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M104 T1 > M104 T1 L5 > Flashcards

M104 T1 L5 Flashcards

1
Q

How much fluid is secreted into the GI tract each day?

A

approx 7 litres

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2
Q

What happens to the majority of secreted fluid in the GI tract?

A

it will be reabsorbed as the contents moves through the GI tract

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3
Q

After reabsorption of secreted fluid in the GI tract, how much is actually excreted daily?

A

about 100 mls

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4
Q

What is the pH of salivary secretions?

A

pH 6-7

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5
Q

What are the three Major salivary glands?

A

Parotid
Submandibular
Sublingual

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6
Q

Where are dispersed minor salivary glands?

A

throughout the mucosa of the mouth and tongue

these occur in the in the lips, cheeks, palate and in the tongue

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7
Q

Where is the parotid gland located?

A

anterior and inferior to the ear

between the skin and the muscle

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8
Q

Where is the duct of the parotid gland located?

A

it enters the oral cavity just above the second molar

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9
Q

What does the parotid gland secrete?

A

Serous, watery secretions containing salivary amylase for starch digestion

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10
Q

What does the submandibular gland secrete?

A

a mixture of serous and mucus containing saliva

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11
Q

Where is the submandibular gland located?

A

inferior to the mandible

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12
Q

Where is the duct of the submandibular gland located?

A

lateral to the lingual frenulum

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13
Q

Where is the sublingual gland located?

A

in the floor of the oral cavity

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14
Q

What does the sublingual gland secrete?

A

thicker mucus dominant secretions for lubrication

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15
Q

Where is the duct of the sublingual gland located?

A

they enter the oral cavity under the tongue

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16
Q

What type of cells does the sublingual gland contain?

A

mucin secreting cells

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17
Q

What percent of saliva is produced by the parotid and submandibular glands?

A

90%

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18
Q

What percent of saliva is made up of water?

A

99.5%

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19
Q

What is the purpose of water in saliva?

A

acts as a solvent which dissolves components of the food to aid in taste
helps with swallowing, initiation of digestion, oral hygiene - keeps bacterial load down in the oral cavity

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20
Q

What is the purpose of electrolytes in saliva?

A

have a buffering capacity, particularly for acidic foods in the oral cavity

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21
Q

What are key enzymes in saliva? (LacLAK)

A 
Lactoferrin
Lysozyme
Lingual lipase (serous salivary glands of tongue)
a-amylase 
Kallikrein
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22
Q

What is the role of a-amylase in saliva?

A

digests starch via hydrolysis of the a-1,4 glycosidic bonds

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23
Q

What three substances does a-amylase degrade starch into?

A

disaccharide maltose
trisaccharide maltotriose
a-dextrin

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24
Q

Up to what percentage of starch digestion can occur through the action of amylase?

A

75%

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25
Q

When does amylase stop digesting starch?

A

when it’s neutralised by the acidic pH of the stomach

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26
Q

What is the role of a-amylase in digestion?

A

to hydrolyse peptidoglycans in the wall of gram negative bacteria so it can keep the level of bacteria in the oral cavity down

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27
Q

What is the role of lingual lipase in digestion?

A

to hydrolyse lipid triglycerides to fatty acid and diglycerides

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28
Q

What enzymes are produced by von Ebner glands ?

A

lingual lipase

amylase

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29
Q

What are the optimal conditions for lingual lipase?

A

acidic pH

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30
Q

What is the role of Lactoferrin in digestion?

A

has anti-microbial properties through the chelation of iron to prevent microbes from multiplying

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31
Q

What is the role of Kallikrein ​in digestion?

A

converts plasma protein a-2- globulin into bradykinin

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32
Q

What is the role of Secretory IgA ​in digestion?

A

it prevents microbial attachment to epithelium

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33
Q

What is the role of myoepithelial cells?

A

they surround the acinar cells and are contractile in nature

they help to drive the primary secretions along the duct

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34
Q

What is the role of ductal cells?

A

modifying primary saliva

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35
Q

What are the unique properties of salivary glands?

