Physiology Flashcards
1
Q
Function of mouth
A
Chops and lubricates food
Starts carb digestion
Propels food to oesophagus
2
Q
Oesophagus
A
Propels food to stomach
3
Q
Stomach
A
Stores and churns food
Continuous carb digestion
Regulates delivery of chyme to duodenum
4
Q
Small intestine
A
Duodenum, jejunum and ileum
Site of digestion and absorption of nutrients
5
Q
Large intestine
A
Caecum, appendix and colon
Colon reabsorbs fluids and electrolytes, stores faecal matter before delivery to rectum
6
Q
Rectum and Anus
A
Regulates expulsion of faeces
7
Q
Mucosa
A
Mucous membrane
Lamina propria
Muscularis mucosae
8
Q
Submucosa
A
Connective tissue
Larger blood and lymph vessels
Glands
Submucous plexus
9
Q
Muscularis externa
A
Circular muscular layer
Myenteric plexus
Longlitudinal muscle layer
10
Q
Serosa
A
Connective tissue
11
Q
Motility
A
Mechanical activity mostly involving smooth muscle
12
Q
Secretion
A
Secretion into lumen of digestive tract occurs from itself and accessory structures in response to the presence of food, hormonal and neural signs
13
Q
Digestion
A
Chemical breakdown by enzymatic hydrolysis of complex foodstuffs to smaller absorbable units
14
Q
Absorption
A
Transfer of absorbable products of digestion from digestive tract to blood or lymph
15
Q
Circular muscle contraction
A
lumen becomes narrower and longer
16
Q
Longitudinal muscle contraction
A
intestine becomes shorter and fatter
17
Q
Muscularis mucosa contraction
A
Change in absorptive and secretory area of mucosa
Mixing activity
18
Q
Electric coupling
A
Adjacent smooth muscles are coupled by gap junctions, electrical currents flow from cell to cell
Hundreds of cells are depolarised and contract at the same time as a synchronous wave
19
Q
Spontaneous activity across coupled cells is driven by
A
specialised pacemaker cells
20
Q
Spontaneous activity across coupled cells is modulated by
A
Intrinsic and extrinsic nerves
Hormones
21
Q
Slow wave electrical activity determines
A
frequency, direction and velocity of rhythmic contraction
22
Q
Slow wave electrical activity is driven by
A
ICC’s
Interstitial Cells of Cajal
23
Q
ICC’s
A
Pacemaker cells located largely between circular and longitudinal muscle layers
24
Q
True of False:
Depolarising waves always cause contraction
A
FALSE
Contraction only occurs if the slow wave amplitude is sufficient to reach a threshold to trigger smooth muscle cell calcium action potentials
25
Force of contraction is related to
Number of action potentials discharged
26
Wether a slow wave reaches the threshold depends on
Neuronal stimuli
Hormonal stimuli
Mechanical stimuli
27
Parasympathetic Innervation - excitatory influence
Increased gastric, pancreatic and small intestine secretion
| Increased blood flow and smooth muscle contraction
28
Parasympathetic Innervation - inhibitory influence
Relaxation of sphincters
29
Sympathetic innervation - excitatory influence
Increased sphincter tone
30
Sympathetic innervation - inhibitory influence
Decreased motility, secretion and blood flow
31
where are cell bodies of enteric nervous system located
Ganglia
32
Local reflex
Peristalsis
33
Short reflex
Intestino-intestinal inhibitory reflex
| Local distension activates sensory neurones, inhibits muscle activity
34
Long reflex
Gastrolineal Reflex
| Increase in gastric activity causing propulsive activity
35
Peristalsis
Wave of relaxation followed by contraction
Precedes short distance along gut in aboral direction
Triggered by distension of gut wall
36
Segmentation
Rhythmic contractions of circular muscle layer that mix and divide luminal content
37
Colonic mass movement
Powerful sweeping contraction that forces faeces into rectum
| Occurs a few times a day
