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GI Physiology Flashcards

(192 cards)

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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
what does absorption involve?
the transfer of the absorbable products of digestion from the digestive tract into the blood or lymph
26
what 2 mechanism can absorption occur by?
transport mechanisms | diffusion
27
motility involves the contraction of all _ muscle layers
3
28
circular muscle contraction makes the lumen ____ and ____.
narrower | longer
29
longitudinal muscle contraction makes the intestine ____ and _____
shorter and fatter
30
contraction of muscularis mucosae changes the ____ of the mucosa helping ______ and ______ it also causes _____ of GI contents
shape absorption secretion mixing movements
31
____ waves cause rhythmical contraction of the GI tract
slow
32
what does the slow wave electrical activity determine about the rhythmical contractions of the GI tract? (3)
frequency direction velocity
33
what are the interstitial cells of cajal (ICCs)?
pacemaker cells that generate and propagate the slow wave
34
where are ICCs usually found within the GI tract?
between circular and longitudinal muscle layers
35
how are the ICCs attached to each other and smooth muscle cells and what does this enable?
they are attached via gap junctions which enables electrical coupling (a current injected into either coupled cell changes the membrane potential of both)
36
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 _____
``` ICCs ICCs smooth muscle cells calcium ion contracts ```
37
do all depolarising slow waves result in smooth muscle contraction?
no
38
when does depolarisation result in smooth muscle contraction?
when the slow wave depolarisation reaches a threshold triggering calcium entry into the smooth muscle cell
39
only slow waves that go above threshold cause contraction (true/false)?
true
40
what determines the force of muscle contraction? (2)
number of APs discharged | duration of the slow wave that is above threshold
41
what 3 things control whether the slow wave amplitude reaches threshold?
neuronal stimuli hormonal stimuli mechanical stimuli
42
_______ innervation of the GI tract is more important than _____ innervation
parasympathetic | sympathetic
43
what is the parasympathetic outflow to the GI tract? (2)
``` vagal nerves spinal nerves (S2-S4) ```
44
parasympathetic postganglionic neurones innervating the GI tract are part of the _____ nervous system
enteric
45
what excitatory influences does the parasympathetic innervation have on the GI tract? (5)
``` increased gastric (stomach) secretion increased pancreatic secretion increased intestinal secretion increased blood flow increased smooth muscle contraction ```
46
what is the division of the autonomic nervous system that govern the functions of the GI tract?
enteric
47
the enteric nervous system is intrinsic/extrinsic
intrinsic (built into GI tract)
48
what other things also exert regulatory influence on the GI tract? (2)
hormones | extrinsic (from the sympathetic and parasympathetic divisions of the ANS)
49
what does the enteric nervous system co-ordinate? (3)
muscular, secretive and absorptive activities of the GI tract
50
what are the 2 major nerve centres in the enteric nervous system?
myenteric plexus | submucous plexus
51
_____ plexus is the major nerve supply to the GI tract
myenteric
52
what is the myenteric plexus?
a chain of interconnected neurones that extends throughout the GI tract
53
what 2 things does the myenteric plexus mainly regulate?
motility | sphincters
54
where is the myenteric plexus located?
between the circular muscle layer and the longitudinal muscle layer
55
where is the submucous plexus located?
in the submucosal tissue
56
what does the submucous plexus mainly regulate?
``` secretion blood vessels (absorption) ```
57
what type of neurons are the majority of the neurons in the enteric nervous system and what do they do?
interneurons | co-ordinate reflexes
58
what are the 3 type of sensory neurons in the enteric nervous system?
mechanoreceptors chemoreceptors thermoreceptors
59
what do effector neurones effect? (4)
smooth muscle layers secretory epithelium endocrine cells blood vessels
60
what are the 5 main motility patterns of the GI tract?
``` peristalsis segmentation colonic mass movement migrating motor complex (MMC) tonic contraction ```
61
peristalsis is a series of ______ muscle contractions that moves food in an ____ directoin
wave-like | aboral
62
what triggers peristalsis?
a bolus that causes distension of the wall of the GI tract resulting in activation of sensory neurons
63
activation of sensory neurons results in altered activity of what kind of neurons?
interneurons
64
motor neurons bring about the ____ change of peristalsis
muscular
65
what 2 segments are created in peristalsis?
