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1MB Gastroenterology - Rafi Ahmed > Physiology > Flashcards

Physiology Flashcards

1
Q

The large intestine is the principal site of dietary nutrient reabsorption. True/False?

A

False

Small intestine is the principle site of dietary nutrient absorption

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2
Q

What are the main functions of the large intestine?

A

Reabsorbs fluid + electrolytes

Stores faecal matter

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3
Q

The exocrine and endocrine “parts” of the pancreas are both part of the GI system. True/False?

A

False

Only the exocrine pancreas is part of the GI system

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4
Q

Name some accessory structures of the GI tract

A

Salivary glands
Pancreas
Liver
Gall bladder

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5
Q

Which muscle - smooth or skeletal - is predominant in the motility of the GI tract?

A

Smooth muscle

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6
Q

Which parts of the GI tract are under skeletal muscle control?

A

Mouth + pharynx
Upper oesophagus
External anal sphincter

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7
Q

Name two polysaccharides

A

Starch

Glycogen

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8
Q

Name two disaccharides

A

Sucrose

Lactose

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9
Q

Name three monosaccharides

A

Glucose
Fructose
Galactose

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10
Q

What are proteins broken down into?

A

Amino acids
Dipeptides
Tripeptides

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11
Q

The apical membrane of an enterocyte faces the lumen. True/False?

A

True

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12
Q

Which membrane of an enterocyte faces the blood?

A

Basolateral membrane

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13
Q

What are the 4 main layers of the GI tract wall, from innermost to outermost?

A

Mucosa
Submucosa
Muscularis externa
Serosa

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14
Q

What is the function of epithelial cells in the mucosa?

A

Absorption

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15
Q

What is the importance/function of the muscularis mucosa?

A

Can change shape/SA to facilitate absorption

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16
Q

What does contraction of circular muscle do to the lumen of the digestive tract?

A

Makes it narrower and longer

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17
Q

What does contraction of longitudinal muscle do to the lumen of the digestive tract?

A

Makes it shorter and fatter

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18
Q

What is the function of gap junctions between adjacent smooth muscle cells?

A

Enable slow wave of contraction to spread across smooth muscle sheet

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19
Q

Which cells drive slow wave electrical activity?

A

Interstitial cells of Cajal (ICCs)

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20
Q

What type of cells are ICCs?

A

Pacemaker cells

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21
Q

What must happen for ICCs to produce contraction?

A

Slow wave amplitude must reach threshold to trigger an action potential

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22
Q

The upstroke of the AP generated by ICCs is mediated by Na+ influx. True/False?

A

False

Mediated by Ca++ influx through Ca++ channels

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23
Q

The force of contraction in the GI tract is related to the number of action potentials discharged from ICCs. True/False?

A

True

The more APs fired, the greater the force of contraction

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24
Q

What determines the basal electrical rhythm of the digestive tract?

A

Slow wave electrical activity

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25
Q

All slow waves trigger contraction. True/False?

A

False

Threshold must be reached first

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26
Q

What is the net direction of luminal contents in the small intestine? Why?

A

Aboral direction

Fduodenum greater than Fileum

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27
Q

What is the net direction of luminal contents in the large intestine? Why?

A

Oral direction

Fdistalcolon greater than Fproximalcolon in order to allow some reabsorption to take place

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28
Q

What connects myenteric and submucosal plexi?

A

Interganglionic fibre tracts

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29
Q

What is the nervous system of the gut called?

A

Enteric nervous system

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30
Q

The parasympathetic system plays a bigger role in the enteric nervous system than the sympathetic system. True/False?

A

True

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31
Q

Parasympathetic outflow is thoraco-lumbar. True/False?

A

False

Cranio-sacral

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32
Q

Which nerve provides parasympathetic cranial outflow?

A

Vagus nerve

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33
Q

Which nerve provides parasympathetic sacral outflow?

A

Pelvic nerves

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34
Q

Post-ganglionic neurones are essentially intrinsic to the ENS. True/False?

