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Gastrointestinal Case > Digestion and Secretion: Stomach > Flashcards

Digestion and Secretion: Stomach Flashcards

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
Q

What is the pH of gastric secretion

A

0.9~1.5

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26
Q

What is the composition of gastric secretion?

A 
HCI
pepsins
intrinsic factor,
mucus
HCO3-
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27
Q

What are mucin glycoproteins and water in the saliva responsible for?

A

lubricating the food to aid swallowing

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28
Q

What are lysozymes in the saliva responsible for?

A

clean and protect the cavity of the mouth

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29
Q

What are alpha-amylases in the saliva responsible for?

A

reducing starch to oligosaccharides

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30
Q

What is of the compositions of the gastric secretion is responsible for assisting absorption of Vitamin B12

A

Intrinsic Factor

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31
Q

What is of the compositions of the gastric secretion is responsible for digesting proteins

A

Pepsins

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32
Q

What are intrinsic factors in the gastric secretion responsible for?

A

assisting absorption of Vitamin B12

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33
Q

What are pepsins in the gastric secretion responsible for?

A

digesting proteins

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34
Q

What are the roles of the stomach in digestion?

A

Reservoir— Gastric motility
Digests proteins
Essential for the absorption of Vitamin B12

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35
Q

What is responsible for secretion of the enzyme pepsinogen in the stomach

A

Glands in the corpus

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36
Q

What are the glands in the corpus responsible for?

A

secretion of the enzyme pepsinogen

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37
Q

What is pepsinogen?

A

Inactive form of pepsin

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38
Q

What of the composition of gastric secretion aids the digestion of proteins?

A

HCl

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39
Q

What is the role of Intrinsic factors in the small intestine?

A

protecting vitamin B 12 from destruction by pancreatic enzymes

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40
Q

What is pepsin

A

Active form of enzyme from pepsinogen

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41
Q

Describe the mucosa of the corpus of the stomach

A

Gastric pits

Lining lamina propria is gastric glands

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42
Q

Which of the gastric glands is predominant

A

Parietal cell

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43
Q

Which gastric cells of the stomach is a large pinky cell with a central nucleus

A

Parietal cell

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44
Q

Describe the parietal cell

A

Large pinky cell with a central nucleus

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45
Q

What are the parietal cells responsible for?

A

Secretion of HCl and Intrinsic factor

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46
Q

What are the cells in the gastric gland?

A

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

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47
Q

What are the chief cells responsible for?

A

Secretion of pepsinogen

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48
Q

What are the types of endocrine cells?

A

ECL cells- Enterochromaffin-like cells
D cells-
G

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49
Q

What are the ECL cells responsible for?

A

Secretion of histamine

50
Q

What are the D cells responsible for?

A

Secretion of Somatostatin

51
Q

What are the mucous neck cells responsible for?

A

Secretion of mucus

52
Q

What cells are in the epithelium of the mucossa of the corpus

A

Surface epithelial cells

53
Q

What is the Surface epithelial cells responsible for?

A

Secretion of HCO3- (bicarbonate)

Some might be secreting mucus

54
Q

What cells are in the antrum of the stomach

A

endocrine cells- G cells

55
Q

What is gastrin used for?

A

Stimulating gastric secretion

56
Q

What is somatostatin used for?

A

Inhibiting gastric secretion

57
Q

What is stimulates gastric secretion?

58
Q

What inhibits gastric secretion?

A

Somatostatin

59
Q

Process of secreting pepsins

A

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
Q

What is the role of HCl

A

Promotes the activation and activity of pepsins
Kills or inhibits microorganisms
Stimulates secretions in the small intestine

61
Q

What happens to parietal cell when secreting HCl

A

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
Q

What does a resting parietal cell look like

A

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
Q

What are canaliculi (one canaliculus)

A

Finger-like projections on the apical membrane of an activated parietal cell

64
Q

What are contained in the tubulovesicles

A

H+ pumps
K+ channels
Cl- channels

65
Q

cellular mechanism of acid secretion -how protons secreted

A

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
Q

What other protein is in the same family of transport proteins as H+ pumps?

A

sodium potassium ATPase

67
Q

What other protein is in the same family of transport proteins as sodium potassium ATPase?

68
Q

What type of transport protein is sodium potassium ATPase

69
Q

What type of transport protein is H+ pumps

70
Q

Whatis the H+ pump in the parietal cell?

A

H+/K+ ATPase

71
Q

cellular mechanism of acid secretion -how protons generated

A

3- H2O + CO2 → H2CO3 → H+ + HCO3-

catalysed by carbonic anhydrase

72
Q

What are the raw materials used to generate protons in parietal cells?

