M104 T1 L5 Flashcards
(162 cards)
1
Q
How much fluid is secreted into the GI tract each day?
A
approx 7 litres
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
3
Q
After reabsorption of secreted fluid in the GI tract, how much is actually excreted daily?
A
about 100 mls
4
Q
What is the pH of salivary secretions?
A
pH 6-7
5
Q
What are the three Major salivary glands?
A
Parotid
Submandibular
Sublingual
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
7
Q
Where is the parotid gland located?
A
anterior and inferior to the ear
between the skin and the muscle
8
Q
Where is the duct of the parotid gland located?
A
it enters the oral cavity just above the second molar
9
Q
What does the parotid gland secrete?
A
Serous, watery secretions containing salivary amylase for starch digestion
10
Q
What does the submandibular gland secrete?
A
a mixture of serous and mucus containing saliva
11
Q
Where is the submandibular gland located?
A
inferior to the mandible
12
Q
Where is the duct of the submandibular gland located?
A
lateral to the lingual frenulum
13
Q
Where is the sublingual gland located?
A
in the floor of the oral cavity
14
Q
What does the sublingual gland secrete?
A
thicker mucus dominant secretions for lubrication
15
Q
Where is the duct of the sublingual gland located?
A
they enter the oral cavity under the tongue
16
Q
What type of cells does the sublingual gland contain?
A
mucin secreting cells
17
Q
What percent of saliva is produced by the parotid and submandibular glands?
A
90%
18
Q
What percent of saliva is made up of water?
A
99.5%
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
20
Q
What is the purpose of electrolytes in saliva?
A
have a buffering capacity, particularly for acidic foods in the oral cavity
21
Q
What are key enzymes in saliva? (LacLAK)
A
Lactoferrin Lysozyme Lingual lipase (serous salivary glands of tongue) a-amylase Kallikrein
22
Q
What is the role of a-amylase in saliva?
A
digests starch via hydrolysis of the a-1,4 glycosidic bonds
23
Q
What three substances does a-amylase degrade starch into?
A
disaccharide maltose
trisaccharide maltotriose
a-dextrin
24
Q
Up to what percentage of starch digestion can occur through the action of amylase?
A
75%
25
When does amylase stop digesting starch?
when it's neutralised by the acidic pH of the stomach
26
What is the role of a-amylase in digestion?
to hydrolyse peptidoglycans in the wall of gram negative bacteria so it can keep the level of bacteria in the oral cavity down
27
What is the role of lingual lipase in digestion?
to hydrolyse lipid triglycerides to fatty acid and diglycerides
28
What enzymes are produced by von Ebner glands ?
lingual lipase
| amylase
29
What are the optimal conditions for lingual lipase?
acidic pH
30
What is the role of Lactoferrin in digestion?
has anti-microbial properties through the chelation of iron to prevent microbes from multiplying
31
What is the role of Kallikrein in digestion?
converts plasma protein a-2- globulin into bradykinin
32
What is the role of Secretory IgA in digestion?
it prevents microbial attachment to epithelium
33
What is the role of myoepithelial cells?
they surround the acinar cells and are contractile in nature
| they help to drive the primary secretions along the duct
34
What is the role of ductal cells?
modifying primary saliva
35
What are the unique properties of salivary glands?
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
36
What happens in Stage 1 of hypotonic saliva formation?
an isotonic plasma-like saliva, which contains water, electrolytes and enzymes, is secreted into a salivary duct by acinar cells
37
What happens in Stage 2 of hypotonic saliva formation?
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
38
What are the ions in NaCl reabsorbed in exchange for in Stage 2 of hypotonic saliva formation?
Na+ reabsorbed in exchange of K+
| Cl- reabsorbed for carbonate ions
39
What is a consequence of the salivary duct being relatively impermeable to water?
AAR there is limited movement of water by osmosis out of the duct lumen following NaCl reabsorption
40
What is the effect of the formation of hypotonic saliva?
the production of a K and bicarbonate-rich hypotonic saliva compared to plasma and the interstitial fluid
41
What is composition of saliva and can this change?
the composition of saliva is always hypotonic
| but it can change with flow rate
42
What is the electrolyte composition of saliva at a high rate of secretion compared to that of saliva at a low rate of secretion?