A

True

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35
Q

Name a local nerve reflex of the GI tract

A

Peristalsis

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36
Q

Name a short nerve reflex of the GI tract

A

Intestino-intestinal reflex

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37
Q

What is the intestino-intestinal reflex?

A

Overdistention in one area of the intestine causes relaxation in the rest of the intestine

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38
Q

Name a long nerve reflex of the GI tract

A

Gastroileal reflex

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39
Q

What is the gastroileal reflex?

A

Stomach signals increase motility of the ileum - open the ileocaecal valve to empty chyme to prepare ileum to receive fresh chyme from the stomach

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40
Q

What happens to the propulsive (oral) segment in peristalsis?

A

Circular muscle contracts

Longitudinal muscle relaxes

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41
Q

What happens to the receiving (aboral) segment in peristalsis?

A

Circular muscle relaxes

Longitudinal muscle contracts

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42
Q

Which substances mediate contraction of circular/longitudinal muscle?

A

ACh

Substance P

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43
Q

Which substances mediate relaxation of circular/longitudinal muscle?

A

VIP

NO

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44
Q

What is the process of segmentation called in the large intestine?

A

Haustration

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45
Q

The upper oesophageal sphincter is controlled by smooth muscle. True/False?

A

False

Skeletal muscle

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46
Q

The lower oesophageal sphincter is controlled by smooth muscle. True/False?

A

True

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47
Q

Which anal sphincter - internal or external - is controlled by skeletal muscle?

A

External anal sphincter

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48
Q

Which receptors are stimulated when food reaches the pharynx? What do they do?

A

Pharyngeal pressure receptors send afferent impulses to the swallowing centre in the medulla

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49
Q

In swallowing, what happens to the larynx? Why?

A

Elevates to prevent food from entering the trachea

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50
Q

In peristalsis, circular fibres in front of the bolus contract. True/False?

A

False

Circular muscle behind the bolus contracts

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51
Q

What happens if food becomes lodged in the oesophagus?

A

Secondary peristaltic wave, more forceful than the first, is triggered locally

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52
Q

What are the 3 major pairs of salivary glands and their locations?

A

Parotids - over the masseter below ears
Submandibular - lower edge of mandible
Sublingual - under tongue

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53
Q

Sublingual salivary gland contribute towards 70% of saliva. True/False?

A

False

Submandibular gland contributes 70% of saliva

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54
Q

How much saliva is contributed to by the parotid glands?

A

25%

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55
Q

What are the antibacterial components of saliva?

A

Lysozyme
Lactoferrin
Immunoglobulins

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56
Q

What is xerostomia?

A

Dry mouth syndrome due to inadequate production of saliva

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57
Q

Primary saliva secretion occurs from where?

A

Acinus

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58
Q

Secondary saliva secretion occurs from where?

A

Duct cells

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59
Q

What does the primary saliva secretion consist of?

A

Na, K, Cl and HCO3

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60
Q

How is the primary saliva secretion modified by duct cells?

A

Remove Na and Cl
Add some K and HCO3
Diluted as no H2O movement

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61
Q

NaCl content of saliva is lower than that of the plasma. True/False?

A

True

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62
Q

Glucose content of saliva is higher than that of the plasma. True/False?

A

False

No glucose in saliva

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63
Q

When flow rate is high, HCO3 content of the saliva increases. True/False?

A

True

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64
Q

How does the simple (unconditioned) reflex stimulate salivary glands to increase saliva production?

A

Pressure receptors in mouth activate in presence of food and sent afferent impulses to salivary centre in the medulla

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65
Q

How does the conditioned reflex stimulate salivary glands to increase saliva production?

A

Think/smell/see food activates cerebral cortex which activates salivary centre in the medulla

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66
Q

Which nerves carry parasympathetic innervation of saliva production control?

A

Facial nerve

Glossopharyngeal nerve

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67
Q

What is the effect of parasympathetic stimulation upon saliva production?