38
Migrating motor complex (MMC)
Powerful sweeping contraction from stomach to terminal ileum
Inhibited by feeding and vagal activity
Triggered by motolin
39
Tonic contraction
Sustained contractions
Low pressure = organs with storage functions
High pressure = sphincters
40
How many sphincters in GI tract
6
41
Sphincters in GI tract
```
Upper oesophageal
Lower oesophageal
Pyloric
Ileocaecal
Internal anal sphincter
External anal sphincter
```
42
Upper oesophageal sphincters
Relaxes to allow swallowing
| Closes during inspiration
43
Lower oesophageal sphincter
Relaxes to permit entry of food to stomach
| Closes to prevent reflux of gastric contents
44
Pyloric sphincter
Regulates gastric emptying
| Prevents duodenal gastric reflux
45
Internal and External anal sphincters
Regulated by defecation reflex
46
normal BMI
20 - 25
47
Overweight BMI
25-30
48
Obese BMI
30-40
49
Morbidly obese BMI
Over 40
50
Lesioning ventromedial hypothalamus
obesity
51
Lesioning lateral hypothalamus
leanness
52
Satiation
Sensation of fullness generated during a meal
53
Satiety
Period of time between termination of one meal and initiation of next
54
Adiposity
State of being obese
55
Satiation signals increase
during meal to limit size
56
Satiation signals
```
CCK
Peptide YY
Glucagon-like peptide
OXM
Obestatin
```
57
Glucaogon-like peptide 1
Released from L cells in response to food ingestion
| Inhibits gastric emptying and reduces food intake
58
OXM
Oxyntomodulin
Released from oxyntic cells and L cells
Acts to suppress appetite
59
Grehlin
Hunger signal
| Increases before meals, decreases after
60
Glutamate, Gaba and opioids
Increase food intake when injected into hypothalamus centre
61
Monoamines
Suppress food intake
62
2 hormones report fat status to brain
Leptin
| Insulin
63
Leptin
made and released from fat cells
64
Insulin
Made and released from pancreatic cells
65
Stomach shape
J shaped bag
| Relaxes to accommodate food from oesophagus
66
What nerve causes stomach to relax
Vagus
67
2 regions of stomach
Orad
| Caudad
68
Orad region
Fundus and proximal body
| Degree of tone and maintained contractile activity
69
Caudad region
Distal body and antrum body
| Rhythmic patterns or contractions, intermittent
70
Orad contraction
No slow wave electrical activity
Tonic, weak contractions
As stomach empties, size slowly decreases
Gastrin decreases contractions and hence rate of stomach emptying
71
Caudad contraction
Slow waves occur
| Phasic peristaltic contraction
72
Retropulsion
Pyloric end of stomach acts as a pump that delivers small amounts of chyme into the duodenum
Simultaneously forces most of its contained material backward into stomach
73
Strength of antral wave determines ...
strength of chyme in stomach
74
Strength of antral wave is determined by
Gastric Factors
| Duodenal Factors
75
Gastric factors
1. Rate of emptying proportional to volume of chyme in stomach
2. Consistency of chyme
(thinner chyme is quicker)
76
Distension increases motility due to
Stretching smooth muscle
Stimulation of intrinsic nerve plexuses
Increased vagus nerve activity and gastrin release
77
Duodenal Factors
1. Duodenum ready to receive chyme
| 2. Stimuli within duodenum that drive neuronal and hormonal response
78
When chyme enters it stimulates
ANS
79
Duodenum releases
CCK
80
2 gland areas
Oxyntic
| Pyloric
81
Gastric mucosa is made up of
Surface lining
Pits
Glands (at the base of pits)
82
Secretions from oxyntic mucosa
```
HCl
Pepsinogen
Intrinsic factor and gastroferrin
Histamine
Mucus
```
83
Pyloric gland area secretions
Gastrin
Somatostatin
Mucus
84
HCl
Activates pepsinogen to pepsin
Denatures protein
Kills micro-organisms ingested with food
85
Pepsingogen
Inactive precursor of pepsin