Na+ & Cl- are always low
| K+ & HCO3- are high
43
What happens during a low rate of secretion?
there is a maximum reabsorption of electrolytes
| hypotonic saliva is produced
44
What are the electrolytes like in hypotonic saliva?
lower concentration of osmotically active electrolytes
45
What happens during a high rate of secretion?
there is reduced reabsorption of electrolytes
| alkaline, HCO3- rich saliva is produced
46
What is the osmolality like in hypotonic saliva?
has an increased osmolality closer to that of primary isotonic saliva
47
How is salivary secretion innervated?
```
by the autonomic NS
parasymp stimulation (more important)
symp (less)
```
48
What happens when there is a stimuli for salivation?
a signal is created via the salivatory nuclei in the medulla
| different nerves are stimulated for the activation of different glands
49
Which two glands does the facial nerve supply?
sublingual
| submandibular
50
Which gland does the glossopharyngeal nerve supply?
the parotid gland
51
What is the effect of parasympathetic stimulation on the salivary glands?
Increase salivary secretion
increases vasodilation
increases myoepithelial cell contraction
52
What are the inhibitors of salivary secretion?
fatigue, sleep, fear, dehydration
53
What is the effect of the symp NS on salivary secretion?
secretion rate increases
| saliva is higher in mucin and enzymes
54
What nerve conveys symp NS action to the salivary glands?
superior cervical ganglion
55
How is an initial vasoconstriction activated in the salivary glands?
noradrenaline is released
| it stimulates alpha adrenergic receptors on the blood vessels surrounding the glands
56
How is a later vasodilation activated in the salivary glands?
the kallikrein enzyme is released
it goes on to act on a-2 globulin
it forms the vasodilator bradykinin - results in vasodilation
57
What are two examples of conditions associated with salivary gland dysfunction?
Sjögren's syndrome
| Xerostomia
58
What are the effects of Sjögren's syndrome?
commonly affects tear and saliva production
dry eyes and dry mouth
(destroys exocrine glands)
59
What are the effects of xerostomia?
dry mouth
| bacterial overgrowth
60
What can bacterial overgrowth in the oral cavity cause?
dental caries
| halitosis
61
What can a dry mouth cause?
inadequate lubrication of the oral cavity
difficulty speaking
difficulty swallowing solid food
62
What do gastric pits branch into?
gastric glands
63
What type of cells do gastric glands contain?
secretory cells
64
What is the role of exocrine cells?
responsible for excreting the components of the gastric juice
65
What is the role of mucous neck cells?
secrete a thin mucus
| joins mucus secreted by surface mucus cells
66
What is the role of parietal cells?
secretes HCl and IF
67
What substances do chief cells secrete?
pepsinogen
rennin
gastric lipase
68
What are the three types of exocrine cells?
mucous neck cells
parietal cells
chief cells
69
What endocrine cells are present in gastric glands?
G cells
70
What two types of cells are present in gastric glands?
endocrine cells
| exocrine cells
71
What do G cells secrete?
the hormone gastrin
72
What do ECL cells secrete?
histamine
73
Where are the two main types of gastric glands?
(80%) gastric/oxyntic glands - body and fundus
| (20%) pyloric glands - antrum
74
What are the exocrine secretions of the gastric/oxyntic glands into the body and fundus of the stomach?
HCl, IF
pepsinogen
mucus
75
What substances are secreted by the paracrine glands in the body and the fundus of the stomach?
histamine by ECL cells
| somatostatin by Delta cells
76
What substances are secreted by the pyloric glands in the antrum of the stomach?
```
mucus
gastrin (endocrine)
somatostatin (endo and exocrine)
```
77
What are the components of gastric juice?
```
Water and electrolytes
Mucus (glycoprotein mucin)
Pepsinogen pro-enzyme
Rennin in neonates only
Gastric lipase
HCl (pH 1-3)
IF
```
78
What is the role of water and electrolytes in gastric juice?
they act as a medium for the action of assets and enzymes
| they allow for the digestion of organic substances to occur
79
What is the role of mucus in gastric juice?
protective function - coats the surface of the stomach
| protects it from the harmful effects of acid and the enzyme pepsin
80
What is the role of Pepsinogen pro-enzyme in gastric juice?
cleaves peptide bonds (protein to smaller peptides)
81
What is the role of renin in gastric juice?
coagulates milk through casein proteolysis
82
What is the role of Gastric lipase in gastric juice?
converts triglycerides to fatty acid and diglycerides
83
What do parietal cells secrete?
