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Gastrointestinal Case > Digestion and Secretion: Stomach > Flashcards

Digestion and Secretion: Stomach Flashcards

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1
Q

What are the salivary glands?

A

Parotid gland
Submandibular gland
Sublingual glands
Minor salivary glands

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2
Q

What does the Parotid gland secrete?

A

serous (i.e. watery) secretion rich in alpha-amylase

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3
Q

What does the Submandibular gland secrete?

A

seromucous secretion

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4
Q

What does the Sublingual gland secrete?

A

seromucous secretion

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5
Q

What do the Minor salivary glands secrete?

A

mucous secretion rich in mucin glycoproteins

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6
Q

Where is the Parotid gland located?

A

At the back of the mouth

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7
Q

Where is the Sublingual gland located?

A

Underneath the tongue in the lower jaw closer to tongue than submandibular gland

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8
Q

Where is the Submandibular gland

A

Underneath the tongue in the lower jaw

closer to jaw than sublingual gland

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9
Q

Where are the minor salivary glands located?

A

Found throughout the mouth

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10
Q

What does the parotid gland do?

A

Start breakdown of amylose

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11
Q

How much saliva is secreted per day?

A

1.5 litres

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12
Q

What is the osmolality of saliva

A

Hypoosmotic

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13
Q

What does Hypoosmotic mean?

A

Lower Ionic composition compared with plasma

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14
Q

What is the osmolality of all components that are not saliva?

A

Isosmotic

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15
Q

What does isosmotic mean?

A

same osmolarity as plasma

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16
Q

What pH is saliva?

A

~7 slightly acidic

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17
Q

What is the composition of saliva

A

mucin glycoproteins, lysozyme, alpha-amylase

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18
Q

What is the functions of saliva?

A

Lubricate the food to aid swallowing
Clean and protect the cavity of the mouth
Reduce starch to oligosaccharides

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19
Q

Which of the compositions of saliva is responsible for lubricating the food to aid swallowing

A

mucin glycoproteins, water

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20
Q

Which of the compositions of saliva is responsible for clean and protect the cavity of the mouth

A

lysozyme

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21
Q

Which of the compositions of saliva is responsible for reducing starch to oligosaccharides

A

alpha-amylase

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22
Q

What is a lyso\yme

A

Antimicrobial factor

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23
Q

How is the stomach divided anatomically?

A

Fundus -top part
Corpus/body - main area and middle
Antrum- bottom part

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24
Q

How much gastric secretion is produced per day?