``` propulsive segment (contraction behind the bolus) receiving segment (relaxation in front of the bolus) ```
66
what muscle contracts in the propulsive segment and what effect does its contraction have?
inner circular muscle contracts | causes constriction behind the bolus pushing it along
67
what muscle contracts in the receiving segment and what effect does its contraction have?
outer longitudinal muscle contracts | shortens the area of the GI tract immediately in front of the bolus
68
segmentation is the _____ contraction of _____ muscle layer that ____ and _____ luminal contents resulting in _____/_____ movements
``` rhythmic circular mixes divides mixing/churning ```
69
what happens to the intestine during segmentation?
it is divided into little pockets and the chyme is propelled back and forwards with no overall movement
70
in segmentation there is no overall movement of chyme through the GI tract, what is the benefit of this?
allows time for digestion and absorption
71
segmentation is the term used to describe certain movements in the small intestine what is the equivalent term for the large intestine?
haustration
72
what is colonic mass movement?
a powerful sweeping contraction that forces faeces into the rectum
73
what are tonic contractions?
sustained contractions
74
tonic contractions generate ____ gradients
pressure
75
what level of pressure do tonic contractions cause in GI organs with a storage function (e.g. stomach)?
low
76
how do most of the neurones of the enteric nervous system live?
in ganglia | a group of neurons living outwith the CNS
77
what is energy homeostasis?
the physiological process of matching energy intake to energy expenditure
78
what is satiation?
the sensation of fullness generated during a meal
79
what is satiety?
the feeling of fullness after a meal
80
what are the two hormones that report fat status to the brain (adiposity signals)?
insulin | leptin
81
the ____ causes the stomach to relax receptively to accommodate food from the oesophagus
vagus
82
what starts protein digestion? (2)
pepsin | HCl
83
what portion of the stomach mixes gastric secretions with stomach content?
propulsion/grinding | remember the different ways the stomach is split up based on the different functions
84
what is food mixed with to produce chyme?
gastric secretions
85
what two sections in the stomach split into for mechanical activity?
orad (fundus and proximal body) | caudad (distal body and pylorus)
86
the orad/caudad stomach has strong muscular contractions in mechanical activity?
caudad
87
which section of the stomach in mechanical activity has phasic contraction and which has tonic contractions?
``` tonic = orad phasic = caudad ```
88
what contraction causes the chyme to be pushed towards the pylorus?
the antral wave which is peristaltic contraction of the midstomach (in the caudad stomach)
89
what is retropulsion?
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
what determines how much chyme gets through the pyloric sphincter?
the strength of antral wave
91
what determines the rate that the stomach empties?
the rate at which chyme travels through the pyloric sphincter
92
what 2 factors govern the the emptying of the stomach?
gastric factors | duodenal factors
93
what are the gastric factors that determine stomach emptying? (2)
volume of chyme (distension increases motility) | consistency of chyme
94
what are the duodenal factors that determine stomach emptying? (3)
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
what is the enterogastric reflex?
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
what does the release of enterogastrones have in gastric emptying?
they are released from the duodenum and inhibit stomach contraction (the hormonal response involved in stomach emptying control)
97
____ acid is produced in the parietal cells and 2 things are produced what are they?
carbonic acid | H+ and bicarbonate are produced from carbonic acid
98
in the parietal cells ______ is pumped out and _____ is pumped into the canaliculus
bicarbonate | chlorine
99
___ and ___ are pumped into the canaliculs of the partietal cells to make ______ acid
H+ Cl- hydrochloric acid
100
what is a secretagogue?
an agent that causes secretion
101
what are the 3 secretagogues that induce acid secretion from parietal cells?
ACh Gastrin Histamine
102
ACh is a secretagogue that works on the _____ receptors of the parietal cells
muscarinic
103
Gastrin is a secretagogue that works on ____ receptors of the parietal cells
gastrin
104
histamine is a secretogogue that works on _____ receptors of the parietal cells
histamine
105
what 2 things reduce the effect of all the secretagogues and inhibit HCl secretion?
prostaglandins | somatostatin
106
what are the 4 functions of the colon?
absorption secretion storage (of faeces) elimination of faeces
107
what does the colon absorb and why? (4)
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
what are coloncytes and what do they do?
surface epithelium of the colon mediate electrolyte absorption
109
what 3 things does the colon secrete?
