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GI > Physiology of Alimentary Canal > Flashcards

Physiology of Alimentary Canal Flashcards

1
Q

what is the alimentary canal

A

the whole passage along which food passes through the body from mouth to anus during digestion

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2
Q

what is the role of sphincters

A

separate functional compartments of the alimentary canal and help control movement of matter inside it

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3
Q

what is the role of the accessory structures

A

produce fluid that drains into the alimentary canal

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4
Q

what are the accessory structures

A

salivary glands, pancreas, liver and gall bladder

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5
Q

what organs and structures make up the alimentary canal

A

mouth and oropharynx, oesophagus, stomach, small intestine, large intestine, rectum and anus, accessory structures

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6
Q

what happens in the mouth and oropharynx

A

chops and lubricates food, carbohydrate digestion started, food propelled to oesophagus

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7
Q

what is the role of the oesophagus

A

muscular tube that propels food to the stomach

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8
Q

what is the role of the stomach

A

stores/churns food, continues carbohydrate and initiates protein digestion, regulates delivery of chyme to duodenum- stops small intestine from being overwhelmed

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9
Q

what is chyme

A

the pulpy acidic fluid which passes from the stomach to the small intestine, consisting of gastric juices and partly digested food

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10
Q

what is the role of the small intestine

A

principle site of digestion and absorption of nutrients

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11
Q

what are the parts of the small intestine

A

duodenum, jejunum and ileum

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12
Q

what are the parts of the large intestine

A

caecum, appendix and colon

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13
Q

what is the role of the colon

A

reabsorbs fluids and electrolytes, stores faecal matter before delivery to rectum

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14
Q

what is the role of the rectum and anus

A

storage and regulated expulsion of faeces

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15
Q

how small do food particles have to be to pass from the stomach into the duodenum

A

2mm

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16
Q

where is fat digestion initiated

A

in the small intestine

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17
Q

what is pepsin

A

enzyme produced in stomach that breaks down proteins

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18
Q

what is amalyse

A

enzyme that breaks down starch into sugars in the small intestine

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19
Q

what organs make the hepatobiliary system

A

liver and gall bladder

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20
Q

what controls the motility of the alimentary canal

A

mostly smooth muscle

skeletal at mouth, pharynx, upper oesophagus and external anal sphincter

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21
Q

what causes secretion in the digestive tract

A

in response to presence of food, hormonal and neural signals

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22
Q

what is the role of secretion in the digestive tract

A

required for digestion, protection and lubrication

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23
Q

what is digestion

A

chemical breakdown by enzymatic hydrolysis of complex foodstuffs to smaller absorbable units

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24
Q

where does physical, mechanical digestion take place

A

mouth, stomach, small intestine

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25
Q

describe absorption in the alimentary canal

A

transfer of the absorbable products of digestion (along with water, electrolytes and vitamins) from the digestive tract to the blood or lymph

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26
Q

what is absorption largely mediated by

A

numerous transport mechanisms

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27
Q

what is the innermost part of the digestive tract wall and what is its role

A

mucosa- absorptive function (eneterocytes)

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28
Q

what makes up the mucosa

A

epithelial cells, exocrine cells, endocrine gland cells, lamina propria

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29
Q

what is the lamina propria composed of

A

capillaries, enteric neurons, immune cells, muscularis mucosae

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30
Q

what is the layer surrounding the mucosa

A

submucosa

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31
Q

what is the submucosa made of

A

elastic connective tissue, larger blood and lymph vessels, glands, nerve network (submucosa plexus)

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32
Q

what is the layer surrounding the submucosa

A

muscularis externa

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33
Q

what is the muscularis externa made of

A

2 layers of muscle and nerve network;
circular muscle layer (controls diameter of lumen), nerve network (myenteric plexus), longitudinal muscle layer (controls length of digestive tract)

