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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
Q

What substances mediate the contraction of circular/longitudinal muscle?

A

ACh

Substance P

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26
Q

What is segmentation?

A

Mixing or churning movements

Rhythmic contractions of the circular muscle late that mix and divide luminal contents

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27
Q

What is segmentation called when it is in the large intestine?

A

Haustration

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28
Q

What are the 6 sphincters of the GI tract?

A 
Upper oesophageal sphincter 
Lower oesophageal sphincter 
Pyloric sphincter
Illeocaecal sphincter 
Internal anal sphincter 
External anal sphincter
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29
Q

What does the oesophageal sphincter do?

A

Relaxes to allow swallowing

Closes during inspiration

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30
Q

What does the lower oesophageal sphincter do?

A

Relaxes to permit food entry into the stomach

Closes to prevent gastric reflux

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31
Q

What does the pyloric sphincter do?

A

Regulates gastric emptying

Usually prevents duodenal gastric reflux

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32
Q

What does the Illeocaecal sphincter do?

A

Regulates flow from ileum to colon

Closes on distension of ileum or proximal colon

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33
Q

What do the internal and external anal sphincters do?

A

Regulated by the defamation reflex

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34
Q

What is the purpose of the palate?

A

Separates mouth from nasal passages

Allows breathing and chewing simultaneously

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35
Q

What is the purpose of the uvula?

A

Seals of nasal passages during swallowing

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36
Q

What is the importance of the tongue?

A

Guides food
Speech
Swallowing
Taste buds

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37
Q

What are the voluntary actions of swallowing?

A

Chewing

Tongue guides bolus into pharynx

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38
Q

What are the involuntary actions of swallowing?

A

Pharyngeal pressure receptors stimulated
Afferent impulse to swallowing centre in medulla
Efferent initiate all or nothing reflex
Upper oesophageal sphincter opens
Food passes through

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39
Q

What coordinated peristalsis in smooth muscle?

A

Enteric nervous system

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40
Q

What is the response to sticky food in throat?

A

Secondary more forceful peristaltic wave

Increased saliva production

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41
Q

What are the functions of saliva?

A

Lubrication
Solvent
Antibacterial
Neutralisation of acid

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42
Q

Where does the primary saliva secretion take place?,

A

Acinus

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43
Q

What secondarily modifies saliva once it is seceded from the acinus?

A

Duct cells

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44
Q

What 2 duodenal factors delay gastric emptying?

A

Enterogastric reflex

Release of entergastrones

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45
Q

What is the enterogastric reflex?

A

Duodenum signals to stomach that it has enough so slow down perostalsis, gastric emptying

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46
Q

What is the effect of entergastrones on gastric emptying?

A

CCK and secretin released from duodenum inhibit stomach contraction

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47
Q

What are gastric pits?

A

Invaginations of the gastric mucosa containing endocrine and exocrine glands

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48
Q

Where is the pyloric gland area located?

A

Antrum

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49
Q

Where is the oxyntic mucosa located?

A

Fundus and body

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50
Q

What cells are contained in the pyloric gland area?

A

D cells

G cells

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51
Q

What do D cells secrete?

A

Somatostatin

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52
Q

What do G cells secrete?

A

Gastrin

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53
Q

What cells are contained in the oxyntic mucosa?

A

Parietal cells
Enterochromaffin-like cells
Chief cells

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54
Q

What do ECL cells secrete?

A

Histamine

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55
Q

What do parietal cells secrete?

A

HCl

Intrinsic factor

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56
Q

What do chief cells secrete?

A

Pepsinogen

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57
Q

What is the role of HCl in the oxyntic mucosa?

A

Converts pepsinogen to pepsin

Kills of most of the ingested microorganisms

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58
Q

What does autocatalytic mean in terms of pepsin?

A

Pepsin triggers further pepsin formation from pepsinogen

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59
Q

What is the role of intrinsic factor in the oxyntic mucosa?

A

Binds vitamin B12

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60
Q

What is the role of histamine in the oxyntic mucosa?

A

Stimulates HCl secretion

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61
Q

What is the role of gastrin in the pyloric gland area?

A

Stimulates HCl secretion

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62
Q

What’s the role of somatostatin in the pyloric gland area?

A

Inhibit HCl secretion

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63
Q

What are secretalogues?

A

Substances promoting the secretion of HCl (gastrin, ACh, histamine)

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64
Q

In response to secretalogues where do proton pumps move from and to in the parietal cell?

A

Move from inactive tubulovesicles in the cytoplasm to being active in the apical membrane

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65
Q

What are the 3 phases of gastric secretion?

