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GI motility Flashcards

1
Q

Where is smooth muscle found in the GI tract?

A

Everywhere except oesophagus

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2
Q

List the factors that regulate appetite in the common domesticated species

A
  • Nervous system
  • Pregastric factors
  • Gastrointestinal and post-absorptive factos
  • Hormonal
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3
Q

Explain how the nervous system regulates appetite in the common domesticated species

A
  • Arcuate nucleus in hypothalamus, many NTs and hormones
  • Lateral hypothalamus = hunger centre
  • Ventromedial hypothalamus = satiety centre
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4
Q

What happens if there is a lesion in the lateral hypothalamus?

A
  • Is the hunger centre

- Animal will become anorexic and lose weight

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5
Q

What happens if there is a lesion in the ventromedial hypothalamus?

A
  • Satiety centre

- Will overeat (and likely become obese)

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6
Q

List some of the pregastric factors that regulate appetite in the domestic animal

A
  • Appearance of food
  • Taste and/or odour of food
  • learned preferences and aversions
  • Psychological factors (fear, depression and social interactions)
  • Ambient temperature
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7
Q

What happens to food intake depending on temperature?

A
  • Cold = increase food intake

- Hot = decrease food intake

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8
Q

Give the gastrointestinal and post-absorptive factors that regulate appetite in the domestic species

A
  • Gastrointestinal fill
  • Stretch receptors send signals via vagus nerve to hypothalamus
  • Full stomach and SI induce satiety
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9
Q

List some of the hormonal factors that regulate appetite in the domestic animal

A
  • Grehlin- stimulator of appetite
  • Nutrients concentration can change concentration of hormone, linked to satiety and hunger
  • Glucose increases hormone levels in satiety centre
  • VFAs inhibit food intake
  • Amino acids stimulate the satiety centre
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10
Q

What is the effect of the sympathetic nervous system on gut motility and glandular secretion?

A
  • Decreases both
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11
Q

What is the effect of the parasympathetic nervous system on gut motility and secretion and how does it carry out its effec?

A
  • reach enteric NS directly
  • Increase motility and secretion
  • PH from vagus stimulates GI
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12
Q

What is the effect of neuropeptide Y (NPY) and orexin on appetite?

A

Stimulate appetite

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13
Q

What is the effect of melanocyte stimulating hormone (MSH) on appetite?

A

Reduces appetite

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14
Q

Explain how the concentration of nutrients affects appetite

A
  • Nutrients such as glucose and amino acids absorbed
  • Concentrations in blood rises
  • Concentration of several hormones rises (CCK, insulin, glucagon)
  • Linked to satiety
  • Glucose increases activity in satiety centre
  • VFAs inhibit food intake in ruminants
  • Amino acids inhibit appetite centre
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15
Q

Describe the parasympathetic control of the internal anal sphincter

A
  • PSNS nerves from S2-4 level of spinal cord
  • Stimualtion causes sphincter to relax
  • ALlows faeces to pass through when rectum and anal canal contract
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16
Q

Describe the sympathetic control of the internal anal sphincter

A
  • Nerves from T11-L2

- Cause sphincter to contract

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17
Q

Describe the control of the external anal sphincter

A
  • Spinal nerves from S2-4

- Skeletal muscle control (voluntary control)

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18
Q

Describe the control fo teh rectum and anal canal

A
  • Smooth muscles controlled by PS nerves from S2-4
  • Pelvic splanchnic nerve stimulates rectum and anal canal to contract
  • Sympathetic nerves from T11-L2 form hypogastric nerve and stimulate rectum and anal canal to relax
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19
Q

What is the major parasympathetic nerve supply to the abdominal viscera?

A
  • Vagus nerve

- travels down neck in vagosympathetic trunk

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20
Q

Describe the thoracic splanchnic nerves

A
  • Arise from sympathetic trunk in thorax
  • Provide sympathetic innervation to abdomen
  • Contains preganglionic sympathetic and GVA fibres
  • Can be divided into greater, lesser and least splanchnic
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21
Q

Describe the greater splanchnic nerve

A
  • From T5-T9
  • Though diaphragm enters abdominal cavity
  • Synapses at coeliac ganglia - coelicaomesenteric plexus
  • Modulates foregut
  • Sympathetic innervation to adrenal medulla
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22
Q

Describe the lesser spanchnic nerve

A
  • T9-10
  • Travels lateral to greater splanchnic nerve
  • Modulates midgut
  • Synapses at superior mesenteric ganglia
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23
Q

Describe the least splanchnic nerve

A
  • T11-12

- Abdomen to renal ganglia

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24
Q

Describe the pelvic splanchnic nerves

A
  • Paired visceral nerves
  • Carry fibres of ANS as well as sensroy from organs
  • Arise from anerior rami of sacral spinal nerves
  • Enter sacral plexus
  • Travel to side’s inferior hypogastric plexus, bilaterally on walls of rectum
  • From there innervate pelvic and genital organs
  • AKA pelvic nerve
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25
Q

