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AY Gastrointestinal > Physiology > Flashcards

Physiology Flashcards

1
Q

What mediates the breakdown of carbohydrates?

A

Amylases & disaccharides

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2
Q

What are proteins broken down into in digestion?

A

Amino acids

Peptides

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3
Q

What mediates the breakdown of proteins?

A

Proteases

Dipeptideases

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4
Q

What are fats broken down to in digestion?

A

Monoglycerides

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5
Q

What mediates the breakdown of fats?

A

Lipases

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6
Q

What are the layers of the digestive tract wall?

A

Mucosa
Submucosa
Muscularis externa
Serosa

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7
Q

What’s the mucosa made of?

A

Epithelial cells
Exocrine cells (secrete digestive juices)
Endocrine gland cells (secrete hormones)
Lamina propria
Muscularis mucosa

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8
Q

What is in the submucosa?

A

Connective tissue
Larger blood and lymph vessels
Submucous plexus

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9
Q

What is the muscularis externa made up of?

A

Circular muscle layer
Myenteric plexus
Longitudinal muscle layer

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10
Q

What is the serosa made of?

A

Connective tissue

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11
Q

What drives slow waves?

A

Interstitial cells of cajal (ICC’s) - pacemaker cells

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12
Q

How to slow waves spread from cell to cell?

A

Via gap junctions

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13
Q

What mediates the upstroke of the slow wave?

A

Voltage-activated Ca2+ channels

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14
Q

What mediates the downstroke of slow waves?

A

Voltage-activated K+ channels

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15
Q

When do slow waves not trigger contraction?

A

If they don’t reach the threshold for action potential

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16
Q

Why does the large intestinal favour the retention of luminal contents?

A

Helps facilitate absorption of water and electrolytes

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17
Q

What is the enteric nervous system?

A

Little brain of the gut

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18
Q

Where are the vast majority of the neurones of the enteric nervous system found?

A

Myenteric and submucous plexus

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19
Q

What is the enteric nervous system comprised of?

A 
Sensory neurones (mechano/chemo/thermoreceptors) 
Internet robes (coordinate reflexes & motor programs)
Effector neurones (supply muscle, vessels, epithelium)
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20
Q

What are the excitatory influences of the parasympathetic nervous system on the GI tract?

A

Increased gastric, pancreatic and small intestinal secretion
Increased blood flow and smooth muscle contraction

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21
Q

Inhibitory influences of the parasympathetic nervous system on the GI tract?

A

Relaxation of some sphincters

Receptive relaxation of stomach

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22
Q

Inhibitory influences of the sympathetic nervous system on the GI tract?

A

Decreased motility secretion and blood flow

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23
Q

What are carbohydrates converted to in digestion?

A

Monosaccharides (mainly glucose, some galactose & fructose)

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24
Q

What substances mediate relaxation of circular/longitudinal muscle?

