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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

A

mucus

25
Q

primary saliva secretion

A

contains amylase

isotonic levels of Na/K/Cl

26
Q

secondary modifications saliva

A

occur as they move along duct

remove NaCl, replaced by K + and HCO3- entering the lumen

27
Q

saliva primary secretion (details)

A

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
Q

secondary saliva modifications (details)

A

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
Q

final composition of saliva

A

final saliva always hypotonic to plasma

- as flow rate increases, less time for secondary modifications

30
Q

saliva proteins

A

alpha amylase and lingual lipase
mucins = glycoproteins
also kallikrein, lysozymes etc,

31
Q

pancreatic primary secretion

A

Cl- accumulated in cell from NKCC on basolateral, efflux into lumen by CFTR
Na+ follows paracellularly

32
Q

pancreatic secondary

A

exchange of Cl- in the lumen with HCO3- via the same exchanger
Na and K enter lumen from paracellular

33
Q

how is autodigestion of the pancreas prevented

A

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
Q

what hormones/ transmitters act on acinar and duct cells

A

ACh and CCK

35
Q

what hormones act only on duct cells

A

gastrin

secretin

36
Q

action of mucus and bicarbonate in stomach

A

combine to prevent acid digestion of the stomach itself

37
Q

stomach humeral factors release and function

A

gastrin - stimulates acid secretion
somatostatin inhibits acid secretion
histamine is a paracrine regulatorn

38
Q

importance of acid secretion

A

creates an antiseptic ante chamber at the start of the GI tract
denatures preteins
promotes truncation of pepsinogen into pepsin

39
Q

what is secreted int he body of stomach

A

acid, pepsinogen and IF

has gastric glands

40
Q

what is secreted in the antrum of stomach

A

gastrin, somatostatin and holds food

more of endocrine function

41
Q

position and function of gastric gland cells

A

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
Q

ionic composition of gastric juice

A

depends on secretory rate
unstimulated - basal secretion from non parietal, so higher Na and Cl
stimulated = more parietal so more HCl

43
Q

unstimualted parietal cells

A

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
Q

common mediator hypothesis

A

histamine very effective

both ACh and gastrin also increase histamine release

45
Q

action of somatostatin from stomach

A 
D cells release
Gi
reduces acid secretion 
ACh inhibits and low liumenal pH stimulates release 
Gastric H.pylori inhibits release
46
Q

pancreatic/ gastric acid secretion in phases

A 
cephalic = 30%, from vagus 
gastric = 60%, distension initiates vasovagal reflex, protein products causes gastrin release
intestinal = 10%, protein digestion stimulates G cells again
47
Q

chief cells action

A

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
Q

mucous cells action

A

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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