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Gastrointestinal > Introduction to GI tract and motility > Flashcards

Introduction to GI tract and motility Flashcards

1
Q

What is the basic structure of the GI tract?

A

It is a series of hollow organs running from the mouth to the anus

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2
Q

What structures separate the hollow organs?

A

Sphincters

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3
Q

What is the function of the mouth and oropharynx?

A

The food is made into smaller pieces and lubricated. Fat and carbohydrate digestion starts and food is propelled to the oesophagus during swallowing

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4
Q

What is the function of the oesophagus?

A

Delivers food to the stomach

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5
Q

What is the function of the stomach?

A

Temporary food storage, continues carbohydrate and fat digestion, initiates protein digestion and regulates the delivery of chyme to the small intestine

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6
Q

What is chyme?

A

A pulpy acid fluid which passes from the stomach to the small intestine. It is made up of gastric juices and partly digested food

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7
Q

What is the function of the small intestine?

A

Principle site of digestion and absorption of nutrients

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8
Q

What is the function of the large intestine?

A

Reabsorbs fluids and electrolytes, stores faecal matter before regulated expulsion

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9
Q

What are the accessory structures of the digestive tract?

A

Salivary glands
Liver and gall bladder (hepatobiliary system)
Pancreas

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10
Q

What type of muscle drives motility of the GI tract?

A

Smooth muscle

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11
Q

What areas of the GI tract have skeletal muscle?

A

Mouth, pharynx, upper oesophagus and external anal sphincter

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12
Q

What are the three different mechanical activity of the GI tract?

A

Propulsive movements
Mixing movements
Tonic contractions

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13
Q

What controls secretions into the lumen of the digestive tract?

A

Hormonal and neural signals

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14
Q

What is the primary protective secretion throughout the length of the GI tract?

A

Mucus

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15
Q

What are the secretions required for?

A

Digestion and protection

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16
Q

What do the digestive secretions contain?

A

Water, electrolytes and organic compounds

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17
Q

What is digestion?

A

It is the biochemical breakdown of complex foodstuffs to smaller, absorbable units

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18
Q

What are carbohydrates broken down into?

A

Polysaccharides and disaccharides are converted to monosaccharides

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19
Q

What enzymes mediate the breakdown of carbohydrates?

A

Amylase and disaccharidases

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20
Q

What are proteins broken down into during digestion?

A

Amino acids, dipeptides and tripeptides

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21
Q

What enzymes mediate the breakdown of protein?

A

Proteases and dipeptidases

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22
Q

What are triglycerides (majority or fats) broken down into?

A

Monoglycerides and free fatty acids

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23
Q

What enzymes mediate the breakdown of triglyercides/

A

Lipases

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24
Q

What is absorption?

A

The transfer of absorbable products of digestion from the digestive tract to the blood or lymph

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25
Q

What are the four layers of the digestive tract wall?

A

Mucosa
Submucosa
Muscularis externa
Serosa

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26
Q

What is the mucosa comprised of?

A 
Epithelial cells
Exocrine cells
Endocrine cells
Lamina propia 
Muscularis mucosa
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27
Q

What does the submucosa contain?

A

Connective tissue
Large blood and lymph vessels
Nerve network - submucous plexus

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28
Q

What is the muscularis externa comprised of?

A

Circular muscle later
Nerve network
Longitudinial muscle layer

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29
Q

What does the serosa contain?

A

Connective tissue

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30
Q

Where foes the myenteric plexus lie?

A

Between the inner and outer layers or smooth muscle in the muscularis externa

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31
Q

What is the result of circular muscle contraction?

A

Lumen becomes narrower and longer

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32
Q

What is the result of longitudinal muscle contraction?

A

Intestine becomes shorter and fatter

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33
Q

What is the function of muscularis mucosae contraction?

A

Change in absorptive and secretory area of mucosa

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34
Q

What is the function of gap junctions?

A

Connect adjacent smooth muscle cells allowing the spread of electrical currents from cell to cell.

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35
Q

What is meant by a functional syncytium?

A

Hundreds of cells depolarise and contract at the same time

36
Q

How is the sponatenous activity of the smooth muscle regulated?

A

Intrinsic (enteric) and extrinsic (automonic) nerves

Hormones

37
Q

How is the electrical activity of the stomach, small intestine and large intestine described?

A

Slow waves - rhythmic patterns of membrane depolarisation and repolarisation that spread from cell to cell via gap junctions
(variation in resting membrane potential)

38
Q

What drives the slow waves?

A

Interstitial cells of Cajal (ICCs) - pacemaker cells

39
Q

When does contraction occur?

A

When the slow wave amplitude is sufficient to trigger action potentials (reaches a threshold) and open voltage gated calcium channels

40
Q

When does relaxation occur?

A

When the slow wave amplitude is sufficient to trigger action potentials (reaches a threshold) and open voltage gated postassium channels

41
Q

How does slow wave electrical activity influence the force of contraction?

A

The longer the slow wave is above threshold the more channels are activated, meaning the greater the force of contraction

42
Q

What do slow waves determine?