K+, bicarbonate and mucus
110
what do crypt cells int the colon mediate?
ion secretion
111
goblets cells in the colon secrete mucus containing? (2)
``` glycoaminoglycans (from a gel) trefoil proteins (which have a protective function) ```
112
what hormone enhances Na+ absorption and K+ secretion from the colon?
aldosterone
113
what are the 3 patterns of motility in the colon?
``` haustration Mass movements (peristaltic propulsive movements/mass movements) defaecation reflex ```
114
what are haustra?
saccules created by the alternating contraction of tendinae coli
115
what is the purpose of haustration?
to slow down transit of material in the colon allowing time for fluid and electrolyte reabsorption
116
what are mass movements?
powerful contraction (caused by simultaneous contraction of large sections of circular muscle) that forces faeces into the rectum
117
where does mass movements often occur?
in the ascending and transverse colon
118
what triggers mass movements?
gastrocolic reflex
119
what triggers the defaecation reflex?
the distension of the rectum wall
120
as well as relaxation of the external anal sphincter what else is required for defaecation to take place?
a build-up of abdominal pressure
121
what are some of the functions of colonic flora? (5)
``` increase intestinal immunity promote motility maintenance of mucosal integrity synthesis of vitamin K and free fatty acids activation of some drugs ```
122
where do intestinal gases come from? (3)
- swallowed air - undigested carbohydrate which is digested by bacteria with gas being produced - fermentation action of the colon
123
where solutes go ____ follows
water
124
what are the 5 ways in which solutes are absorbed that lead to water absorption?
Na+/glucose co-transport Na+/amino acid co-transport Na+/H+ exchange Parallel Na+/H+ and Cl-/HCO3- exchangeEpithelial Na+ channels (ENaC)
125
what stimulates Na+/H+ exchange?
presence of bicarbonate
126
what hormone stimulates increased epithelial Na+ channels?
aldosterone
127
does Cl- secretion or absorption lead to diarrhoea?
secretion (usually Cl- absorption outweighs Cl- secretion)
128
activation of what chlorine channel resulting in an increased Cl- secretion leading to diarrhoea?
CFTR (cystic fibrosis transmembrane conductance regulator)
129
what do the chief cells in the gastric mucosa produce?
pespinogen (inactivated form of pepsin)
130
what do the enterochromaffin-like cells in the gastric mucosa produce?
histamine (which stimulates HCl production)
131
what 3 things do the parietal cells of the gastric mucosa produce and what are their functions?
1. HCl (activates pepsinogen to pepsin) 2. intrinsic factor (for vitamin B12 absorption) 3. gastroferrin (for iron absorption)
132
what do G cells produce?
gastrin
133
what does gastrin do?
stimulates HCl secretion
134
what do D cells produce/
somatostatin
135
during the cephalic (1st) phase of gastric acid secretion before food enters the stomach what does the vagus nerve stimulate? (4)
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
distension of the stomach is detected via ______ and results in _______
mechanoreceptors | increased acid secretion
137
vagus nerve activity _____ upon cessation of eating and after stomach emptying
decreases
138
when pH falls as food exits the stomach D cells are _____ so ______ is released leading to a decrease in gastric secretion
no longer inhibited | somatostatin =
139
what does mucus in the stomach prevent?
acid reaching the stomach cells
140
what happens in the mucus/gel layer in the stomach is not maintained?
peptic ulcers will form
141
what is secreted into the mucus layer of the stomach to keep it buffered?
bicarbonate
142
what are the 3 functions of prostaglandins?
reduce acid secretion increase mucus and bicarbonate flow increase mucosal flow
143
what is the gastroileal reflex?
peristalsis in the iluem and the opening of the ileocecal valve
144
what stimulates the gastroileal reflex? (2)
gastrin and CCK
145
what is the function of the migrating motor complex in the small intestine and what is it?
