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Anatomy - abdominal aorta > Motility of GI tract > Flashcards

Motility of GI tract Flashcards

1
Q

What are 4 physiological processes of the GI system

A

Motility, secretion, digestions and absorption

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2
Q

What are sphincters made of?

A

Smooth muscle that acts as a valve of a reservoir for holding luminal content adequately

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3
Q

What does dysregulation of the activity of sphincters result in?

A

GI motility disorders

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4
Q

What are the major layers of the gut wall?

from lumen of GI tract to the abdominal cavity

A

Mucosa, submucosa, muscularis externa and serosa

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5
Q

What are the parts of the mucosa? (from lumen to the abdominal cavity)

A

Epithelium, lamina propria and muscularis mucosae

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6
Q

What are the parts of the submucosa? (from lumen to the abdominal cavity)

A

Submucosal nerve plexus

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7
Q

What are the parts of the muscularis externa? (from lumen to the abdominal cavity)

A

Circular muscle and myenteric nerve plexus

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8
Q

What are the parts of the serosa? (from the lumen to the abdominal cavity)

A

Longitudinal muscle and ducts from external endocrine glands(Liver pancreas, salivary glands)

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9
Q

What does the epithelial layer consist of?

A
  • Exocrine gland cells

- Endocrine cells

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10
Q

What do the exocrine cells in the epithelial layer of the gut wall produce?

A
  • Mucous and digestive enzymes
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11
Q

What do the endocrine cells in the epithelial layer of the gut wall produce?

A
  • GI hormones into the blood

- Constitute gut endocrine system

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12
Q

What is cholecystokinin released in response to?

A

Fat and protein in the gut lumen

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13
Q

What does the lamina propria consist of?

A
  • Small blood vessels
  • Nerve fibers
    Lymphatic cells/tissue(GALT - gut associated lymphatic tissue)
  • Loose connective tissue
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14
Q

What are the functions of GALT?

A

1) Secretes antibodies to specific food or bacterial antigens
2) Triggers immunological reactions against them leading to mucosal inflammation and damage
3) Provides permission of immunological tolerance to potentially immunologic dietary substances and gut flora

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15
Q

What is an example of an GALT reaction?

A

Activation of this local GI immune system involved in celiac disease and inflammatory bowel diseases such as ulcerative colitis and crohn’s disease

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16
Q

What does the muscularis mucosa consist of?

A

Thin layers of smooth muscle responsible for controlling mucosal blood and GI secretion(contraction throws mucosa into folds/ridges)

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17
Q

What does the submucosa consist of?

A
  • Loose CT, large blood vessels, lymphatic vessels
  • glands in some GI regions
  • Submucosa nerve plexus - meissners plexus
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18
Q

What does the meissners plexus/submucosal nerve plexus regulate?

A

Coordinates intestinal absorption and secretion through its innervation of the glandular epithelium, intestinal endocrine cells, and submucosal blood vessels

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19
Q

What does the muscularis externa consist of?

A
  • Thick muscle whose contraction contributes to major gut motility(segmentation and peristalsis)
  • Two substantial layers of smooth muscle cells
  • Myenteric nerve plexus - Auerbach’s(lies between muscle layers)
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20
Q

What are the two substantial layers of smooth muscle cells?

A

Inner circular and outer longitudinal layer(circular layer 3-5x as thick as outer longitudinal)

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21
Q

What does the serosa contain?

A
  • Connective tissue.
  • Several major structures enter through the serosa, including blood vessels, extrinsic nerves, and the ducts of the large accessory exocrine glands
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22
Q

What nervous pathway is the enteric nervous system a part of?

A

Intrinsic pathway

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23
Q

What are the parts of the enteric nervous system?

A

The ENS is functionally organised as the submucosal plexus and myenteric plexus

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24
Q

What is the function of the myenteric(auerbach’s) plexus?

A

Is mainly involved with control of gut motility and innervates the longitudinal and circular smooth muscle layers

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25
Q

What nervous pathway is the gut-brain axis a part of?

A

Extrinsic pathway

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26
Q

How is the ENS linked to the central nervous system?

