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9.5 - GI PHYSIOLOGY > GI secretions > Flashcards

GI secretions Flashcards

1
Q

Types of saliva secretions

A 
Mucous = contain mucin, more viscous 
Serous = more watery, contain alpha amylase
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2
Q

Salivary gland structure

A

Acinus and duct cells

intercalated duct -> intralobular duct -> interlobular duct and then main duct

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3
Q

Functions of saliva

A 
Serous = moistening oral mucosa, lubrication
Mucous = lubrication, diffusion barrier for protection
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4
Q

Saliva stage 1 secretion

A

Acinar cells secrete an isotonic fluid, similar to plasma levels of Na+/Cl- and water
Composition mirrors plasma

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5
Q

Saliva stage 2 secretion

A 
Modification by duct cells
Removal of NaCl and replaced by K+/HCO3-
Cl-/HCO3- exchanger on apical membrane 
Saliva always hypotonic to plasma 
As flow rate increases, there is less time for secondary modifications
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6
Q

Saliva regulation

A

PNS: ACh increases primary secretions and rate of flow, binds to M3, Gq, phos. protein kinases
SNS: NA binds to alpha receptors, Gq causes more amylase secretion and more viscous saliva, also through beta receptors

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7
Q

Pancreatic secretion components

A

Similar to saliva, efflux of Cl- from acinar cells through CFTR
Secondary: exchange in lumen of Cl- for HCO3-

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8
Q

Proteins in pancreatic secretions

A

Precursors to active enzymes
Drain into the descedning duodenum
Proteases, amylases, lipases, nucleases

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9
Q

Phases of digestion

A

Cephalic: sight, smell, taste of food (increases pancreatic and salivary by ACh)
Gastric: distension of the stomach (increases pancreatic by gastrin and ACh release)
Intestinal: presence of certain products in the duodenum (secretin, CCK), distension of duodenum

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10
Q

Nervous regulation of pancreatic secretion

A

ACh from vagus, higher command and vasovagal reflex

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11
Q

Pancreatic hormonal regulation

A

Gastrin: from G cells in antrum of stomach, from distension of stomach
Secretin: from S cells of duodenum, from H+ in duodenum
CCK: from duodenum, stimulated by FA
Somatostatin: inhibits secretions
ACh: higher command and vasovagal reflex triggered by amino acids and FA in duodenum

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12
Q

Gastric secretion components

A

H+, pepsinogen, mucus, bicarbonate, intrinsic factor

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13
Q

IF function

A

In small intestine for vitamins B12 absorption

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14
Q

Gastric gland cell types

A

Chief: pepsinogen secretion
Parietal: acid
Surface epithelial: mucus and bicarbonate
Neuroendocrine: hormones

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15
Q

Acid secretion mechanism

A

Insertion of vesicles with the H+/K+ ATPase in their membrane into the plasma membrane of parietal cells
Pump H+ into cell in exchange for K+, K+ recycles out
Cl- into lumen from bicarbonate exchanger on the basolateral
water follows to create HCl

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16
Q

H+/K+ ATPase inhibitor

A

Omeprazole

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17
Q

Regulation of acid secretion

A

Induced by kinase activity

  • ACh from vagus, M3 and IP3
  • Gastrin from G cells, from stimulated neurones or protein products in lumen, IP3 and PKC
  • Histamine (paracrine), released from enterochromaffin-like cells, activates cAMP, H2 receptors
  • Inhibit = somatostatin (Gi)
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18
Q

Histamine antagonist

A

Ranitidine, blocks H2 receptors

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19
Q

Mucous cells

A

Produce mucin, glycoprotein with high viscosity

Combines with water, ions and phospholipids to create a mucus gel

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20
Q

Peptic ulcer cause and treatment

A

Potential cause: Helicobactor pylori bacteria
Antacids: aluminium hydroxide
H2 inhibitor: ranitidine
Proton pump inhibitor: omeprazole

