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Gastrointestinal Block > GI Physiology > Flashcards

GI Physiology Flashcards

1
Q

what does oral mean in terms of movement?

A

towards the mouth

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2
Q

what does aboral mean in terms of movement?

A

away from the mouth

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3
Q

what some functions of the mouth and oropharynx? (4)

A

chops food
lubricates food
starts carbohydrate digestion
propels food towards the oesophagus

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4
Q

what enzyme is in saliva that digests carbohydrate?

A

amylase

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5
Q

what is the function of the oesophagus?

A

to propel food towards the stomach

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6
Q

what some functions of the stomach? (5)

A

churn food
store food before delivery into the intestines
regulate the delivery of chyme to the duodenum
continues carbohydrate digestion
starts protein digestion

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7
Q

what enzyme is involved in protein digestion?

A

pepsin

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8
Q

what is chyme?

A

semi-digested material

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9
Q

name the 3 parts of the small intestine

A

duodenum
jejunum
ileum

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10
Q

what are some of the functions of the small intestine? (2)

A

continued digestion by enzymes released from the pancreas

absorption of nutrients

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11
Q

what makes up the large intestine? (3)

A

caecum
appendix
colon (ascending, transverse, descending, sigmoid)

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12
Q

what are some of the functions of the colon? (2)

A

reabsorption of fluid and electrolytes

stores faecal matter before delivery to the rectum

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13
Q

what is the function of the rectum and anus?

A

regulate expulsion of faeces

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14
Q

how are the accessory structures of the alimentary canal attached to it?

A

by ducts

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15
Q

name the accessory structures of the alimentary canal (4)

A

salivary glands
pancreas
liver
gall bladder

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16
Q

what are the 4 major functions of the alimentary canal?

A

motility
secretion
digestion
absorption

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17
Q

motility is the _____ activity of the GI tract

A

mechanical

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18
Q

the motility of the GI tract mostly involves ______ muscle

A

smooth

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19
Q

where is motility controlled by skeletal muscle? (4)

A

mouth
pharynx
upper oesophagus
external anal sphincter

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20
Q

what are secretions produced in response to? (3)

A

food
hormonal signals
neural signals

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21
Q

what are the functions of GI tract secretions?

A

digestion
protection
lubrication

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22
Q

what are the 2 types of digestion?

A

chemical

physical

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23
Q

what is chemical digestion?

A

the breakdown of foodstuffs (at a molecular level) into smaller absorbable units by enzymatic hydrolysis

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24
Q

what is physical digestion?

A

the breakdown of foodstuffs into physically smaller (increasing the S.A. for enzymes to interact)

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25
Q

what does absorption involve?

A

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

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26
Q

what 2 mechanism can absorption occur by?

A

transport mechanisms

diffusion

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27
Q

motility involves the contraction of all _ muscle layers

A

3

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28
Q

circular muscle contraction makes the lumen ____ and ____.

A

narrower

longer

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29
Q

longitudinal muscle contraction makes the intestine ____ and _____

A

shorter and fatter

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30
Q

contraction of muscularis mucosae changes the ____ of the mucosa helping ______ and ______ it also causes _____ of GI contents

A

shape
absorption
secretion
mixing movements

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31
Q

____ waves cause rhythmical contraction of the GI tract

A

slow

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32
Q

what does the slow wave electrical activity determine about the rhythmical contractions of the GI tract? (3)

A

frequency
direction
velocity

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33
Q

what are the interstitial cells of cajal (ICCs)?

A

pacemaker cells that generate and propagate the slow wave

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34
Q

where are ICCs usually found within the GI tract?

A

between circular and longitudinal muscle layers

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35
Q

how are the ICCs attached to each other and smooth muscle cells and what does this enable?

A

they are attached via gap junctions which enables electrical coupling (a current injected into either coupled cell changes the membrane potential of both)

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36
Q

the steps of smooth muscle contraction:

  1. slow waves in the ___
  2. slow waves spread from the ___ to _______
  3. the depolarisation causes ______ entry
  4. smooth muscle _____
A 
ICCs
ICCs
smooth muscle cells
calcium ion
contracts
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37
Q

do all depolarising slow waves result in smooth muscle contraction?

A

no

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38
Q

when does depolarisation result in smooth muscle contraction?

A

when the slow wave depolarisation reaches a threshold triggering calcium entry into the smooth muscle cell

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39
Q

only slow waves that go above threshold cause contraction (true/false)?

A

true

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40
Q

what determines the force of muscle contraction? (2)

A

number of APs discharged

duration of the slow wave that is above threshold

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41
Q

what 3 things control whether the slow wave amplitude reaches threshold?

