Flashcards in Structure of GI Tract and Motility Deck (73):
What structure of the GI tract, chop food, lubricate it, start carbohydrate and fat digestion and propel food to oesophagus?
Mouth and oropharynx
What structure of the GI tract, delivers food to the stomach?
What structure of the GI tract stores food temporarily, continues carbohydrate and fat digestion and regulates delivery of chyme to the small intestine?
What structure in the GI tract is the principal site of digestion and absorption of nutrients?
What structure of the GI tract reabsorbs fluids and electrolytes and stores faecal matter before regulated expulsion?
What are the three accessory structures of the GI tract?
Salivary glands, pancreas and the liver and gall bladder (hepatobiliary system)
What are the four basic digestive processes?
What type of muscle does mechanical activity for motility in the mouth, pharynx, upper oesophagus and external anal sphincter?
In motility, what are the three types of movements?
1. Propulsive movements
2. Mixing movements
3. Tonic contractions
What do digestion and protection both require?
What three things does digestive secretion contain?
3. Organic compounds
What is the term for the biochemical breakdown (enzymatic hydrolysis) of complex foodstuffs to smaller, absorbable units?
In digestion, what are carbohydrates [mostly polysaccharides such as starch and glycogen] converted to, and what mediates this conversion?
Monosaccharides (glucose, galactose and fructose)
Mediated by amylases and dissacharidases.
In digestion, what are proteins converted to and what mediates it?
Amino acids, dipeptides and tripeptides
Mediated by proteases and dipeptidases
In digestion, what are fats converted to [mostly triglycerides] and what mediates it?
Monoglycerides and free fatty acids.
Mediated by lipases
What term is given to the process involving the transfer of the absorbable products of digestion from the digestive tract to the blood or lymph?
What part of the digestive tract wall has: epithelial cells, exocrine cells, endocrine gland cells, lamina propria and muscularis mucosa? State the components roles also.
Mucosa. Epithelial cells - absorption. Exocrine cells - secrete digestive juices. Endocrine gland cells - secrete digestive hormones. Lamina propria - capillaries, enteric neurones and immune cells.
What structure of the digestive tract wall contains connective tissue, larger blood and lymph vessels and a nerve network - submucosa plexus?
What part of the digestive tract wall is a circular muscle layer, has a nerve network - myenteric plexus and longitudinal muscle layer?
What is the outer layer of the digestive tract wall and what does it contain?
Serosa - connective tissue
What does circular muscle contraction do to the lumen?
Becomes narrower and longer
What does longitudinal muscle contraction do to the intestine?
Becomes shorter and fatter
What does muscularis mucosae contraction do to the mucosa?
Change in absorptive and secretory area of mucosa
What are adjacent smooth muscle cells in the GI tract coupled by?
What do gap junction between smooth muscle cells of the GI tract form, by allowing spread of electrical currents from cell to cell?
Functional syncytium in which hundreds of cells are depolarised and contract at the same time.
What two factors modulate spontaneous smooth muscle activity in the GI tract?
1. Intrinsic (enteric) and extrinsic (autonomic) nerves
2. Numerous hormones
In the stomach, small intestine and large intestine, what does spontaneous electrical activity occur as?
In the GI tract, what determines maximal frequency, direction and velocity of rhythmic contractions?
Slow wave electrical activity
What drives slow waves?
Interstitial cells of Cajal - pacemaker cells
When does contraction only occur?
When the slow wave amplitude is sufficient to trigger action potentials
In slow wave amplitude - what mediates upstroke and what mediates downstroke?
Upstroke - calcium ions
Downstroke - potassium ions
What is force of contraction related to?
Number of action potentials discharged
Where are interstitial cells of Cajal located?
Between longitudinal and circular muscle layers and in the submucosa
In the enteric nervous system, where are cell bodies located?
In ganglia largely within the myenteric and submucous plexus
What is another name for the myenteric and submucosa plexus?
Myenteric - Auerbach's
What are ganglia in the enteric nervous system connected by?
Interganglionic fibre tracts
What forms a complete reflex circuit that can operate independently of the rest of the nervous system, but is strongly modulated by hormones and extrinisc nerve input?
Enteric nervous system
What three neurones comprise the enteric nervous system?
1. Sensory neurones
3. Effector neurones
What type of neurones supply longitudinal and circular muscle, secretory epithelium, endocrine cells and blood vessels?
In the parasympathetic innervation of the GI tract, what do preganglionic fibres release?
What do preganglionic fibres synpase with, in the essence post-ganglinic neurones within the ENS? (parasmpathetic)
What innervation increases gastric, pancreatic and small intestinal secretion, blood flow and smooth muscle contraction?
What does parasympathetic innervation of GI tract inhibit?
Relaxation of some sphincters, receptive relaxation of stomach.
In the sympathetic innervation of GI tract, where do preganglionic fibres, releasing ACh, synapse?
In the prevertebral ganglia.
In the sympathetic innervation of GI tract, what do postganglionic fibres, releasing NA, innervate?
Mainly enteric neurones
What is the inhibitory influence of sympathetic innervation of GI tract?
Decreased motility, secretion and blood flow
Give an example of local reflex, short reflex and long reflex?
Local - peristalsis
Short - intestino-intestinal inhibitory reflex
Long - gastroileal reflex
What is peristalsis triggered by?
Distension of the gut wall
In perstalsis, what happens after distension activates sensory neurones?
Altered activity of interneurones
What do altered activity of interneuornes cause?
Altered activity of motoneurones
When circular muscle contracts, what is released from excitatory motoneurone?
ACh and substance P
When circular muscle contracts during perstalsis, what happens to longitudinal muscle and what two substances cause this?
Release of VIP and NO from inhibitory motoneurone
In the propulsive segment of perstalsis, what does the longirtudinal and circular muscle do?
Circular - contracts
Longitudinal - relaxes
In the receiving segment of perstalsis, what does the circular and longitudinal muscle do?
Circular - relaxes
Longitudinal - contracts
What is the term for rhythmic contractions of the circular muscle layer that mix and divide luminal contents?
What is segmentation called in the large intestine?
What are tonic contractions?
Sustained contractions found in the sphincters of teh GI tract
What two sphincters have skeletal muscle?
Upper oesophageal sphincter
External anal sphincter
What action closes the upper oesophageal sphincter?
What does closure of the lower oesophageal sphincter prevent?
Reflux of gastric contents to the oesophagus
What does the pyloric sphincter prevent?
Duodenal gastric reflux
What opens and what closes the ileocecal sphincter?
Distension of ileum opens, distension of proximal colon closes
What reflexes mediate chewing?
Masseteric and diagastric reflexes
What structure seperates the mouth from nasal passages, sllowing breathing and chewing simultaneously?
What structure helps seal off nasal passages during swallowing?
Where is the major location of taste buds?
On the tongue
What structure has tonsils on side walls which are lymphoid tissues?
Where does the tongue force a bolus?
Into pharynx at back of mouth
What does pressure of bolus at rear of mouth stimulate?
Pharyngeal pressure receptors
What do the pharyngeal pressure receptors do?
Afferent impulses to swallowing centre in medulla
What does the swallowing centre in the brain inhibit?
The respiratory centre
What triggers primary peristaltic wave and closure of the upper oesophageal sphincter?
Swallowing centre in medulla