A

VIP

NO

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25
What substances mediate the contraction of circular/longitudinal muscle?
ACh | Substance P
26
What is segmentation?
Mixing or churning movements | Rhythmic contractions of the circular muscle late that mix and divide luminal contents
27
What is segmentation called when it is in the large intestine?
Haustration
28
What are the 6 sphincters of the GI tract?
``` Upper oesophageal sphincter Lower oesophageal sphincter Pyloric sphincter Illeocaecal sphincter Internal anal sphincter External anal sphincter ```
29
What does the oesophageal sphincter do?
Relaxes to allow swallowing | Closes during inspiration
30
What does the lower oesophageal sphincter do?
Relaxes to permit food entry into the stomach | Closes to prevent gastric reflux
31
What does the pyloric sphincter do?
Regulates gastric emptying | Usually prevents duodenal gastric reflux
32
What does the Illeocaecal sphincter do?
Regulates flow from ileum to colon | Closes on distension of ileum or proximal colon
33
What do the internal and external anal sphincters do?
Regulated by the defamation reflex
34
What is the purpose of the palate?
Separates mouth from nasal passages | Allows breathing and chewing simultaneously
35
What is the purpose of the uvula?
Seals of nasal passages during swallowing
36
What is the importance of the tongue?
Guides food Speech Swallowing Taste buds
37
What are the voluntary actions of swallowing?
Chewing | Tongue guides bolus into pharynx
38
What are the involuntary actions of swallowing?
Pharyngeal pressure receptors stimulated Afferent impulse to swallowing centre in medulla Efferent initiate all or nothing reflex Upper oesophageal sphincter opens Food passes through
39
What coordinated peristalsis in smooth muscle?
Enteric nervous system
40
What is the response to sticky food in throat?
Secondary more forceful peristaltic wave | Increased saliva production
41
What are the functions of saliva?
Lubrication Solvent Antibacterial Neutralisation of acid
42
Where does the primary saliva secretion take place?,
Acinus
43
What secondarily modifies saliva once it is seceded from the acinus?
Duct cells
44
What 2 duodenal factors delay gastric emptying?
Enterogastric reflex | Release of entergastrones
45
What is the enterogastric reflex?
Duodenum signals to stomach that it has enough so slow down perostalsis, gastric emptying
46
What is the effect of entergastrones on gastric emptying?
CCK and secretin released from duodenum inhibit stomach contraction
47
What are gastric pits?
Invaginations of the gastric mucosa containing endocrine and exocrine glands
48
Where is the pyloric gland area located?
Antrum
49
Where is the oxyntic mucosa located?
Fundus and body
50
What cells are contained in the pyloric gland area?
D cells | G cells
51
What do D cells secrete?
Somatostatin
52
What do G cells secrete?
Gastrin
53
What cells are contained in the oxyntic mucosa?
Parietal cells Enterochromaffin-like cells Chief cells
54
What do ECL cells secrete?
Histamine
55
What do parietal cells secrete?
HCl | Intrinsic factor
56
What do chief cells secrete?
Pepsinogen
57
What is the role of HCl in the oxyntic mucosa?
Converts pepsinogen to pepsin | Kills of most of the ingested microorganisms
58
What does autocatalytic mean in terms of pepsin?
Pepsin triggers further pepsin formation from pepsinogen
59
What is the role of intrinsic factor in the oxyntic mucosa?
Binds vitamin B12
60
What is the role of histamine in the oxyntic mucosa?
Stimulates HCl secretion
61
What is the role of gastrin in the pyloric gland area?
Stimulates HCl secretion
62
What's the role of somatostatin in the pyloric gland area?
Inhibit HCl secretion
63
What are secretalogues?
Substances promoting the secretion of HCl (gastrin, ACh, histamine)
64
In response to secretalogues where do proton pumps move from and to in the parietal cell?
Move from inactive tubulovesicles in the cytoplasm to being active in the apical membrane
65
What are the 3 phases of gastric secretion?
Cephalic (before food reaches stomach) Gastric (when food is in stomach) Intestinal (after food has left stomach)
66
What is involved in the cephalic phase?
Stomach is prepared to receive food by conditioned reflex from chewing/swallowing leading to gastric secretion through ACh and GRP
67
What is involved in the gastric phase?
Distension due to presence of food activates mechanoreceptors to augment secretion
68
What is involved in the intestinal phase?
Gastric secretion through secretin, CCK and somatostatin as stomach empties
69
What is the important of the mucus gel layer in mucus secreting cells?
Stops pepsin/HCl damaging the cells
70
What are the 3 main constituents of food eaten?
Carbohydrates Lipids Proteins
71
What are the 2 types of digestion in the small intestine?
Luminal digestion | Membrane digestion
72
What enzymes mediate luminal digestion?
Pancreatic enzymes secreted into the duodenum
73
Where are enzymes that mediate membrane digestion?