A

2l

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25
What is the pH of gastric secretion
0.9~1.5
26
What is the composition of gastric secretion?
``` HCI pepsins intrinsic factor, mucus HCO3- ```
27
What are mucin glycoproteins and water in the saliva responsible for?
lubricating the food to aid swallowing
28
What are lysozymes in the saliva responsible for?
clean and protect the cavity of the mouth
29
What are alpha-amylases in the saliva responsible for?
reducing starch to oligosaccharides
30
What is of the compositions of the gastric secretion is responsible for assisting absorption of Vitamin B12
Intrinsic Factor
31
What is of the compositions of the gastric secretion is responsible for digesting proteins
Pepsins
32
What are intrinsic factors in the gastric secretion responsible for?
assisting absorption of Vitamin B12
33
What are pepsins in the gastric secretion responsible for?
digesting proteins
34
What are the roles of the stomach in digestion?
Reservoir— Gastric motility Digests proteins Essential for the absorption of Vitamin B12
35
What is responsible for secretion of the enzyme pepsinogen in the stomach
Glands in the corpus
36
What are the glands in the corpus responsible for?
secretion of the enzyme pepsinogen
37
What is pepsinogen?
Inactive form of pepsin
38
What of the composition of gastric secretion aids the digestion of proteins?
HCl
39
What is the role of Intrinsic factors in the small intestine?
protecting vitamin B 12 from destruction by pancreatic enzymes
40
What is pepsin
Active form of enzyme from pepsinogen
41
Describe the mucosa of the corpus of the stomach
Gastric pits | Lining lamina propria is gastric glands
42
Which of the gastric glands is predominant
Parietal cell
43
Which gastric cells of the stomach is a large pinky cell with a central nucleus
Parietal cell
44
Describe the parietal cell
Large pinky cell with a central nucleus
45
What are the parietal cells responsible for?
Secretion of HCl and Intrinsic factor
46
What are the cells in the gastric gland?
Mucous neck cell - top of the glands not as well known to be in the gland region Parietal cell Chief cell endocrine cell- D cells or ECL cells
47
What are the chief cells responsible for?
Secretion of pepsinogen
48
What are the types of endocrine cells?
ECL cells- Enterochromaffin-like cells D cells- G
49
What are the ECL cells responsible for?
Secretion of histamine
50
What are the D cells responsible for?
Secretion of Somatostatin
51
What are the mucous neck cells responsible for?
Secretion of mucus
52
What cells are in the epithelium of the mucossa of the corpus
Surface epithelial cells
53
What is the Surface epithelial cells responsible for?
Secretion of HCO3- (bicarbonate) | Some might be secreting mucus
54
What cells are in the antrum of the stomach
endocrine cells- G cells
55
What is gastrin used for?
Stimulating gastric secretion
56
What is somatostatin used for?
Inhibiting gastric secretion
57
What is stimulates gastric secretion?
Gatrin
58
What inhibits gastric secretion?
Somatostatin
59
Process of secreting pepsins
Chief cells will secrete pepsinogen into the lumen of the gastric glands By exocytosis pepsinogen converted to pepsin spontaneously but is promoted by an acidic environment ( Neutral- very slow) HCl important in accelerating the production of pepsin Pepsin then used to promote more converting of pepsinogen
60
What is the role of HCl
Promotes the activation and activity of pepsins Kills or inhibits microorganisms Stimulates secretions in the small intestine
61
What happens to parietal cell when secreting HCl
Morphological changes that accompany HCI secretion Tubulovesicles from resting state are inserted into apical membrane in activated form Surface area of the apical membrane increases massively membrane with more Hi-pumps, K+ and Cl- channels Surface area increased by canaliculi
62
What does a resting parietal cell look like
https://thumbs.dreamstime.com/z/parietal-cell-close-up-secreting-hydrochloric-acid-intrinsic-factor-located-stomach-gastric-glands-85697195.jpg Tubulovesicles under the apical membrane
63
What are canaliculi (one canaliculus)
Finger-like projections on the apical membrane of an activated parietal cell
64
What are contained in the tubulovesicles
H+ pumps K+ channels Cl- channels
65
cellular mechanism of acid secretion -how protons secreted
1- H+ pump on apical membrane use the energy of ATP hydrolysis (ATP → ADP + Pi) to pump protons out of cell in exchange for potassium ions coming into the cell 2- For exchange of potassium from outside of cell need a source of extracellular potassium ions which is provided by apical K+ channels- gated pathway for potassium ions to exit cell 1 and 2 provides the protons for HCL secretion
66
What other protein is in the same family of transport proteins as H+ pumps?
sodium potassium ATPase
67