A

The ENS is linked to the central nervous system via the sensory and motor nerves of the parasympathetic nervous system( PNS “rest and digest”) and the sympathetic system(fight or flight)

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27
Q

Describe the parasympathetic innervation for the GI

A

Preganglionic vagus nerve innervates oesophagus, stomach, small intestine, liver, pancreas, caecum, appendix, ascending colon, transverse colon

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28
Q

What does the parasympathetic activity stimulate?

A

Parasympathetic activity stimulates motility and secretions

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29
Q

What level do the sympathetic pre-ganglionic fibres for the GIT arise from?

A

T8-L2

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30
Q

Where are the postganglionic cell bodies for the sympathetic GI innervation located?

A

Celiac, inferior and superior mesenteric ganglia

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31
Q

What is the effect of sympathetic activity on the GI?

A

Sympathetic activity inhibits gut motility and secretion and causes constriction of sphincters

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32
Q

Describe the myenteric or auerbach’s plexus

A
  • A thin layer array of ganglia, ganglion cells, and inter-ganglionic nerve tracts that serve to interconnect the plexus between the circular and longitudinal muscle layers
  • Many of these neurons have projections into adjacent muscle layers, where they are either excitatory or inhibitory, but some are interneurons involved in integrative functions for control of gut motility
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33
Q

What does the myenteric/auerbach’s plexus innervate?

A

Innervates longitudinal muscles and the outer lamella of the circular muscle layer

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34
Q

Describe the submucosal/meissner’s plexus?

A
  • Between the submucosal layers and circular muscle
  • Neurons that are functionally distinct from those of the myenteric plexus and, relative to intestinal motor function
  • Appear to be projecting mainly to the inner lamella of the circular muscle layer
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35
Q

What is hirschprung’s disease?

A

A congenital absence of the myenteric plexus, usually involving a portion of the distal colon

The pathologic aganglionic section of large bowel lacks peristalsis and undergoes continuous spasm, leading to a functional obstruction and severe constipation

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36
Q

What do the smooth muscles act as in motility?

A

Functional syncytium

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37
Q

What do the slow waves in the pacemaker display represent?

A

Slow waves - Spontaneous oscillations in the membrane potential(The distal stomach is the first location in the smooth muscle to exhibit

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38
Q

What is frequency of slow waves referred to?

A

Basic electrical rhythm (BER) or slow wave rhythm

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39
Q

What is the first location in the smooth muscle to exhibit slow waves

A

Distal stomach

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40
Q

During which period do slow waves occur?

A

Resting phase

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41
Q

What are spike potentials

A

Spike potentials are triggered if the peak of a slow wave depolarises the membrane to a threshold potential

42
Q

How are spike potentials triggered?

A

Ca2+ channels open

Ca2+ entry into smooth muscle cells occurs during spike potentials and triggers muscle contraction

43
Q

What is the purpose of BER?

A

Major function of BER is to determine when contractions can occur in a certain area of a bowel

44
Q

How is the force of contraction in smooth muscles determined?

A

Force of contraction is determined by the number of spikes fired within each wave, which in turn depend on neural and hormonal input

45
Q

What are the 2 major types of contractile responses

A

Segmentation and peristalsis

46
Q

What is the origin of the basic electrical rhythm?

A

Caused by a network of fibroblast-like cells called the interstitial cells of cajal, which are positioned between the longitudinal and the circular muscle layers

47
Q

How do excitatory transmitters work?

A

Cause non-selective cation channels in the smooth muscle cells to open; the resting membrane potential is depolarized and more slow waves cross the threshold for the generation of a spike potential

48
Q

How do inhibitory transmitters work?

A

Often act by opening the K+ channels in smooth muscle cells, hyperpolarizing the membrane potential and preventing the slow waves from reaching threshold

49
Q

How does amitriptyline work?

A

Amitriptyline is an anticholinergic drug and a tricyclic antidepressant that inhibits the effects of acetylcholine systemically to reduce the generation of spike potentials

50
Q

What are the side effects of anticholinergic drugs?

A
  • Xerostomia(dry mouth)
  • Constipation
  • Ileus
  • Nausea and vomiting
51
Q

What are the three types of gastrointestinal movements?

A
  • Segmentation
  • Tonic contraction
  • Peristalsis
52
Q

Where does segmentation mainly occur?