Enzymes situated at the brush border of epithelial cells
74
What is involved in the process of absorption?
Absorbable products of digestion are transferred across both the apical and basolateral membranes of enterocytes (absorptive cells of the GI tract)
75
What is the overall process of digestion and absorption called?
Assimilation
76
What are the 2 forms of starch?
Amylose | Amylopectin
77
What are the 2 forms of oligosaccharides?
Sucrose | Lactose
78
What are the 2 monosaccharides?
Glucose | Fructose
79
What must dietary carbohydrates be converted to in order to the be absorbed?
Monosaccharides
80
What enzyme breaks down starch to oligosaccharides?
Alpha amylase
81
Where is alpha amylase secreted?
Saliva and in pancreas
82
Where are oligosaccharides broken down to monosaccharides?
At brush border
83
What enzymes break down oligosaccharides to monosaccharides?
Oligosaccharidases
84
What bonds does alpha amylase break?
Internal alpha 1,4 linkages but not terminal alpha 1,4 linkages
85
What is the role of lactase?
Breaks down lactose to glucose and galactose
86
What is the action of sucrase?
Hydrolyses sucrose to glucose and fructose
87
Why is isomaltase unique?
Only enzyme that can split the branching alpha 1,6 linkages of alpha-limit dextrins
88
What are the causes of lactose intolerance?
Primary lactase deficiency Secondary lactase deficiency Congenital lactase deficiency
89
In patients who are lactose intolerant ingest lactose what does the ileum colonic microflora produce?
Short chain fatty acids Hydrogen CO2 Methane
90
Physical signs of lactose intolerance
Bloating Abdominal pain Flatulence
91
What can undigested lactose cause?
Acidification of the colon | Increased osmotic load - loose stool and diarrhoea
92
Where are the final products of carbohydrate digestion absorbed?
Duodenum & jejunum
93
How are glucose and galactose absorbed into enterocytes?
Secondary active transport mediated by SGLT1
94
How is fructose absorbed into enterocytes?
Facilitated diffusion mediated by GLUT5
95
How do monosaccharides exit enterocytes?
Facilitated diffusion by GLUT2
96
How many pathways exist for protein digestion?
4
97
What denatures proteins in the stomach?
HCl
98
What is the role of pepsin in protein digestion?
Cleaves proteins into peptides
99
What is the pH range of pepsin?
1.8 to 3.5
100
Is pepsin essential for protein digestion?
No
101
What are the 3 endopeptidases involved in digestion in the duodenum?
Trypsin Chymotripsin Elastase
102
What are the 2 exopeptidases involved in digestion in the duodenum?
Procaroxypeptidase A | Procaroxypeptidase B
103
What is the product of endopeptidases breakdown?
Oligopeptides
104
What is the product of exopeptidases breakdown?
Single amino acids
105
Where are amino acids absorbed?
Brush border | Basolateral membrane
106
What transfers oligopeptidases across the apical membrane?
The H+/oligosaccharide co-transporter PepT1
107
All amino acid transporters across the apical membrane are Na+ dependent. True/False?
False | Some are Na independent
108
All amino acid transporters exiting the enterocyte are Na+ independent. True/False
True.
109
What are the 3 brush border enzymes in protein digestion?
Aminopeptidase Carboxypeptidase Dipeptidase
110
How are di- and tri-peptides absorbed?
Via H+-dependent mechanism at brush border
111
What enzyme in the mouth slightly aids lipid digestion?
Lingual lipase
112
What enzyme in the stomach digests lipids?
Gastric lipase
113
What is the main lipid digestion enzyme in the duodenum?
Pancreatic lipase
114
What aids pancreatic lipase in the digestion of lipids in the duodenum?
Bile salts from gallbladder
115
How is the optimum pH for pancreatic lipase achieved in the duodenum?
HCO3- in pancreatic juice neutralises stomach acid
116
What stimulates bile salt secretion from the gallbladder?
CCK
117
What conditions can result from failure to secrete bile salts?.
Steatorrhoea - lipid malabsorption (fat in faeces) | Secondary vitamin deficiency due to failure to absorb lipid vitamins
118
How do bile salts help pancreatic lipase in the digestion of lipids?
Increase surface area for attack by pancreatic lipase
119
What else is secreted with pancreatic lipase into the duodenum to aid digestion?
Colipase
120
Where are long chain fatty acids resynthesised into triglycerides?
Endoplasmic reticulum
121
After long chain fatty acids are resynthesised into triglycerides what happens to them?
They are incorporated into chylomicrons
122
Where do chylomicron enter the systemic circulation?
Subclavian vein via the thoracic duct
123
What enzyme metabloises chylomicron triglyceride?
Lipoprotein lipase
124
Where are chylomicron triglycerides metabolised?
Capillaries
125
What cells endocytose chylomicron remnant?
Hepatocytes
126
What happens to the cholesterol released from chylomicron remnant?
Stored Secreted unaltered in bile Oxidised to bile salts
127
How does ezetimibe lower cholestrol?
Binds to NPC1L1 prevents internalisation and thus cholestrol absorption