What is the function of the pelvic splanchnic nerves

A
  • regulate emptying urinary bladder
  • Opening and closing of internal urethral sphincter
  • Influence motility in rectum
  • Sexual functions
26
Q

Describe the enteric nervous system

A
  • Can operate independently of brain and spinal cord
  • Within wall of digestive tract
  • Submucosal and myenteric
  • Sensroy cells react to different stimuli
  • Motor cells connect to either smooth muscle cells or epithelial cells
  • Short reflex arc occurs within ENS (most stimulatory, some inhibitory)
  • Input from SNS and PSNS
  • Respond and control loca conditions
27
Q

What stimuli do the sensory cells of the ENS respond to?

A
  • pH
  • Stretch
  • Irriation
  • Changes in nutrition concentration
28
Q

What is the function of the submucosal plexus?

A
  • Local secretion
  • Absorption
  • Muscle movements
29
Q

Where is the submucosal plexus located?

A
  • In lamina submucosa

- Best developed in small intestine

30
Q

What is the function of the myenteric plexus?

A
  • Motor innervation to circular and longitudinal muscle layers
  • Secretomotor innervation of mucosa
  • Projections to gall bladder, pancreas, sympathetic ganglia
31
Q

Where is the myenteric plexus located?

A

Between the longitudinal and circular muscle

32
Q

Describe the short reflex arc

A
  • 2 nerve plexuses on wall of GI tract
  • Plexuses synapse with each other - attaching with either/both smooh muscles or glandular cells
  • Excitatory fibres cholinergic (oral direction), inhibitory fibres nitric oxide (aboral direction)
  • Short reflex arcs let GI tract self-control activities
  • Involved in promotion of peristaltic contractions
33
Q

Describe teh long reflex arcs between the ENS and ANS

A
  • ENS independent from rest of NS
  • Connections modulate secretion adn motility within GI tract
  • Influence glands/smooth muscles (PSNS) whereas SNS inhibits PSNS and controls local blood flow
  • Interneurons between ENS and ANS relay info between sensory neurons and PSNS
  • Attaches to post-ganglionic PSNS pathways
  • Can be excitatory or inhibitory dependent on cell type
34
Q

What is the action os the SNS in the gut?

A
  • Acts on PSNS pathway (gland and smooth muscle cell) to inhibit secretion/contracion
  • Also directly to cause vasoconstriction in local blood supply
  • Blood directed to vital organs for fight and flight response
35
Q

What is meant by “electrical coupling” of the smooth muscle cells in the GIT?

A
  • Gap junctions between smooth muscle cells = electrical coupling
  • Regulated connection between cells, allows movement of molecules, ions and electrical impulses because cytoplasms are connected
36
Q

What is the importance of electrical coupling in the GIT smooth muscle?

A
  • Allows synchronised contraction as is seen in peristalsis
  • Distension of hollow organs - contract simultaneously and allow diameter of hollow organ to change more or less in one motion
37
Q

Breifly outline the key features of smooth muscle

A
  • Involuntary
  • Single nucleus
  • Spindle shaped
  • Arranged in sheets
  • Cells contain actin and myosin filaments
  • Not striated - myofilaments not arracnged in sarcomeres
  • Lack T-tubules
  • Poorly developed sarcoplasmic reticulum (compared to skeletal muscle)
38
Q

Where is smooth muscle located in the GI tract?

A
  • Distal oesophagus (some species)
  • Stomach
  • Small intestine
  • Large intestine
39
Q

What are slow waves in GIT smooth muscle?

A
  • Waves generated and propagated by nterstitial cells of Cajal
  • Spread through gap junctions between smooth muscle cells similar to myocardial auto-rhythmic cells
  • Control motility
  • Can’t cause a smooth muscle contraction
  • Prepare smooth muscle for when chyme arrives
40
Q

Explain how slow waves prime the smooth muscle for contractions

A
  • Does not cause contractions, just prepares
  • Higher amplitude of slow wave, higher frequency of spike potentials
  • Means more contractions are possible
41
Q

Describe the interstitial cells of Cajal

A
  • Modified smooth muscle cells
  • Central to GI motility regulation
  • Function as pacemaker for gut contraction
  • Different frequencies in different parts of GI tract
  • Modulated by nervous andhormonal input
  • Amplify neuronal input
42
Q

Explain how chyme influences the cells of Cajal

A
  • Activates the cells of Cajal
  • Frequency independent of neuronal and hormonal inputs
  • Frequency and strength of contraction stimulated by PSNS and SNS
  • Increased vagal fibre activity increases contraction strength
  • Chyme enters intestine - short reflex activates cells of Cajal
  • More chyme = stronger contractions
43
Q