HCl and IF
84
What is the pH of the stomach?
pH 1 - 3
85
What are the roles of HCl in the stomach?
converts pro-enzyme pepsinogen to pepsin
denatures proteins
kills microorganisms
86
What is the role of IF in the stomach?
allows for the absorption of vitamin B12 in the ileum
87
What is vitamin B12 used for?
erythropoiesis in the bone marrow
88
What condition is caused by a vitamin B12 deficiency?
pernicious anaemia
89
What is the structure of parietal cells?
an intracellular branched canalicular structure
| are packed with tubulovesicles in resting state
90
What are parietal cells packed with?
mitochondria
| tubulovesicles
91
What do the tubulovesicles in parietal cells contain?
carbonic anhydrase
other enzymes
HK-ATPase
92
What happens to tubulovesicles when the cell is stimulated to produce acid?
they fuse with the canalicular membrane to form microvilli
| HCl is formed at these microvilli and secreted
93
Where are tubulovesicles located?
on the apical membrane
94
How is acid secreted into the gastric lumen from parietal cells?
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
Where are hydrogen ions derived from?
from the activity of carbonic anhydrase
| when it catalyses the formation of bicarbonate ions from co2 and water
96
What are the three major routes by which gastric acid is secreted?
ACh release
gastrin release
histamine release
97
How does gastrin release result in the secretion of gastric acid?
is released from G cells
enters the bloodstream
returns to parietal cell membrane
98
What is the effect of vagal innervation on gastric acid secretion?
results in the secretion of ACh
| this regulates hydrogen secretion
99
What is the effect of histamine release on gastric acid secretion?
released from ECL cells
| histamine binds to the H2 receptors on the parietal cell membrane
100
How do all gastric acid secretion pathways work?
by second messenger intracellular pathways
101
What is the chain of events by which gastrin and ACh trigger HCl secretion from parietal cells?
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
What substances interrupt stages of the parietal cell acid secretion pathway?
somatostatin
| mucosal prostaglandin
103
How does somatostatin reduce acid secretion from parietal cells?
it works as an antagonist against histamine at the H2 receptor
104
How do NSAIDs increase acid secretion from parietal cells?
they inhibit somatostatin (antagonist against histamine)
| so secretion increases
105
How do prostaglandins interact with the parietal cell acid secretion pathway?
released by D cells to inhibit AC (adenylate cyclase)
| so they stop histamine from causing acid secretion
106
What three pharmalogical drugs inhibit gastric acid? (OCA)
Omeprazole
Cimetidine
Atropine
107
What is the role of the H+/K+-ATPase?
proton pump - to pump out H+ of the acid from parietal cells into the gastric lumen
108
What drug inactivates the H+/K+-ATPase proton pump?
Omeprazole
109
What is the effect of Cimetidine?
it inhibits stimulus for acid secretion
| it antagonises the activity of histamine at the H2 receptor
110
What is the effect of Atropine?
it inhibits muscarinic receptors and vagal stimulation of acid secretion
111
What is the secretion of gastrin triggered by?
vagus nerve
distention of the stomach
the presence of partially digested peptide fragments
112
How does gastrin increase the rate of digestion once released into circulation?
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
What are the three phases of gastric secretion?
Cephalic
Gastric
Intestinal (excitatory & inhibitory)
114
What type of innervation is cephalic gastric secretion regulated by?
vagal innervation - the sight, smell of food
115
What triggers the "gastric" phase of gastric secretion?
once the bolus hits the stomach
116
What is the effect of the vagus relating to cephalic gastric secretion?
it stimulates the production of gastric juice by parietal and chief cells
it stimulates the production of the hormone gastrin
117
What type of innervation is "gastric" secretion regulated by?
local neural secretatory reflexes
| vagal stimulation
118
What is the effect of "gastric" secretion?
promotes the secretions of parietal, chief, mucal and G cells
119
How does "gastric" secretion stimulate parietal cells?
directly
| indirectly - via ECL histamine release
120
What are the two types of intestinal gastric secretion phase?