A

Small intestine

53
Q

Purpose of segmentation

A

For mixing food with enzymes. Closely spaced contractions of circular smooth muscle followed by relaxation. No net forward movement.

54
Q

Describe how peristaltic contractions occur?

A

Longitudinal smooth muscle contracts first, followed half way through its contraction by the circular muscle.

Longitudinal relaxes during latter half of circular contraction which leads to a progressive wave.

Distension of gut by food is trigger for peristalsis so the net effect is food propulsion along GI tract

55
Q

What is the migrating motor complex? (MCC)

A

Intervals of strong propulsive contractions, which pass down the distal stomach and small intestine

The propulsions sweep the stomach and small intestine of indigestible materials and is an intrinsic property of the GI tract that does not require external innervation

56
Q

How often does the migrating motor complex occur?

A

Every 90 mins

57
Q

What can cause a loss of migrating motor complexes

A

Radiotherapy

58
Q

What might occur as a result of the loss of migrating motor complexes?

A

Bacterial overgrowth in the small intestine

59
Q

What is paralytic ileus

A

Temporary cessation of gut motility

60
Q

Most common cause of paralytic ileus

A

Abdominal surgery

61
Q

What are other common causes of paralytic ileus?

A

Infection or inflammation in the abdominal cavity, electrolyte abnormalities and drug ingestion

62
Q

Signs and symptoms of paralytic ileus

A
  • Nausea
  • Vomiting
  • Abdominal distension
  • Absent bowel sounds
63
Q

What is under voluntary control in deglutition?

A
  • Bolus of food is formed in the mouth by mastication

- Propelled to oropharynx as the tongue moves up and back against the hard palate

64
Q

What does the bolus formed during swallowing stimulate?

A
  • Bolus stimulates mechanoreceptors in pharynx - glossopharyngeal (IX) afferent impulses to swallowing centre
  • Efferent impulses from vagus(x) to pharynx, oesophagus and palate for co-ordinated muscle contraction
65
Q

What does the vagus(x) cause during deglutition?

A
  • Soft palate elevates and superior constrictor of pharynx contracts to close off nasopharynx
  • Respiration inhibited
  • Larynx rises so that epiglottis covers trachea
  • Upper oesophageal sphincter relaxes and bolus enters
  • Peristaltic wave initiated in pharynx continues length of oesophagus
  • This wave 7-10s
66
Q

What happens if peristaltic wave in swallowing is insufficient?

A

Vago-vagal reflex triggers second

67
Q

How long is the oesophagus?

A

25cm

68
Q

What is the oesophagus made of?

A

Upper 1/3 skeletal, striated muscle, lower 2/3 smooth

69
Q

What happens to the oesophagus upon swallowing?

A
  • The upper oesophageal sphincter briefly relaxes, allowing the food bolus to pass into the oesophagus
  • A contractile(peristaltic) wave sweeps down the oesophagus
  • The lower oesophageal sphincter and the proximal stomach relax to allow the bolus to enter the stomach
70
Q

Why are there no spontaneous contractions in the oesophagus?

A

No pacemakers in oesophageal muscle

71
Q

What is achalasia?

A

Condition characterised by dysphagia which results from the failure of the lower oesophageal sphincter to relax

72
Q

What are the causes of achalasia?

A

Cause unknown, but evidence shows that many patients lose ganglionic cells of myenteric plexus, or neural defects in the vagal dorsal nucleus of the brainstem

73
Q

What is gastro-oesophageal reflux disease

A

Occurs when lower oesophageal is incompetent, allowing the flow of gastric juice and contents back into the oesophagus

Since gastric juices are corrosive to oesophageal mucosa, the distal oesophagus becomes inflammed and sometimes ulcerated

74
Q

What are the functions of the stomach?

A

Storage, mixing and gastric emptying

75
Q

Where is the pacemaker for the stomach located

A

Pacemaker is located in the longitudinal layer, greater curvature in the mid-portion

76
Q

What is the effect of vagal or gastrin stimulation on the probability of spike potentials?

A

Probability of spike potentials is increased

77
Q

What is receptive relaxation?