A

Cephalic (before food reaches stomach)
Gastric (when food is in stomach)
Intestinal (after food has left stomach)

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66
Q

What is involved in the cephalic phase?

A

Stomach is prepared to receive food by conditioned reflex from chewing/swallowing leading to gastric secretion through ACh and GRP

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67
Q

What is involved in the gastric phase?

A

Distension due to presence of food activates mechanoreceptors to augment secretion

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68
Q

What is involved in the intestinal phase?

A

Gastric secretion through secretin, CCK and somatostatin as stomach empties

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69
Q

What is the important of the mucus gel layer in mucus secreting cells?

A

Stops pepsin/HCl damaging the cells

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70
Q

What are the 3 main constituents of food eaten?

A

Carbohydrates
Lipids
Proteins

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71
Q

What are the 2 types of digestion in the small intestine?

A

Luminal digestion

Membrane digestion

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72
Q

What enzymes mediate luminal digestion?

A

Pancreatic enzymes secreted into the duodenum

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73
Q

Where are enzymes that mediate membrane digestion?

A

Enzymes situated at the brush border of epithelial cells

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74
Q

What is involved in the process of absorption?

A

Absorbable products of digestion are transferred across both the apical and basolateral membranes of enterocytes (absorptive cells of the GI tract)

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75
Q

What is the overall process of digestion and absorption called?

A

Assimilation

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76
Q

What are the 2 forms of starch?

A

Amylose

Amylopectin

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77
Q

What are the 2 forms of oligosaccharides?

A

Sucrose

Lactose

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78
Q

What are the 2 monosaccharides?

A

Glucose

Fructose

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79
Q

What must dietary carbohydrates be converted to in order to the be absorbed?

A

Monosaccharides

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80
Q

What enzyme breaks down starch to oligosaccharides?

A

Alpha amylase

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81
Q

Where is alpha amylase secreted?

A

Saliva and in pancreas

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82
Q

Where are oligosaccharides broken down to monosaccharides?

A

At brush border

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83
Q

What enzymes break down oligosaccharides to monosaccharides?

A

Oligosaccharidases

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84
Q

What bonds does alpha amylase break?

A

Internal alpha 1,4 linkages but not terminal alpha 1,4 linkages

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85
Q

What is the role of lactase?

A

Breaks down lactose to glucose and galactose

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86
Q

What is the action of sucrase?

A

Hydrolyses sucrose to glucose and fructose

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87
Q

Why is isomaltase unique?

A

Only enzyme that can split the branching alpha 1,6 linkages of alpha-limit dextrins

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88
Q

What are the causes of lactose intolerance?

A

Primary lactase deficiency
Secondary lactase deficiency
Congenital lactase deficiency

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89
Q

In patients who are lactose intolerant ingest lactose what does the ileum colonic microflora produce?

A

Short chain fatty acids
Hydrogen
CO2
Methane

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90
Q

Physical signs of lactose intolerance

A

Bloating
Abdominal pain
Flatulence

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91
Q

What can undigested lactose cause?

A

Acidification of the colon

Increased osmotic load - loose stool and diarrhoea

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92
Q

Where are the final products of carbohydrate digestion absorbed?

A

Duodenum & jejunum

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93
Q

How are glucose and galactose absorbed into enterocytes?

A

Secondary active transport mediated by SGLT1

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94
Q

How is fructose absorbed into enterocytes?

A

Facilitated diffusion mediated by GLUT5

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95
Q

How do monosaccharides exit enterocytes?

A

Facilitated diffusion by GLUT2

96
Q

How many pathways exist for protein digestion?

A

4

97
Q

What denatures proteins in the stomach?

A

HCl

98
Q

What is the role of pepsin in protein digestion?

A

Cleaves proteins into peptides

99
Q

What is the pH range of pepsin?

A

1.8 to 3.5

100
Q

Is pepsin essential for protein digestion?

A

No

101
Q

What are the 3 endopeptidases involved in digestion in the duodenum?

A

Trypsin
Chymotripsin
Elastase

102
Q

What are the 2 exopeptidases involved in digestion in the duodenum?

A

Procaroxypeptidase A

Procaroxypeptidase B

103
Q

What is the product of endopeptidases breakdown?

A

Oligopeptides

104
Q

What is the product of exopeptidases breakdown?

A

Single amino acids

105
Q

Where are amino acids absorbed?

A

Brush border

Basolateral membrane

106
Q

What transfers oligopeptidases across the apical membrane?

A

The H+/oligosaccharide co-transporter PepT1

107
Q

All amino acid transporters across the apical membrane are Na+ dependent. True/False?

