GI physiology Flashcards
1
Q
what is the digestive purpose of the mouth
A
chewing
moistens and lubricates food
begins digestion of polysaccharide
2
Q
what is the purpose of the small intestine
A
digestion and absorption of most substances
3
Q
what is the purpose of the large intestin
A
storage and concentration of undigested matter
salt and water absorption
defecation
vitamin K absorption
4
Q
what is the purpose of the pancreas
A
secretion of enzymes and bicarbonate in order to digest carbs, fats, proteins and nucleic acids
5
Q
what is the purpose of bicarbonate
A
to neutralise HCl entering the small intestine
6
Q
what is the purpose of bile
A
solubilise fats
7
Q
what is the purpose of the liver
A
bile
bicarbonate
eliminate waste products and trace metals
8
Q
what is the purpose of the gall bladder
A
store and concentrate bile
9
Q
what are the 5 main physiological processes of the GI tract
A
motility secretion digestion absorption excretion
10
Q
what are the defence mechanisms of the gut
A
Gut associated lymph tissue GALT
organised aggregates of lymphoid tissue- Peyer’s patches
immune cells- lymphocytes and mast cells
gastric acid, mucin, peristalsis and epithelium
11
Q
what is the lamina propria
A
loose connective tissue with cappilaries, neurones and immune cells
12
Q
what is the muscularis mucosae
A
thin smooth muscle layer of the mucosa
13
Q
where is striated muscle found
A
pharynx, upper oesophagus and external anal sphincter
14
Q
how is food moved along the GI tract
A
rhythmic contraction and relaxation of GI wall and sphincters
15
Q
what muscle types surround the myenteric plexus
A
circular and longitudinal
16
Q
what type of smooth muscle is found in the GI tract
A
single unit
17
Q
what does Ca2+ bind to in order to initiate contraction
A
calmodulin
18
Q
how do neuronal and hormonal inputs affect contraction
A
change the force of contraction but not the speed
19
Q
what links adjacent cells in single unit smooth muscle
A
gap junctions
20
Q
what does calcium calmodulin do
A
activates inactive myosin light chain kinase
21
Q
what does the active myosin light chain kinase do
A
phosphorylates myosin
22
Q
what does latch state contraction do
A
maintains high tension
maintains the cross bridge binding with low atp consumption
23
Q
how does smooth muscle relax
A
decrease in Ca2
leads to dissociation of Ca- calmodulin which leads to inactivation of myosin light chain kinase
which leads to dephosphorylation of myosin
cross bridges break
myosin phosphatase removes phosphate from the myosin
24
Q
what causes slow waves in smooth muscle
A
interstitial cells of Cajal which are pacemaker cells found in the myenteric plexus
25
what is the intrinsic rate of the pacemaker cells
3-12 per minute
3 in the stomach
12 in the duodenum
26
what are the stages in slow wave generation
Depolarisation due to the cyclical opening of voltage
gated Ca2+ channels
1. Increase in the intracellular Ca2+ concentration
2. Opening of Ca2+ dependent K+ channels
3. Increased K+ permeability leads to slow
hyperpolarisation
4. Voltage gated Ca2+ channels close and intracellular
Ca2+ concentration falls
5. Ca2+ dependent K+ channels close
6. Voltage gated Ca2+ channels open
27
what stimulates the spikes in membrane potential
stretch
acetylcholine
parasympathetic
28
what stimulates hyperpolarisation
norepinephrine
| sympathetics
29
what acts as a lubricant during chewing
mucin which is a glycoprotein
30
how is reflex chewing initiated
by food in mouth which is relayed from mechanoreceptors to the brain stem initiates a reflex pattern of activity in chewing muscles
31
what are the 3 phases of swallowing
oral phase
pharyngeal phase
oesophageal phase
32
where is the swallowing centre
medulla and lower pons
33
what innervates the lower oesophagus
vagal motor
34
describe the swallowing refelex
1. Upper oesophageal sphincter opens to allow bolus of food to enter
oesophagus
2. Upper oesophageal sphincter closes
3. Primary peristaltic contraction mediated by swallowing reflex involves a
series of coordinated contractions creating a region of high pressure
behind the bolus (accelerated by gravity)
4. Lower oesophageal sphincter opens mediated by peptidergic nerves in
the vagus releasing VIP (vasoactive intestinal peptide)