What other protein is in the same family of transport proteins as sodium potassium ATPase?
H+ pumps
68
What type of transport protein is sodium potassium ATPase
P-ATPase
69
What type of transport protein is H+ pumps
P-ATPase
70
Whatis the H+ pump in the parietal cell?
H+/K+ ATPase
71
cellular mechanism of acid secretion -how protons generated
3- H2O + CO2 → H2CO3 → H+ + HCO3- | catalysed by carbonic anhydrase
72
What are the raw materials used to generate protons in parietal cells?
Water and carbon dioxide
73
cellular mechanism of acid secretion - CO2 Source
Simple diffusion of the gas across the basal lateral membrane
74
cellular mechanism of acid secretion - H2O Source
Aquaporins on the basal lateral membane allow water to travel into cells
75
What are aquaporins
Water channels
76
cellular mechanism of acid secretion - HCO3- dipsosal
Anion exchanger - HCO3- exchanged for CL- into cell HCO3- delivered into blood vessels of mucosa In fed state- alkaline tide
77
What is an antiporter
cotransporter and integral membrane protein involved in secondary active transport of two or more different molecules or ions across a phospholipid membrane such as the plasma membrane in opposite directions, one into the cell and one out of the cell.
78
What is a uniporter
membrane transport protein that transports a single species of substrate (charged or uncharged) across a cell membrane. It may use either facilitated diffusion and transport along a diffusion gradient or transport against one with an active transport process.
79
What is a symporter
A symporter is an integral membrane protein that is involved in the transport of two different molecules across the cell membrane in the same direction. The symporter works in the plasma membrane and molecules are transported across the cell membrane at the same time, and is, therefore, a type of cotransporter.
80
What is an alkaline tide?
alkalinisation of blood vessels condition, normally encountered after eating a meal, where during the production of hydrochloric acid by parietal cells in the stomach, the parietal cells secrete bicarbonate ions across their basolateral membranes and into the blood, causing a temporary increase in pH.
81
cellular mechanism of acid secretion - Cl- secretion
gated pathway for chloride movement Cl- exits down favorable electro-chemical gradient into the lumen of the gastric gland sodium potassium ATPase aids in this too
82
cellular mechanism of acid secretion - regulating pH
sodium potassium ATPase result in inwardly directed sodium concentration gradients across the basal lateral membrane Used by other transporters in the cell
83
cellular mechanism of acid secretion - K+ excretion down the basal lateral membrane - importance
K+ excretion down basal lateral membrane into interstitial space Driving chloride out of cell K+ out of apical membrane hence H+ into lumen of gastric gland
84
How is mucus secreted in the gastric glands? 35:03
Exocytosis by mucous neck cells and some surface epithelial cells
85
What secretes gastrin?
G endocrine cells
86
What secretes HCO3-?
surface epithelial cells
87
What secretes mucus?
Mucous neck cells and some surface epithelial cells
88
What secretes HCl?
Parietal cell
89
What secretes Intrinsic factors?
Parietal cells
90
What secretes Pepsinogen?
Chief Cells
91
What secretes histamine?
ECL endocrine cells - Enterochromaffin-like cells
92
What secretes somatostatin?
D endocrine cells
93
Secretion of bicarbonate
Sodium/ Potassium ATPase maintains electrochemical gradient Not made in the surface epithelial cells Secondary active transport- symporter using sodium conc gradient to bring HCO3- across basal lateral membrane then secreted across the apical membrane through anion channels
94
How is the mucus and HCO3- secretion regulated?
Dominant nervous regulation → Acetycoline taste activate vagal nerves and the vagal nerve will release acetylcholine acetylcholine will stimulate mucus secretion via calcium signaling stimulate a bicarbonate secretion via calcium signaling → Prostaglandins
95
What is the role of prostaglandins in surface epithelial cells?
Inhibiting acid secretion | Stimulating secretion of mucus and HCO3-
96
What is the physiological protective mechanisms of the gastric mucosa?
Gastric mucosal/ diffusion barrier - Mucus covers surface epithelial cells mucus is impregnated with bicarbonate At apical membrane of epithelial cells bicarbonate conc is high the closer to the gastric lumen the lower the conc of HCO3- and the higher the proton concentration
97
What does the gastric mucosal barrier rely on ?
Mucus and Bicarbonate
98
What is the anatomical protective mechanisms of the gastric mucosa?
apical membrane of surface epithelial cells are impermeable to protons Tight junctions - No paracellular pathways for proton movement
99
What is viscous fingering? Why is this important
HCl shooting in the gastric lumen | Slow movement may cause damage to epithelial cells