A

Water and carbon dioxide

73
Q

cellular mechanism of acid secretion - CO2 Source

A

Simple diffusion of the gas across the basal lateral membrane

74
Q

cellular mechanism of acid secretion - H2O Source

A

Aquaporins on the basal lateral membane allow water to travel into cells

75
Q

What are aquaporins

A

Water channels

76
Q

cellular mechanism of acid secretion - HCO3- dipsosal

A

Anion exchanger - HCO3- exchanged for CL- into cell
HCO3- delivered into blood vessels of mucosa
In fed state- alkaline tide

77
Q

What is an antiporter

A

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
Q

What is a uniporter

A

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
Q

What is a symporter

A

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
Q

What is an alkaline tide?

A

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
Q

cellular mechanism of acid secretion - Cl- secretion

A

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
Q

cellular mechanism of acid secretion - regulating pH

A

sodium potassium ATPase result in inwardly directed sodium concentration gradients across the basal lateral membrane
Used by other transporters in the cell

83
Q

cellular mechanism of acid secretion - K+ excretion down the basal lateral membrane - importance

A

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
Q

How is mucus secreted in the gastric glands? 35:03

A

Exocytosis by mucous neck cells and some surface epithelial cells

85
Q

What secretes gastrin?

A

G endocrine cells

86
Q

What secretes HCO3-?

A

surface epithelial cells

87
Q

What secretes mucus?

A

Mucous neck cells and some surface epithelial cells

88
Q

What secretes HCl?

A

Parietal cell

89
Q

What secretes Intrinsic factors?

A

Parietal cells

90
Q

What secretes Pepsinogen?

A

Chief Cells

91
Q

What secretes histamine?

A

ECL endocrine cells - Enterochromaffin-like cells

92
Q

What secretes somatostatin?

A

D endocrine cells

93
Q

Secretion of bicarbonate

A

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
Q

How is the mucus and HCO3- secretion regulated?

A

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
Q

What is the role of prostaglandins in surface epithelial cells?

A

Inhibiting acid secretion

Stimulating secretion of mucus and HCO3-

96
Q

What is the physiological protective mechanisms of the gastric mucosa?

A

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
Q

What does the gastric mucosal barrier rely on ?

A

Mucus and Bicarbonate

98
Q

What is the anatomical protective mechanisms of the gastric mucosa?

A

apical membrane of surface epithelial cells are impermeable to protons
Tight junctions - No paracellular pathways for proton movement

99
Q

What is viscous fingering? Why is this important

A

HCl shooting in the gastric lumen

Slow movement may cause damage to epithelial cells

100
Q

What is HCl shooting in the gastric lumen termed as?

A

Viscous fingering

101
Q

Stimulation of HCl secretion- the three physiological agonists? (extracellular)

A

Acetylcoline- nerves
Gastrin - peptide hormone
Histamine- paracrine factor
Directly AND indirectly

102
Q

What receptor does acetylcholine interact with to directly stimulate acid secretion (extracellular)

A

M3 receptor

103
Q

What receptor does gastrin interact with to directly stimulate acid secretion (extracellular)

A

CCK-B receptor

104
Q

What receptor does histamine interact with to directly stimulate acid secretion (extracellular)

A

H2 receptor

105
Q

What is the indirect stimulation of acid secretion (extracellular)

A

Nerves (enteric neuron) stimulating enterochromaffin-like cells to secrete histamine
Gastrin targets enterochromaffin-like cells

106
Q

Which physiological agonists use calcium signalling intra cellular pathways to regulate HCl secretion

A

Gastrin

Acetylcholine

107
Q

Which physiological agonists use cAMP intra cellular pathways to regulate HCl secretion

108
Q

Which intracellular signalling pathway does gastrin use to regulate HCl secretion?

A

Calcium signalling

109
Q

Which intracellular signalling pathway does histamine use to regulate HCl secretion?

110
Q

Which intracellular signalling pathway does acetylcholine use to regulate HCl secretion?

A

Calcium signalling

111
Q

What part of the process of acid secretion are the physiological agonists stimulating?

A

Insertion of tubulovesicles

112
Q

What are the three phases of control of gastric secretion?

A

Cephalic phase
Gastric phase
Intestinal phase

113
Q

Control of gastric secretion: cephalic phase

A

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
Q

Control of gastric secretion: gastric phase

A

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
Q

Control of gastric secretion: intestinal phase with stimulation

A

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
Q

Control of gastric secretion: intestinal phase with inhibition

A

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
Q

Control of gastric secretion: gastric phase with inhibition

A

*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
Q

What is gastric emptying?

A

Delivery of chyme from the stomach to the duodenum

119
Q

Compare the speed of gastric emptying for different substances from fast to slow

A

.carbohydrates > proteins > fats&raquo_space; indigestible solids

120
Q

the rate of gastric emptying does not exceed

the rate at which.. what processes? why?

A 
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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