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A Physiology > 6.3. Function of the salivary glands and regulation of salivary secretion. Gastric secretion and its control. > Flashcards

6.3. Function of the salivary glands and regulation of salivary secretion. Gastric secretion and its control. Flashcards

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1
Q

I. Basics
1. What are general principles of secretory functions of GI-tract?

A
  • Exocrine glands (salivary glands, pancreas, liver)
  • Glands of gut wall (crypts of Lieberkühn, Brunner’s gland)
  • Intestinal mucosa
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2
Q

I. Basics
2. What are the 2 main functions of secretion?

A
  1. Protection (chemical, mechanical, immunological)
  2. Digestion + absorption (dilution + lubrication of chyme)
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3
Q

I. Basics
3A. What are the 2 types of products secreted?

A
  1. Inorganic
  2. Organic
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4
Q

I. Basics
3B. What are the secreted organic products?

A
  • Water (essential for aqueous environment + dilution function)
  • Electrolytes (HCl- = gastric acid, HCO3- = buffer acidic chyme, Na+ + Cl- for H2O secretion)
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5
Q

I. Basics
3C. What are the secreted inorganic products?

A
  1. Proteins
    - Digestive enzymes: break down macromolecules into smaller molecules -> absorb them
    - Mucin: lubrication for the chyme + is sticky, so it coats the inner surface of the gut wall -> inhibits direct contact between chyme + gut wall
    - Immunoglobulins: protective (immunological) role
  2. Humoral agents
    - Bile acids/salts
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6
Q

I. Basics
4. What is the mechanism of secretion?

A
  • Exocytosis: e.g. digestive enzymes released from vesicles by Ca2+/cAMP-signals
  • H2O + electrolyte secretion via ion transport (mainly driven by Cl- - active transport)
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7
Q

I. Basics
5A. What are the 2 types of regulation of secretion?

A
  1. Local regulation
  2. Systemic regulation
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8
Q

I. Basics
5B. What are features of systemic regulation?

A
  • SYM + PARA act via the ENS
  • PARA: ↑ rate of secretion, in response to meals
  • SYM: dual effects – sometimes inhibits/activates secretory functions
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9
Q

II. Salivary secretion
1. What is the amount of daily salivary secretion?

A

Daily secretion: 800 – 1500mL/day (90% of production during meals)
=> pH~7

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10
Q

II. Salivary secretion
2. What is the Composition of saliva?

A

H2O, electrolytes (Na+, K+, Ca2+, Mg2+, Cl-, HCO3-), salivary amylase, lingual lipase, IgA, lysozyme, mucin

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11
Q

II. Salivary secretion
3A. What are the functions of saliva

A
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12
Q

II. Salivary secretion
3B. Explain the Antimicrobial effect of saliva?

A

secretory IgA + lysozyme = enzyme which cleaves bacterial cell
wall

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13
Q

II. Salivary secretion
3C. Explain the Ca2+-binding proteins (trapped in mucins) function of saliva?

A

keeps the teeth healthy
- Excessive teeth brushing + washing will lead to removal of these proteins -> decay

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14
Q

III. Major salivary glands
1. What is the general structure of salivary glands?

A
  • Tubuloalveolar structure
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15
Q

III. Major salivary glands
2. Give the classification of acinar portion

A
  • Acinar portion of gland is classified into:
    +) Serous: contains vesicles, zymogen granules
    +) Mucous: produces mucin (glycoprotein)
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16
Q

III. Major salivary glands
3. How is salivary secretion drained?

A

Intralobular intercalated duct
-> Intralobular striated ducts
-> Interlobular ducts
-> Interlobular excretory ducts
-> Main excretory ducts

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17
Q

III. Major salivary glands
4. What are the features of extrinsic glands?

A

Extrinsic (lie outside the oral cavity) glands
- Parotid gland = serous gland
- Sublingual gland = mostly mucous
- Submandibular gland mixed