A

there is a large volume of saliva produced compared to mass of gland
the saliva produced has a low osmolarity compared to blood plasma
there is a relatively high K+ concentration

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36
Q

What happens in Stage 1 of hypotonic saliva formation?

A

an isotonic plasma-like saliva, which contains water, electrolytes and enzymes, is secreted into a salivary duct by acinar cells

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37
Q

What happens in Stage 2 of hypotonic saliva formation?

A

as the saliva moves along the duct lumen, ductal cells secrete HCO3- and K+ ions and reabsorb NaCl, all through membrane transporter proteins
produces a HCO3- and K+ rich hypotonic saliva

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38
Q

What are the ions in NaCl reabsorbed in exchange for in Stage 2 of hypotonic saliva formation?

A

Na+ reabsorbed in exchange of K+

Cl- reabsorbed for carbonate ions

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39
Q

What is a consequence of the salivary duct being relatively impermeable to water?

A

AAR there is limited movement of water by osmosis out of the duct lumen following NaCl reabsorption

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40
Q

What is the effect of the formation of hypotonic saliva?

A

the production of a K and bicarbonate-rich hypotonic saliva compared to plasma and the interstitial fluid

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41
Q

What is composition of saliva and can this change?

A

the composition of saliva is always hypotonic

but it can change with flow rate

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42
Q

What is the electrolyte composition of saliva at a high rate of secretion compared to that of saliva at a low rate of secretion?

A

Na+ & Cl- are always low

K+ & HCO3- are high

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43
Q

What happens during a low rate of secretion?

A

there is a maximum reabsorption of electrolytes

hypotonic saliva is produced

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44
Q

What are the electrolytes like in hypotonic saliva?

A

lower concentration of osmotically active electrolytes

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45
Q

What happens during a high rate of secretion?

A

there is reduced reabsorption of electrolytes

alkaline, HCO3- rich saliva is produced

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46
Q

What is the osmolality like in hypotonic saliva?

A

has an increased osmolality closer to that of primary isotonic saliva

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47
Q

How is salivary secretion innervated?

A 
by the autonomic NS 
parasymp stimulation (more important)
symp (less)
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48
Q

What happens when there is a stimuli for salivation?

A

a signal is created via thesalivatorynuclei in the medulla

different nerves are stimulated for the activation of different glands

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49
Q

Which two glands does the facial nerve supply?

A

sublingual

submandibular

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50
Q

Which gland does the glossopharyngeal nerve supply?

A

the parotid gland

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51
Q

What is the effect of parasympathetic stimulation on the salivary glands?

A

Increase salivary secretion
increases vasodilation
increases myoepithelial cell contraction

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52
Q

What are the inhibitors of salivary secretion?

A

fatigue, sleep, fear, dehydration

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53
Q

What is the effect of the symp NS on salivary secretion?

A

secretion rate increases

saliva is higher in mucin and enzymes

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54
Q

What nerve conveys symp NS action to the salivary glands?

A

superior cervical ganglion

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55
Q

How is an initial vasoconstriction activated in the salivary glands?

A

noradrenaline is released

it stimulates alpha adrenergic receptors on the blood vessels surrounding the glands

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56
Q

How is a later vasodilation activated in the salivary glands?

A

the kallikrein enzyme is released
it goes on to act on a-2 globulin
it forms the vasodilator bradykinin - results in vasodilation

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57
Q

What are two examples of conditions associated with salivary gland dysfunction?

A

Sjögren’s syndrome

Xerostomia

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58
Q

What are the effects of Sjögren’s syndrome?

A

commonly affects tear and saliva production
dry eyes and dry mouth
(destroys exocrine glands)

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59
Q

What are the effects of xerostomia?

A

dry mouth

bacterial overgrowth

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60
Q

What can bacterial overgrowth in the oral cavity cause?

A

dental caries

halitosis

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61
Q

What can a dry mouth cause?

A

inadequate lubrication of the oral cavity
difficulty speaking
difficulty swallowing solid food

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62
Q

What do gastric pits branch into?

A

gastric glands

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63
Q

What type of cells do gastric glands contain?

A

secretory cells

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64
Q

What is the role of exocrine cells?

A

responsible for excreting the components of the gastric juice

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65
Q

What is the role of mucous neck cells?