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34
Q

what is the outermost layer of the digestive tract wall

A

serosa

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35
Q

what is the serosa made of

A

connective tissue

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36
Q

what immune cells are in the lamina propria

A

lymphocytes and mast cells

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37
Q

how long is the digestive tract

A

7-10 m

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38
Q

what is a role of the serosa

A

secrete lubricant to move abdominal content smoothly

39
Q

what causes the lumen to become narrower and longer

A

circular muscle contraction

40
Q

what causes the intestine to become shorter and fatter

A

longitudinal muscle contraction

41
Q

what happens when muscularis mucosae contract

A

there is changes in the absorptive and secretory area of the mucosa (folding), mixing activity

42
Q

what controls the skeletal muscle involved with gastrointestinal motility

A

autonomic control

43
Q

describe how smooth muscle in the GI tract is electrically coupled

A

adjacent smooth muscle cells are coupled by gap junctions which allow the spread of electrical currents forming a functional syncytium which allows a slow wave of depolarisation to spread across the muscle sheet

44
Q

what is the term used to describe hundreds of muscle cells contracting at the same time

A

single unit smooth muscle

45
Q

what modulates the spontaneous activity across the syncytium which is driven by the pacemaker cells

A

intrinsic (enteric) and extrinsic (autonomic) nerves

hormones

46
Q

how does spontaneous electrical activity occur as in the stomach and small intestine

A

in slow waves - rhythmic patterns of membrane depolarization and repolarization that spread from cell to cell via gap junctions

47
Q

what does the slow wave electrical activity determin

A

max frequency, direction and velocity of rhythmic contractions

48
Q

what pacemaker cells that are interspersed between the far more numerous smooth muscle cells

A

interstitial cells of Cajal (ICCs)

49
Q

when only can contraction occur

A

only when the slow wave amplitude is sufficient to trigger smooth muscle cell action potentials

50
Q

what is the force of contraction related to

A

number of action potentials discharged

51
Q

where are the interstitial cells of cajal located

A

in the submucosa

52
Q

do all slow waves trigger contraction

A

no (slow waves in background- BER- only reach threshold when stimulated)

53
Q

what determines whether slow wave amplitude reaches contraction

A

neuronal stimuli, hormonal stimuli, mechanical stimuli

54
Q

what does BER (basic electrical rhythm do to luminal contents in the small intestine

A

drive it in the aboral (rectum) direction

55
Q

what does BER (basic electrical rhythm do to luminal contents in the large intestine

A

favours retention of luminal contents, facilitating absorption of water and electrolytes

56
Q

how is the GI tract innervated with parasympathetics

A

pre ganglionic fibres (that release ACh) synapse with ganglion cells within the ENS

57
Q

what is the ENS

A

division of autonomic nervous system in the GI tract, pancreas and gallbladder

58
Q

what are the parasympathetic excitatory influences of the GI tract

A

causes increased;

  • gastric, pancreatic and small intestine secretion
  • blood flow
  • smooth muscle contraction
59
Q

what are the parasympathetic inhibitory influences of the GI tract

A

causes relaxation of some sphincters, receptive relaxation of stomach

60
Q

where does the parasympathetic stimulation of the GI tract arise from

A

medulla oblongata for majority, sacral spinal chord for the distal ends on the large intestine

61
Q

what is more important in the GI tract para or symp

A

para

62
Q

how does the sympathetic system innervate the GI tract

A

pre ganglionic fibres releasing ACh synapse in the prevertebral ganglia. postganglionic fibres releasing NA innervate mainly enteric neurones

63
Q

what excitatory influences does the sympathetic system have on the GI tract

A

increased sphincter tone

64
Q

what inhibitory influences does the sympathetic system have on the GI tract

A

decreased motility, secretion and blood flow

65
Q

what are the 3 prevertebral ganglia involved with the sympathetic system

A

celiac, superior mesenteric, inferior mesenteric

66
Q

what do nerves from the thoraco-lumbar region innervate

A

distal end of the stomach, small intestine, oesophagus, proximal large intestine, distal large intestine

