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semester 2 > GI physiology > Flashcards

GI physiology Flashcards

1
Q

components of alimentary canal/GI tract from mouth - anus (6)

A
  • mouth and oropharynx
  • oesophagus
  • stomach
  • small intestine
  • large intestine
  • rectum and anus
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2
Q

accessory structures of alimentary canal/GI tract (3)

A
  • salivary glands
  • pancreas
  • liver and gall bladder (hepatobiliary system)
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3
Q

what separates the different compartments of the GI tract

A

sphincters (circular rings of smooth muscle)

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4
Q

function of mouth and oropharynx (3)

A
  • chop food and lubrication (to ease movement)
  • carb (and limited fat) digestion
  • propel food to oesophagus
  • > alpha amylase breaks down things
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5
Q

function of oesophagus

A

-delivers food to stomach

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6
Q

function of stomach (3)

A
  • stores food temporarily
  • carb, fat AND protein digestion
  • regulates delivery of chyme to SI
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7
Q

what type of muscle is oesophagus

A
  • 1/3 skeletal

- 2/3 smooth muscle

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8
Q

function of small intestine (2)

A
  • principle site of digestion

- absorption of nutrients

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9
Q

components of small intestine (3)

A
  • duodenum
  • jejunum
  • ileum
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10
Q

function of large intestine (2)

A
  • reabsorption of fluids and electrolytes

- stores faecal matter before regulated expulsion

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11
Q

function of rectum and anus

A

regulated expulsion of faeces

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12
Q

role of pancreas

A

secretes digestive enzymes

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13
Q

function of liver (2)

A
  • produces bile

- suspends fat droplets

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14
Q

4 basic digestive processes (4)

A
  • motility
  • secretion
  • digestion
  • absorption
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15
Q

3 types of movement of food/motility (3)

A
  • propulsive movements (peristalsis)
  • mixing movements (segmentation)
  • tonic contractions
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16
Q

what triggers secretion

A

-hormonal and neural signals

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17
Q

function of secretion

A

-required for digestion and protection

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18
Q

where does secretion occur

A

into the lumen of the GI tract from the GI tract itself and accessory structures

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19
Q

what do digestive secretions contain (3 plus eg’s)

A
  • water (large vol. borrowed from plasma)
  • electrolytes (Na, K, HCO3, Cl)
  • organic compounds (enzymes, bile salts, mucus etc)
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20
Q

what occurs during digestion

A
  • complex foodstuffs broken down into smaller more absorbable units by enzymatic hydrolysis
  • mediated by diff. enzymes
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21
Q

what are carbs broken down to during digestion

A

-carbs (mostly polysaccharides) and some disaccharides (sucrose) -> monosaccharides (glucose, galactose and fructose)

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22
Q

what are proteins broken down to during digestion

A

constituent amino acids, dipeptides and tripeptides

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23
Q

what enzymes mediate carbohydrate digestion (2)

A

amylases and disaccharides

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24
Q

what enzymes mediate protein digestion (3)

A

proteases, dipeptidases and tripeptidases

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25
Q

what are fats broken down to during digestion

A

fats (mostly triglycerides) -> monoglycerides and free fatty acids

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26
Q

what enzymes mediate fat digestion

A

lipases

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27
Q

what are absorbed from the digestive tract to the blood, or lymph

A

-absorbable products of digestion (along with water, electrolytes and vitamins)

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28
Q

what mediates absorption

A

numerous transport mechanisms

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29
Q

what are the layers of the digestive tract wall (from inside out) (4)

A
  • mucosa
  • submucosa
  • muscularis externa
  • serosa
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30
Q

what controls motility

A
  • mostly smooth muscle (circular, longitudinal layers and the muscular mucosae)
  • skeletal muscle in the mouth, pharynx, upper oesophagus and external anal sphincter
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31
Q

what happens when circular muscle contracts during motility

A

lumen becomes narrower and longer

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32
Q

what happens when longitudinal muscle contracts during motility

A

intestine becomes shorter and fatter

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33
Q

what occurs when muscularis mucosae contracts during motility

A
  • change occurs in the absorptive and secretory area of mucosa (folding)
  • mixing activity occurs
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34
Q

where are ICC’s located in relation to the muscles of the GI tract (2)