21
Q

saliva flow rate

A 
basal = 0.5ml/min
stimulated = up to 5ml/min
22
Q

types of salivary gland

A 
parotid = serous, 25%
submandibular = both, 75%
sublingual = mucus, 5%
23
Q

serous secretions supplemented by

A

alpha amylase

24
Q

mucous secretions mainly contain

25
primary saliva secretion
contains amylase | isotonic levels of Na/K/Cl
26
secondary modifications saliva
occur as they move along duct | remove NaCl, replaced by K + and HCO3- entering the lumen
27
saliva primary secretion (details)
acinar cells secrete isotonic NaCl - basolateral NKCC accumulates Cl- in cell which diffuses into lumen - Na+ pumped out of basolateral by ATPase, diffuse into lumen paracellularly - K+ diffuses across apical - water follows by osmosis
28
secondary saliva modifications (details)
action by duct cells - Na+ absorbed by ENaC and apical Na-H exchange - Na+ exits on the Na-K ATPase - Cl- reabsorbed through transporter with HCO3-, exits on basolateral - HCO3- secretion into lumen in exchange for Cl-, formed in the cell from CO2 hydration - K+ accumulated in cells from ATPase, enters lumen through the K/H exchanger - low water permeability
29
final composition of saliva
final saliva always hypotonic to plasma | - as flow rate increases, less time for secondary modifications
30
saliva proteins
alpha amylase and lingual lipase mucins = glycoproteins also kallikrein, lysozymes etc,
31
pancreatic primary secretion
Cl- accumulated in cell from NKCC on basolateral, efflux into lumen by CFTR Na+ follows paracellularly
32
pancreatic secondary
exchange of Cl- in the lumen with HCO3- via the same exchanger Na and K enter lumen from paracellular
33
how is autodigestion of the pancreas prevented
packaging the enzymes as zymogens lacking enzyme activity | presence of protease inhibitors in secretory vesicles, presence of non-digestive proteases to degrade active enzymes
34
what hormones/ transmitters act on acinar and duct cells
ACh and CCK
35
what hormones act only on duct cells
gastrin | secretin
36
action of mucus and bicarbonate in stomach
combine to prevent acid digestion of the stomach itself
37
stomach humeral factors release and function
gastrin - stimulates acid secretion somatostatin inhibits acid secretion histamine is a paracrine regulatorn
38
importance of acid secretion
creates an antiseptic ante chamber at the start of the GI tract denatures preteins promotes truncation of pepsinogen into pepsin
39
what is secreted int he body of stomach
acid, pepsinogen and IF | has gastric glands
40
what is secreted in the antrum of stomach
gastrin, somatostatin and holds food | more of endocrine function
41
position and function of gastric gland cells
parietal = base and neck, secrete HCl and IF chief = base and neck, secrete pepsinogen endocrine = base, secrete regulators like gastrin and somatostatin mucus neck cells = neck and secrete mucus superficial epithelium = secrete mucus and bicarbonate
42
ionic composition of gastric juice
depends on secretory rate unstimulated - basal secretion from non parietal, so higher Na and Cl stimulated = more parietal so more HCl
43
unstimualted parietal cells
lots of tubulovesicels in the sub apical cytoplasm vesicles contain H+-K+ ATPase proteins stimulation of acid secretion triggers vesicle insertion into plasma membrane - ATPase inactive in vesicles
44
common mediator hypothesis
histamine very effective | both ACh and gastrin also increase histamine release
45
action of somatostatin from stomach
``` D cells release Gi reduces acid secretion ACh inhibits and low liumenal pH stimulates release Gastric H.pylori inhibits release ```
46
pancreatic/ gastric acid secretion in phases
``` cephalic = 30%, from vagus gastric = 60%, distension initiates vasovagal reflex, protein products causes gastrin release intestinal = 10%, protein digestion stimulates G cells again ```
47
chief cells action
secrete pepsinogens activated by N terminal truncation, spontaneous activation in acidic lumen low pH for optimum activity pepsin ingests 1/5 of protein protein release from fusion of granules with apical membrane, stimulated by ACh, gastrin, CCK, secretin
48
mucous cells action
secrete mucin, large glycoprotein with high viscosity combines with water, ions and phospholipids to create a mucous gel, barrier to H+ ions stimualted by ACh

9.5 - GI PHYSIOLOGY (7 decks)

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