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26 Cards in this Set
- Front
- Back
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Is GI muscle a single or multi-unit smooth muscle?
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Single unit - visceral muscle has gap junctions that couples the cells and act as a single unit
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Are actin and myosin arrangements highly structured in smooth muscle?
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No
not highly organised in rows like skeletal muscle |
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Which cells act as pacemakers in the GI tract?
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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 range of lengths?
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plasticity
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What effect does vagal stimulation have on gut mobility?
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increases through ACh
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What effect does CCK have on gut mobility?
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decreases
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What effect does GIP have on gut mobility?
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decreases
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What effect does secretin have on gut mobility?
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decreases
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Which has the highest rate of spontaeneous activity - stomach, duodenum, jejunum or ileum?
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= duodenum
13 contractions /min |
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Which is involved in peristalsis longitudinal or circular smooth muscle?
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Both
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What are the functions of the motility of the GI tract?
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mixing and propulsion
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What factors is mobility dependent on interaction between?
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Smooth muscle
Enteric nervous system Autonomic n.s. Hormones |
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Describe GI Smooth muscle activity?
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1. Visceral smooth muscle show rhythmic cycles of activity initiated by pacemaker cells = interstitial Cell of Cajal
2. Peristalsis = waves of movement to move a bolus 3. Segmentation = Churn and fragment a bolus 4. Spinchter tone and relaxation |
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Describe the factors influencing GI motility?
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1. Smooth muscle functional syncytium (network of muscle cells connected by intercalated discs)
electrical activity of muscle cells spike potentials result in contraction 2. Neural control - Autonomic + Enteric -Parasympathetic (vagus) Excitatory = ACh Inhibitory = VIP, ADP -Sympathetic Inhibitory = NA 3. Hormonal endocrine - gastrin, CCK, motilin local - paracrine, neurocrine |
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Describe the muscle layer of the stomach?
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Inside to Outside:
Oblique Circular Longitudinal |
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What is the importance of muscle layers of the stomach?
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layers give rise to contraction in segments
allowing food to be moved back and forth |
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Describe the response of the stomach to filling?
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1. Stomach pressure remains constant until ~1l of food
2. Relative unchanging pressure results from intrinsic ability of muscle to exhibit PLASTICITY 3. Peristaltic waves move towards pylorus at rate of 3 per minute 4. Basal electric rhythm is initiated by pacemaker cells, the interstitial cells of Cajal |
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Where in the stomach does the most vigorous peristalsis and mixing occur?
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Near the pylorus
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Describe the movement of chyme int the stomach?
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Either:
1. delivered in small amounts (about 3ml) to duodenum or 2. forced back into stomach for further mixing |
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Describe the regulation of gastric mixing?
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Regulated by:
-neural enterogastric reflex -hormonal (enterogastrone) mechnisms These mechanisms involve gastric secretion and duodenal filling |
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Describe the movement of chyme through the GI tract depending on content?
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Carbohydrate-rich chyme moves through duodenum quickly while
Fat-rich chyme is digested much more slowly causing food to remain in stomach longer |
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Describe the hormonal regulation of gastric activity?
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1. Secretin - Stimulate HCO3- secretion and inhibit stomach activity
2. CCK stimulates gall bladder contraction and emptying inhibit stomach activity 3. GIP - gastric inhibitory peptide inhibits gastric contractions 4. Motilin - increases gastric motility increases intestinal mobility |
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Describe neuronal regulation of gastric mobility?
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Short reflexes operating in the enteric nervous system inhibit gastric secretion/contraction
Long reflexes operating via CNS alter autonomic nerve activity |
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Describe the enteric nervous system?
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Two interconnected plexuses:
myenteric submucosal Seperate division of the ANS -contains complete reflex pathways -sensory, motor and interneurons Can regulate GI function indepently of CNS |
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Describe the ENS plexuses?
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Myenteric
-regulate smooth muscle contraction excitatory nuerotransmitter = ACh inhibitory neurotransmitter = ADH , VIP Submucosal -regulation of endocrine and exocrine cell secretion excitatory neurotransmitters = ACh and VIP Both plexuses regulate: absorption, blood flow, GI cell growth |
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How many neurons does the ENS contain?
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10-100 million
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