A
  • in between the longitudinal and circular muscle layers

- within the submucosal layer

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35
Q

what controls the spontaneous electrical and contractile activity of the GI tract (3)

A
  • intrinsic (enteric) and extrinsic (autonomic) nerves

- various hormones

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36
Q

where in the GI tract does the spontaneous electrical activity occur as slow waves (3)

A
  • stomach
  • small intestine
  • large intestine
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37
Q

what are slow waves

A

-‘rhythmic patterns of membrane depolarisation and repolarisation that spread cell- cell via gap junctions aka ICC’s’

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38
Q

what drives/controls slow waves

A

ICC’s (interstitial cells of cajal) = pacemaker cells

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39
Q

why are ICC’s described as gap junctions

A

electrically couple to each other and adjacent smooth muscle cells to allow the spread of electrical current from cell-cell and allow hundreds of cells to depolarise and contract at once (functional synctium)

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40
Q

what do slow waves determine (3)

A

max. frequency, direction and velocity of rhythmic contractions

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41
Q

when does muscle contraction occur

A

-only if slow wave amplitude reaches threshold/signif to trigger action potential

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42
Q

what determines the force of muscle contractions

A

the number of action potentials discharged

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43
Q

what determines the upstroke of slow wave action potentials

A

voltage activated calcium channels

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44
Q

what determines the downstroke of slow wave action potentials

A

voltage activated potassium channels

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45
Q

what does the basic/ basal electrical rhythm determine

A

the frequency of contractions in the GI tract

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46
Q

what determines the basic/basal electrical rhythm

A
  • slow waves

- differs along length of GI tract as not all slow waves trigger action potentials as threshold must be reached

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47
Q

what determines whether slow waves amplitude reaches threshold (3)

A
  • neuronal stimuli
  • mechanical stimuli
  • hormonal stimuli
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48
Q

BER frequency in the stomach

A

3 slow waves per min

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49
Q

BER frequency in the small intestine (2)

A
  • approx 10-12 slow waves per min in duodenum

- 8 slow waves in terminal ileum (tends to drive luminal contents to aboral direction)

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50
Q

BER frequency in the large intestine (2)

A
  • approx 8 slow waves per min in proximal colon
  • approx 16 slow waves per min in distal colon (favours retention of luminal contents facilitating absorption of of water and electrolytes)
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51
Q

intrinsic supply of GI tract

A

enteric nervous system (ENS), modulated by hormones and extrinsic nerve output

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52
Q

where are ganglia of enteric nervous system located

A
  • within myenteric (auerbach’s) plexus and submucous (meissner’s) plexus
  • ganglia are connected by the interganglionic fibre tracts
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53
Q

where is the myenteric plexus located

A

in the muscularis external layer of GI tract

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54
Q

what does the enteric nervous system coordinate muscular, secretive and absorptive activities via (3)

A
  • sensory neurones
  • interneurones (coordinate reflexes and motor programs)
  • effector neurones (excitatory and inhibitory motor neurones)
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55
Q

what do effector neurones (excitatory and inhibitory motor neurones) of GI tract supply (4)

A
  • longitudinal and circular smooth muscle layers (for modifying motility)
  • secretory epithelium
  • endocrine cells (for varying secretion of GI hormones)
  • blood cells
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56
Q

extrinsic innervation of GI tract

A

-autonomic: parasympathetic and sympathetic

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57
Q

parasympathetic supply of GI tract (2)

A
  • via vagal nerves signalling to the dorsal vagal complex of medulla oblongata
  • pelvic nerves from the sacral region of spinal cord (S2-S4)
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58
Q

sympathetic supply of GI tract

A

-spinal nerves from the thoracolumbar region

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59
Q

in which ganglia do the preganglionic sympathetic nerves synapse before supplying GI tract (4)

A
  • superior cervical ganglion
  • celiac ganglion
  • superior mesenteric ganglion
  • inferior mesenteric ganglion
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60
Q

neurotransmitter of parasympathetic system supplying GI tract

A

-acetylcholine at synapse between preganglionic fibres and ganglion cells (in essence post ganglionic neurones) within the ENS

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61
Q

neurotransmitter of sympathetic system supplying GI tract

A
  • acetylcholine at synapse between preganglionic fibres and prevertebral ganglion
  • noradrenaline between postganglionic fibres and enteric structures/other structures
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62
Q

excitatory influences of parasympathetic nervous system on GI tract (3)