| Pepsin once formed activates pepsinogen (autocatalytic)
86
Instrinsic factor and Gastroferrin
Bind vitamin B12 and Fe2+
| Facilitates absorption
87
Histamine
Stimulates HCl secetion
88
Mucus
Protective
89
Gastrin
stimulates HCl secretion
90
Somatostatin
Inhibits HCL secretion
91
Secretion of HCL by gastric parietal cell
1. CA combines with Co2 to form unstable carbonic acids
2. Rapidly dissociates to H+, Na+ and HCO3-
3. H+ transports across membrane to lumen of gastric pit
4. H+ pumped out is swapped for a K+ which 'enters cell'
5. HCO3- goes out to plasma via antiporter in exchange of Cl- which enters cytoplasm
6. Cl- eventually leaves cell through CFTR channel
7. H+ and Cl- combine in lumen and canaliculus creates HCl
92
Secretagogues
3 stimuli helping acid secretion
| Cause trafficking in proton pumps to canalicular area where the become active
93
3 secretagogues
ACh
Gastrin
Histamine
94
3 phases of gastric secretion
Cephalic
Gastric
Intestinal
95
Cephalic phase
In head, before food reaches stomach, preparing it to receive food
96
Gastric phase
When food is in stomach
97
Intestinal phase
After food has left stomach, chyme enters SI causing weak stimulation of gastric secretion
98
Steps of the gastric phase
1. Stimuli (sight smell)
2. Causes activation of vagus nerve
3. Drives acid secretion
99
Mechanisms of acid secretion in gastric phase
1. Stimulates neurones present in enteric part of stomach, neurotransmitter released, works of G cells, release gastrin into blood, acid secretion
2. Stimulates neurones, releases ACh, acts on muscarinic cells, increased acid secretion
3. Stimulates neuornes, releases ACh, releases Histamine, increased acid secretion
4. Stimulates neurones, release ACH, somatostatin inhibited, increased acid secretion
5. Food arrives at stomach, distension, recognised by mechanoreceptor, ACh etc.
6. Food arrives at stomach, distension, G cells release gastrin, etc.
7. Pepsin in stomach, hydrolyses proteins, releases digestive products, phenylamine activates G cells, low pH = release somatostatin etc.
100
Drugs that can affect acid secretion
PPI
H2 receptor antagonists
Muscarinic receptor antagonists
NSAIDS
101
PPI
Inhibits M3, G and H2
Irreversibly
Decreases secretion
102
Example of PPI
Omeprazole
103
H2 receptor antagonist
Block histamine H2 receptors
Comp and reversibly
Decreases sec secretion
104
Example of H2 receptor antagonists
Ranitadine
105
Example of Muscarinic receptor antagonist
Pirenzepine
106
NSAIDS
PGE2 produced, decreases acid secretion
Formed by arachidonic acid
CXO used to convert
If CXO inhibited, acid secretion increases
107
Why doesn't the stomach digest itself?
Some gastric glands, pits and surface mucosa secrete a mucosa gel layer Prevents protons and acid from reaching surface stomach cells
Gel layered buffered, creating pH gradient, 2 at top, 7 at bottom
108
PGE2
Reduce acid secretion in parietal cells
Increase mucous and HCO3- secretion
Increase mucosal blood flow to wash away H+
109
Drug treatment of peptic ulcer aims to
Reduce acid secretion
Increase mucosal resistance
Eradicate H. Pylori
110
Side effect of NSAIDS
Trigger gastric ulceration
Cause bleeding
Can be prevented with PGE1
111
Mechanisms of anti-secretory activity
Irreversible inhibition of PPI
Competitive antagonism of Histamine H2 receptors
Competitive antagonism of M1 and M3 ACh receptors
Antagonism of CKK2 receptors
112
3 parts of small intestine
Duodenum
Jejunum
Ileum
113
Small intestine receives
Chyme from stomach
Pancreatic juice from pancreas (via pyloric sphincter)
Bile from liver and gall bladder
(via sphincter of oddi)
114
Small intestine secretes
Intestinal juices
115
Motility in SI causes