A

Large volume
Watery
Enzyme rich

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68
Q

What is the effect of sympathetic stimulation upon saliva production?

A

Low volume
Thick
Mucus rich

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69
Q

What are the 4 main anatomical areas of the stomach?

A

Fundus
Body
Antrum
Pylorus

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70
Q

Where does most mixing/churning of food take place in the stomach?

A

Antrum

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71
Q

What is the substance produced when food mixes with gastric secretions?

A

Chyme

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72
Q

Name a substance which can be absorbed by the stomach

A

Ethanol

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73
Q

Thickness of smooth muscle lining decreases distally in the stomach. True/False?

A

False

Increasing thickness distally (antrum thickness greater than fundus thickness)

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74
Q

What occurs in Retropulsion?

A

Peristaltic wave forces chyme against closed pyloric sphincter, so chyme bounces back and undergoes more mixing

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75
Q

Name 2 gastric factors promoting gastric emptying

A

Volume of chyme (larger volume increases motility due to distention)
Consistency of chyme (thinner liquid facilitates emptying)

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76
Q

Which 2 duodenal factors delay gastric emptying?

A

Enterogastric reflex

Release of enterogastrones

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77
Q

What is the enterogastric reflex?

A

Duodenum signals to stomach that it has enough chyme so slow down emptying/peristaltic contraction

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78
Q

What is the effect of enterogastrones on gastric emptying?

A

CCK and secretin release from duodenum inhibit stomach contraction

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79
Q

Where is the pyloric gland area located?

A

Antrum

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80
Q

Where is the oxyntic mucosa area located?

A

Fundus and Body

81
Q

Which cells are contained in the pyloric gland area?

A

D cells

G cells

82
Q

What do D cells secrete?

A

Somatostatin

83
Q

What do G cells secrete?

A

Gastrin

84
Q

Which cells are contained in the oxyntic mucosa?

A

Parietal cells
Enterochromaffin-like cells
Chief cells

85
Q

What do ECL cells secrete?

A

Histamine

86
Q

What do parietal cells secrete?

A

HCl

Intrinsic factor

87
Q

What do chief cells secrete?

A

Pepsinogen

88
Q

What does autocatalytic mean with regards to pepsinogen and pepsin?

A

Pepsin formation triggers further pepsin formation from pepsinogen

89
Q

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

A

Binds vitamin B12

90
Q

What is the role of histamine in the oxyntic mucosa?

A

Stimulates HCl secretion

91
Q

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

A

Stimulates HCl secretion

92
Q

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

A

Inhibits HCl secretion

93
Q

In the gastric parietal cell, present in the gastric pit of the ____ ____, CO2 and H2O combine under the enzyme ____ ____ which dissociates to form _ and ___.
___ is transported out of the cell via an antiporter in exchange for __, which is driven out into the canaliculus.
_ is secreted into the canaliculus via the ___ ___, and combines with __ to form ___.

A

In the gastric parietal cell, present in the gastric pit of the oxyntic mucosa, CO2 and H2O combine under the enzyme carbonic anhydrase which dissociates to form H+ and HCO3.
HCO3 is transported out of the cell via an antiporter in exchange for Cl, which is driven out into the canaliculus.
H+ is secreted into the canaliculus via the proton pump, and combines with Cl to form HCl.

94
Q

What are Secretagogues?

A

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

95
Q

In response to Secretagogues, 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

96
Q

What are the 3 phases of gastric secretion?

A

Cephalic
Gastric
Intestinal

97
Q

What is involved in the cephalic phase?

A

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

98
Q

What is involved in the gastric phase?

A

Distention due to food causes mechanoreceptors to augment secretion

99
Q

What is involved in the intestinal phase?

A

Gastric secretion is halted through secretin, CCK and somatostatin as the stomach empties

100
Q

What is the importance of the mucus gel layer on the surface of mucous secreting cells?

A

Prevents pepsin/HCl reaching the apical surface of the cells and damaging the cells

101
Q

What are the two forms of starch?

