What does motility in the large intestine involve? Segmentation, peristalsis, mass movement and a number of reflexes that control contraction and relaxation.
Created by: robertspedding



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