A

False

Some are Na independent

108
Q

All amino acid transporters exiting the enterocyte are Na+ independent. True/False

A

True.

109
Q

What are the 3 brush border enzymes in protein digestion?

A

Aminopeptidase
Carboxypeptidase
Dipeptidase

110
Q

How are di- and tri-peptides absorbed?

A

Via H+-dependent mechanism at brush border

111
Q

What enzyme in the mouth slightly aids lipid digestion?

A

Lingual lipase

112
Q

What enzyme in the stomach digests lipids?

A

Gastric lipase

113
Q

What is the main lipid digestion enzyme in the duodenum?

A

Pancreatic lipase

114
Q

What aids pancreatic lipase in the digestion of lipids in the duodenum?

A

Bile salts from gallbladder

115
Q

How is the optimum pH for pancreatic lipase achieved in the duodenum?

A

HCO3- in pancreatic juice neutralises stomach acid

116
Q

What stimulates bile salt secretion from the gallbladder?

A

CCK

117
Q

What conditions can result from failure to secrete bile salts?.

A

Steatorrhoea - lipid malabsorption (fat in faeces)

Secondary vitamin deficiency due to failure to absorb lipid vitamins

118
Q

How do bile salts help pancreatic lipase in the digestion of lipids?

A

Increase surface area for attack by pancreatic lipase

119
Q

What else is secreted with pancreatic lipase into the duodenum to aid digestion?

A

Colipase

120
Q

Where are long chain fatty acids resynthesised into triglycerides?

A

Endoplasmic reticulum

121
Q

After long chain fatty acids are resynthesised into triglycerides what happens to them?

A

They are incorporated into chylomicrons

122
Q

Where do chylomicron enter the systemic circulation?

A

Subclavian vein via the thoracic duct

123
Q

What enzyme metabloises chylomicron triglyceride?

A

Lipoprotein lipase

124
Q

Where are chylomicron triglycerides metabolised?

A

Capillaries

125
Q

What cells endocytose chylomicron remnant?

A

Hepatocytes

126
Q

What happens to the cholesterol released from chylomicron remnant?

A

Stored
Secreted unaltered in bile
Oxidised to bile salts

127
Q

How does ezetimibe lower cholestrol?

A

Binds to NPC1L1 prevents internalisation and thus cholestrol absorption

128
Q

What is satiation?

A

Sensation of fullness

129
Q

What are the 5 signals involved in satiation?

A 
CCK
Peptide YY (PYY) 
GLP-1
Oxyntomodulin (OXM) 
Obestatin
130
Q

Where is CCK secreted from?

A

Enters endocrine cells in the duodenum and jejunum

131
Q

How does the CCK signal travel to the brain?

A

Sensory nerves

132
Q

What is CCK released in proportion to?

A

Lipids and proteins a meal

133
Q

What is PYY secreted from?

A

Endocrine mucosal L-cells of the GI tract

134
Q

What does PPY do?

A

Inhibits gastric motility, slows emptying and reduces food intake

135
Q

Where is GLP-1 released from?

A

L cells

136
Q

What is GLP-1 released in response to?

A

Food ingestion

137
Q

What does GLP-1 do?

A

Inhibits gastric emptying and reduces food intake

138
Q

Where is OXM released from?

A

L cells of small intestine after a meal

139
Q

What is the purpose of OXM?

A

Suppresses appetite

140
Q

What is the function of obestatin?

A

Reduce food intake

141
Q

The gene that produces obestatin also produces _______.

A

Ghrelin

142
Q

What does ghrelin do?

A

Stimulates food intake

143
Q

Where are hunger/satiety signals sensed in the brain?

A

Hypothalamus

144
Q

What 2 hormones report the fat status to the brain?

A

Leptin

Insulin

145
Q

Where is leptin made and released from?

A

Fat cells

146
Q

Where is insulin made and released?

A

Pancreatic cells

147
Q

What does reduced leptin levels increase?

A

Appetite

148
Q

Can bariatroc surgery reverse insulin resistance?

A

Yes

149
Q

What are the 3 parts of the small intestine?

A

Duodenum
Jejunum
Ileum

150
Q

What does the small intestine receive?

A

Chyme from stomach (pyloric sphincter)
Pancreatic juice from stomach (via sphincter of oddi)
Bile from gallbladder (via sphincter of oddi)

151
Q

What valve joins the small and large bowel?

A

Illeocaecal valve

152
Q

What 3 adaptations make the small intestine good for absorption?

A

Circular folds
Villi
Micro villi (the brush border)

153
Q

What do G cells of the gastric antrum (mainly) and duodenum secrete?