A

Amylose

Amylopectin

102
Q

Amylose and amylopectin are branched chain molecules. True/False?

A

False

Amylose isn’t but amylopectin is branched

103
Q

Which type of bond links glucose monomers in amylose?

A

alpha-1,4

104
Q

Which type of bonds link glucose monomers in amylopectin?

A

alpha-1,4

alpha-1,6 for branched chain

105
Q

Glycogen is a branched chain polysaccharide. True/False?

A

True

106
Q

Which type of bond links glucose monomers in glycogen?

A

alpha-1,4

alpha-1,6

107
Q

Name two oligosaccharides (disaccharides)

A

Lactose

Sucrose

108
Q

Which monomers make up sucrose?

A

Glucose and fructose

109
Q

Which monomers make up lactose?

A

Glucose and galactose

110
Q

Which enzyme carries out luminal digestion of starch?

A

alpha-amylase

111
Q

What is starch broken down into in luminal digestion?

A

Oligosaccharides - e.g. maltose

112
Q

Which enzymes carry out brush border digestion of maltose, lactose and sucrose?

A

Maltase
Lactase
Sucrase-isomaltase

113
Q

What are oligosaccharides such as lactose, maltose and sucrose broken down into in brush border digestion?

A

Monosaccharides - e.g. glucose, fructose, galactose

114
Q

Alpha-amylase breaks down all alpha-1,4 glucose linkages. True/False?

A

False

Only breaks down linear internal links - not terminal links, hence no production of glucose

115
Q

Lactase can only break down lactose. True/False?

A

True

116
Q

How is isomaltase unique?

A

It is the only enzyme that can split the branching of alpha-1,6 linkages

117
Q

What is lactose intolerance?

A

Inability to digest lactose, caused by lactase insufficiency

118
Q

Absorption of monosaccharides involves entry via the basolateral membrane and exit via the apical membrane. True/False?

A

False

Other way around!

119
Q

What is meant by secondary active transport?

A

Transport either via cotransport or antiport

120
Q

What are oligopeptides?

A

Dipeptides
Tripeptides
Some tetrapeptides
[products of protein digestion]

121
Q

What denatures proteins in the stomach?

A

HCl

122
Q

Which enzyme cleaves protein into peptides in the stomach?

A

Pepsin

123
Q

Is pepsin essential for protein digestion?

A

No

124
Q

What are the active enzymes that digest protein in the duodenum?

A 
Trypsin
Chymotrypsin
Elastase
Procaroxypeptidase A
Procaroxypeptidase B
125
Q

Where does most fat digestion take place?

A

Small intestine

126
Q

Which enzyme cleaves off fatty acids from triglycerides in the stomach?

A

Gastric lipase

127
Q

What is the main lipid digesting enzyme in the duodenum?

A

Pancreatic lipase

128
Q

What do bile salts do to large lipid droplets?

A

Emulsify them into smaller droplets with a larger SA to increase affinity for lipase

129
Q

Which enzyme acts as a cofactor for lipase to help it gain access to the triglyceride chain?

A

Colipase

130
Q

What is a mixed micelle?

A

Emulsified fat globule containing monoglyceride, fatty acids, phospholipid, bile salt and cholesterol

131
Q

How are short and medium -chain fatty acids absorbed into capillaries?

A

Exit basolateral membrane via diffusion

132
Q

What happens to long-chain fatty acids and monoglycerides once in the enterocyte?

A

Resynthesised to triglyceride in the ER and incorporated into chylomicrons

133
Q

What coats the cholesterol ester-triglyceride complex to form a chylomicron?

A

Apolipoprotein (apo-B48)

134
Q

How does the chylomicron exit the enterocyte? Where does it go?

A

Exocytosis into the lymphatic system

135
Q

Which enzyme metabolises chylomicrons?

A

Lipoprotein lipase

136
Q

What carries the free fatty acids and glycerol released by chylomicron degradation?

A

Albumin

137
Q

What does a chylomicron remnant consist of?