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18
Q

III. Major salivary glands
5. What are the features of Intrinsic glands?

A

Intrinsic (found within the oral cavity):
- buccal, labial, palatine glands (mucous glands)
=> intrinsic salivary glands constantly secrete saliva to keep oral cavity moist

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19
Q

IV. The two-stage model of salivary secretion
1A. What are the features of primary acinar secretion of saliva?

A

Primary secretion: PRIMARY ACINAR SECRETION
- proteins, water, electrolytes are produced by acinar cells
- isotonic + the [major ions] is similar to that in the plasma
- the primary-acinar-secretion transport ions to transport fluid (H2O)
=> secondary active Cl—transport

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20
Q

IV. The two-stage model of salivary secretion
1B. Make a schematic diagram of primary acinar secretion

A
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21
Q

IV. The two-stage model of salivary secretion
2A. What are the features of Secondary secretion?

A

Secondary secretion: DUCT CELL SECRETION/ABSORPTION
- Primary secretion is modified as it passes through ducts that absorb Na+ and Cl-, and secrete K+ and HCO3-
- Secondary secretion has both secretory and absorptive functions
- Since there are no aquaporins + the epithelium is tightly connected => H2O-impermeable epithelium

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22
Q

IV. The two-stage model of salivary secretion
2B. Make a schematic diagram of Secondary secretion?

A
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23
Q

IV. The two-stage model of salivary secretion
4. Explain the salivary flow rate

A
  • Rate of secretion does affect the composition of saliva
  • Saliva is hypotonic/hypoosmotic to plasma at all flow rates
  • [HCO3-] in saliva exceeds that in plasma except at extremely low flow rates
  • The duct epithelium is bound tightly together and lacks expression of aquaporin, and therefore H2O cannot follow the ions to maintain isotonicity at moderate or high flow rates
    => The higher the flow rate, the shorter time for ionic modifications by the duct cells -> resulting saliva will become like the 1st secretion
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24
Q

V. Regulation of salivary secretion
1. Regulation of salivary secretion is neural or hormonal?

A

EXCLUSIVELY NEURAL!

