Gastrointestinal system Flashcards
what are the layers of the gut wall and their functions?
(lumen)
- mucosa: presents epithelial cells, comes in contact with lumen if the gut
- submucosa: supports mucosa and allows its movement by muscularis externa, contains submucosal plexus (nerves)
- muscularis externa: has inner longitudinal smooth muscle and outer circular smooth muscle with myenteric nerve plexus between the layers
- serosa: loose connective tissue w mucus that allows frictionless interaction with other organs
4 functions of gastrointestnal system
- motility
- secretion
- digesttion
- absorption
what are three ways that the mucosa increases surface area?
- plicae circularis (folds in intestinal lining)
- villi (finger-like projections on surface of plicae/folds in epithelial cells)
- microvilli (finger-like projections on surface of epithelial cells/ folds in folds)
2 structures of ENS in gut wall?
- submucosal plexus: controls the mucosa for secretion, absorption, movement of villi
- myenteric plexus: between smooth muscle layers of muscularis externa, controls the muscularis for motility
3 phases of gastirc regulation
- cephalic phase (preparative)
- gastric phase (digestive)
- intestinal phase (digest/absorb)
explain intrinsic neural regulation of GI tract, include its function, receptors and name its two reflex pathways
intrinsic neural regulation is by the ENS, its function is to respond to the GI luminal contents, and it uses chemo, Osmo, and mechanoreceptors to respond to detect luminal conditions. it can respond by either the myenteric plexus (controls motility) or the submucosal plexus (controls secretion)
explain extrinsic neural regulation of GI tract, including how it functions, receptors, signal pathway, and effectors
extrinsic neural regulation is by the CNS, its function is to integrate response to external stimuli, acts via the ENS/ modulates the activity of ENS indirectly
explain how parasympathetic nervous system regulates GI function, including receptors used
PNS acts to stimulate activity, acetylcholine acting on muscarinic cholinergic receptors
explain how the sympathetic nervous system regulates GI function, including receptors used
SNS acts to inhibit GI activity, noradrenaline acts on alpha adrenoreceptors
explain hormonal regulation of GI function, including function, receptors (and cells) used, and effectors
function of hormonal regulation is to respond to GI luminal contents (GI lumen contents). utilises chemo, osmo, and mechanreceptors. enteroendocrine cells in epithelial layer secrete hormones (basolateral pole has secretory granules/hormones). effectors = smooth muscle cells and secretory cells.
what is unique about GI smooth muscle cells? x 4
- Gi smooth muscle cells can be spontaneously active w periods of inactivity over time
- enteric smooth muscle cells can be connected electrically via gap junctions
- physically connected via adherins
- muscle cells act together as a single unit, therefore called UNITARY smooth muscle
what and where are the GI pacemaker cells and what do they do?
interstitial cells of cajal: located in the myenteric plexus and generate slow waves of contraction via cyclic changes in Na+/K+ ATPase and K+ membrane permeability.
two ways interstitial cells of cajal are regulated
regulated by hormones and neurotransmitters
explain the fasting state of motility and its importance
the fasting state of motility is called the migrating motor complex (MMC) is important for:keeping things moving through GI tract, remove residual secretions/undigested materials, regulate turnover of epithelial cells.
the MMC contains three distinct periods that occur once every 2hours: a period of intense activity, a period of low/no activity, and a period of intermittent activity.
summarise the process of swallowing (x 3 oral events, x 3 esophageal events)
- initiation by stretch receptors: food forced onto pharynx by tongue, sensed by stretch receptors and brainstem initiated swallowing
- soft palate: pushes upward and prevents food from entering nasal passage
- epiglottis: moves down to cover entrance to trachea
- upper esophageal sphincter: relaxes and allows food passage
- lower esophageal sphincter: opens(relaxes at the start of swallowing, food enters stomach, closes after peristalsis wave)
- esophagus (peristalsis): smooth muscle contracts, peristalsis pushes food to stomach and lasts about 9 seconds