A

Cholesterol and phospholipid

138
Q

Which protein allows cholesterol absorption?

A

NPC1L1 protein

139
Q

How does the scaffold containing cholesterol bound to NPC1L1 move around the cell?

A

Via myosin runners

140
Q

When calcium concn is low, it is absorbed via Ca channels. Which vitamin increases expression for these channels?

A

Vitamin D

141
Q

Ferric iron can be absorbed by the enterocyte. True/False?

A

False

Must be converted to ferrous iron (Fe2)

142
Q

What is the other mechanism (other than receptor transport) by which iron can be absorbed by the enterocyte?

A

Through haem - haem is taken up and degraded by haem oxidase

143
Q

What is the storage form of iron called?

A

Ferratin

144
Q

What are the ranges for normal BMI?

A

18.5-25

145
Q

What are the ranges for BMI classed as overweight?

A

25-29

146
Q

What are the ranges for BMI classed as obese?

A

30-39

147
Q

What are the ranges for BMI classed as morbidly obese?

A

Greater than 40

148
Q

How is obesity “a disease of the brain”?

A

The brain sees new fat/weight as normal, and attempts to lose weight are seen as a threat to survival, so the new weight is defended

149
Q

Lesioning ventromedial hypothalamus causes leanness. True/False?

A

False

Lesioning ventromedial hypothalamus causes obesity

150
Q

Which lesioning part of the hypothalamus causes leanness?

A

Lateral part

151
Q

Define satiation

A

Feeling of fullness during/following a meal

152
Q

Define satiety

A

Period from end of one meal to beginning of next

153
Q

What effects do satiation signals have during a meal?

A

Increased signals limit meal size, i.e. you can’t eat anymore

154
Q

What is ghrelin?

A

A hunger signal - levels increase before a meal and decrease after a meal

155
Q

Which 2 hormones report the “fat status” of fat stores to the brain?

A

Leptin

Insulin

156
Q

Levels of leptin and insulin increase in the blood as more fat is stored. True/False?

A

True

157
Q

Reduced leptin mimics starvation. True/False?

A

True

158
Q

Name a drug that can be prescribed to tackle obesity

A

Orlistat

159
Q

How does Orlistat work?

A

Inhibits pancreatic lipase to decrease triglyceride absorption

160
Q

Vomiting is due to stomach contraction. True/False?

A

False

Stomach, oesophagus + sphincters are relaxed

161
Q

Which centre coordinates vomiting in the brainstem?

A

Vomiting centre (VC) in the medulla oblongata

162
Q

Does nausea always cause vomiting?

A

No

163
Q

Toxic materials stimulate enterochromaffin cells to release which mediator of vomiting?

A

5-HT (serotonin)

164
Q

Which 3 stimulants stimulate the CTZ in the brainstem to act on the VC to initiate vomiting?

A

Toxins
Mechanical activity/disease
Motion sickness

165
Q

What effects do vagal efferents have on the oesophagus, stomach and small intestine in the vomiting reflex?

A

Oesophagus shortens
Stomach relaxes
Small intestine retrograde contraction

166
Q

Place the parts of the small intestine in order from shortest to longest

A

Duodenum (0.25m)
Jejunum (2.5m)
Ileum (3m)

167
Q

Which 3 components increase the SA of the small intestine?

A

Circular folds
Villi
Microvilli

168
Q

Where is gastrin secreted from?

A

G cells of stomach + duodenum

169
Q

Where is CCK secreted from?

A

I cells of duodenum + jejunum

170
Q

Where is secretin secreted from?

A

S cells of duodenum

171
Q

Where is motilin secreted from?

A

M cells of duodenum + jejunum

172
Q

Where is ghrelin secreted from?

A

Gr cells of stomach, small intestine + pancreas

173
Q

Distention, gastrin, CCK, secretin + parasympathetic activity all enhance the secretion of intestinal juice. True/False?

A

True

174
Q

What is the migrating motor complex in the small intestine?