A

secrete a thin mucus

joins mucus secreted by surface mucus cells

66
Q

What is the role of parietal cells?

A

secretes HCl and IF

67
Q

What substances do chief cells secrete?

A

pepsinogen
rennin
gastric lipase

68
Q

What are the three types of exocrine cells?

A

mucous neck cells
parietal cells
chief cells

69
Q

What endocrine cells are present in gastric glands?

70
Q

What two types of cells are present in gastric glands?

A

endocrine cells

exocrine cells

71
Q

What do G cells secrete?

A

the hormone gastrin

72
Q

What do ECL cells secrete?

73
Q

Where are the two main types of gastric glands?

A

(80%) gastric/oxyntic glands - body and fundus

(20%) pyloric glands - antrum

74
Q

What are the exocrine secretions of the gastric/oxyntic glands into the body and fundus of the stomach?

A

HCl, IF
pepsinogen
mucus

75
Q

What substances are secreted by the paracrine glands in the body and the fundus of the stomach?

A

histamine by ECL cells

somatostatin by Delta cells

76
Q

What substances are secreted by the pyloric glands in the antrum of the stomach?

A 
mucus 
gastrin (endocrine)
somatostatin (endo and exocrine)
77
Q

What are the components of gastric juice?

A 
Water and electrolytes
Mucus (glycoprotein mucin) 
Pepsinogen pro-enzyme
Rennin in neonates only
Gastric lipase
HCl (pH 1-3)  
IF
78
Q

What is the role of water and electrolytes in gastric juice?

A

they act as a medium for the action of assets and enzymes

they allow for the digestion of organic substances to occur

79
Q

What is the role of mucus in gastric juice?

A

protective function - coats the surface of the stomach

protects it from the harmful effects of acid and the enzyme pepsin

80
Q

What is the role of Pepsinogen pro-enzyme in gastric juice?

A

cleaves peptide bonds (protein to smaller peptides)

81
Q

What is the role of renin in gastric juice?

A

coagulates milk through casein proteolysis

82
Q

What is the role of Gastric lipase in gastric juice?

A

converts triglycerides to fatty acid and diglycerides

83
Q

What do parietal cells secrete?

A

HCl and IF

84
Q

What is the pH of the stomach?

85
Q

What are the roles of HCl in the stomach?

A

converts pro-enzyme pepsinogen to pepsin
denatures proteins
kills microorganisms

86
Q

What is the role of IF in the stomach?

A

allows for the absorption of vitamin B12 in the ileum

87
Q

What is vitamin B12 used for?

A

erythropoiesis in the bone marrow

88
Q

What condition is caused by a vitamin B12 deficiency?

A

pernicious anaemia

89
Q

What is the structure of parietal cells?

A

an intracellular branched canalicular structure

are packed with tubulovesicles in resting state

90
Q

What are parietal cells packed with?

A

mitochondria

tubulovesicles

91
Q

What do the tubulovesicles in parietal cells contain?

A

carbonic anhydrase
other enzymes
HK-ATPase

92
Q

What happens to tubulovesicles when the cell is stimulated to produce acid?

A

they fuse with the canalicular membrane to form microvilli

HCl is formed at these microvilli and secreted

93
Q

Where are tubulovesicles located?

A

on the apical membrane

94
Q

How is acid secreted into the gastric lumen from parietal cells?

A

its driven by the presence of a H / K - ATP proton pump in the apical membrane of the parietal cell
it drives the active secretion of H+
HCO3- exchanged for Cl- in the basal lateral membrane of the parietal cell
causes an alkaline tide - when the gastric venous blood becomes alkaline postprandially
Cl- diffuses into lumen

95
Q

Where are hydrogen ions derived from?

A

from the activity of carbonic anhydrase

when it catalyses the formation of bicarbonate ions from co2 and water

96
Q

What are the three major routes by which gastric acid is secreted?

A

ACh release
gastrin release
histamine release

97
Q

How does gastrin release result in the secretion of gastric acid?

A

is released from G cells
enters the bloodstream
returns to parietal cell membrane

98
Q

What is the effect of vagal innervation on gastric acid secretion?