A

Gastrin

154
Q

What do I cells in the duodenum and jejunum secrete?

A

CCK

155
Q

What do the S cells in the duodenum secrete?

A

Secretin

156
Q

What do M cells in the duodenum and jejunum secrete?

A

Motilin

157
Q

What is an incretin?

A

Act upon B cells in the pancreas and stimulate the release of insulin

158
Q

Example of an incretin?

A

GIP

GLP-1

159
Q

What do K cells secrete in the duodenum and jejunum?

A

GIP

160
Q

What do the L cells of the gut secrete?

A

GLP-1

161
Q

What do Gr cells secrete?

A

Ghrelin

162
Q

What receptors do the secretions of the small intestine act on?

A

G-protein coupled receptors

163
Q

What mechanism control the secretion of intestinal juices into the intestine?

A 
Distension, irritation 
Gastrin
CCK 
Secretin 
Parasympathetic nerve activity 
Sympathetic nerve activity
164
Q

What effect does parasympathetic nerves have on the secretion of intestinal juices?

A

Increases secretion

165
Q

What effect does sympathetic nerves have on the secretion of intestinal juices?

A

Decreases secretion

166
Q

What do the small intestinal juices contain?

A

Mucus from goblet cells (for protection)
Aqueous salt for enzymatic digestion
No digestive enzymes

167
Q

What can excessive secretion of intestinal juices cause?

A

Secretory diarrhoea

168
Q

What activates segmentation in the small intestine?

A

Pacemaker cells (slow wave)

169
Q

What hormone triggers segmentation in the empty ileum (gastrointestinal reflex)?

A

Gastrin

170
Q

What trigger the migrating motor complex (MMC)?

A

Motilin

171
Q

What suppresses the MMC?

A

Gastrin

CCK

172
Q

What are endocrine secretions of the pancreas?

A

Insulin a Ms glucagon into the blood

173
Q

What cells secrete digestive enzymes in the pancreas?

A

Acinus cells

174
Q

What cells in the pancreas secrete aqueous NaHCO3- solution?

A

Duct cells

175
Q

What professes are secreted from the pancreas?

A

Trypsinogen
Chymotrypsinogen
Procarboxypeptidase A and B

176
Q

Other than pro teases what other pancreatic enzymes are secrete to digest food?

A

Pancreatic amylase

Pancreatic lipase

177
Q

What is the purpose of HCO3 solution secreted from duct cells
L

A

Neutralise acidic chyme entering the duodenum
Provides optimum pH for pancreatic enzyme function
Protects mucosa from erosion from acid

178
Q

What is the 3 phases of pancreatic secretion?

A

Cephalic
Gastric
Intestinal

179
Q

What are the sections of the large intestine?

A

Colon (ascending, transverse, descending, sigmoid)
Caecum
Appendix
Rectum

180
Q

What are the functions of the large intestine?

A 
Absorption of H2O, Na+ and Cl- 
Secretion of K+, HCO3- and mucus 
Absorption of short chain fatty acids 
Reservoir 
Periodic elimination of faeces
181
Q

What is Haustration?

A

Contraction of circular muscle causes Haustration (sacs) mixes content and allows time for fluid and electrolyte reabsorption

182
Q

What triggers ar involved in the gastronomic response?

A

Gastrin

Extrinsic nerve plexuses

183
Q

What is the parasympathetic/sympathetic involvement in the deflection reflex?

A

Relaxation and contraction of external anal sphincter (skeletal muscle)

184
Q

What cause flactulence?

A

Bacteria in colon attack forms of carb which are indigestible to humans

185
Q

What is constipation?

A

Presence of hard dried faeces within the colon. Results from delay in defaecation and enhanced absorption of H2O

186
Q

Causes of constipation

A

Ignoring the need to go
Decreased colonic motility (diet, metabolic disorders, age)
Obstruction of faecal movement
Impairment of motility/defaecation reflex

187
Q

Example of a disease that can cause impairment of the motility/defaecation reflex

A

Hirschsprung’s disease

188
Q

Symptoms of constipation

A

Abdominal discomfort
Headache
Loss of appetite
General malaise

189
Q

Is absorption a passive or active process?

A

Passive

190
Q

Definition of diarrhoea

A

Loss of fluid and salutes from the GI tract in excess of 500ml per day

191
Q

Intestinal fluid movement is always coupled to solute movement. True/False.

A

True.

192
Q

What are the routes by which water be absorbed?

A

Transcellular

Paracellular

193
Q

What is the main ion involved in water absorption?

A

Na+

194
Q

What are the 2 major mechanism or Na+ absorption?