A

neuronal stimuli
hormonal stimuli
mechanical stimuli

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42
Q

_______ innervation of the GI tract is more important than _____ innervation

A

parasympathetic

sympathetic

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43
Q

what is the parasympathetic outflow to the GI tract? (2)

A 
vagal nerves
spinal nerves (S2-S4)
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44
Q

parasympathetic postganglionic neurones innervating the GI tract are part of the _____ nervous system

A

enteric

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45
Q

what excitatory influences does the parasympathetic innervation have on the GI tract? (5)

A 
increased gastric (stomach) secretion
increased pancreatic secretion
increased intestinal secretion 
increased blood flow
increased smooth muscle contraction
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46
Q

what is the division of the autonomic nervous system that govern the functions of the GI tract?

A

enteric

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47
Q

the enteric nervous system is intrinsic/extrinsic

A

intrinsic (built into GI tract)

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48
Q

what other things also exert regulatory influence on the GI tract? (2)

A

hormones

extrinsic (from the sympathetic and parasympathetic divisions of the ANS)

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49
Q

what does the enteric nervous system co-ordinate? (3)

A

muscular, secretive and absorptive activities of the GI tract

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50
Q

what are the 2 major nerve centres in the enteric nervous system?

A

myenteric plexus

submucous plexus

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51
Q

_____ plexus is the major nerve supply to the GI tract

A

myenteric

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52
Q

what is the myenteric plexus?

A

a chain of interconnected neurones that extends throughout the GI tract

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53
Q

what 2 things does the myenteric plexus mainly regulate?

A

motility

sphincters

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54
Q

where is the myenteric plexus located?

A

between the circular muscle layer and the longitudinal muscle layer

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55
Q

where is the submucous plexus located?

A

in the submucosal tissue

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56
Q

what does the submucous plexus mainly regulate?

A 
secretion
blood vessels (absorption)
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57
Q

what type of neurons are the majority of the neurons in the enteric nervous system and what do they do?

A

interneurons

co-ordinate reflexes

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58
Q

what are the 3 type of sensory neurons in the enteric nervous system?

A

mechanoreceptors
chemoreceptors
thermoreceptors

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59
Q

what do effector neurones effect? (4)

A

smooth muscle layers
secretory epithelium
endocrine cells
blood vessels

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60
Q

what are the 5 main motility patterns of the GI tract?

A 
peristalsis
segmentation
colonic mass movement
migrating motor complex (MMC)
tonic contraction
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61
Q

peristalsis is a series of ______ muscle contractions that moves food in an ____ directoin

A

wave-like

aboral

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62
Q

what triggers peristalsis?

A

a bolus that causes distension of the wall of the GI tract resulting in activation of sensory neurons

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63
Q

activation of sensory neurons results in altered activity of what kind of neurons?

A

interneurons

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64
Q

motor neurons bring about the ____ change of peristalsis

A

muscular

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65
Q

what 2 segments are created in peristalsis?

A 
propulsive segment (contraction behind the bolus)
receiving segment (relaxation in front of the bolus)
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66
Q

what muscle contracts in the propulsive segment and what effect does its contraction have?

A

inner circular muscle contracts

causes constriction behind the bolus pushing it along

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67
Q

what muscle contracts in the receiving segment and what effect does its contraction have?

A

outer longitudinal muscle contracts

shortens the area of the GI tract immediately in front of the bolus

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68
Q

segmentation is the _____ contraction of _____ muscle layer that ____ and _____ luminal contents resulting in _____/_____ movements

A 
rhythmic
circular
mixes
divides
mixing/churning
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69
Q

what happens to the intestine during segmentation?

A

it is divided into little pockets and the chyme is propelled back and forwards with no overall movement

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70
Q

in segmentation there is no overall movement of chyme through the GI tract, what is the benefit of this?

A

allows time for digestion and absorption

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71
Q

segmentation is the term used to describe certain movements in the small intestine what is the equivalent term for the large intestine?

A

haustration

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72
Q

what is colonic mass movement?

A

a powerful sweeping contraction that forces faeces into the rectum

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73
Q

what are tonic contractions?

A

sustained contractions

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74
Q

tonic contractions generate ____ gradients

A

pressure

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75
Q

what level of pressure do tonic contractions cause in GI organs with a storage function (e.g. stomach)?

A

low

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76
Q

how do most of the neurones of the enteric nervous system live?

A

in ganglia

a group of neurons living outwith the CNS

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77
Q

what is energy homeostasis?

A

the physiological process of matching energy intake to energy expenditure

78
Q

what is satiation?

A

the sensation of fullness generated during a meal

79
Q

what is satiety?