Mixing of chyme with digestive juices
Slow propulsion of chyme aborally (peristalsis)
Removal of undigested residues to large intestine via ileocaecal valve
116
Longest part of SI
Jejunum
117
Smallest part of SI
Duodenum
118
Mixing and propulsion of chyme
1. Segmentation
2. Peristalsis occuring as few localised contractions
(MMC)
119
Secretion of SI
```
Gastrin
Secretin
CCK
Glucose Dependant Insulinotropic
GLP-1
Motilin
Grehlin
```
120
Gastrin
From G cells of gastric antrum
Stimulates H+ secretion by gastric parietal cells
Stimulates growth of parietal cells
121
Secretin
From S cells of duodenum
Released in response to H+ and fatty acids in lumen
Promotes secretion of pancreatic and biliary HCO3-
122
CCK
From I cells of duodenum and jejunum
Released in response to monoglycerides, free fatty acids, aa's in lumen
Inhibits gastric emptying
Causes secretion of pancreatic enzymes needed for digestion
Stimulates relaxation of shpincter of Oddi
Potentiates action of secretin
123
Glucose dependant insulinotropic
From K cells
Released in response to glucose, aa's and fatty acids
Stimulates release of insulin from pancreatic B cells
Inhibits gastric emptying
124
GLP-1
From I cells
Stimulates insulin secretion
Inhibits glucagon secretion
Decreases gastric emptying and appetite
125
Motilin
From M cells
Secretes during fasting
Initiates MMC
126
Ghrelin
From Gr cells
| Stimulates appeptite
127
All peptide hormones act on what receptors
G-protein couples
128
Pancreatic secretion
Endocrine
| Exocrine
129
Endocrine secretions
Insulin and glucagon - secreted to blood
130
Exocrine secretion
Digestive enzymes, NaHCO3-, secreted to duodenum collectively
131
Why do duct cells secrete alkaline fluid into duodenum
Neutralises acidic chyme
Provides optimum pH for pancreatic enzymes
Protects mucosa from erosion by acid
132
Luminal digestion
Mediated by pancreatic enzymes secreted into duodenum
133
Membrane digestion
Mediated by enzymes situated at brush border of epithelial cells
134
Assimilation
Overall process of digestion and absorption
135
Alpha amylase
Breaks down internal 1-4 linkages but not terminal ones so no glucose created
136
How are glucose and galactose absorbed
Secondary active transport mediated by SGLT1
137
How is fructose absorbed
Secondary active transport mediated by GLUT5
138
How do monosaccharides get absorbed
Through GLUT2
139
Digestion in stomach
HCL denatures proteins
| Pepsin cleaves proteins into peptides
140
Digestion in duodenum
Uses 5 pancreatic proteases
141
Trypsin, chymotrypsin and elastase
Endopeptidases
142
Procarboxypeptidase A
| Procarboxypeptidase B
Exopeptidases
143
Main lipid digestive enzymes in adults
TAG lipase
144
Failure to secrete bile salts results in
```
Lipid malabsorption (Steatorrhea)
Secondary vitamin deficiency
```
145
Role of bile salts
Increase surface area for attack by pancreatic lipase
| Block TAG's
146
Colipase
Binds to bile salts and allows TAG's
147
How is cholesterol absorbed
By endocytosis in clatherin coated pits (NPC1L1)
148
Ezetimibe
Binds to NPC1L1 to prevent internalisation
149
How is Fe2+ absorbed
Binds to gastroferrin in stomach
150
How is B12 absorbed
1. B12 ingested in food, bound to proteins
2. Stomach acid releases B12 from protein
3. Haptocorcin, from saliva binds, with B12
4. Stomach parietal cells release intrinsic factor
5. Pancreatic proteases digest haptocorcin, B12 released
6. B12 binds to intrinsic factor
7. B12/intrinsic factor absorbed by endocytosis
151
What is B12 not present in
Vegetables
152
Who is susceptible to a B12 deficiency
Vegans
153
Haustra
Sac like bulges in large intestine
| Caused by taenia coli and circular muscle layers
154
Colon function
```
Absorp Na+, Cl-, H20