A

Increases in stomach pressure triggers dumping and reflux

Following ingestion, there is an increase in fibre length without change in tone which permits increase in size without increase in intragastric pressure

78
Q

What is receptive relaxation mediated by?

A

Vagus as part of end of swallowing reflex

79
Q

How is mixing in the stomach regulated?

A
  • Distension of stomach activates mechanoreceptors, ENS/extrinsic
  • Gastrin release in response to food in stomach also stimulates stomach motility
80
Q

What does an increase in chyme cause in the stomach?

A

Increase in chyme in stomach induces antral contractions and opening of sphincter as peristaltic wave approaches

81
Q

What is the rate of gastric content emptying related to?

A

Empties at a rate proportional to volume, pH, physical and chemical nature

As contents become isotonic, empties more rapidly

82
Q

What is the enterogastric reflex?

A

Enterogastric reflex inhibits emptying

It stimulates pyloric contractions and also increases tone of pyloric sphincter to prevent emptying, thereby preventing the upper small intestine from being overwhelmed

83
Q

What causes the release of secretin, GIP and CCK

A

The presence of fatty acids/monoglycerides in duodenum(not emulsified) and low pH which causes decreased gastric emptying

84
Q

Which cells release secretin

A

S-cells

85
Q

Which cells release GIP and CCK

A

K and I cells

86
Q

What is the short reflex via which gastric chyme causes decreased gastric emptying

A

Gastric chyme –> Acid, fat digestion products, hypo- or hypertonic solutions –> duodenal mechanoreceptor, chemoreceptor, osmoreceptors –> ENS –> decreased gastric emptying

87
Q

What is the long reflex via which gastric chyme causes decreased gastric emptying

A

CNS is stimulated which decreases parasympathetic activity and increases sympathetic activity

Decreased parasympathetic activity causes decreased gastric emptying

88
Q

What is dumping syndrome?

A

Rapid emptying of gastric contents into small intestine. Characterised by nausea, pallor, sweating, vertigo, and sometimes fainting within mins after a meal or ingestion of a hypertonic solution.

89
Q

What is gastroparesis?

A

A condition characterized by impaired or absent ability of the stomach to empty.

90
Q

Which patients occasionally suffer from gastroparesis?

A

Severely diabetic patients who develop autonomic neuropathy

the loss of vagal stimulation to the stomach impairs antral systole, preventing the proper digestion and emptying of gastric contents. (patients often complain of early satiety, abnormal bloating and nausea)

91
Q

What is segmentation?

A

Multiple short contractions(1-2cm), frequency varies along a proximal to distal gradient(10-12/min proximal; 6/min distal ileum)

The decreasing gradient of BER frequency promotes the distal movement of intestinal chimes

92
Q

What is peristalsis?

A

Short range(-10cm) contractions(BER)

93
Q

What is the effect of villus movements in the small intestine?

A

Villus movements; swaying and piston-like movements - to mix and to drain lymphatics of fat absorption

Stimulated by extrinsic and intrinsic factors

94
Q

What is intestinal blind loop syndrome?

A

Impaired small intestinal peristalsis can lead to abnormally high levels of bacteria and lead to diarrhoea and/or steatorrhoea(fecal fat excretion)

95
Q

What type of muscles does the large intestine have?

A

Colon lacks continuous layer of longitudinal muscles, instead muscles are organised in 3 thick bands - taeniae coli

96
Q

What are haustrations?

A

Segmental contractions of circular muscles divide the colon into segments called haustrations and represent the main motor activity of the colon

97
Q

When does mass movement occur in the large intestine?

A

Mass movement occurs when segmental contraction of the left colon disappears and simultaneous contraction of the right colon propels its content distally

98
Q

When do mass movements occur in the large intestine?

A

Occurs several times a day but especially after meal - referred to gastric colic reflex

99
Q

Describe the type of innervation of the 2 sphincters

A
  • Internal anal sphincter involuntary
  • External anal sphincter voluntary(skeletal muscle)
  • Afferent stimulation leads to parasympathetic signal to relax internal sphincter
100
Q

How is the external anal sphincter controlled?

A

If voluntary relaxation of external sphincter does not occur via pudendal nerve, reverse peristalsis returns to colon

Anatomy - abdominal aorta (10 decks)

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