Describe segmentation peristalsis in the small intestine

A
  • Only occurs here
  • Mixing of chyme with digestive juices
  • Brings particles of food into contact with wall where nutrients can be absorbed
  • Localised, rhythmic contraction of circular smooth muscles that constrict intestine into segments
  • Can move chyme in both directions = greater mixing
44
Q

Describe propulsive peristalsis

A
  • Series of wave like muscle contractions, move food along tract
  • Begins in oesophagus when food bolus swallowed
  • Alternatig contractions between longitudinal and circular
  • One way movement (aboral)
  • Stretch receptors open as bolus down oesophagus, longitudinal contract, circular relax (opens space)
  • Behind bolus C contract, L relax
  • Chyme shunted forwards
45
Q

What are the stages of swallowing?

A
  • Oral phase
  • Pharyngeal phase
  • Oesophageal phase
46
Q

What occurs in the oral phase of swallowing?

A

Bolus formed, transported to pharynx

47
Q

What occurs in the pharyngeal phase of swallowing?

A
  • Receives bolus
  • Pushes to oesophagus
  • Mechanoreceptors present here
48
Q

What occurs in the oesophageal phase of swallowing?

A
  • Bolus in oesophagus

- Peristalsis starts

49
Q

Describe the motility in the upper stomach

A
  • Low frequency sustained contractions
  • Generates basal pressure within stomach
  • Pressure gradient from stomach to SI and thus responsible for gastric emptying
  • Swallowing of food and consequent gastric distension inhibits contraction of this region of stoamch
  • Allows ballowing out and formation of reservoir without significant increase in pressure
50
Q

Describe the motility in the lower stomach

A
  • Strong peristaltic waves of contraction
  • Increase in amplitude nearer to pylorus
  • Effective gastric grinding
  • Distension stimulates this type of contraction
  • Accelerate liquefaction and hence gastric emptying
  • In pylorus, contractions obliterate lumen
  • So chyme delivered in spurts to SI
51
Q

Briefly outline the control of gastric motility

A
  • Complex set of neural and hormonal signals
  • Nervous control: ENS (and PSNS and SNS)
  • Hormonal - lots, gastrin CCK
  • Patterns of gastric motility arise from smooth muscle cells integrating large number of inhibitory and stimulatory signals
52
Q

List the factors affecting monogastric stomach emptying

A
  • Pacemaker cells and rate of contraction
  • The stomach
  • Hormonal
  • The duodenum
  • Solids empty in linear fashion
  • Neural
  • Emptying of liquids
  • Presence of fat in small intestine
53
Q

Explain how pacemaker cells and rate of contraction affect monogastric stomach emptying

A
  • Cells of Cajal in cranial portion of stomach
  • Spontaneous oscillations in membrane potential of Cajal cells transferred to smooth muscle cells surrounding them via gap junctions = synchronicity of muscle cells
  • Cells influenced by neural and hormonal factors
  • No action potential in Cajal = no contraction of gastric muscle
54
Q

Explain how conditions within the stomach affect stomach emptying

A
  • Stimulatory signals in the stomach (inhibitory in the duodenum)
  • Expansion of stoamch after meal - activation of mechanoreceptors initiates reflexes
  • Short reflexes in stomach wall and long reflexes in vagal nerves lead to ACh release
  • Larger meal, greater expansion of stomach stronger contractionof stomach = more rapid emptying of first part of stomach
55
Q

Explain the hormonal control of stomach emptying

A
  • Gastrin
  • Secreted by epithelial cells when food present (peptides in stomach) and in dilation of stomach
  • Increase contraction of smooth muscle cells
  • Dilate pyloric sphincter
  • High gastrin stimulates emptying
56
Q

Explain hwo the duodenum affects stomach emptying

A
  • Has greatest effect on emptying
  • Can act to inhibit contractions from stomach and increases tension on the pyloric sphincter
  • Increased pressure in duodenal lumen, low pH (high acid content reduces stomach emtyping), high fat concentration, high peptide concentration, high osmolarity
  • If fat present in proximal duodenum, stomach will not empty further
57
Q

Explain the neural control of stomach emptying

A
  • Long reflexes - inhibit stomach emptying by inhibiting activity in SNS fibres, inhibiting vagal nerves
  • Short reflexes inhibit cells of Cajal
58
Q

What is the enterogastric reflex?

A

A reflex stimulated by the duodenum and stomach, that inhibits gastric motility and secretion of gastric acid

59
Q

What are the major factors that inhibit stomach emptying?

A
  • Low pH in duodenum
  • High fat content in duodenum
  • High pressure in duodenum
  • High osmolarity in duodenum
  • High concentration of peptides in duodenum
60
Q

What are the hormones that inhibit gastric emptying and where are they released?

A
  • Released from proximla part of SI
  • Secretin
  • CCK
  • Gastric inhibitory peptide

GI (31 decks)

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