Excitatory
| Inhibitory
121
What triggers the intestinal phase of gastric secretion?
when chyme enters the duodenum
122
What happens during the excitatory intestinal phase of gastric secretion?
when chyme is pH3 or more, peptides in the duodenum will stimulate gastric secretions via vagus and gastrin
123
What happens during the inhibitatory intestinal phase of gastric secretion?
when chyme is pH2 or less
mechanical distention
the presence of protein breakdown products
the presence of hypo/hyper-osmotic products
124
What substances inhibit gastric secretion during the inhibitatory intestinal phase? (CGS)
CCK
GIP
Secretin
125
Why is the gastric mucosa not damaged by the presence of pH1 and peptide digesting enzymes?
viscous mucosal barrier
| tight paracellular junctions
126
What is the mucus layer of the gastric mucosa made by?
the glands in the surface mucous secreting it
127
What is the main gastric mucosa made up of?
mucopolysaccharides
| proteins
128
How does the mucus layer in the gastric mucosa help to neutralise hydrogen ions?
the basic side chains in mucin
| the HCO3- secreted from surface epithelial cells
129
How do tight junctions between epithelial cells help to protect the gastric mucosa?
they act as a barrier to any acid moving paracellularly and damaging the underlying cell surface
130
What is the barrier like that protects the gastric mucosa from damage?
there is an unstirred mucus layer of pH 7
| pepsinogen is not activated so it prevents enzymatic and chemical damage
131
What condition is triggered when the gastric mucosal barrier fails?
Gastritis
132
What is gastritis most commonly caused by?
an infection by the bacteria Helicobacter pylori
133
What is the primary cause of peptic ulcer disease?
the bacteria Helicobacter pylori
134
Why is Helicobacter pylori bacteria in the gastric mucosal barrier a problem?
Gram negative bacteria produce urease which forms ammonia from urea
Ammonia neutralizes bactericidal acid and is toxic to mucosal barrier
135
What are the less common causes of gastritis?
smoking, large amounts of alcohol
NSAIDs
chronic stress
136
How do NSAIDs cause gastritis?
they inhibit COX to reduce the synthesis of acid regulatory prostaglandin
137
What occurs when the gastric mucosal barrier has sustained acute damage?
rapid regeneration via restitution - rapid division of stem cells located in the neck of gastric glands
138
What is Autoimmune atrophic gastritis caused by?
the antibody mediated destruction of gastric parietal cells
139
What are the effects of autoimmune atrophic gastritis?
hypochlorhydria
| IF deficiency
140
What type of cells release somatostatin?
delta cells
141
Where are delta cells located? (SIP)
stomach
intestine
pancreatic islets
142
How is the somatostatin hormone circulated from delta cells?
paracrine - acts locally
| endocrine - systemic via bloodstream
143
What substances are inhibited when somatostatin is released from the hypothalamus?
growth hormone and TSH
144
What substances are inhibited when somatostatin is released from the pancreas?
pancreatic hormones such as insulin and glucagon
145
What are the cells in the pancreas?
```
alpha
beta
delta
exocrine (duct and acinar cells)
f cells
```
146
What do alpha cells secrete?
glucagon
147
What do beta cells secrete?
insulin
148
What do acinar cells secrete?
digestive enzymes
149
What do f cells cells secrete?
pancreatic PPTs
150
What is the main role of Histamine 2 receptors?
to stimulate gastric acid secretion
151
What are some of the roles of H2 receptors?
to stimulate gastric acid secretion
to regulate GI motility
to regulate intestinal secretion
152
What are alpha2 globulins involved in?
inflammation
153
What are beta globulins involved in?
transporting substances
| immunity
154
What is the difference between endocrine and exocrine glands?
exocrine - secretes to an epithelial surface
| endocrine - secrete directly into the bloodstream
155
What is the effect of ACh on
vasodilation, slows HR
increases bodily secretions
contracts SMOOTH muscles
156
What NS is ACh an NT of?
parasymp NS
157
Which NT do cholinergic neurons mainly use?
ACh
158
What does AChE hydrolyse ACh into?
acetic acid and choline
159
What are the symptoms of a cholinergic crisis?
SLUDGE (Salivation, Lacrimation, Urination, Defecation, GI distress, Emesis)
160
What area does [the upper ("neck") region of the fundic glands] actually refer to?
near the glands' openings into the bottoms of gastric pits
161
What is the main role of gastric inhibitory peptide?
to stimulate insulin secretion
162
What is the largest salivary gland?
the parotid glands
