Lecture 27 Flashcards
What does gastrointestinal motility function to do? How does it occur?
Gastrointestinal motility occurs at a controlled rate via propulsion and storage, it also functions for mechanical digestion for ingestion and to increase surface area. It helps in mixing and exposing the food to absorptive surfaces.
It occurs via smooth muscle layers (muscularis) but in the mouth skeletal is used and in the oesophagus both skeletal and smooth work to control motility.
How does GI smooth muscle contraction work and how can it be altered?
GI smooth muscle contracts without external input, its spontaneous activity is controlled by the basic electrical rhythm (slow wave, spontaneous variations in membrane potential, this produces action potentials and results in contraction). The BER strength of contraction is regulated by nervous and hormonal reflexes (frequency can’t be changed), the strength difference is achieved by either depolarizing or hyperpolarizing the resting membrane potential, increasing the amount of threshold potentials reached during one depolarisation.
How does the enteric nervous system work and what does it do?
The enteric nervous system determines the type of motility that occurs, a number of different motility patterns occur because of coordination of GI muscles by this nervous system e.g peristalsis or segmentation. It is dependent on local feedback loops (senses what is going on in a particular part of the lumen and generating a particular response).
What are the types of motility patterns and what do they involve?
The types of mobility patterns are fasting (4-5 hours after a meal and repeated every 2 hours, it starts in the stomach and travels to the small intestine, then the large. It has three periods: inactivity, intermittent activity and then intense activity, these function for house keeping/clearing out leftover mucous, secretions and epithelial cells) and feeding (storage occurs mainly in the stomach and acts to stop movement of food material, it involves relaxation of smooth muscle to allow for more storage, peristalsis occurs from the oesophagus to the large intestine and acts to propel food, segmenta).
How do peristalsis and segmentation occur?
Peristalsis is strong contraction of the smooth muscle behind what we are trying to move, segmentation occurs via contraction on both sides of the material, this seperates and mixes the material.
What are some specific motility patterns and how do they work/ what do they function to do?
Chewing functions to reduce size of food, mix the food with saliva and taste the food, control occurs voluntarily via skeletal muscle as well as reflex control of the strength, frequency and side which chewing occurs on. Swallowing (deglutition) functions for rapid transfer of material from the mouth to the stomach via creation of a pressure gradient, control is initiated at will (voluntarily) and proceeds reflexively (involuntarily). Gastric motility during fasting shrinks the GI tract to a smaller volume and migrates the motor complex. During eating a series of motility patterns occur which are associated with storage, mixing, mechanical digestion and controlling of delivery to the intestines.
What are two major tasks which occur in the stomach?
Storage occurs in the proximal part of the stomach, it occurs via receptive relaxation (the oesophagus sends a signal to the gastric muscle to relax because food is going to enter, this is initiated by swallowing, this reduces the thickness and makes it more highly distensible). Peristalsis also occurs in the stomach, it begins on the greater curvature (back of stomach) it spreads the contents to the antrum. Initially they are quite weak (up to 60 mins) but get more intense from 60-300 minutes due to larger amounts of gastrin production. it acts to provide propulsion and combined with the pyloric sphincter to provide retropulsion (mixing and mechanical digestion of the food as it bounces back from the closed sphincter).
How does controlled deliver of food occur to the small intestine?
Controlled delivery of chyme (food) to the small intestine occurs via regulation of gastric emptying through gastric motility. The composition of the food modifies the rate of emptying (solids slower than liquids, fats also slow gastric emptying). The duodenum controls the stomach via gastric inhibitory peptide (hormonal) and neurally via the enterogastric reflex.
What motility patterns and functions do the small intestine and colon have?
The small intestine functions for chemical digestion of food and absorption of nutrients, salt and water. It needs motility for mixing, exposing material to absorptive surfaces and for propulsion. The motility patterns are different for fasting and feeding (mainly segmentation but also peristalsis). The large intestine (colon) functions for temporary storage of faeces and regulation of the salt and water content of the faeces, motility patterns can be inactivity, segmentation (once per 30 mins) or mass movements (3-4 times per day to force faeces into the rectum).