128
What is satiation?
Sensation of fullness
129
What are the 5 signals involved in satiation?
``` CCK Peptide YY (PYY) GLP-1 Oxyntomodulin (OXM) Obestatin ```
130
Where is CCK secreted from?
Enters endocrine cells in the duodenum and jejunum
131
How does the CCK signal travel to the brain?
Sensory nerves
132
What is CCK released in proportion to?
Lipids and proteins a meal
133
What is PYY secreted from?
Endocrine mucosal L-cells of the GI tract
134
What does PPY do?
Inhibits gastric motility, slows emptying and reduces food intake
135
Where is GLP-1 released from?
L cells
136
What is GLP-1 released in response to?
Food ingestion
137
What does GLP-1 do?
Inhibits gastric emptying and reduces food intake
138
Where is OXM released from?
L cells of small intestine after a meal
139
What is the purpose of OXM?
Suppresses appetite
140
What is the function of obestatin?
Reduce food intake
141
The gene that produces obestatin also produces _______.
Ghrelin
142
What does ghrelin do?
Stimulates food intake
143
Where are hunger/satiety signals sensed in the brain?
Hypothalamus
144
What 2 hormones report the fat status to the brain?
Leptin | Insulin
145
Where is leptin made and released from?
Fat cells
146
Where is insulin made and released?
Pancreatic cells
147
What does reduced leptin levels increase?
Appetite
148
Can bariatroc surgery reverse insulin resistance?
Yes
149
What are the 3 parts of the small intestine?
Duodenum Jejunum Ileum
150
What does the small intestine receive?
Chyme from stomach (pyloric sphincter) Pancreatic juice from stomach (via sphincter of oddi) Bile from gallbladder (via sphincter of oddi)
151
What valve joins the small and large bowel?
Illeocaecal valve
152
What 3 adaptations make the small intestine good for absorption?
Circular folds Villi Micro villi (the brush border)
153
What do G cells of the gastric antrum (mainly) and duodenum secrete?
Gastrin
154
What do I cells in the duodenum and jejunum secrete?
CCK
155
What do the S cells in the duodenum secrete?
Secretin
156
What do M cells in the duodenum and jejunum secrete?
Motilin
157
What is an incretin?
Act upon B cells in the pancreas and stimulate the release of insulin
158
Example of an incretin?
GIP | GLP-1
159
What do K cells secrete in the duodenum and jejunum?
GIP
160
What do the L cells of the gut secrete?
GLP-1
161
What do Gr cells secrete?
Ghrelin
162
What receptors do the secretions of the small intestine act on?
G-protein coupled receptors
163
What mechanism control the secretion of intestinal juices into the intestine?
``` Distension, irritation Gastrin CCK Secretin Parasympathetic nerve activity Sympathetic nerve activity ```
164
What effect does parasympathetic nerves have on the secretion of intestinal juices?
Increases secretion
165
What effect does sympathetic nerves have on the secretion of intestinal juices?
Decreases secretion
166
What do the small intestinal juices contain?
Mucus from goblet cells (for protection) Aqueous salt for enzymatic digestion No digestive enzymes
167
What can excessive secretion of intestinal juices cause?
Secretory diarrhoea
168
What activates segmentation in the small intestine?
Pacemaker cells (slow wave)
169
What hormone triggers segmentation in the empty ileum (gastrointestinal reflex)?
Gastrin
170
What trigger the migrating motor complex (MMC)?
Motilin
171
What suppresses the MMC?
Gastrin | CCK
172
What are endocrine secretions of the pancreas?
Insulin a Ms glucagon into the blood
173
What cells secrete digestive enzymes in the pancreas?
Acinus cells
174
What cells in the pancreas secrete aqueous NaHCO3- solution?
Duct cells
175
What professes are secreted from the pancreas?
Trypsinogen Chymotrypsinogen Procarboxypeptidase A and B
176
Other than pro teases what other pancreatic enzymes are secrete to digest food?
Pancreatic amylase | Pancreatic lipase
177
What is the purpose of HCO3 solution secreted from duct cells L
Neutralise acidic chyme entering the duodenum Provides optimum pH for pancreatic enzyme function Protects mucosa from erosion from acid
178
What is the 3 phases of pancreatic secretion?
Cephalic Gastric Intestinal
179
What are the sections of the large intestine?
Colon (ascending, transverse, descending, sigmoid) Caecum Appendix Rectum
180
What are the functions of the large intestine?
``` Absorption of H2O, Na+ and Cl- Secretion of K+, HCO3- and mucus Absorption of short chain fatty acids Reservoir Periodic elimination of faeces ```
181
What is Haustration?
Contraction of circular muscle causes Haustration (sacs) mixes content and allows time for fluid and electrolyte reabsorption
182
What triggers ar involved in the gastronomic response?
Gastrin | Extrinsic nerve plexuses
183
What is the parasympathetic/sympathetic involvement in the deflection reflex?
Relaxation and contraction of external anal sphincter (skeletal muscle)
184
What cause flactulence?
Bacteria in colon attack forms of carb which are indigestible to humans
185
What is constipation?
