GI Lecture 4 - Gastric Motility

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  • Created by: LBCW0502
  • Created on: 06-10-19 14:41
Is the GI muscle a single or multi-unit smooth muscle?
Single unit - visceral muscle has gap junctions that couples the cells and acts as a single unit
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Which mechanism operates in smooth muscle to reduce use of ATP?
Latch bridge mechanism
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Are actin and myosin arrangements highly structured in smooth muscle?
No, not arranged in highly organised rows like skeletal muscle
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Which cells act as pacemakers in the GI tract?
Interstitial cells of Cajal
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What is the term used to describe smooth muscle when it is able to function over a wide range of lengths?
Plasticity
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What effects do the following have on gastric motility - vagal stimulation, CCK, GIP, secretin?
Vagal stimulation (increase). CCK (decrease). GIP (decrease). Secretin (decrease)
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What has the fastest rate of spontaneous activity - stomach, duodenum, ileum or colon?
Duodenum - about 13 contractions per minute
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Which is involved in peristalsis - circular or longitudinal smooth muscle?
Both
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Outline the autonomic NS - parasympathetic
Vagal nuclei and sacral spinal cord. Vagus and pelvic nerves to enteric NS (myenteric plexus, submucosal plexus) - smooth muscle, secretory cells, endocrine cells, blood vessels
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Outline the autonomic NS - sympathetic
CNS, sympathetic ganglia (near spinal cord). Pre-ganglionic fibres, post-ganglionic fibres to enteric NS (myenteric plexus, submucosal plexus) - smooth muscle, secretory cells, endocrine cells, blood vessels
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What is gastrointestinal motility?
The functional expression of smooth muscle contraction
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What are the functions of motility?
Mixing and propulsion
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Motility is dependent on interaction between what?
Smooth muscle, enteric NS, autonomic NS, hormones
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Describe features of GI smooth muscle contractile activity
Visceral smooth muscle shows rhythmic cycles of activity (pace maker cells, interstitial cells of Cajal). Peristalsis (waves that move a bolus). Segmentation (churn and fragment a bolus). Sphincter tone and relaxation
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Which factors influence GI motility? (1)
Smooth muscle functional syncytium, electrical activity of muscle cells, slow waves (pacemaker potentials, basal electrical rhythm), spike potentials result in contraction
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Which factors influence GI motility? (2)
Neural control (autonomic and enteric NS, parasympathetic, vagus nerve, excitatory fibres ACh, inhibitory fibres VIP/ADP, sympathetic, inhibitory effects of noradrenaline)
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Which factors influence GI motility? (3)
Hormonal control (endocrine, gastrin, CCK and motilin, local, paracrine, neurocrine)
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What are the stomach muscle layers?
Serosa, tela subserosa, muscularis, oblique fibres of muscle wall, circular muscle layer, longitudinal muscle layer, submucosa, lamina muscularis mucosae, mucosa, lamina propria, epithelium, gastric glands, gastric pits
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What is the response of the stomach to filling? (1)
Stomach pressure remains constant until ~ 1L of food ingested. Relative unchanging pressure results form intrinsic ability of smooth muscle to exhibit 'plasticity'. Peristaltic waves move towards pylorus at rate of 3 per minute
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What is the response of the stomach to filling? (2)
Basic electrical rhythm is initiated by pacemaker cells, the interstitial cells of Cajal
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Describe features of gastric contractile activity
Most vigorous peristalsis and mixing occurs near pylorus. Chyme is either - delivered in small amounts (about 3 mL) to the duodenum or forced backward into the stomach for further mixing. Pyloric valve closed, filling, pyloric valve slightly opened
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Describe the regulation of gastric emptying (1)
Regulated by neural enterogastric reflex and hormonal (enterogastrone) mechanisms. Inhibits gastric secretion and duodenal filling. Carbohydrates-rich chyme quickly moves through duodenum
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Describe the regulation of gastric emptying (2)
Fat laden chyme is digested more slowly causing food to remain in the stomach longer
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Describe the regulation of gastric activity - hormonal control (1)
Hormonal control. Secretin (stimulate bicarbonate secretion, inhibit stomach activity). Cholecystokinin (stimulates gallbladder contraction and emptying, inhibit stomach activity). Gastric inhibitory peptide (inhibits gastric acid secretions)
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Describe the regulation of gastric activity - hormonal control (2)
Motilin (increases gastric motility, increases intestinal motility)
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Describe the regulation of gastric activity - hormonal control (3)
Presence of fatty, hypertonic, acidic chyme in duodenum. Duodenal entero-endocrine cells. Secrete secretin, CCK, GIP. Inhibit contractile force and rate of stomach emptying decline. Duodenal stimuli decline (inhibition
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Describe the regulation of gastric activity - neuronal control (1)
Short reflexes operating in the enteric NS, inhibit gastric secretion/contraction. Long reflexes operating via the CNS alter autonomic nerve activity
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Describe the regulation of gastric activity - neuronal control (2)
Presence of fatty, hypertonic, acidic chyme in duodenum. Chemoreceptors and stretch receptors. Target via short reflexes (enteric neurones). Target via long reflexes (CNS centres, increase SNS activity, decrease parasympathetic activity)
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Describe the regulation of gastric activity - neuronal control (3)
Inhibit contractile force and rate of stomach emptying decline. Duodenal stimuli decline (inhibition)
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Describe features of the enteric NS
Two interconnected plexuses (myenteric and submucosal). Separate division of ANS (contains complete reflex pathways, sensory, motor, interneurones). Can regulate GI function independently of CNS
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Describe features of the ENS plexuses
Myenteric (regulation of smooth muscle contraction, excitatory/ACh, inhibitory/VIP). Submucosal (regulation of endocrine/exocrine cell secretion, excitatory/ACh, VIP). Both plexuses regulate absorption, blood flow, GI, cell growth
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The ENS contains how many neurones?
10-100 million neurones - sensory, motor, interneurons
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What are the ENS neurotransmitters?
Peptides (SP, CCK, VIP, gastrin, somatostatin). Amino acids (GABA). Biogenic amines (noradrenaline, dopamine, histamine, serotonin, ACh)
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State features of the reflex control of gut activity
CNS. Splanchnic and vagal afferents. Parasympathetic/sympathetic efferents. Local efferents. Myenteric plexus, submucosal plexus. Chemoreceptors, mechanoreceptors in gut wall. Gut wall muscle, endocrine cells, secretory cells, blood vessel
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Card 2

Front

Which mechanism operates in smooth muscle to reduce use of ATP?

Back

Latch bridge mechanism

Card 3

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Are actin and myosin arrangements highly structured in smooth muscle?

Back

Preview of the front of card 3

Card 4

Front

Which cells act as pacemakers in the GI tract?

Back

Preview of the front of card 4

Card 5

Front

What is the term used to describe smooth muscle when it is able to function over a wide range of lengths?

Back

Preview of the front of card 5
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