67
Q

what is the main role of the myenteric (auerbach’s plexus)

A

mainly regulates motility and sphincters

68
Q

what is the main role of the submucous (meissner’s) plexus

A

mainly modulates epithelia and blood vessels

69
Q

is the enteric nervous system intrinsic or extrinsic to the GI tissue, explain

A

intrinsic- many of the nerve cell bodies in the submucosa are post ganglionic parasympathetic fibres and are classed as part of the ENS

70
Q

how do reflex circuit in the ENS operate

A

can run independantly but hormones and extrinsic nerves exert a strong regulatory influence

71
Q

what does the ENS coordinate

A

musclur, secretive and absorptive activities

72
Q

what neurons produce the activities that the ENS co ordinates

A 
sensory neurons (mechano, chemo and thermo receptors)
interneurons (majority, co ordinate reflexes and motor programs)
effector neurons (excitatory and inhibitory motor neurones supplying both smooth muscle layers, secretory epithelium, endocrine cells and blood vessels)
73
Q

what do nerve reflexes in the GI tract control

A

motor and secretory activity

74
Q

what is the relfex pathway

A

sensory neuron, interneurone, effector neurone

75
Q

give an example of a local relflex

A

peristalsis

76
Q

give and example of a short reflex

A

intestino-intestinal inhibitory reflex (local distension activates sensory neurones exciting sympathetic pre-ganglionic fibres that cause inhibition of muscle activity in adjacent areas)

77
Q

give an example of a long relfex

A

gastroileal reflex (increase in gastric activity causes increased propulsive activity in the terminal ileum)

78
Q

what is peristalsis

A

a wave on relaxation, followed by contraction that normally proceeds along the gut in an aboral direction

79
Q

what triggers peristasis

A

distension of the gut wall

80
Q

what is released when muscles relax and from what

A

VIP and NO released from inhibitory motoneurone

81
Q

what is released when circular muscles contract and from what

A

ACh and substance P from excitatory motor motorneurone

82
Q

what does distention of the GI tract activate

A

sensory neurones- mechanoreceptors- which alter the activity of the smooth muscle layers which propel the matter through the tract

83
Q

describe segmentation

A

motility pattern- contraction of alternative places in that causes mixing/ churning movements, rhythmic contractions of the circular muscle layer that mix and divide luminal contents. happens in small and large intestine. In large intestine is called haustration.

84
Q

describe colonic mass movement

A

motility pattern- powerful sweeping contraction across the large intestine that forces faeces into the rectum from the colon

85
Q

describe migrating motor complex

A

motility pattern-
powerful sweeping contraction from stomach to terminal ileum, cleans out the small intestine from the duodenum to the colon to make room for next meal

86
Q

describe tonic contractions

A 
motility contractions- sustained contractions: low pressure (organs with a major storage function e.g. stomach) maintain a degree of tone 
high pressure (sphincters)
87
Q

what is the role of the sphincters

A

usually one way valves, maintain positive resting pressure relative to two adjacent structures, exert a constant tone

88
Q

what in general causes opening and closing of the sphincters

A

stimuli (pressure) proximal and distal

89
Q

what is the role of the upper oesophageal sphincter and what type of muscle is it

A

relaxes to allow swallowing and closes during inspiration

90
Q

what is the role of the lower oesophageal sphincter

A

relaxes to permit entry of food into the stomach, closes to prevent reflux of gastric contents to the oesophagus

91
Q

what is the role of the pyloric sphincter

A

regulates gastric emptying and usually prevents duodenal gastric reflux

92
Q

what is the role of the ileocaecal valve

A

regulates flow from ileum to caecum, distention of ileum opensm distention of proximal colon closes

93
Q

what are the role of internal and external anal sphincters regulated by

A

defaecation reflex

94
Q

most sphincters are smooth muscle, which ones are skeletal

A

upper oesophageal, external anal

GI (64 decks)

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