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
what triggers the migrating motor complex in the small intestine/
motilin
147
what are enteroendocrine cells?
cells within the gut that secrete hormones
148
migrating motor complex occurs in which state?
fasting
149
what suppresses the migrating motor complex? (2)
gastrin and CCK
150
what 5 things enhance secretion of intestinal juices/
``` distension irritation gastrin CCK Secretin parasympathetic nerve activity ```
151
what decreases the secretion of intestinal juices?
sympathetic nerve activity
152
what is contained within the intestinal juices/
mucus aqueous salt for enzymatic digestion (from the crypts of liberkuhn) *does not contain digestive enzymes*
153
where are pancreatic enzymes stored and what are they released in response to?
``` zymogen granules (found in acinar cells) elevated Ca2+ ```
154
what is contained within pancreatic juice?
digestive enzymes | sodium bicarbonate
155
what are the functions of pancreatic juice? (2)
neutralises the acidic chyme entering the duodenum and protects the stomach from acid supplies enzymes for digestion
156
what are the pancreatic enzymes? (3)
Proteases = trypsinogen (which is inactive but is then activated and activates other inactive proteases) pancreatic amylase pancreatic lipase
157
what are the 2 ways in which digestion is accomplished in the small intestine?
luminal digestion | membrane digestion
158
what enzymes mediate luminal digestion?
pancreatic enzymes
159
what enzymes mediate membrane digestion?
enzymes situated at the brush border of epithelial cells
160
what is sucrose digested into and by which enzyme?
fructose and glucose | sucrase
161
what are carbohydrates broken into before they are able to be absorbed?
monosaccharides
162
what are carbohydrates broken down into before they can be broken down into monosaccharides?
oligosaccharides
163
what is a protease?
an enzyme which breaks down proteins and peptides
164
what is a peptidase?
an enzymes which break down peptides into amino acids
165
what does HCl do that aids digestion?
starts to denature proteins making it easier for pepsin to digest them
166
what are the potential 3 products of carbohydrate digestion?
glucose galactose fructose (all of which can be absorbed)
167
how are glucose and galactose absorbed into enterocytes?
SGLT1 (sodium glucose co-transporter)
168
how is fructose absorbed into enterocytes?
GLUT5
169
how do glucose, galactose and fructose exit enterocytes?
GLUT2
170
amino acid absorption is either Na+dependent or Na+-independent (true/false)
true
171
how do amino acids exit enterocytes?
Na+-independent transporters
172
how are olgiopeptides absorbed into enterocytes?
H+/oligopeptide co-transporter (PepT1)
173
what do fats have to be converted into to be digested/
an emulsion
174
bile salts are involved in the ______ of fats
emulsification
175
what happens as a result of bile salts not being secreted?
``` lipid malabsorption (causing steratorrhoea) secondary vitamin deficiency due to failure to absorb fat-soluble vitamins ```
176
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?
colipase
177
what is made by the pancreas and helps the body digest fat?
lipases
178
what transports the products of fat digestion to enterocytes?
mixed micelles
179
what is transferred between mixed micelles and the apical membrane of enterocytes?
the products of fat digestion (free fatty acids and monoglycerides)
180
how do long chain fatty acids reach the bloodstream?
incorporated into chylomicrons
181
what is the name of the protein that is mainly responsible for cholesterol absorption?
niemann-pick-C1-like 1 protein
182
what 2 molecules are key in calcium absorption?
calcitirol | calicium calbindin D
183
what form of iron is absorbable?
ferrous
184
how is the unabsorbable form of iron (ferric form) converted into the absorbable form of iron (ferrous)? (2)
HCl | Vitamin C
185
fat-soluble vitamins (A, D, E, K) are incorporated into _____ and transported into _____ they are then incorporated into _____/____-and distributed by intestinal ______
mixed micelles enterocytes chylomicrons/VLDLs lymphatics
186
______ is essential for vitamin B12 absorption
intrinsic factor
187
what are the cytochrome p450 family of mono-oxygenases?
a large family of enzymes in the liver that participate in drug metabolism mediating phase 1 oxidation reactions of drugs
188
what produces bile?
hepatocytes | cholangiocytes
189
what does bile do?
participates in the digestion and absorption of fats and the excretion of products of metabolism
190
what is the fate of bile during meals?
it is stored and concentrated in the gallbladder
191
what is enterohepatic recycling?
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
what do bile acid sequestrants do/
the bind to components of bile in the GI tract preventing their reabsorption

Gastrointestinal Block (8 decks)

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