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Gastrointestinal > Alimentary Canal > Flashcards

Alimentary Canal Flashcards

1
Q

What are the four activities of the alimentary canal?

A

Motility, secretion (required for digestion, protection and lubrication), digestion, absorption.

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2
Q

What are the four main layers of the digestive tract wall?

A

Mucosa -> submucosa -> muscularis externa -> serosa

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3
Q

What makes up the mucosa (from lumen outwards)?

A

Epithelial cells -> exocrine cells -> endocrine gland cells -> lamina propria (capillaries, enteric neurones, immune cells) -> muscularis mucosae.

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4
Q

What makes up the submucosa?

A

Connective tissue, larger blood and lymph vessels, glands, nerve network (submucous plexus).

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5
Q

What makes up the muscularis externa?

A

Circular muscle layer, nerve network (myenteric plexus), longitudinal muscle layer.

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6
Q

What is the serosa composed of?

A

Connective tissue.

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7
Q

Where is there skeletal muscle in the GI tract?

A

Mouth, pharynx, upper oesophagus and external anal sphincter.

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8
Q

What are the 3 smooth muscle layers in the GI tract?

A

Circular layer, longitudinal layer and the muscular mucosae..

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9
Q

What does contraction of the muscularis mucosae cause?

A

Change in absorptive and secretory area of mucosa (folding), mixing activity.

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10
Q

What allows the smooth muscle cells of the GI tract to become depolarised and contract at the same time as a synchronous wave (functional syncytium)?

A

Gap junctions allowing spread of electrical currents from cell to cell.

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11
Q

What is single unit smooth muscle?

A

Smooth muscle that all contracts together.

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12
Q

What is the activity of the pacemaker cells modified by?

A

Intrinsic (enteric) nerves, extrinsic (autonomic) nerves and numerous hormones.

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13
Q

What are the waves of depolarisation that occur in the digestive tract called?

A

Slow waves.

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14
Q

What are the pacemaker cells in the GI tract called?

A

Interstitial cells of Cajal (ICCs).

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15
Q

What does the slow wave amplitude have to be to cause contraction?

A

Sufficient to trigger SMC action potentials.

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16
Q

What ion currents cause the upstroke and downstroke of smooth muscle cell action potentials?

A

Upstroke is calcium current, downstroke is potassium current.

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17
Q

Where in the GI tract wall are ICCs located?

A

Between the longitudinal and circular muscle layers and in the submucosa.

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18
Q

What is the basic electrical rhythm?

A

The rate at which slow waves occur in the different organs.

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19
Q

What determines whether slow wave amplitude reaches threshold?

A

Neuronal stimuli, hormonal stimuli, mechanical stimuli.

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20
Q

What effect do these stimuli have on the membrane potential of smooth muscle cells?

A

They depolarise smooth muscle cells rather than influence slow waves directly.

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21
Q

What is the BER frequency in the stomach?

A

3 slow waves per minute.

22
Q

What is the BER in the duodenum and terminal ileum respectively and in what direction does this drive luminal contents?

A

Duodenum - approximately 12 waves per minute. Terminal ileum - approximately 8 waves per minute. Drives in aboral direction.

23
Q

What is the BER for the proximal and distal (sigmoid) colon respectively and what direction does this drive luminal contents?

A

Proximal - 8 per minute.

Distal - 16 per minute. Drives in oral direction.

24
Q

Why does the large intestine drive luminal contents in oral direction?

A

It favours retention of luminal contents facilitating reabsorption of water and electrolytes.

25
Q

Where do pregangionlic parasympathetic nerves synapse in the GI tract?

A

Within the enteric nervous system.

26
Q

Where does the parasympathetic innervation of the GI tract come from?

A

Vagal nerves and sacral spinal nerves (form the pelvic nerves).

27
Q

What are the influences of parasympathetic excitation on the GI tract?

A

Excitatory: increased gastric, pancreatic and small intestinal secretion, blood flow and smooth muscle contraction.
Inhibitory: relaxation of some sphincters, receptive relaxation of stomach.