A

Strong peristaltic contraction spanning from stomach to end of ileum which clears debris and mucus between meals (housekeeper - migrating “mother” complex!)

175
Q

Gastrin and CCK trigger the migrating motor complex. True/False?

A

False

Motilin triggers it; CCK and gastrin inhibit it

176
Q

The exocrine pancreas secretes digestive enzymes from ____ cells and aqueous salt from ____ cells, collectively called pancreatic juice

A

The exocrine pancreas secretes digestive enzymes from acinar cells and aqueous salt from duct cells

177
Q

What does the aqueous salt solution released from pancreatic duct cells do?

A

Neutralises acidic chyme in the duodenum

178
Q

In the duodenum, proton is lost/added to blood and bicarbonate is lost/added to lumen; in the stomach, proton is lost/added to lumen and bicarbonate lost/added to blood

A

In the duodenum, proton is lost to blood and bicarbonate is added to lumen; in the stomach, proton is added to lumen and bicarbonate lost to blood

179
Q

Acid/chyme in duodenum stimulates/inhibits the release of secretin, which stimulates/inhibits release of intestinal juice from pancreas

A

Acid/chyme in duodenum stimulates the release of secretin, which stimulates release of intestinal juice from pancreas

180
Q

Fat and protein in the duodenum stimulates/inhibits the release of CCK, which stimulates/inhibits release of intestinal juice from pancreas

A

Fat and protein in the duodenum stimulates the release of CCK, which stimulates release of intestinal juice from pancreas

181
Q

Describe haustration

A

Intermittent contraction of circular muscle in proximal colon at slow rate to allow contents to move but leave enough opportunity for reabsorption

182
Q

Which nerve conveys efferents to cause either relaxation or contraction of the external anal sphincter?

A

Pudendal nerve

183
Q

Reabsorption of water is largely driven by the reabsorption of which salt?

A

Sodium

184
Q

Which mechanism is the most major in Na reabsorption in the post-prandial period in the jejunum?

A

Na-glucose and Na-amino acid cotransport

185
Q

What is the effect of cAMP, cGMP and Ca2+ on NaCl absorption?

A

Reduce NaCl absorption

186
Q

Where do epithelial Na channels (ENaC) mediate Na absorption?

A

Distal colon

187
Q

Where does blood from the hepatic artery and hepatic portal vein meet and mix in the liver?

A

Sinusoids (fenestrated capillaries that enable blood to leak out into space of Disse)

188
Q

The liver is made up of hexagonal lobules. List the vessels and ducts contained in each lobule

A 
Central vein (branch of hepatic vein)
Portal triad (hepatic portal branch + hepatic artery branch + bile duct)
189
Q

What is the direction of blood flow in a liver lobule?

A

Inwardly through sinusoids towards the central vein

190
Q

What is the direction of bile flow in a liver lobule?

A

Outwardly through canaliculi towards the bile duct

191
Q

Canaliculi are formed by the basolateral membrane. True/False?

A

False

Canaliculi are formed by the apical membrane

192
Q

Which membrane faces the space of Disse?

A

Basolateral membrane

193
Q

Which 3 types of cell are located in the sinusoidal spaces?

A

Endothelial cells
Kuppfer cells
Stellate (Ito) cells

194
Q

What is the function of endothelial cells in the sinusoidal space?

A

Fenestrated structure allows passage of solute, but not cells

195
Q

What is the function of Kuppfer cells in the sinusoidal space?

A

Macrophages that remove bacterial matter and dead RBCs

196
Q

What is the function of Stellate (Ito) cells in the sinusoidal space?

A

Store vitamin A within the space of Disse

May deposit collagen, beginning liver cirrhosis

197
Q

Most bile is secreted by bile duct cells. True/False?

A

False

Most is secreted by the liver

198
Q

Most of the bile entering the duodenum is reabsorbed in the terminal ileum. True/False?

A

True

1MB Gastroenterology - Rafi Ahmed (23 decks)

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