A
  • increased gastric (stomach), pancreatic and small intestinal secretion
  • increased blood flow
  • smooth muscle contraction
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63
Q

inhibitory influences of parasympathetic nervous system on GI tract (2)

A
  • relaxation of some sphincters

- receptive relaxation of stomach

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64
Q

inhibitory influences of sympathetic nervous system on GI tract (3)

A
  • decreased motility
  • decreased secretion
  • decreased blood flow
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65
Q

what has greater functional effect on GI tract: the parasympathetic or sympathetic nervous system

A

parasympathetic

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66
Q

nerve reflexes that occur due to receptor activation and modulate the motor and secretory function of the GI tract (3)

A
  • local reflex (intrinsic, all elements of reflex located within GI tract itself)
  • short reflex (extrinsic involves autonomic nervous system)
  • long reflex (extrinsic, known as long reflex as autonomic reflexes involve long pathways between the central nervous system and digestive system)
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67
Q

eg. of local reflex of GI tract

A

-peristalsis

68
Q

eg. of short reflex of GI tract

A

-eg. intestino-intestinal inhibitory reflex (local distension/enlargement activates sensory neurones exciting sympathetic preganglionic fibres that cause inhibition of muscle activity in adjacent areas)

69
Q

sensory receptors of the GI tract

A
  • mechanoreceptors (pressure receptors sensitive to stretch or tension within the wall)
  • chemoreceptors (sensitive to chemical components)
  • thermoreceptors
70
Q

eg. of long reflex of GI tract

A

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

71
Q

major patterns of motility in the GI tract (3)

A
  • peristalsis
  • segmentation
  • tonic contractions
72
Q

what is peristalsis

A

-wave of contraction that normally proceeds along the gut in aboral direction triggered by distension of gut wall

73
Q

what happens to the muscles at the propulsive segment of GI tract during peristalsis (2)

A
  • longitudinal muscles relax (due to release of neurotransmitters VIP/vasoactive intestinal peptide and NO/nitric oxide from inhibitory motoneurone)
  • circular muscle contracts (due to release of neurotransmitter acetylcholine and substance P/peptide neurotransmitter from excitatory motoneurone)
74
Q

what happens to the muscles at the receiving segment of GI tract during peristalsis (2)

A
  • longitudinal muscles contract (due to the release of Ach and substance P/peptide neurotransmitter from excitatory motoneuron)
  • circular muscle relaxes due to release of VIP/vasoactive intestinal peptide and NO/nitric oxide from inhibitory motoneurone)
75
Q

describe segmentation

A
  • mixing or churning movements

- rhythmic contractions of the circular muscle layer that mix and divide luminal contents

76
Q

where does segmentation occur (2)

A
  • in small intestine (in fed state)

- in large intestine

77
Q

what is haustration

A

segmentation in the large intestine

78
Q

what are tonic contractions

A

sustained contractions found in the sphincters of the GI tract

79
Q

what are the sphincters of GI tract composed of

A

specialised circular, generally smooth muscle

-skeletal = UES and external sphincter

80
Q

name the sphincters of the GI tract (6)

A
  • upper oesophageal sphincter (UES)
  • lower oesophageal sphincter (LOS)
  • pyloric sphincter
  • ileocecal valve
  • internal (smooth muscle) and external (skeletal muscle) sphincters
  • sphincter of oddi (where pancreatic contents enter the duodenum)
81
Q

function of GI sphincters (2)

A
  • act as one way valves by maintaining positive resting pressure
  • open and close due to stimuli/pressure proximal and distal to sphincter (opens due to +ve pressure above, closes due to +ve pressure below)
82
Q

function of upper oesophageal sphincter (UES) (2)

A
  • relaxes to allow swallowing

- closes during inspiration

83
Q

function of lower oesophageal sphincter (LOS) (2)

A
  • relaxes to permit entry of food to the stomach

- closes to prevent the reflux of gastric contents into the oesophagus

84
Q

function of pyloric sphincter (2)