A

the feeling of fullness after a meal

80
Q

what are the two hormones that report fat status to the brain (adiposity signals)?

A

insulin

leptin

81
Q

the ____ causes the stomach to relax receptively to accommodate food from the oesophagus

A

vagus

82
Q

what starts protein digestion? (2)

A

pepsin

HCl

83
Q

what portion of the stomach mixes gastric secretions with stomach content?

A

propulsion/grinding

remember the different ways the stomach is split up based on the different functions

84
Q

what is food mixed with to produce chyme?

A

gastric secretions

85
Q

what two sections in the stomach split into for mechanical activity?

A

orad (fundus and proximal body)

caudad (distal body and pylorus)

86
Q

the orad/caudad stomach has strong muscular contractions in mechanical activity?

A

caudad

87
Q

which section of the stomach in mechanical activity has phasic contraction and which has tonic contractions?

A 
tonic = orad
phasic = caudad
88
Q

what contraction causes the chyme to be pushed towards the pylorus?

A

the antral wave which is peristaltic contraction of the midstomach (in the caudad stomach)

89
Q

what is retropulsion?

A

when the chyme that doesn’t make it through the pyloric sphincter bangs off it and travels back into the stomach for further mixing

90
Q

what determines how much chyme gets through the pyloric sphincter?

A

the strength of antral wave

91
Q

what determines the rate that the stomach empties?

A

the rate at which chyme travels through the pyloric sphincter

92
Q

what 2 factors govern the the emptying of the stomach?

A

gastric factors

duodenal factors

93
Q

what are the gastric factors that determine stomach emptying? (2)

A

volume of chyme (distension increases motility)

consistency of chyme

94
Q

what are the duodenal factors that determine stomach emptying? (3)

A

the duodenum has to be ready to receive chyme
the delivery of chyme has to match the ability of the small intestine to digest and absorb
stimuli which drive neuronal and hormonal responses in the duodenum

95
Q

what is the enterogastric reflex?

A

a reflex that means the stretching of the duodenual wall results in the inhibition of gastric motility and reduces stomach emptying (the neuronal response involved in stomach emptying control)

96
Q

what does the release of enterogastrones have in gastric emptying?

A

they are released from the duodenum and inhibit stomach contraction (the hormonal response involved in stomach emptying control)

97
Q

____ acid is produced in the parietal cells and 2 things are produced what are they?

A

carbonic acid

H+ and bicarbonate are produced from carbonic acid

98
Q

in the parietal cells ______ is pumped out and _____ is pumped into the canaliculus

A

bicarbonate

chlorine

99
Q

___ and ___ are pumped into the canaliculs of the partietal cells to make ______ acid

A

H+
Cl-
hydrochloric acid

100
Q

what is a secretagogue?

A

an agent that causes secretion

101
Q

what are the 3 secretagogues that induce acid secretion from parietal cells?

A

ACh
Gastrin
Histamine

102
Q

ACh is a secretagogue that works on the _____ receptors of the parietal cells

A

muscarinic

103
Q

Gastrin is a secretagogue that works on ____ receptors of the parietal cells

A

gastrin

104
Q

histamine is a secretogogue that works on _____ receptors of the parietal cells

A

histamine

105
Q

what 2 things reduce the effect of all the secretagogues and inhibit HCl secretion?

A

prostaglandins

somatostatin

106
Q

what are the 4 functions of the colon?

A

absorption
secretion
storage (of faeces)
elimination of faeces

107
Q

what does the colon absorb and why? (4)

A

Na+, Cl- and H2O to condense ileocaecal matter into stool

short chain fatty acids (which are produces as a result of fermentation of carbohydrate that hasn’t been absorbed by the small intestine)

108
Q

what are coloncytes and what do they do?

A

surface epithelium of the colon

mediate electrolyte absorption

109
Q

what 3 things does the colon secrete?

A

K+, bicarbonate and mucus

110
Q

what do crypt cells int the colon mediate?

A

ion secretion

111
Q

goblets cells in the colon secrete mucus containing? (2)

A 
glycoaminoglycans (from a gel)
trefoil proteins (which have a protective function)
112
Q

what hormone enhances Na+ absorption and K+ secretion from the colon?

A

aldosterone

113
Q

what are the 3 patterns of motility in the colon?

A 
haustration
Mass movements (peristaltic propulsive movements/mass movements)
defaecation reflex
114
Q

what are haustra?

A

saccules created by the alternating contraction of tendinae coli

115
Q

what is the purpose of haustration?

A

to slow down transit of material in the colon allowing time for fluid and electrolyte reabsorption

116
Q

what are mass movements?