A

Na+/glucose cotransport

Na+/amino acids cotransport

195
Q

How is Cl- absorbed parallel to Na+?

A

Na+ transport creates transepithelial potential in which the lumen is negative

196
Q

What stimulates Na+ exchange at the apical membrane in the duodenum?

A

Alkaline environment of the lumen in the jejunum

197
Q

Why is the lumen of the jejunum alkaline?

A

Presence of bicarbonate from the pancreas

198
Q

What is the primary mechanism of Na+ transport in the interdigestive period?

A

Na+/H+ exchange

Cl/HCO3- exchange

199
Q

What regulates Na+/H+ and Cl-/HCO3- exchange?

A

cAMP
cHMP
Ca2+!

200
Q

What effect do cAMP, cGMP and Na+ have on NaCl absorption?

A

Reduce NaCl absorption

201
Q

What clinical condition does reduction in NaCl cause?

A

Diarrhoea

202
Q

What channels mediate electrogenic Na+ absorption in the distal colon?

A

Epithelial Na+ channels

203
Q

Are epithelial Na+ channels regulate by cAMP and cGMP?

A

No they are increased by aldosterone

204
Q

What cells are involved in Cl- secretion?

A

Crypt cells

205
Q

What are the 3 processes involved in Cl- secretion?

A

Na+/K+ ATPase
Na+/K+/2Cl- co-transporter
K+ channels

206
Q

What gene when activated causes Cl- secretion?

A

CFTR

207
Q

What can activate the CFTR gene?

A

Bacterial enterotoxins
Hormones and neurotransmitters
Immune cell products
Some laxatives

208
Q

Activation of CFTR occurs indirectly as a result of the generation of?

A

cAMP
cGMP
Ca2+

209
Q

Causes of diarrhoea

A

Impaired absorption of NaCl
Non absorbable or poorly absorbable solute in intestinal lumen
Hyper motility
Excessive secretion

210
Q

How does cholera causes secretory diarrhoea?

A

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
Q

How do oral rehydration salts work?

A

Cause increased absorption of Na+ and glucose by SGLT1 which causes accompanying absorption of H2O

212
Q

What are the 2 blood supplies to the liver?

A

Hepatic portal vein

Hepatic artery

213
Q

Where in the liver does arterial and venous blood mix?

A

Liver sinusoids

214
Q

What vessel travels through the centre of the liver?

A

Hepatic vein

215
Q

What is in the portal triad?

A

Hepatic portal vein
Hepatic artery
Bile duct

216
Q

Where does blood flow when it enters the liver in the portal triad?

A

Inward through sinusoids to the central vein

217
Q

What cells secrete bile?

A

Hepatocytes

218
Q

What does bile flow through and in what direction?

A

Outwardly through canaliculi

219
Q

What are the 2 parts of the epithelium formed by hepatocytes?

A

Basolateral membrane

Apical membrane

220
Q

What does the apical membrane in the liver form?

A

Canaliculi

221
Q

What does the basolateral membrane face?

A

Space of Disse (pericellular space)

222
Q

What is in sinusoidal spaces?

A

Endothelial cells
Kuppfer cells
Stellate cells

223
Q

What type of cell are Kuppfer cells?

A

Macrophages

224
Q

What is the role of endothelial cells in the liver?

A

Allow free movement of salutes but not cells

225
Q

What are stellate cells in the liver important for?

A

Storage of vitamin A

226
Q

Where is bile stored and concentrated in between meals?

A

Gallbladder

227
Q

Chyme stimulate gallbladder smooth muscle contract through which 2 mechanisms?

A

CCK

Vagal impulses

228
Q

What mediates the opening of the sphincter of oddi?

A

CCK

229
Q

What ducts allow the spurt of bile into the duodenum?

A

Cystic and common bile ducts

230
Q

What is bile made of?

A

Secretion of hepatocytes

Secretion of bile duct cells

231
Q

What is the role of bile?

A

Digestion and absorption of fats

232
Q

What pH is the secretion of bile duct cells?

A

Alkaline

233
Q

What is the composition of hepatic bile?

A 
Primary bile acids (colic and cenodeoycholic acids) 
Water and electrolytes 
Lipids and phospholipids 
Cholesterol 
IgA 
Bilirubin
234
Q

What process do bile salts undergo after being reansorbed by active transport in the terminal ileum?

A

Enterohepatic recycling

235
Q

What are bile salts synthesised from?

A

Cholesterol

236
Q

What is the rate of synthesis of bile salts dependent on?

A

The hepatic portal vein concentration of the salts

AY Gastrointestinal (21 decks)

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