A
  • regulates gastric emptying

- usually prevents duodenal gastric reflux

85
Q

function of ileocecal valve

A
  • regulates flow from ileum to colon
  • > distension of ileum closes valve
  • > distension of proximal colon closes valve
86
Q

what regulates the internal and external sphincters

A

the defecation reflex

87
Q

3 pairs of major salivary glands (3)

A
  • parotid
  • submandibular
  • sublingual
88
Q

where are minor salivary glands present (5)

A
  • lips
  • cheeks
  • palate
  • oropharynx
  • tongue
89
Q

type of salivary secretion from parotid gland

A

-serous/watery

90
Q

type of salivary secretion from submandibular gland

A

-mixed (mucous/serous)

91
Q

type of salivary secretion from sublingual gland

A

-mucous (thick viscous saliva with more mucoprotiens)

92
Q

what cells secrete saliva into the duct system

A

acinar cells

93
Q

how is primary saliva altered as it passes through duct

A
  • duct reabsorbs ions (sodium chloride)
  • potassium is secreted into saliva from duct and bicarbonate enters glands to help neutralise saliva and raise pH (to prevent decay)
94
Q

osmolarity of primary saliva

A

=isotonic (contains water and electrolytes, sodium and chloride)

95
Q

osmolarity of secondary/ final saliva entering the mouth

A

=hypotonic (contains some proteins, electrolytes, potassium and bicarbonate ions)

96
Q

function of resting secretion (3)

A

= very small amount of saliva at constant rate

-keeps mouth and oropharynx moist, lubricated and protected

97
Q

what neurotransmitters causes contraction of muscles of GI tract (2)

A
  • acetylcholine

- substance P/peptide

98
Q

what neurotransmitters causes relaxation of muscles of GI tract (2)

A
  • Nitric Oxide

- vasoactive intestinal peptide (VIP)

99
Q

how many times do you swallow per minute during resting salivary secretion

A

2/3

100
Q

what sensory receptors are activated during eating and stimulate secretion of saliva (5)

A
  • gustatory receptors (taste receptors on tongue)
  • mechanoreceptors (pressure/pushing/vibration)
  • olfactory receptors (sense of smell)
  • nociceptors (pain will trigger response)
  • higher centres in the brain trigger reflex activation of secretory pathways
101
Q

varying effect of stimulus on single gland secretions

A

-volume and composition varies depending on the type and duration of stimulus

102
Q

components of whole mouth saliva (3)

A
  • mixed secretions of all glands (variable volumes and contents)
  • debris
  • other oral fluids (e.g. gingival crevicular fluid)
103
Q

contributions to unstimulated whole saliva (4)

A
  • parotid = 20%
  • submandibular = 65%
  • sublingual = 7-8%
  • minor glands = 7-8%
104
Q

contributions to stimulated whole saliva (4)

A
  • parotid = 50%
  • submandibular = 30%
  • sublingual = 10%
  • minor glands = 10%
105
Q

average resting salivary flow rate

A

0.3 +/- 0.22ml per min

106
Q

average stimulated salivary flow rate

A

1.7 +/- 2.1 ml per min

107
Q

total daily salivary flow rate

A

between 500-700ml per day

108
Q

inorganic compounds of saliva and their functions (7)

A
  • sodium
  • potassium
  • chloride
  • fluoride (helps to reminilarise enamel)
  • calcium (enamel protection)
  • phosphate (enamel protection/calcium phosphate)
  • bicarbonate (buffer)
109
Q

organic compounds of saliva (9)

A
  • carb
  • blood group substances
  • glucose
  • lipids
  • cortisol
  • amino acids
  • urea
  • ammonia
  • proteins (all synthesised in the gland)
110
Q

functions of saliva (10)

A
  • protects tissues
  • enhances taste
  • lubricates food
  • speeds oral clearance of food
  • facilitates removal of carbohydrates
  • neutralises organic acids
  • inhibits demineralisation/enhances reminerilisation
  • recycles ingested fluoride to the mouth
  • discourages bacterial growth
  • proteins sustain enamel surface
111
Q

components of saliva involved in digestion (2)

A
  • amylase (hydrolyses starch to maltose/maltose triose)

- lipase (fat digestion)

112
Q

protein components of saliva with microbial characteristics (3)

A
  • lysosome
  • sialoperoxidase
  • lactoferrin
113
Q

function of stratherins (protein component of saliva) (2)