A

The basal electrical rhythm (BER) - which varies along the length of the GI tract

43
Q

What factors influence whether the slow wave amplitude reaches the threshold?

A

Neuronal, hormonal and mechanical stimuli

44
Q

What does the slow wave frequency set?

A

The maximum frequency at which the muscle can contract

45
Q

What is the enteric nervous system?

A

The ‘little brain of the gut’
about 100million neurons
A complete reflex circuit that can operate independently of the rest of the nervous system

46
Q

Where is the enteric nervous system located?

A

In the GI tissue. Cell bodies are located in ganglia largely within the myenteric and submucous plexus

47
Q

How are the ganglia connected?

A

Interganglionic fibre tracts

48
Q

What is the enteric nervous system comprised of?

A

Sensory neurones
Interneurones
Effector neurones

49
Q

What is the neurotransmitter for the parasympathetic system?

A

Acetlycholine

50
Q

What is the excitatory influence of the parasympathetic branch of the enteric nervous system?

A

Increased gastric, pancreatic and small intestinal secretion
Blood flow and muscle

51
Q

What is the inhibitory influence of stimulation of the parasympathetic branch on the enteric nervous system?

A

Relaxation of some sphincters

Receptive relaxation of the stomach

52
Q

What is the inhibitory influence of stimulation of the sympathtic nerves?

A

Decreased motility, secretion and blood flow

53
Q

What are the three broad types of reflex that occur in the GI tract?

A

Local reflex
Short reflex
Long reflex

54
Q

What is an example of a local reflex?

A

Peristalsis

55
Q

What is an example of a short reflex?

A

Intestino-intestinal inhibitory reflex

56
Q

What is an example of a long reflex?

A

Gastroileal reflex

57
Q

What is peristalsis?

A

A wave of contraction that normally proceeds along the gut in an aboral direction (away form the mouth)

58
Q

What triggers peristalsis?

A

Distension of the gut wall triggers interneurons that in turn trigger the motor neurons

59
Q

What is the name of the segment before the food?

A

Propulsive segment

60
Q

What is the name of the segment after the food?

A

Receiving segment

61
Q

Describe the motility pattern segmentation?

A

Rhythmic contractions of the circular muscle layer that mix and divide luminal contents (area of relaxed muscle between the contracted circular muscle forms a sac)

62
Q

What is name for segmentation in the large intestine?

A

Haustration

63
Q

What are tonic contractions?

A

Sustained contractions found in the sphincters of the GI tract

64
Q

How many sphincters are there in the GI tract?

65
Q

How do sphincters work?

A

Act as a one way valve, maintain positive resting pressure relative to two adjacent structures

66
Q

Describe the upper oesophageal sphincter?

A

Skeletal muscle
Relaxes to allow swallowing
Closes during inspiration

67
Q

Describe the lower oesphageal sphincter

A

Relaxes to permit entry of food to the stomach

Closes to prevent reflux of gastric contents to the oesophagus

68
Q

Describe the pyloric sphincter

A

Regulates gastric emptying and usually prevents duodenal gastric reflux

69
Q

Describe the ileocecal sphincter

A

Regulates flow from the ileum to colon

Opens due to distension of the ileum, closes due to distension of proximal colon

70
Q

What reflex regulates the internal and external sphincters?

A

Defecation relex

71
Q

Which sphincters have skeletal muscle?

A

Upper oesophageal and external sphincter

72
Q

What is the function of the lips?

A

Containment of food

Speech

73
Q

What is the function of the teeth?

A

Mastication
Food is broken down and mixed with saliva
This stimulates taste buds which then increases salivary, gastric, pancreatic and bile secretion

74
Q

What is the function of the palate?

A

Separates the mouth from the nasal passage, allows breathing and chewing simultaneously

75
Q

What is the function of the uvula?

A

Helps seal off nasal passages during swallowing

76
Q

What is the function of the tongue?

A

Guides food
Important in speech and swallowing
Major location of taste buds

77
Q

What is the function of the pharynx?

A

Common pathways for the respiratory and digestive systems

78
Q

What is deglutition?

A

The action/process of swallowing

79
Q

What is swallowing?

A

The movement of food from the mouth to the stomach

80
Q

What are the two stages of swallowing?

A

Oropharyngeal stage

Oesophageal stage

81
Q

Describe the oropharyngeal stage

A

Mouth –> pharynx –> oesophagus (1 second)

Bolus formed –> food passes through pharynx into oesophagus

82
Q

What happens to prevent food entering the nasal passages when swallowing?

A

Soft palate rises
Tongue presses against the hard palate
Uvula presses against the back of the throat

83
Q

What happens to prevent food entering the trachea during swallowing?

A

Elevation of the larynx
Tilting of the epiglottis
Vocal cords close across the glottis
The swallowing centre inhibits the resipiratory centre of the brain
Pharyngeal muscles contract and force the bolus into oesphagus

84
Q

What allows food into the oesophagus?

A

Opening of the upper oesophageal sphincter

85
Q

Describe the oesophageal stage of swallowing

A

Oesophagus –> stomach (4-10 seconds)

Gastrointestinal (11 decks)

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