28
Q

What are the ganglia that sympathetic fibres innervating the GI tract synapse in?

A

The prevertebral ganglia (particularly celiac, superior mesenteric and inferior mesenteric.

29
Q

What do postganglionic sympathetic fibres innervate?

A

Mainly enteric neurones.

30
Q

What effects does sympathetic excitation have on the GI tract?

A

Excitatory influences: increased sphincter tone.

Inhibitory influences: decreased motility, secretion and blood flow.

31
Q

Where are the cell bodies of the enteric nervous system (ENS) located?

A

In ganglia connected by fibre tracts within the myenteric (Auerbach’s) plexus and the submucous (Meissner’s) plexus.

32
Q

What are the roles of the 2 enteric plexuses?

A

Myenteric: mainly regulates motility and sphincters.
Submucous: mainly modulates epithelia and blood vessels.

33
Q

What is meant when it is said that the ENS is intrinsic to GI tissue?

A

Reflex circuits can operate independently.

34
Q

What are the 3 types of neurones in the enteric nervous system?

A

Sensory neurones, interneurones and effector neurones

35
Q

What type of sensory neurones are there in the ENS?

A

Mechanoreceptors, chemoreceptors and thermoreceptors.

36
Q

What is the function of interneurones?

A

Co-ordinate reflexes and motor programs.

37
Q

What do the effector neurones of the ENS supply?

A

Both smooth muscle layers, secretory epithelium, endocrine cells and blood vessels.

38
Q

Describe where a local reflex, a short reflex and a long reflex go to?

A

Local reflex - just in ENS.
Short reflex - prevertebral ganglion.
Long reflex - brain.

39
Q

Give an example of a local, short and long reflex.

A

Local - peristalsis.
Short - interstino-intestinal inhibitory reflex (local distension causes inhibition of muscle activity in adjacent areas).
Long - gastroileal reflex (increase in gastric activity causes increase propulsive activity in the terminal ileum).

40
Q

Define peristalsis.

A

A wave of relaxation, followed by contraction, that normally proceeds along the gut in an aboral direction, triggered by distension of the gut wall.

41
Q

What happens in the oral side of the food bolus when distension activates sensory neurones?

A

Alters activity of interneurones -> alters activity of motor neurones -> longitudinal muscle relaxes (release of VIP and NO from inhibitory motorneurone) and circular muscle contracts (release of ACh and substance P from excitatory motoneurone).

42
Q

What happens to the aboral side of the food bolus when distension activates sensory neurones?

A

Alters activity of interneurones -> alters activity of motor neurones -> longitudinal muscle contracts (release of ACh and substance P from excitatory motorneurone and circular muscle relaxes (release of VIP and NO from inhibitory motorneurone).

43
Q

Other than peristalsis, name all the major motility patterns in the GI tract.

A

Segmentation, colonic mass movement, migrating motor complex (MMC), tonic contractions.

44
Q

What is segmentation and where does it occur?

A

Rhythmic contractions of the circular muscle layer that mix and divide luminal contents. Small intestine (in fed state) and large intestine (called haustration).

45
Q

What is colonic mass movement?

A

Powerful sweeping contraction that forces faeces into the rectum (occurs few times a day).

46
Q

What is the migrating motor complex?

A

Powerful sweeping contraction from stomach to terminal ileum.

47
Q

Give examples of low pressure and high pressure tonic contractions (sustained contractions).

A

Low pressure - organs with a major storage function e.g. stomach.
High pressure - sphincters.

48
Q

What causes opening and closing of a sphincter in general?

A

Stimuli proximal: opening. Stimuli distal: closing.

49
Q

What are all the sphincters called?

A

Upper oesophageal sphincter (UOS), lower oesophageal sphincter (LOS), pyloric sphincter, ileocecal valve, internal and external anal sphincters.

50
Q

When does the upper oesophageal sphincter open and close?

A

Opens to allow swallowing, closes during inspiration.

51
Q

What is the function of the pyloric sphincter?

A

Regulates gastric empyting, usually prevents duodenal gastric reflux.

Gastrointestinal (26 decks)

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