A
  • manage calcium

- also have microbial functions

114
Q

what is salivary secretion dependant upon

A

reflex activity (very little is spontaneous)

115
Q

salivary secretion stimuli (8)

A
  • gustatory
  • masticatory
  • olfactory
  • psychic (contributes very little to salivary secretion)
  • visual
  • thermoreceptive
  • possibly nociceptive
  • combinations of the above
116
Q

gustatory salivary reflex

A
  • stimuli delivered to gustatory receptors in taste buds

- basic tastes cause salivary secretion

117
Q

effect of one sided chewing on salivary secretion (2)

A
  • higher rate of secretion on side of chewing

- preferred side of chewing has larger parotid gland

118
Q

which salivary gland does the olfactory salivary reflex involve (2)

A

either:

  • parotid (true olfactory parotid gland reflex does not exist in humans)
  • submandibular gland
119
Q

function of the stomach (5)

A
  • starting point for digestion of proteins
  • mixes food with gastric secretions to produce chyme
  • limited amount of absorption
  • stores food before passing it into the small intestine as chyme for further digestion/absorption
  • secretes gastric juice from gastric pits in the gastric mucosa
120
Q

anatomy of stomach (3 components)

A
  • fundus
  • body
  • antrum
121
Q

sphincter between stomach and duodenum (SI)

A

pylorus

122
Q

defecation

A

the discharge of faeces from the body

123
Q

what is the funds (anatomy of stomach) (3)

A
  • thin smooth muscle layer next to oesophagus
  • receives food but little mixing
  • usually pocket of gas
124
Q

describe the body of the stomach (3)

A
  • thin smooth muscle of middle section
  • little mixing occurs
  • food stored here
125
Q

describe the antrum of the stomach (3)

A
  • thicker smooth muscle next to duodenum
  • highly contractile
  • much mixing occurs here
126
Q

what breaks down proteins in stomach (2)

A
  • pepsin

- HCl

127
Q

what is the most potent stimulus for the gustatory salivary reflex

A
  • SOUR/ACID stimulus is the most potent

- followed by salt then bitter and sweet

128
Q

what neurotransmitters stimulate contraction of the GI tract muscles (2)

A

-Ach
-substance P/peptide neurotransmitter
(from excitatory motoneuron)

129
Q

what neurotransmitters stimulate relaxation of the GI tract muscles (2)

A

-VIP/vasoactive intestinal peptide
-NO/nitric oxide
(from inhibitory motoneuron)

130
Q

what determines whether chyme escapes through the pyloric sphincter

A

the strength of antral wave

131
Q

what factors determine the strength of the antral wave (2)

A
  • gastric

- duodenal

132
Q

gastric factors that determine the strength of the antral wave (2)

A
  • rate of emptying is proportional to the vol. of chyme in the stomach
  • consistency of chyme
133
Q

how does an increase in the vol of chyme in stomach/distension increase motility (4)

A
  • stretch of smooth muscle
  • stimulation of intrinsic nerve plexuses
  • increased vagal nerve activity
  • gastrin increases
134
Q

what is gastrin

A
  • hormone which stimulates secretion of gastric juice

- secreted into the bloodstream by the stomach wall in response to the presence of food

135
Q

which consistency of chyme favours stomach emptying

A

finely divided, thick liquid chyme

136
Q

gastric factors that can decrease strength of antral wave/delay gastric emptying

A
  • neuronal response

- hormonal response

137
Q

which neuronal reflex decreases antral peristaltic activity/gastric emptying

A

-enterogastric reflex through signals from intrinsic nerve plexuses and autonomic nervous system

138
Q

which hormone released from the duodenum inhibits stomach contraction?