A

powerful contraction (caused by simultaneous contraction of large sections of circular muscle) that forces faeces into the rectum

117
Q

where does mass movements often occur?

A

in the ascending and transverse colon

118
Q

what triggers mass movements?

A

gastrocolic reflex

119
Q

what triggers the defaecation reflex?

A

the distension of the rectum wall

120
Q

as well as relaxation of the external anal sphincter what else is required for defaecation to take place?

A

a build-up of abdominal pressure

121
Q

what are some of the functions of colonic flora? (5)

A 
increase intestinal immunity
promote motility
maintenance of mucosal integrity
synthesis of vitamin K and free fatty acids
activation of some drugs
122
Q

where do intestinal gases come from? (3)

A
  • swallowed air
  • undigested carbohydrate which is digested by bacteria with gas being produced
  • fermentation action of the colon
123
Q

where solutes go ____ follows

A

water

124
Q

what are the 5 ways in which solutes are absorbed that lead to water absorption?

A

Na+/glucose co-transport
Na+/amino acid co-transport
Na+/H+ exchange
Parallel Na+/H+ and Cl-/HCO3- exchangeEpithelial Na+ channels (ENaC)

125
Q

what stimulates Na+/H+ exchange?

A

presence of bicarbonate

126
Q

what hormone stimulates increased epithelial Na+ channels?

A

aldosterone

127
Q

does Cl- secretion or absorption lead to diarrhoea?

A

secretion (usually Cl- absorption outweighs Cl- secretion)

128
Q

activation of what chlorine channel resulting in an increased Cl- secretion leading to diarrhoea?

A

CFTR (cystic fibrosis transmembrane conductance regulator)

129
Q

what do the chief cells in the gastric mucosa produce?

A

pespinogen (inactivated form of pepsin)

130
Q

what do the enterochromaffin-like cells in the gastric mucosa produce?

A

histamine (which stimulates HCl production)

131
Q

what 3 things do the parietal cells of the gastric mucosa produce and what are their functions?

A
  1. HCl (activates pepsinogen to pepsin)
  2. intrinsic factor (for vitamin B12 absorption)
  3. gastroferrin (for iron absorption)
132
Q

what do G cells produce?

A

gastrin

133
Q

what does gastrin do?

A

stimulates HCl secretion

134
Q

what do D cells produce/

A

somatostatin

135
Q

during the cephalic (1st) phase of gastric acid secretion before food enters the stomach what does the vagus nerve stimulate? (4)

A
  1. neurotransmitter action (release of ACh to activate parietal cells)
  2. endocrine action (release of gastrin from G cells to stimulate HCl production)
  3. paracrine action (release of histamine from ECL to activate parietal cells)
  4. inhibits D cells so they don’t produce somatostatin
136
Q

distension of the stomach is detected via ______ and results in _______

A

mechanoreceptors

increased acid secretion

137
Q

vagus nerve activity _____ upon cessation of eating and after stomach emptying

A

decreases

138
Q

when pH falls as food exits the stomach D cells are _____ so ______ is released leading to a decrease in gastric secretion

A

no longer inhibited

somatostatin =

139
Q

what does mucus in the stomach prevent?

A

acid reaching the stomach cells

140
Q

what happens in the mucus/gel layer in the stomach is not maintained?

A

peptic ulcers will form

141
Q

what is secreted into the mucus layer of the stomach to keep it buffered?

A

bicarbonate

142
Q

what are the 3 functions of prostaglandins?

A

reduce acid secretion
increase mucus and bicarbonate flow
increase mucosal flow

143
Q

what is the gastroileal reflex?

A

peristalsis in the iluem and the opening of the ileocecal valve

144
Q

what stimulates the gastroileal reflex? (2)

A

gastrin and CCK

145
Q

what is the function of the migrating motor complex in the small intestine and what is it?

A

it is a strong peristaltic contraction which passes the length of the small intestine to clean out undigested residues from the small intestine into the large intestine

146
Q

what triggers the migrating motor complex in the small intestine/

A

motilin

147
Q

what are enteroendocrine cells?

A

cells within the gut that secrete hormones

148
Q

migrating motor complex occurs in which state?

A

fasting

149
Q

what suppresses the migrating motor complex? (2)

A

gastrin and CCK

150
Q

what 5 things enhance secretion of intestinal juices/

A 
distension
irritation
gastrin
CCK
Secretin
parasympathetic nerve activity
151
Q

what decreases the secretion of intestinal juices?

A

sympathetic nerve activity

152
Q

what is contained within the intestinal juices/

A

mucus
aqueous salt for enzymatic digestion (from the crypts of liberkuhn)
does not contain digestive enzymes

153
Q

where are pancreatic enzymes stored and what are they released in response to?