5. Receptive relaxation of the orad region of the stomach
6. Lower oesophageal sphincter closes
35
what may result from achalasia (absence of relaxation)
dysphagia
failure of lower oesophageal sphincter to relax
impaired peristalsis in distal regions
could be caused by Selective loss of neurons which regulate the lower oesophageal sphincter by releasing vasoactive intestinal
peptide (VIP)
36
what does the parasympathetic NS do
stimulate gastric smooth muscle motility and secretions
37
what does the sympathetic NS do
inhibit motility and secretions
38
what myenteric nerves innervate the stomach
parasympathetic innervation via the vagus
| sympathetic via the coeliac ganglion
39
how does the stomach receive sensory innervation
sensory receptors and the ENS
| and centrally via the vagal and splanchnic nerves
40
what can the stomach sense
(pressure, distension,
| pH, pain
41
what layers make up the muscularis externa
oblique, circular and longitudinal muscle
42
what is the orad
upper proximal part of the stomach which distends in order to make room for food
the stomach can be increased to 1.5 l
43
what afferent information is sent via the vagus
Mechanoreceptors associated with chewing, oesophageal
and stomach distension relay information to CNS via
sensory neurons
44
what efferent information is sent via the vagus
efferent information from the CNS causes orad relaxation
45
what neuropeptide is released from postganglionic peptidergic vagal neurons in order to relax the orad
vasoactive intestinal peptide
46
what part of the stomach is responsible for mixing
thick muscular wall of the caudad
– contraction waves begin in the middle of the body, move
distally with increasing strength towards the pylorus
47
describe the contraction patterns of the stomach
1. propulsion - bolus is pushed towards the closed pylorus
2. grinding - the antrum churns the trapped material
3. retropulsion -bolus is pushed back towards the proximal stomach
some food may be allowed to exit via the pylorus
48
what is the slow wave frequency of the stomach
3-5 per min
49
what factors affect the force of contraction
para. stimulation, gastrin and motilin increase AP frequency and force of contraction
50
what are Migrating myoelectric complexes
• mediated by motilin – released from endocrine cells in the
upper GI tract
occur every 90 minutes
Clear stomach of residue remaining from previous
meal
51
how long does it take to empty the gastric contents after a meal
3 hours
52
what Physical factors affect
| emptying
1. Liquids empty more rapidly than solids
2. Isotonic fluids empty more rapidly than
hypo- or (especially) hypertonic fluids
3. Solids must be reduced to particles
53
what is the effect of fat on the GI system
cholecystokinin is secreted
54
what is the function of the small intestine
1. Mixes chyme with digestive enzymes and
pancreatic secretions
2. Exposes nutrients to the intestinal mucosa
for absorption
3. Propels unabsorbed chyme into large
intestine
55
how many waves are in the duodenum
12 per minute
56
how many waves are in the ileum
9 per minute
57
what coordinates contraction
ENS
58
what causes orad contraction
aCh and substance P
59
what causes caudad relaxation
VIP and nitric oxide
60
what is the taeniae coli
longitudinal muscle concentrated in 3 bands
61
what parts of the colon are innervated by the vagus
caecum, ascending colon and transverse colon
62
what parts of the colon are innervated by the pelvic nerves
• Descending and sigmoid colon, rectum and anal canal
Stimulation causes expulsive contractions of the distal colon
63
what does the sympathetic ns do to the colon
stops colonic movements
64
why might the faeces be retained
Na+ and water retention
65
what are the haustra
the sac like segments of the colon
66
why would you have hard faeces in constipation
more water is absorbed because more time in GI tract
67
what reflexes cause propulsion of faeces into the rectum
gastrocolic and duodenocolic reflexes
68
what is the gastro colic reflex
Distension of the stomach by food increases the
motility of the colon and the frequency of mass
movements in the large Intestine
Afferent limb in the stomach mediated by the
parasympathetic nervous system.
The efferent limb of the reflex increasing colon
motility is mediated by CCK and gastrin.