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25
V. Regulation of salivary secretion 2. What are the 2 types of regulation of salivary secretion?
1. Parasympathetic nervous system (PARA) - gets activated in response to meal 2. Sympathetic nervous system (SYM) - ↑fluid secretion
26
V. Regulation of salivary secretion 3. Describe regulation of salivary secretion by Parasympathetic nervous system (PARA)
1. Parasympathetic nervous system (PARA) – gets activated in response to meal - VIP (acts on vessels in sal.glands)-Gs -> vasodilation -> fluid secretion↑↑ - ACh (acts on acinar cells) – M3-ACh-R (Gq) -> Ca2+-signal -> 2 effects: 1) Exocytosis ↑ (amylase/lipase can be excreted) 2) Constrict acinar cells -> gaps between them get bigger -> paracellular fluid movement ↑ -> fluid secretion↑
27
V. Regulation of salivary secretion 3. Describe regulation of salivary secretion by Sympathetic nervous system (SYM)
Sympathetic nervous system (SYM) - ↑fluid secretion - NE -> β2-AR -> mucin secretion↑ ( -> content + volume↑) - NE -> α1-AR (vessels) -> vasoconstriction -> fluid secretion↓
28
VI. Gastric secretion 1. What are general features of Gastric secretion?
- Gastric mucosa secretes gastric juice which is a mixture of secretory products of various cells - Various cells parallelly secrete into the gastric lumen - 1-1,5 L/day - Composed of water, electrolytes (H+, Cl-), HCO3-, proteins (mucin, digestive enzymes)
29
VI. Gastric secretion 2. What is the amount of gastric secretion per day?
1-1,5 L/day
30
VI. Gastric secretion 3. What is gastric secretion composed of?
Composed of water, electrolytes (H+, Cl-), HCO3-, proteins (mucin, digestive enzymes)
31
VI. Gastric secretion 4. What are functions of gastric juice?
- H+ (proton) is important for digestion, killing microbes and disinfecting food - Conversion of inactive pepsinogen to active pepsins -> chemical digestion of proteins - Intrinsic factor – essential for absorption of vitamin B12 (if not present = severities!) - Protection of mucosa, by HCO3- + mucin, against the acidic luminal environment (if not present = ulcer) - H2O lubricates chyme, food etc.
32
VI. Gastric secretion 5. What is gastric pit?
opening of a duct into which gastric glands empty
33
VI. Gastric secretion 6. What are the types of cells in gastric glands?
Gastric glands have several types of cells that secrete unique substances: - Parietal cells: HCl + intrinsic factor (B12) - Chief cells: digestive enzymes (pepsinogen) => Surface epithelial cells: HCO3-, mucins -> protect mucosa from gastric acid
34
VI. Gastric secretion - Parietal cell 7A. What are the features of parietal cell?
35
VI. Gastric secretion - Parietal cell 7B. What are the 2 forms of parietal cell?
inactive + active
36
VI. Gastric secretion - Parietal cell 7C. What are the features of inactive/resting form of parietal cell?
Inactive/resting form: has a tubulovesicular apparatus in the cytoplasm + IC canaliculus
37
VI. Gastric secretion - Parietal cell 7D. What are the features of Active form of parietal cell?
(1) tubulovesicular membranes fuse with PM of canaliculi = ↑ surface area (2) high quantity of mitochondria for huge energy demand
38
VI. Gastric secretion - Parietal cell 8. Make a schematic diagram of Parietal cell secretion
39
VI. Gastric secretion - Parietal cell 9. What does it mean when we have prolonged vomitting?
Prolonged vomiting -> metabolic alkalosis - Refill of gastric lumen by H+ - Produce HCO3-, which goes to the blood -> alkalosis
40
VI. Gastric secretion - Parietal cell 10. Why are parietal cells important?
Parietal cells are important for: - Gastric acid secretion - H2O secretion - Intrinsic factor secretion (via exocytosis)
41
VI. Gastric secretion - Parietal cell 11. How is parietal cell regulated?
The parietal cell is regulated by: - Neural pathway: ACh from neuron - Hormonal pathway: Gastrin from bloodstream - Paracrine pathway: Histamine (paracrine mediator)
42
VII. Regulation of gastric acid secretion 1. What is the most important regulator of gastric acid secretion?
The most important regulator of gastric acid secretion is the G-cell => secrete gastrin, which acts directly on parietal cells or ECL cells
43
VII. Regulation of gastric acid secretion 2A. What are the causes for G-cells activation?
The most important regulator of gastric acid secretion is the G-cell => secrete gastrin, which acts directly on parietal cells or ECL cells
44