A

-enterogastrones (eg.secretin and cholecystokinin CCK)

139
Q

which stimuli within duodenum drives the neuronal and hormonal response which delay stomach emptying (4)

A
  • fat
  • acid
  • hypertonicity
  • distension
140
Q

why does the presence of fat cause/require a delay in gastric emptying

A

for digestion and absorption in the small intestine

141
Q

why does the presence of acid cause/require a delay in gastric emptying

A

for neutralisation (by bicarbonate secreted from the pancreas)

142
Q

why does hypertonicity cause delay in gastric emptying

A
  • products of carb and protein digestion draw water into small intestine
  • danger of reduced plasma vol and circulatory disturbances
143
Q

secretions from the gastric glands of oxyntic mucosa (5)

A
  • HCl
  • pepsinogen
  • intrinsic factor
  • histamine
  • mucus
144
Q

function of HCl secreted in stomach (3)

A
  • activates pepsinogen to pepsin
  • denatures protein
  • kills most micro-organisms ingested with food
145
Q

what is pepsinogen secreted in stomach

A
  • inactive precursor of the peptidase, pepsin

- pepsin once formed activates pepsinogen

146
Q

function of intrinsic factor secreted in stomach

A

binds vitamin B12 allowing absorption in terminal ileum

147
Q

function of mucus secreted in stomach

A

protection

148
Q

what hormone stimulates HCl secretion in stomach

A

gastrin

149
Q

what hormone inhibits HCl secretion in the stomach

A

somatostatin

150
Q

gastric secretions in the pyloric gland area (3)

A
  • gastrin
  • somatostatin
  • mucus
151
Q

what cells secrete somatostatin

A

D cells present in the pyloric gland area (PGA)

152
Q

what cells secrete gastrin

A

G cells present in the pyloric gland area (PGA)

153
Q

what cells secrete pepsinogen

A

chief cells present in gastric glands of the oxyntic mucosa

154
Q

what is secreted from parietal cells present in gastric glands of the oxyntic mucosa (2)

A
  • HCl

- intrinsic factor

155
Q

what are the 2 diff gastric glands and where are they (2)

A
  • glands in the pyloric gland area (PGA) at area of antrum

- gastric glands of oxyntic mucosa (OM) at area of fundus and body

156
Q

describes the steps involved in HCl secretion from gastric parietal cell (present in gastric glands of oxyntic mucosa) (8)

A
  • CO2 + H2O -> H2CO3 (CA)
  • H2CO3 -> (H+) + (HCO3-)
  • HCO3- exits via Cl-/HCO3- antiporter
  • Cl- builds up in cell and eventually leaves
  • H+ exits via H+/K+ ATPase
  • (H+) + (Cl-) -> HCl
  • H+ exchanges for K+
  • K+ returns to lumen (K+ channel) or to interstitial fluid (Na+/K+ ATPase)
157
Q

3 molecules that stimulate HCl secretion from parietal cell (and where they come from)

A
  • ACh (enteric neurones)
  • gastrin (G cells in PGA)
  • histamine (ECL cells)
158
Q

how does gastrin cause an increase in HCl secretion from parietal cell

A

stimulates histamine release from ECL cells

159
Q

hormone that inhibits HCl secretion from parietal cell

A

somatostatin (from D cells in PGA)

160
Q

where is HCl secreted in stomach

A

into canaliculi (deep invaginations of plasma membrane) of the oxyntic mucosa

161
Q

effect of secretagogues (substances which promote secretion) on H+/K+ ATPase in gastric parietal cells

A
  • in parietal resting state = within cytoplasmic tubulovesicles
  • parietal stimulated state = traffics to apical membrane into extended microvilli
162
Q

phases of gastric secretion (3)

A
  • cephalic (in head phase, prepares stomach for food)
  • gastric (when food is in stomach)
  • intestinal (after food has left stomach)
163
Q

stimuli of cephalic phase of gastric secretion (6)

A
  • sight
  • smell
  • taste
  • conditioned reflexes
  • chewing
  • swallowing
164
Q

what happens in cephalic phase of gastric secretion (5)

A
  • activation of enteric neurons (via parasympathetic preganglionic neurons traveling in the vagus nerve)
  • > release of ACh
  • > activation of ECL cell to release histamine
  • > activation of G cell to release gastrin which stimulates ECL cell to release histamine
  • > activation of D cell to release ss to inhibit G cell releasing gastrin
165
Q

factors that stimulate gastric secretion in the gastric phase (3)

A
  • distension (via mechanoreceptors)
  • protein digested products stimulate G cells to release gastrin
  • food acts as buffer raising pH, somatostatin no longer needed
166
Q

factors that reduce gastric secretion in intestinal phase (3)

A
  • SI factors switch off secretion
  • factors that reduce gastric motility reduce secretion
  • secretion of somatostatin (low pH during meals)

semester 2 (9 decks)

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