A

results in the secretion of ACh

this regulates hydrogen secretion

99
Q

What is the effect of histamine release on gastric acid secretion?

A

released from ECL cells

histamine binds to the H2 receptors on the parietal cell membrane

100
Q

How do all gastric acid secretion pathways work?

A

by second messenger intracellular pathways

101
Q

What is the chain of events by which gastrin and ACh trigger HCl secretion from parietal cells?

A

activate PLC
catalyses the formation of IP3
causes the release of intracellular calcium stores
histamine binds to the H2 receptor
it activates adenylate cyclase to form cAMP
activates protein kinase
this ultimately triggers acid secretion from the parietal cell

102
Q

What substances interrupt stages of the parietal cell acid secretion pathway?

A

somatostatin

mucosal prostaglandin

103
Q

How does somatostatin reduce acid secretion from parietal cells?

A

it works as an antagonist against histamine at the H2 receptor

104
Q

How do NSAIDs increase acid secretion from parietal cells?

A

they inhibit somatostatin (antagonist against histamine)

so secretion increases

105
Q

How do prostaglandins interact with the parietal cell acid secretion pathway?

A

released by D cells to inhibit AC (adenylate cyclase)

so they stop histamine from causing acid secretion

106
Q

What three pharmalogical drugs inhibit gastric acid? (OCA)

A

Omeprazole
Cimetidine
Atropine

107
Q

What is the role of the H+/K+-ATPase?

A

proton pump - to pump out H+ of the acid from parietal cells into the gastric lumen

108
Q

What drug inactivates the H+/K+-ATPase proton pump?

A

Omeprazole

109
Q

What is the effect of Cimetidine?

A

it inhibits stimulus for acid secretion

it antagonises the activity of histamine at the H2 receptor

110
Q

What is the effect of Atropine?

A

it inhibits muscarinic receptors and vagal stimulation of acid secretion

111
Q

What is the secretion of gastrin triggered by?

A

vagus nerve
distention of the stomach
the presence of partially digested peptide fragments

112
Q

How does gastrin increase the rate of digestion once released into circulation?

A

it acts on parietal cells and chief cells to upregulate the secretion of acid and pepsinogen
it is responsible for lower oesophageal sphincter contraction
it increases motility in the stomach for mixing and peristalsis
it relaxes the pyloric sphincter so that the contents of the stomach move into the duodenum

113
Q

What are the three phases of gastric secretion?

A

Cephalic
Gastric
Intestinal (excitatory & inhibitory)

114
Q

What type of innervation is cephalic gastric secretion regulated by?

A

vagal innervation - the sight, smell of food

115
Q

What triggers the “gastric” phase of gastric secretion?

A

once the bolus hits the stomach

116
Q

What is the effect of the vagus relating to cephalic gastric secretion?

A

it stimulates the production of gastric juice by parietal and chief cells
it stimulates the production of the hormone gastrin

117
Q

What type of innervation is “gastric” secretion regulated by?

A

local neural secretatory reflexes

vagal stimulation

118
Q

What is the effect of “gastric” secretion?

A

promotes the secretions of parietal, chief, mucal and G cells

119
Q

How does “gastric” secretion stimulate parietal cells?

A

directly

indirectly - via ECL histamine release

120
Q

What are the two types of intestinal gastric secretion phase?

A

Excitatory

Inhibitory

121
Q

What triggers the intestinal phase of gastric secretion?

A

when chyme enters the duodenum

122
Q

What happens during the excitatory intestinal phase of gastric secretion?

A

when chyme is pH3 or more, peptides in the duodenum will stimulate gastric secretions via vagus and gastrin

123
Q

What happens during the inhibitatory intestinal phase of gastric secretion?

A

when chyme is pH2 or less
mechanical distention
the presence of protein breakdown products
the presence of hypo/hyper-osmotic products

124
Q

What substances inhibit gastric secretion during the inhibitatory intestinal phase? (CGS)

A

CCK
GIP
Secretin

125
Q

Why is the gastric mucosa not damaged by the presence of pH1 and peptide digesting enzymes?

A

viscous mucosal barrier

tight paracellular junctions

126
Q

What is the mucus layer of the gastric mucosa made by?

