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Gastrointestinal > Structure and Motility > Flashcards

Structure and Motility Flashcards

1
Q

what is the alimentary canal

A

series of hollow organs running from mouth to anus (oral to aboral) that are separated by sphincters, controlling movement

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2
Q

function of mouth and oropharynx

A

chops and lubricates food
starts carbohydrate digestions via salivary glands
delivers food oesophagus

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3
Q

function of oesophagus

A

muscular tube that propels food to stomach

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4
Q

function of stomach

A

stores/churns food
continues carbohydrate, initiates protein digestion via gastric glands that contain digestive enzymes
regulates delivery of chyme to duodenum

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5
Q

what is chyme

A

thinly divided particles of food, small enough to leave stomach and enter the duodenum of the small intestine

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6
Q

function of small intestine

A

made up of duodenum, jejunum and ileum

principal site of digestion and absorption of nutrients - in particular the duodenum and jejunum

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7
Q

function of large intestine

A

made up of caecum, appendix and colon
colon - reabsorbs fluid and eelectrolytes (not absorbed in small intestine), stores faecal matter and further digestion by bacteria (vitamin K)

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8
Q

function of rectum and anus

A

regulated expulsion of faeces

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9
Q

accessoy structures of alimentary canal

A

salivary glands - parotid, sublingual and submandibular glands
liver and gallbladder - hepatobiliary system
exocrine pancreas

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10
Q

general structure of digestive tract wall - 4 layers

A

mucosa - inside
submucosa
muscularis externa
serosa - outside

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11
Q

general structure of digestive tract wall - mucosa

A 
mucous membrane (epithelial, exocrine gland and endocrine gland cells)
lamina propia (capillaries, enteric neurones, gut associated lymphoid tissue)
muscularis mucosae
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12
Q

general structure of digestive tract wall - submucosa

A

connective tissue
larger blood and lymph vessels
glands
submucous plexus (enteric nervous system)

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13
Q

general structure of digestive tract wall - muscularis externa

A 
circular muscle layer
myenteric plexus (controls muscle)
longitudinal muscle layer
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14
Q

general structure of digestive tract wall - serosa

A

connective tissue

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15
Q

4 major functions of alimentary canal

A

motility
secretion
digestion
absorption

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16
Q

describe motility of alimentary canal

A

mechanical activity mostly involving smooth muscle - circular, longitudinal layers and the muscularis mucosa

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

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17
Q

describe secretion of alimentary canal

A

into the lumen of the digestive tract occurs from itself and accessory structures in response to the presence of food, hormonal and neural signals
required for - digestion, protection and lubrciation

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18
Q

describe digestion of alimentary canal

A

chemical breakdown by enzymatic hydrolysis of complex foodstuffs to smaller, absorbale, units

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19
Q

describe absorption of alimentary canal

A

transfer the absorbable products of digestion (with water, electrolytes and vitamins) from the digestive tract to the blood, or lymph - mediated by numerous transport mechanisms

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20
Q

circular muscle contraction

A

lumen becomes narrower and longer

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21
Q

longitudinal muscle contraction

A

intestine becomes shorter and fatter

22
Q

muscularis mucosae contraction

A

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

23
Q

describe electrically coupled smooth muscle cells

A

adjacent smooth muscle cells are coupled by gap junctions, electrical currents flow from cell to cell
this allows for a slow, synchronous wave of depolarisation to spread across muscle sheets - single unit smooth muscle as opposed to multiunit smooth muscle (do not contract in isolation)

24
Q

describe specialised pacemaker cells of the electrically coupled smooth muscle cells

A

specialised pacemaker cells drive spontaneous activity across the coupled cells
this is modulated by;
intrinsic (enteric) and extrinsic (autonomic) nerves
numerous hormones

25
Q

describe electrical activity of the stomach, small and large intestine

A

spontaneous electrical activity occurs as slow waves - rhythmic patterns of membrane depolarisation and repolarisation that spread from cell to cell via gap junctions

26
Q

describe slow wave electrical activity and how it is driven

A

determines the frequency, direction and velocity of rhythmic contractions
is driven by interstitial cells of Cajal (ICCs) - pacemaker cells (calcium dependent channels)
ICCs are located largely between the circular and longitudinal muscle layers

27
Q

describe ICCs in slow wave electrical activity

A

ICCs form gap junctions with each other and smooth muscle cells electrically coupling them
slow waves in ICCs drive slow waves in the smooth muscle cells coupled to them - depolarising slow waves do not necessarily result in smooth muscle contraction
some ICCs form a bridge between nerve endings and smooth muscle cells