II. Regulation of gastric acid secretion 2B. What are the parasympathetic NT that activate G-cells?
- ACh - GRP (gastrin-releasing-peptide)
45
II. Regulation of gastric acid secretion 2C. How does wall tension activate G-cell?
- Wall tension (presence of ingested food)
46
II. Regulation of gastric acid secretion 2D. How does NE activate G-cell?
- NE -> β2-AR -> GA secretion (SYM NS) => Gastrin can act as an endocrine regulator, because it travels with blood
47
II. Regulation of gastric acid secretion 3. What are the inhibitors of gastric acid secretion?
- Somatostatin - Prostaglandins
48
II. Regulation of gastric acid secretion 4. What are the features of ECL (enterochromaffin-like) cells?
- Activated by PARA or by gastrin - Releases histamine (acts as a paracrine mediator), which acts on parietal cells
49
II. Regulation of gastric acid secretion 5A. What are the 2 phases that gastric acid secretion can be regulated?
50
II. Regulation of gastric acid secretion 5B. How is gastric acid secretion regulated at cephalic phase?
smell + taste of food can ↑GA secretion via vagal N stimulation (PARA)
51
II. Regulation of gastric acid secretion 5C. How is gastric acid secretion regulated at gastric phase?
- produces the largest stimulation of gastric secretion during postprandial period (after meal) => Stimulates GA secretion => Efferent fibers release ACh to activate the cells in the gastric epithelium => Vagal stimulation results in secretion of pepsinogen, mucus, HCO3- and IF
52
II. Regulation of gastric acid secretion 6. What happen in Vagovagal reflex?
- Activated by the presence of food in the stomach in the gastric phase - Distention and stretch of the stomach wall are detected by afferent fibers in the wall, which in turn stimulates brainstem and thereby drive activity of vagal efferent fibers
53
II. Regulation of gastric acid secretion 7. What happen in Feedback regulation of gastric acid secretion?
- Presence of the acid in the antrum + pylorus induces a negative feedback loop to inhibit the parietal cell - When the luminal pH < 3, somatostatin is released from the D-cell, which acts on G-cells in a paracrine manner to decrease GA secretion
54
III. Signal transduction mechanism in the parietal cells 1. What are the 2 main signals?
1. cAMP + Ca2+-signals will ↑GA secretion 2. PG + SST-signals will ↓GA secretion
55
III. Signal transduction mechanism in the parietal cells 2. The role of cAMP + Ca2+-signals in Signal transduction mechanism in the parietal cells?
cAMP + Ca2+-signals will ↑GA secretion, because: 1. Parietal cell gets activated: endomembranes fuse with apical membranes -> transporters translocated + ↑surface area 2. Enhance activity of those transporters
56
III. Signal transduction mechanism in the parietal cells 3. The role of PG + SST-signals in Signal transduction mechanism in the parietal cells?
G + SST-signals will ↓GA secretion - Will protect from ‘’over secretion’’ of GA - PG produced by cyclooxygenase (COX) -> aspirin can inhibit PG formation -> inhibit basal- inhibitory-effect of Gi-signaling -> too much aspirin destroys mucosa -> ulcers
57
IV. The ionic composition of gastric juice 1. What does The ionic composition of gastric juice depend on?
The ionic composition of gastric juice depends on the rate of secretion
58
IV. The ionic composition of gastric juice 2. The ionic composition of gastric juice depends on the rate of secretion => Explain
The ionic composition of gastric juice depends on the rate of secretion - If we have basal GA secretion, we can secrete a significant amount of Na+ and Cl-, and low K+ + H+ - If secretion rate increases => H+-secretion increases as well
59
IV. The ionic composition of gastric juice 3. What is the amount of Basal acid output (BAO)?
1,5 – 2,5mmol H+/hour
60
IV. The ionic composition of gastric juice 4. What is the amount of peak acid output?
Peak acid output (PAO) – in response of meal - Female: 25mmol H+/hour - Male: 35mmol H+/hour (because of ↑nr. of parietal cells)
61
V. Surface epithelial cells 1. Where are Surface epithelial cells present?
- The surface epithelial (SE) cells are present everywhere in the gastric mucosa, because they have an important protective role - The cells are located on the superficial layer of the mucosa,
62
V. Surface epithelial cells 2. What do Surface epithelial cells constitute of? The role of these components?