A

the glands in the surface mucous secreting it

127
Q

What is the main gastric mucosa made up of?

A

mucopolysaccharides

proteins

128
Q

How does the mucus layer in the gastric mucosa help to neutralise hydrogen ions?

A

the basic side chains in mucin

the HCO3- secreted from surface epithelial cells

129
Q

How do tight junctions between epithelial cells help to protect the gastric mucosa?

A

they act as a barrier to any acid moving paracellularly and damaging the underlying cell surface

130
Q

What is the barrier like that protects the gastric mucosa from damage?

A

there is an unstirred mucus layer of pH 7

pepsinogen is not activated so it prevents enzymatic and chemical damage

131
Q

What condition is triggered when the gastric mucosal barrier fails?

132
Q

What is gastritis most commonly caused by?

A

an infection by the bacteria Helicobacter pylori

133
Q

What is the primary cause of peptic ulcer disease?

A

the bacteria Helicobacter pylori

134
Q

Why is Helicobacter pylori bacteria in the gastric mucosal barrier a problem?

A

Gram negative bacteria produce urease which forms ammonia from urea
Ammonia neutralizes bactericidal acid and is toxic to mucosal barrier

135
Q

What are the less common causes of gastritis?

A

smoking, large amounts of alcohol
NSAIDs
chronic stress

136
Q

How do NSAIDs cause gastritis?

A

they inhibit COX to reduce the synthesis of acid regulatory prostaglandin

137
Q

What occurs when the gastric mucosal barrier has sustained acute damage?

A

rapid regeneration via restitution - rapid division of stem cells located in the neck of gastric glands

138
Q

What is Autoimmune atrophic gastritis caused by?

A

the antibody mediated destruction of gastric parietal cells

139
Q

What are the effects of autoimmune atrophic gastritis?

A

hypochlorhydria

IF deficiency

140
Q

What type of cells release somatostatin?

A

delta cells

141
Q

Where are delta cells located? (SIP)

A

stomach
intestine
pancreatic islets

142
Q

How is the somatostatin hormone circulated from delta cells?

A

paracrine - acts locally

endocrine - systemic via bloodstream

143
Q

What substances are inhibited when somatostatin is released from the hypothalamus?

A

growth hormone and TSH

144
Q

What substances are inhibited when somatostatin is released from the pancreas?

A

pancreatic hormones such as insulin and glucagon

145
Q

What are the cells in the pancreas?

A 
alpha
beta
delta
exocrine (duct and acinar cells)
f cells
146
Q

What do alpha cells secrete?

147
Q

What do beta cells secrete?

148
Q

What do acinar cells secrete?

A

digestive enzymes

149
Q

What do f cells cells secrete?

A

pancreatic PPTs

150
Q

What is the main role of Histamine 2 receptors?

A

to stimulate gastric acid secretion

151
Q

What are some of the roles of H2 receptors?

A

to stimulate gastric acid secretion
to regulate GI motility
to regulate intestinal secretion

152
Q

What are alpha2 globulins involved in?

A

inflammation

153
Q

What are beta globulins involved in?

A

transporting substances

immunity

154
Q

What is the difference between endocrine and exocrine glands?

A

exocrine - secretes to an epithelial surface

endocrine - secrete directly into the bloodstream

155
Q

What is the effect of ACh on

A

vasodilation, slows HR
increases bodily secretions
contracts SMOOTH muscles

156
Q

What NS is ACh an NT of?

A

parasymp NS

157
Q

Which NT do cholinergic neurons mainly use?

158
Q

What does AChE hydrolyse ACh into?

A

acetic acid and choline

159
Q

What are the symptoms of a cholinergic crisis?

A

SLUDGE (Salivation, Lacrimation, Urination, Defecation, GI distress, Emesis)

160
Q

What area does [the upper (“neck”) region of the fundic glands] actually refer to?

A

near the glands’ openings into the bottoms of gastric pits

161
Q

What is the main role of gastric inhibitory peptide?

A

to stimulate insulin secretion

162
Q

What is the largest salivary gland?

A

the parotid glands

M104 T1 (15 decks)

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