100
What is HCl shooting in the gastric lumen termed as?
Viscous fingering
101
Stimulation of HCl secretion- the three physiological agonists? (extracellular)
Acetylcoline- nerves Gastrin - peptide hormone Histamine- paracrine factor Directly AND indirectly
102
What receptor does acetylcholine interact with to directly stimulate acid secretion (extracellular)
M3 receptor
103
What receptor does gastrin interact with to directly stimulate acid secretion (extracellular)
CCK-B receptor
104
What receptor does histamine interact with to directly stimulate acid secretion (extracellular)
H2 receptor
105
What is the indirect stimulation of acid secretion (extracellular)
Nerves (enteric neuron) stimulating enterochromaffin-like cells to secrete histamine Gastrin targets enterochromaffin-like cells
106
Which physiological agonists use calcium signalling intra cellular pathways to regulate HCl secretion
Gastrin | Acetylcholine
107
Which physiological agonists use cAMP intra cellular pathways to regulate HCl secretion
Histamine
108
Which intracellular signalling pathway does gastrin use to regulate HCl secretion?
Calcium signalling
109
Which intracellular signalling pathway does histamine use to regulate HCl secretion?
cAMP
110
Which intracellular signalling pathway does acetylcholine use to regulate HCl secretion?
Calcium signalling
111
What part of the process of acid secretion are the physiological agonists stimulating?
Insertion of tubulovesicles
112
What are the three phases of control of gastric secretion?
Cephalic phase Gastric phase Intestinal phase
113
Control of gastric secretion: cephalic phase
mediated by vagus nerve Vagus nerve switching off inhibitory mechanism (In resting state- somatostatin from D cell prevents acid secretion from parietal cell) Activating parietal cells: Stimulation from the three physiological agonists (questions already on this but can still recap) Entirely dependent on vagal nerve Accounts for up to 30% total volume of secretion Occurs before food enters stomach
114
Control of gastric secretion: gastric phase
Controlled by vagovagal reflex, hormones and paracrine factors - Accounts for 50% of gastric secretion *Stimulation of secretion -distention of the wall of the stomach as a result of filling up with food which activates vagovagal reflex - mechanoreceptors Stretching of mechanoreceptors activate sensory neurons, connected interneurons then signaling from the enteric nervous system backup via the parasympathetic nervous system back up to the brain stem brainstem directly stimulating acid secretion by the parietal cell G cells stimulated to secrete gastrin gastrin is directly targeting the parietal cell -Digested proteins activate chemo receptor which are on the apical membrane of the G cells in the antrum When stimulated releases gastrin to target secretory/parietal cell
115
Control of gastric secretion: intestinal phase with stimulation
Early in gastric emptying: Gastric chyme pH > 3, STIMULATION predominates Later in gastric emptying: Gastric chyme pH <3, INHIBITION predominates Stimulation of secretion- Distention of duodenum detected by mechanoreceptors activating vagovagal reflex duodenum brain stem and then the brain stem via the parasympathetic nervous system communicating to the G cells in the stomach communicating also directly to the parietal cell same as cephalic phase Digested proteins detected by chemoreceptors in the apical facing membrane of the G cell in the lining of the duodenum which activates gastrin release to the parietal cell
116
Control of gastric secretion: intestinal phase with inhibition
Acid detected in duodenum by chemoreceptors on the S cells S cells secrete secretin secretin would travel via the blood vessels to the stomach Direct inhibition of parietal cells or indirect via G cells in the antrum Interact with D cells to release somatostatin which will inhibit the three physiological agonists
117
Control of gastric secretion: gastric phase with inhibition
*Inhibition of the secretion - D cell in atrium have apical membrane chemoreceptor detect HCl If HCl detected release of somatostatin inhibits G calls and parietal cells Digestion products( esp fat) in the duodenum detected by chemoreceptors on the I cells secrete cholecystokinin which has an inhibitory effect on parietal cells
118
What is gastric emptying?
Delivery of chyme from the stomach to the duodenum
119
Compare the speed of gastric emptying for different substances from fast to slow
.carbohydrates > proteins > fats >> indigestible solids
120
the rate of gastric emptying does not exceed | the rate at which.. what processes? why?
``` acid can be neutralized fat can be emulsified the small intestine processes chyme As a result of control mechanisms in the intestinal phase ```

Gastrointestinal Case (11 decks)

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