Presence of hard dried faeces within the colon. Results from delay in defaecation and enhanced absorption of H2O
186
Causes of constipation
Ignoring the need to go Decreased colonic motility (diet, metabolic disorders, age) Obstruction of faecal movement Impairment of motility/defaecation reflex
187
Example of a disease that can cause impairment of the motility/defaecation reflex
Hirschsprung's disease
188
Symptoms of constipation
Abdominal discomfort Headache Loss of appetite General malaise
189
Is absorption a passive or active process?
Passive
190
Definition of diarrhoea
Loss of fluid and salutes from the GI tract in excess of 500ml per day
191
Intestinal fluid movement is always coupled to solute movement. True/False.
True.
192
What are the routes by which water be absorbed?
Transcellular | Paracellular
193
What is the main ion involved in water absorption?
Na+
194
What are the 2 major mechanism or Na+ absorption?
Na+/glucose cotransport | Na+/amino acids cotransport
195
How is Cl- absorbed parallel to Na+?
Na+ transport creates transepithelial potential in which the lumen is negative
196
What stimulates Na+ exchange at the apical membrane in the duodenum?
Alkaline environment of the lumen in the jejunum
197
Why is the lumen of the jejunum alkaline?
Presence of bicarbonate from the pancreas
198
What is the primary mechanism of Na+ transport in the interdigestive period?
Na+/H+ exchange | Cl/HCO3- exchange
199
What regulates Na+/H+ and Cl-/HCO3- exchange?
cAMP cHMP Ca2+!
200
What effect do cAMP, cGMP and Na+ have on NaCl absorption?
Reduce NaCl absorption
201
What clinical condition does reduction in NaCl cause?
Diarrhoea
202
What channels mediate electrogenic Na+ absorption in the distal colon?
Epithelial Na+ channels
203
Are epithelial Na+ channels regulate by cAMP and cGMP?
No they are increased by aldosterone
204
What cells are involved in Cl- secretion?
Crypt cells
205
What are the 3 processes involved in Cl- secretion?
Na+/K+ ATPase Na+/K+/2Cl- co-transporter K+ channels
206
What gene when activated causes Cl- secretion?
CFTR
207
What can activate the CFTR gene?
Bacterial enterotoxins Hormones and neurotransmitters Immune cell products Some laxatives
208
Activation of CFTR occurs indirectly as a result of the generation of?
cAMP cGMP Ca2+
209
Causes of diarrhoea
Impaired absorption of NaCl Non absorbable or poorly absorbable solute in intestinal lumen Hyper motility Excessive secretion
210
How does cholera causes secretory diarrhoea?
Cholera toxin enters enterocyte Causes increased activity of adenylyl curate Increased conc of cAMP cAMP stimulates CFTR Hypersecretion of Cl- with Na+ and water following
211
How do oral rehydration salts work?
Cause increased absorption of Na+ and glucose by SGLT1 which causes accompanying absorption of H2O
212
What are the 2 blood supplies to the liver?
Hepatic portal vein | Hepatic artery
213
Where in the liver does arterial and venous blood mix?
Liver sinusoids
214
What vessel travels through the centre of the liver?
Hepatic vein
215
What is in the portal triad?
Hepatic portal vein Hepatic artery Bile duct
216
Where does blood flow when it enters the liver in the portal triad?
Inward through sinusoids to the central vein
217
What cells secrete bile?
Hepatocytes
218
What does bile flow through and in what direction?
Outwardly through canaliculi
219
What are the 2 parts of the epithelium formed by hepatocytes?
Basolateral membrane | Apical membrane
220
What does the apical membrane in the liver form?
Canaliculi
221
What does the basolateral membrane face?
Space of Disse (pericellular space)
222
What is in sinusoidal spaces?
Endothelial cells Kuppfer cells Stellate cells
223
What type of cell are Kuppfer cells?
Macrophages
224
What is the role of endothelial cells in the liver?
Allow free movement of salutes but not cells
225
What are stellate cells in the liver important for?
Storage of vitamin A
226
Where is bile stored and concentrated in between meals?
Gallbladder
227
Chyme stimulate gallbladder smooth muscle contract through which 2 mechanisms?
CCK | Vagal impulses
228
What mediates the opening of the sphincter of oddi?
CCK
229
What ducts allow the spurt of bile into the duodenum?
Cystic and common bile ducts
230
What is bile made of?
Secretion of hepatocytes | Secretion of bile duct cells
231
What is the role of bile?
Digestion and absorption of fats
232
What pH is the secretion of bile duct cells?
Alkaline
233
What is the composition of hepatic bile?
``` Primary bile acids (colic and cenodeoycholic acids) Water and electrolytes Lipids and phospholipids Cholesterol IgA Bilirubin ```
234
What process do bile salts undergo after being reansorbed by active transport in the terminal ileum?
Enterohepatic recycling
235
What are bile salts synthesised from?
Cholesterol
236
What is the rate of synthesis of bile salts dependent on?
The hepatic portal vein concentration of the salts

AY Gastrointestinal (21 decks)

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