The cells are located on the superficial layer of the mucosa, and constitute of: - Inorganic constituents: Na+, Cl-, HCO3- - Organic constituents: mucin => Mucin and HCO3- fulfill the protective role of the SE-cells
63
V. Surface epithelial cells 3. What do Surface epithelial cells do in response to meal?
In response to meals -> more GA produced -> more mucin + HCO3- is needed for protection
64
V. Surface epithelial cells 4. How is the surface of stomach protected?
The surface of the stomach is protected by the gastric mucosal barrier
65
V. Surface epithelial cells 5. What are the features of the gastric mucosal barrier?
- It is a sticky narrow layer (0,2mm thick) – dense in mucin - Buffering by the HCO3—rich secretion and the restraint to convective mixing caused by the high viscosity of the mucus layer, allow the pH at the cell surface to remain near 7, whereas the pH in the gastric juice in the lumen is 1 to 2
66
V. Surface epithelial cells 6. What are the features of mucin?
Mucin = glycoprotein (80% of weight is carbohydrate) - Pepsin can cleave the peptide parts => Need to have a continuous renewal of mucins, because pepsin can degrade the mucin molecules
67
VI. Chief cells 1. Where are chief cells located?
- Located in the fundus + body of the stomach - Chief cells are located in deep locations of the gastric pit
68
VI. Chief cells 2. What is the role of chief cells?
- Responsible for production of pepsinogen (protein degradation) + gastric lipase (lipid breakdown) – activated by low pH - In response to meal, they will secrete digestive enzymes
69
VI. Chief cells 3. What is the mechanism of chief cells?
- Pepsinogen secretion stimulated by gastrin (Gq), ACh (M3), histamine (Gs), secretin
70
VI. Chief cells 4. What is the stimulus for the release of chief cells?
- Neural (PARA via ENS): ACh - Humoral: secretin, gastrin, CCK => ↑chief cell digestive enzyme secretion
71
VII. Secretion of small intestine 1A. What are the features of Secretion of small intestine in case of the small intestinal mucosa?
72
VII. Secretion of small intestine 1B. What is the amount of secretion in case of the small intestine mucosa?
Secretion: 1,5 – 2,0 L/day
73
VII. Secretion of small intestine 1C. What is in the solution of secretion in case of the small intestine mucosa?
- Mostly water + isosmotic solution (contains a HCO3--rich solution for neutralizing acidic content) - Has no digestive enzyme production (mucosa not responsible for digestion) - Huge amount of mucin is produced => Huge amount of fluid secretion => Maintain the fluidity of chyme => Washes away microorganisms
74
VII. Secretion of small intestine 2. What happen if we have Diarrhea?
Diarrhea -> metabolic acidosis: - Continuous production of fluid from small intestine - Lose HCO3- from body -> acidosis
75
VIII. Secretion of large intestine: 1. Is Secretion of large intestine different from that of small intestine?
YES!!! It is different from small intestine mucosal secretion, since the structures differ
76
VIII. Secretion of large intestine: 2. What are the features of secretion of large intestine?
YES!!! It is different from small intestine mucosal secretion, since the structures differ
77
IX. Regulation of secretion 1. The regulation of secretion is both NEURAL and HUMORAL => T/F?
FALSE!!! ONLY NEURAL!!!
78
IX. Regulation of secretion 2. What are the 4 types of secretion regulation?
1. Para 2. SYM 3. ENS 4. Paracrine mediators
79
IX. Regulation of secretion 3. Describe PARA regulation of secretion
PARA -> secretion↑ (VIP, ACh) - VIP (Gs -> cAMP-signal -> phosphorylation + translocation (PKA) of CFTR channels -> more CFTR channels) = effects of cholera toxin (watery diarrhea) - Cholera toxin can irreversibly activate the Gα-s-subunits -> cAMP-signal will be continuously high -> more abundant + more permeable Cl-channels (due to phosphorylation)
80
IX. Regulation of secretion 4. Describe SYM regulation of secretion
secretion↓
81
IX. Regulation of secretion 5. Describe ENS regulation of secretion
secretion↑ - Distension of intestinal wall/chemoreceptor cells which are activated
82
IX. Regulation of secretion 6. Describe secretion regulation by Paracrine mediators => T/F?
Paracrine mediators -> serotonin (5-HT) - Activation of local immune system in the small intestine, via serotonin- production -> increased fluid production can happen -> wash out potentially harmful microorganisms
83
IX. Regulation of secretion 7. Make a schematic diagram of Cl- regulation in small intestine

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