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Gastrointestinal physiology > Salivary and pancreatic secretion > Flashcards

Salivary and pancreatic secretion Flashcards

1
Q

What are similarities between salivary and exocrine pancreas secretions?

A

Both have branching ductile arrangement into which epithelial secretions are released

Both secretions aid digestion

Secretions are composed of water, electrolytes and some digestive enzymes

Glands compromise secretory units made up of acinus

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2
Q

How much fluid does the GI tract secrete per day?

A

7l

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3
Q

What are the 4 main GI secretions?

A

Saliva
Gastric juice
Pancreatic juice
Bile

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4
Q

What is the main role of salivar?

A

Lubricates ingested food, forms a protective buffer and initiates digestion of starch (enzymes).

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5
Q

What is the main role of pancreatic juice?

A

Alkaline pancreatic juice neutralises stomach acid, and completes digestion of ingested foodstuffs (enzymes).

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6
Q

What is an acinus?

A

Up to 100 acinar cells that line an intercalated duct

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7
Q

What do intercalated ducts drain into?

A

Intralobular ducts

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8
Q

What do intralobular ducts drain into?

A

Interlobular

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9
Q

What do interlobular ducts drain into?

A

Main salivary or pancreatic duct

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10
Q

What cells secrete salivar?

A

Acinar cells

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11
Q

What are the three types of salivary glands, what do they produce, what relative contribution?

A

Parotid: produces watery (serous) secretion amounting to 25% of total

Submandibular: produces both serous and mucous secretions, 70%

Sublingual: produces mucous secretion, 5%

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12
Q

What do serous salivary secretions contain?

A

alpha amylase

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13
Q

What do mucous salivary secretions contain?

A

mucin

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14
Q

Where do primary secretions arrive?

A

Intercalated duct

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15
Q

What is secreted in primary secretion from salivary and acinar cells?

A

Isotonic NaCl (composition same as in plasma)

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16
Q

Which channels facilitate isotonic NaCl secretion in primary secretion?

A

Basolateral NKCC, Cl-, Na+ and K+ enter cell

Cl- inside cell exits via apical Cl- channel

Na+ out via basolateral Na/KATPase and K+ out via basolateral channel

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17
Q

What causes primary Na+ secretion, how is it secreted?

A

Electrical gradient generated by Cl- movement

Na+ diffuses between cells via TJs (paracellular)

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18
Q

How does water get added to primary secretions?

A

Moves by osmosis

AQP and paracellular

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19
Q

Where does secondary modification of ionic content occur?

A

Excretory duct

20
Q

How do duct cells modify primary secretion in saliva?

A

NaCl reabsorption

K+ and HCO3- secretion

21
Q

How is NaCl reabsorbed in modification of primary salivar?

A

Na+ reabsorbed via Enac or NHE (apical), and exit via Na/KATPase

Cl- reabsorbed via ClHCO3- and exit via Cl- channel

22
Q

How is bicarbonate secreted in modification of primary salivar?

A

HCO3- secreted in exchange for Cl-

HCO3- formed by hydration of CO2 in cell (H+ lost by basolateral NHE1)

23
Q

How is K+ secreted in modification of primary salivar?

A

K+ accumulated in cells by ATPase, lost to lumen through K+/H+ exchanger

24
Q

What does secondary modification do to luminal fluid from salivary glands?

A

Becomes hypotonic because more ions exit than enter duct and little water reabsorbed due to low water permeability

25
Q

What happens to saliva as flow rate increases, why?

A

Saliva secretion more similar to plasma (isotonic)

Because less time for modification

26
Q

What happens to HCO3- as flow rate increases, why?

A

Stays same despite less time for modification

Agonists that stimulate saliva secretion (secretin) also stimulate HCO3- secretion

27
Q

What effect does parasympathetic stimulation have on salivary secretion?

A

Primary secretion stimulated and reduce secondary modification

Large volumes of watery saliva made

28
Q

How does parasympathetic stimulation stimulate salivary secretion (pathway)?

A

ACh on M3 leads to Increased Ca2+ in acinar cells

Stimulate PK
Activates Cl- apical and K+ basolateral channel

Phosphorylation of cytoskeletal elements induces export of protein containing vesicles (e,g, amylase)

29
Q

Which branch of autonomic system has a greater effect on salivary secretion?

A

Parasympathetic

30
Q

How does symp stimulation affect salivary secretion?

A

Beta receptor produces cAMP activates PKA

Amylase secretion from vesicles stimulated.

Viscous saliva made

31
Q

What is kallikrein (salivar protein)?

A

Cleaves proteins to yield vasodilator peptides (e.g. bradykinin)

32
Q

What % of pancreas is exocrine?

A

90%

33
Q

Are pancreas secretions constitutive or regulated?

A

Constitutive but can be upregulated

34
Q

What can stimulate pancreatic secretions 10 fold?

A

ACh M3 stimulation or CCK receptor activation

i.e. Gq - IP3 and increased Ca2+

35
Q

What does primary secretion from pancreatic acinar cells do?

A

Hydrates digestive enzyme protein released from acinar cells

36
Q

What enzymes are released from acinar cells?

A

Proteases, amylase, lipases and nucleases

37
Q

How is autodigestion prevented in pancreas?

A

Packaged as zymogen
Protease inhibitors in granules

Non digestive proteases which degrade active enzyme

38
Q

Is primary secretion the same in the pancreas as it is in the salivary glands?

A

Yes

39
Q

What do pancreatic duct cells do in secondary modification?

A

Secrete isotonic NaHCO3- (neutralises acid)

HCO3- from hydration of CO2, lost via apical Cl-/HCO3- exchanger.

Na+ and H2O follow extracellularly

Cl- leaves cell by basolateral Cl- channel

40
Q

What happens in each phase of digestion?

A

Cephalic phase (i.e. see, smell, thought of food): mediated by ACh

Gastric phase: stomach distension, vagal stimulation (ACh) of GRP containing neurones leads to gastrin release form G cells in antrum

Intestinal phase: duodenum ph <4.5, duodenum distension, AA and FA in duodenum, mediated by ACh, secretin and CCK

41
Q

Which enzymes act on pancreatic duct cells (not acinar cells)?

A

Gastrin and secretin

42
Q

Which protiens act on acinar and duct cells?

A

CCK and ACh

43
Q

What do goblet cells in ducts in pancreas do?

A

Secrete mucus which facilitate lubrication, offer mechanical protection and bind pathogens

44
Q

What mainly increases saliva secretions?

A

ACh

45
Q

Cells of the exocrine pancreas secreting pancreatic enzymes

A

Acinar cells

Gastrointestinal physiology (5 decks)

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