69
what is the rectosphincteric reflex
As rectum fills with faeces, the smooth muscle of the rectum
| contracts and the internal anal sphincter relaxes but the external anal spincter remains closed
70
where is the vomiting centre
in the medulla
71
how does vomiting work
* Reverse peristalsis in small intestine
* Relaxation of the stomach and pylorus
* Forced inspiration to increase abdominal pressure
* Relaxation of the lower oesophageal sphincter
* Forceful expulsion of gastric and duodenal content
72
what afferent information stimulates vomiting
* Vestibular system
* Back of throat
* GI tact
* Chemoreceptor trigger zone in the 4th ventricle
73
what are the main breakdown products of carbohydrate absorption
glucose
galactose
fructose
74
how are glucose and galactose absorbed
Na dependant cotransport
75
how is fructose absorbed
facilitated diffusion
76
what is SGLT1
```
sodium dependent
glucose transporter 1 located
on the apical membrane
transports glucose and
galactose
```
77
what is GLUT5
glucose transporter 5
transports fructose across the
apical membrane
78
how does protein digestion happen
in the stomach with pepsin
| then in the small intestine with pancreatic and brush border proteases
79
where is alpha amylase found
mouth
80
what is endopeptidase
hydrolyses the interior peptide bonds of proteins
81
what is exopeptidase
hydrolyses one amino acid at a time from the exterior
82
how are pancreatic proteases secreted in the small intestine
as inactive precursors
83
how is trypsinogen activated
brush border enzyme enterokinase to the active form trypsin
84
what does trypsin do
catalyses the conversion of other inactive precursors to active enzymes
85
how are amino acids absorbed from the small intestine
Na dependant co transport
86
how are dipeptides and tripeptides absorbed from the small intestine
H+ dipeptide cotransport
87
where does fat digestion begin
stomach with the action of lingual and gastric lipases
88
how is fat digestion completed
in the small intestine with the action of pancreatic enzymes
89
what is fat digested to
glycerol and free fatty acids
90
what is the function of gastric lipase
digest fats
| slow the rate of gastric emptying so that pancreatic enzymes are able to digest lipid
91
where is cholecystokinin secreted from
I cells of the duodenal and jejunal mucosa in response to the presence of monoglycerides and fatty acids and peptides
92
what substances emulsify dietary lipids
Bile salts, lysolecithin and products of lipid digestion
93
what does emulsification produce
small droplets of lipids
dispersed in an aqueous solution creating a large
surface area for pancreatic enzyme digestion
94
what pancreatic enzymes complete lipid digestion
pancreatic lipase, cholesterol
| ester hydrolase and phospholipaseA2 and the protein, colipase
95
what are chylomicrons made from
fats, cholesterol (inside) and proteins (outside)
96
how do chylomicrons enter the blood
lacteals to thoracic duct which empties into the blood stream
97
how are fatty acids absorbed
bile salts which form micelles
98
what are Crypts of Lieberkuhn in the small intestine for
secretion
99
what are colonic glands for
secretion
100
how often are villous cells replaced
approx. every 2-3 days
101
where is the majority of water reabsorbed
small intestine
102
where is sodium reabsorbed
jejunum, ileum and colon
103
what cells in the pancreas produce digestive enzymes
basophillic cells
stimulated by CCK
104
what cells in the pancreas produce bicarbonate ions
centroacinar cells stimulated by secretin
105
where is the submucosal plexus
between the submucosa and the circular muscle layer
106
what is found in the sub mucosa
```
– Loose connective tissue
– Larger blood vessels
– Lymphatics
– Secretory glands
– Enteric neurones in the submucosa -submucosal plexus
```
107
what is found in the muscularis externa
– Inner layer of circular muscle
– Outer layer of longitudinal muscle
– Enteric neurones between the muscle layers – myenteric plexus
108
what is found in the serosa
outer layer of connective tissue and squamous epithelia
109
what is the extrinsic autonomic NS
sympathetic and parasympathetic
110
what is the intrinsic component of the ANS
enteric NS
Meissner's plexus (submucosal)
and Auerbach's plexus- myenteric
111
describe the organisation of the somatic NS
single motorneurone
no ganglia
ACh
112
describe the sympathetic organisation
have ganglia close to the spinal cord which secrete ACh
have long
postganglionic neurones
thoracolumbar (ps is craniosacral)
norepinephrine is secreted postganglion
113
what are the 3 plexuses in the sympathetic GI supply
coeliac plexus
sup mesenteric
inferior mesenteric
114
what reflexes are controlled by the ENS
secretion, peristalsis, mixing, inhibition
115
what reflexes travel from the GI tract to the prevertebral sympathetic ganglia and then back to the GI tract
reflexes that transmit signals to other areas of the stomach
gastrocolic, enterogastric, colonoilial
116
what reflexes travel from the GI tract to the brain stem or spinal cord
reflexes controlling motility and secretion
pain reflexes which inhibits the GI tract
defecation which produces reflex contractions
117
what is catarrh
a build up of mucus in a body cavity
| results from inflammation of the mucus membrane