and fatty acids
Secrete K+, HCO3- and mucous
Stores colonic content
Eliminate faeces
```
155
Mucosa of colon
No villi
| Has colonic folds, crypts and microvilli
156
Colonocytes
Mediate electrolyte absorption
157
Crypt cells
mediate ion absorption
158
Goblet cells secrete
mucous
159
Haustration
Non-propulsive segmentation
160
Peristaltic propulsive movement
Mass movement
161
Defection
Periodic egestion
162
Defecation reflex
1. Mass movement
2. Activation of rectal stretch receptors
3. Activation of pelvic nerve
4. Activates parasympathetic efferents
5. Contraction of smooth muscle of colon and rectum
163
Pudenal Nerve
Keep your guts off the floor
| Control defecation
164
Colonic flora
Increase intestinal immunity by competition with pathogenic microbes
Promote motility
Synthesise vitamin K2 and fatty acids
Activate some drugs
165
Retching
Rhythmic reverse peristalsis of stomach and oesophagus
166
Vomiting
1. Suspension of intestinal slow wave activity
2. Retrograde contractions from ileum to stomach
3. Suspension of breathing
4. Relaxation of LOS, contraction of diaphragm and abdominal muscles compress stomach
5. Ejection of gastric components through UOS
167
Where is vomiting co-ordinated
Vomiting centre in the medulla oblongata of brain stem
168
Where does Na+/glucose and Na+/amino acid co-transport occur
Small Intestine
169
Where does Na+/H+ exchange occur
Duodenum and jejunum
| Stimulated by luminal HCO3-
170
Where does parallel Na+/H+ exchange and Cl+/HCO3- exchange occur
Ileum and colon
| Regulated by cAMP
171
SGLT1
1. 2 Na bind
2. Affinity for glucose increases, glucose binds
3. Na+ and glucose translocate from extracellular to intracellular
4. 2 Na+ dissociate, affinity for glucose fails
5. Glucose dissociates
172
Rehydration therapy exploits
SGLT1
| Absorption of Na+ and glucose causes accompanying H20 to also be absorbed
173
Role of liver in metabolism
Carbohydrate metabolism
Fat metabolism
Protein metabolism
174
Role of liver in hormone metabolism
Deactivation (insulin, glucagon, ADH, steroid)
| Activation
175
Liver stores
```
Fat soluble vitamins
Water soluble vitamin B12
Iron
Copper
Glycogen
```
176
Bile between meals
Stored and concentrated in gall bladder
177
Bile during meals
Chyme in duodenum stimulates gall bladder smooth muscle to contract
Sphincter of Oddi opens
Bile spurts into duodenum
178
Laparascopic Cholecystectomy
Best treatment for symptomatic stones
179
Ursodeoxycholic acid
For patients with unimpaired gall bladder function with small radioulcent stones
180
Morphine/Buprenophine
Biliary colic
Constricts sphincter of oddi
Raises intrabiliary pressure
181
Atropine or GTN
Relief of biliary spasm
182
How much bile salts are lost in faeces
5%
| Rest is absorbed in terminal ileum by active transport and undergoes enterohepatic recycling
183
Bile acid sequestrants
Binds to bile acids preventing reabsorption
| Lowers plasma conc indirectly
184
When are bile acid sequestrants used
Hyperlipidaemia
| Cholestatic jaundice
185
Examples of bile acid sequestrants
Colveselam, colestipol, colestyramine
186
Phase 1 of Drug Metabolsim
Right liver
Oxidation, reduction, hydrolysis
Makes drugs more polar, adds a chemically reactive group permitting conjugation
187
Phase 2 of drug metabolism
Left liver
Conjugation
Adds endogenous compound increasing polarity
188
CTP450
Metabolising enzyme in liver
| Paracetamol and other drugs mess this up
189
Hepatic Encephalopathy
Detoxification of NH3 to urea doesn't occur in severe hepatic failure
Blood NH3 levels rise = coma
190
Treat HE
Lactulose (converts ammonium which is not absorbed)
| Antibiotics (minimally absorbed, suppress colonic flora and inhibit ammonia generation)
