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GI motility Flashcards

(60 cards)

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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
What is the function of the pelvic splanchnic nerves
- regulate emptying urinary bladder - Opening and closing of internal urethral sphincter - Influence motility in rectum - Sexual functions
26
Describe the enteric nervous system
- 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
What stimuli do the sensory cells of the ENS respond to?
- pH - Stretch - Irriation - Changes in nutrition concentration
28
What is the function of the submucosal plexus?
- Local secretion - Absorption - Muscle movements
29
Where is the submucosal plexus located?
- In lamina submucosa | - Best developed in small intestine
30
What is the function of the myenteric plexus?
- Motor innervation to circular and longitudinal muscle layers - Secretomotor innervation of mucosa - Projections to gall bladder, pancreas, sympathetic ganglia
31
Where is the myenteric plexus located?
Between the longitudinal and circular muscle
32
Describe the short reflex arc
- 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
Describe teh long reflex arcs between the ENS and ANS
- 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
What is the action os the SNS in the gut?
- 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
What is meant by "electrical coupling" of the smooth muscle cells in the GIT?
- 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
What is the importance of electrical coupling in the GIT smooth muscle?
- 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
Breifly outline the key features of smooth muscle
- 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
Where is smooth muscle located in the GI tract?
- Distal oesophagus (some species) - Stomach - Small intestine - Large intestine
39
What are slow waves in GIT smooth muscle?
- 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
Explain how slow waves prime the smooth muscle for contractions
- Does not cause contractions, just prepares - Higher amplitude of slow wave, higher frequency of spike potentials - Means more contractions are possible
41
Describe the interstitial cells of Cajal
- 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
Explain how chyme influences the cells of Cajal
- 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
Describe segmentation peristalsis in the small intestine
- 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
Describe propulsive peristalsis
- 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
What are the stages of swallowing?
- Oral phase - Pharyngeal phase - Oesophageal phase
46
What occurs in the oral phase of swallowing?
Bolus formed, transported to pharynx
47
What occurs in the pharyngeal phase of swallowing?
- Receives bolus - Pushes to oesophagus - Mechanoreceptors present here
48
What occurs in the oesophageal phase of swallowing?
- Bolus in oesophagus | - Peristalsis starts
49
Describe the motility in the upper stomach
- 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
Describe the motility in the lower stomach
- 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
Briefly outline the control of gastric motility
- 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
List the factors affecting monogastric stomach emptying
- 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
Explain how pacemaker cells and rate of contraction affect monogastric stomach emptying
- 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
Explain how conditions within the stomach affect stomach emptying
- 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
Explain the hormonal control of stomach emptying
- 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
Explain hwo the duodenum affects stomach emptying
- 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
Explain the neural control of stomach emptying
- Long reflexes - inhibit stomach emptying by inhibiting activity in SNS fibres, inhibiting vagal nerves - Short reflexes inhibit cells of Cajal
58
What is the enterogastric reflex?
A reflex stimulated by the duodenum and stomach, that inhibits gastric motility and secretion of gastric acid
59
What are the major factors that inhibit stomach emptying?
- Low pH in duodenum - High fat content in duodenum - High pressure in duodenum - High osmolarity in duodenum - High concentration of peptides in duodenum
60
What are the hormones that inhibit gastric emptying and where are they released?
- Released from proximla part of SI - Secretin - CCK - Gastric inhibitory peptide

GI (31 decks)

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