28
Q

describe contraction in the intestine

A

occurs only if the slow wave (basic electrical rhythm) amplitude is sufficient to reach a threshold to trigger smooth muscle calcium action potentials
force is related to number of action potentials discharged (driven in turn by the duration of the slow wave that is above threshold)
slow waves vary in frequency along length of GI tract

29
Q

stimuli dependent for slow wave amplitude to meet threshold

A

neuronal stimuli
hormonal stimuli
mechanical stimuli - e.g. presence of food

generally act to depolarise smooth muscle cells (by changing the starting point - membrane potential) rather than influence slow waves directly - depolarisation shifts slow wave peak to threshold

30
Q

autonomic innervation of GI tract - parasympathetic nerves

A

vagal nerves (sensory and motor) from medulla oblongata
pelvic nerves from sacral spinal cord
pre-ganglionic fibres (neurotransmitter - ACh) synapse with ganglion cells within the enteric nervous system (ENS)

31
Q

excitatory influences of parasympathetic nerves of GI tract

A

increased gastric, pancreatic and small intestinal secretion
increased blood flow
increased smooth muscle contraction

32
Q

inhibitory influences of parasympathetic nerves of GI tract

A

relaxation of some sphincters

receptive relaxation of stomach

33
Q

autonomic innervation of GI tract - sympathetic nerves

A

functionally less important than parasympathetic
superior cervical ganglion and pre-vertebral ganglia (celiac, superior mesenteric and inferior mesenteric) from thorco-lumbar region
pre-ganglionic fibres (neurotransmitter - ACh) synapse in the pre-vertebral ganglia
post-ganglionic fibres (neurotransmitter - NA) innervate mainly enteric neurones, but also other structures

34
Q

excitatory influences of sympathetic nerves of GI tract

A

increased sphincter tone

35
Q

inhibitory influences of sympathetic nerves of GI tract

A

decreased motility
decreased secretion
decreased blood flow

36
Q

describe the enteric nervous system (ENS)

A

very complex
cell bodies are located in ganglia, connectived by fibre tracts wihtin;
myenteric (Aurebach’s) plexus
submucous (Meissner’s) plexus

intrinsic to GI tissue - reflex circuits operate independently but influenced by hormones and extrinsic nerves
co-ordinates muscular, secretive and absorptive activities

37
Q

function of myenteric plexus

A

regulates motility and sphincters

38
Q

function of submucous plexus

A

modulates epithelia and blood vessels

39
Q

how does the ENS co-ordinate its activities

A

via (in order);
sensory neurones - mechanoreceptors etc.
interneurones
effector neurones

40
Q

example of local reflex (major motility pattern)

A

peristalsis;
PP - wave of relaxation, followed by contraction that normally proceeds a short distance along the gut in an aboral direction - triggered by distension of the gut wall

41
Q

example of 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

42
Q

example of long reflex

A

gastroileal reflex (a vago-vagal reflex) - increase in gastric activity causes increased propulsive activity in the terminal ileum

43
Q

major motility patter - segmentation (mixing or churning movements)

A

rhythmic contractions of circular muscle layer that mix and divide luminal contents
occurs in small intestine (in fed state) and in large intestine (haustration)

44
Q

major motility patter - colonic mass movement

A

powerful sweeping contraction that forces faeces into rectum

45
Q

major motility patter - migrating motor complex

A

powerful sweeping contraction from stomach to terminal ileum

46
Q

major motility patter - tonic contractions

A

sustained contractions;
low pressure - organs with major storage function
high pressure - sphincters

47
Q

sphincters of GI tract

A

6 in total
circular, generally smooth, muscle
act as one way valves by maintaining positive resting pressure relative to 2 adjacent structures - e.g. oesophagus and stomach
stimuli (positive) proximal and distal to sphincter cause opening and closing respectively

48
Q

upper oesophageal sphincter

A

skeletal muscle
relaxes to allow swallowing
closes during inspiration

49
Q

lower oesophageal sphincter

A

relaxes to permit entry of food to the stomach

closes to prevent reflux of gastric contents to the oesophagus

50
Q

pyloric sphincter

A

regulates gastric emptying

usually prevents duodenal gastric reflux

51
Q

ileocaecal valve

A

regulates flow from ileum to caecum

distension of ileum opens, distension of proximal colon closes

52
Q

internal (smooth muscle) and external (skeletal muscle) anal sphincters

A

regulated by defaecation reflex

Gastrointestinal (71 decks)

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