A 
zymogen granules (found in acinar cells)
elevated Ca2+
154
Q

what is contained within pancreatic juice?

A

digestive enzymes

sodium bicarbonate

155
Q

what are the functions of pancreatic juice? (2)

A

neutralises the acidic chyme entering the duodenum and protects the stomach from acid

supplies enzymes for digestion

156
Q

what are the pancreatic enzymes? (3)

A

Proteases = trypsinogen (which is inactive but is then activated and activates other inactive proteases)
pancreatic amylase
pancreatic lipase

157
Q

what are the 2 ways in which digestion is accomplished in the small intestine?

A

luminal digestion

membrane digestion

158
Q

what enzymes mediate luminal digestion?

A

pancreatic enzymes

159
Q

what enzymes mediate membrane digestion?

A

enzymes situated at the brush border of epithelial cells

160
Q

what is sucrose digested into and by which enzyme?

A

fructose and glucose

sucrase

161
Q

what are carbohydrates broken into before they are able to be absorbed?

A

monosaccharides

162
Q

what are carbohydrates broken down into before they can be broken down into monosaccharides?

A

oligosaccharides

163
Q

what is a protease?

A

an enzyme which breaks down proteins and peptides

164
Q

what is a peptidase?

A

an enzymes which break down peptides into amino acids

165
Q

what does HCl do that aids digestion?

A

starts to denature proteins making it easier for pepsin to digest them

166
Q

what are the potential 3 products of carbohydrate digestion?

A

glucose
galactose
fructose
(all of which can be absorbed)

167
Q

how are glucose and galactose absorbed into enterocytes?

A

SGLT1 (sodium glucose co-transporter)

168
Q

how is fructose absorbed into enterocytes?

A

GLUT5

169
Q

how do glucose, galactose and fructose exit enterocytes?

A

GLUT2

170
Q

amino acid absorption is either Na+dependent or Na+-independent (true/false)

A

true

171
Q

how do amino acids exit enterocytes?

A

Na+-independent transporters

172
Q

how are olgiopeptides absorbed into enterocytes?

A

H+/oligopeptide co-transporter (PepT1)

173
Q

what do fats have to be converted into to be digested/

A

an emulsion

174
Q

bile salts are involved in the ______ of fats

A

emulsification

175
Q

what happens as a result of bile salts not being secreted?

A 
lipid malabsorption (causing steratorrhoea)
secondary vitamin deficiency due to failure to absorb fat-soluble vitamins
176
Q

bile salts increase the surface area of the fat that can be attacked by pancreatic lipase but physically blocks the access for the enzyme. What solves this problem?

A

colipase

177
Q

what is made by the pancreas and helps the body digest fat?

A

lipases

178
Q

what transports the products of fat digestion to enterocytes?

A

mixed micelles

179
Q

what is transferred between mixed micelles and the apical membrane of enterocytes?

A

the products of fat digestion (free fatty acids and monoglycerides)

180
Q

how do long chain fatty acids reach the bloodstream?

A

incorporated into chylomicrons

181
Q

what is the name of the protein that is mainly responsible for cholesterol absorption?

A

niemann-pick-C1-like 1 protein

182
Q

what 2 molecules are key in calcium absorption?

A

calcitirol

calicium calbindin D

183
Q

what form of iron is absorbable?

A

ferrous

184
Q

how is the unabsorbable form of iron (ferric form) converted into the absorbable form of iron (ferrous)? (2)

A

HCl

Vitamin C

185
Q

fat-soluble vitamins (A, D, E, K) are incorporated into _____ and transported into _____ they are then incorporated into _____/____-and distributed by intestinal ______

A

mixed micelles
enterocytes
chylomicrons/VLDLs
lymphatics

186
Q

______ is essential for vitamin B12 absorption

A

intrinsic factor

187
Q

what are the cytochrome p450 family of mono-oxygenases?

A

a large family of enzymes in the liver that participate in drug metabolism mediating phase 1 oxidation reactions of drugs

188
Q

what produces bile?

A

hepatocytes

cholangiocytes

189
Q

what does bile do?

A

participates in the digestion and absorption of fats and the excretion of products of metabolism

190
Q

what is the fate of bile during meals?

A

it is stored and concentrated in the gallbladder

191
Q

what is enterohepatic recycling?

A

when bile salts are reabsorbed by enterocytes and transported back to the liver (only some of the bile salts are lost in the faeces and most are reabsorbed)

192
Q

what do bile acid sequestrants do/

A

the bind to components of bile in the GI tract preventing their reabsorption

Gastrointestinal Block (8 decks)

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