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GIGU > Secretions of the GI Tract and Pancreas > Flashcards

Secretions of the GI Tract and Pancreas Flashcards

1
Q

Acinar cells

A

Secrete initial saliva

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2
Q

Myoepithelial cells

A

Have motile extensions

When stimulated by neural input, contract to eject saliva into mouth

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3
Q

Intercalated duct

A

Saliva in the intercalated duct is similar in ionic composition to plasma

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4
Q

Striated duct and ductal cells

A

Lined by columnar epithelial cells
Ductal cells modify the initial saliva to produce the final hypotonic saliva
They also modify concentrations of various electrolytes - actively absorb Na, passively absorb Cl, actively secrete K+
Ductal cells are impermeable to water

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5
Q

Saliva composition and comparison to plasma

A

Saliva is composed of H2O, electrolytes, a-amylase, lingual lipase, kallikrein and mucus
It is hypotonic compared to plasma- has increased K+ and HCO3, decreased Na and Cl

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6
Q

Parasympathetic innervation of salivary glands

A

Facial and glossopharyngeal nerves give off presynaptic nerves which synapse in autonomic ganglia and then give off branches to glands
Increases saliva production, HCO3 and enzyme secretions
Causes contraction of myoepithelial cells
Parasympathetic effect dominates

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7
Q

Sympathetic innervation of salivary glands

A

Preganglionic nerves originate at the cervical ganglion, whose postganglionic fibers extend to the glands in the periarterial spaces
Same effects as parasympathetic, but is not used often

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8
Q

Components of gastric juice

A 
HCl- converts pepsinogen to pepsin
Pepsinogen
Mucus - helps neutralize acids with HCO3
Intrinsic factor
H2O
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9
Q

Oxyntic gland area

A

Area of gastric mucosa
Located in proximal 80% of the stomach
Secretes acid

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10
Q

Pyloric gland

A

Area of gastric mucosa in distal 20% of stomach (antrum)

Synthesizes and releases gastrin

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11
Q

Cells in body of stomach

A 
Parietal cells (secrete HCl and intrinsic factor)
Chief cells- secrete pepsinogen
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12
Q

Cells in antrum

A

Mucus cells- secrete mucus, HCO3 and pepsinogen
G cells- secrete gastrin into the circulation (not into stomach. gastrin increases H/K ATPase activity and increases acidity)

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13
Q

Parietal cells cellular mechanism of HCl secretion

A

HCO3/Cl antiporter pumps HCO3 into blood and chloride into cell
H/K ATPase antiporter pumps K into cell and H into stomach
Chloride follows H+ into stomach

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14
Q

Non-parietal vs parietal gastric juice

A

Gastric juice is a mixture of non parietal and parietal juices
Non parietal is a basal alkaline secretion of constant and low volume consisting of K, Na and Cl
Parietal is slightly hyperosmotic and Cl is the only anion present (Cations include H+ of course)

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15
Q

Vagus nerve effect on parietal cells

A

Causes ACh release which activates M3 receptor on parietal cells and the H/K ATPase increases secretion
Also causes GRP release which activates G cells to secrete gastrin- further activating parietal cells

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16
Q

Effect of prostaglandins on H+ secretion

A

D cells secrete somatostatin which inhibits H+ secretion by acting on G cells
Prostaglandins also inhibit H+ secretion

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17
Q

Omeprazole

A

Blocks H/K ATPase in stomach

18
Q

Atropine

A

Blocks ACh effects on M3 receptor, reducing H+ secretion (blocks vagal pathway)
Will not block vagal effects on gastrin secretion because the neurotransmitter at the synapse on G cells is GRP
It does block the ACh potentiated effects of histamine and gastrin though

19
Q

Cimetidine

A

Blocks H2 receptor from binding histamine and reduces H+ secretion
This blocks the direct action of histamine, but also blocks the potentiated effects of ACh and gastrin- because gastrin and ACh also activate histamine release

20
Q

Regulation of gastrin release by somatostatin and vagus

A

Somatostatin acts on G cells to inhibit gastrin release
Vagal stimulation causes gastrin release by releasing GRP and inhibiting release of somatostatin
Gastrin itself will increase somatostatin release as negative feedback system
H+ also triggers release of somatostatin

21
Q

Examples of potentiated effects: histamine and ACh

A

Histamine potentiates the actions of ACh and gastrin

ACh potentiates the actions of histamine and gastrin

22
Q

Cephalic phase of gastric secretion

A

Accounts for 30% of HCl secretion in response to meal
Simulated by smelling/tasting, chewing, swallowing
Vagus nerves stimulates parietal cells via ACh
Vagus nerve stimulates g-cells to release gastrin, further activating parietal cells
Produces enzymatic secretion
This phase is abolished by a vagotomy

23
Q

Gastric phase

A

Accounts for 60% of HCl released in response to a meal
Stimulated by stomach distension and presence of broken down proteins, AAs and peptides
Distension activates mechanoreceptors in mucosa of oxyntic and pyloric glands
Produces enzymatic secretion
Vagus nerve activates parietal cells via direct/indirect pathways

24
Q

Intestine phase

A

Accounts for 5-10% of HCl secreted in response to a meal
Distension of small intestine stimulates acid secretion
Digested protein stimulates acid secretion via direct effect on parietal cells and via gastrin secretion from intestinal G cells
Produces enzymatic and aqueous secretions

25
Q

What is most important stimulus for pepsinogen secretion

A

Vagus nerve stimulation

H+ triggers local cholinergic reflexes that stimulate chief cells to secrete pepsinogen

26
Q

Intrinsic factor

A

Required for B12 absorption in the ileum
Secreted by parietal cells
Failure to secrete IF is associated with achlorhydria and with absence of parietal cells

27
Q

Protective factors of gastric mucosa

A

HCO3 and mucus
Prostaglandins
Mucosal blood flow
Growth factors

28
Q

Damaging factors of gastric mucosa

A 
H+ and pepsin
H. pylori
NSAIDs
Stress
Smoking
Alcohol
29
Q

Zollinger-Ellison syndrome

A

Large secretion of gastrin by duodenal or pancreatic neuroendocrine tumors
Increases parietal cell mass, inhibits the absorption of sodium and water by the small intestine
Creates ulcers due to excess H+
Low pH inactivates pancreatic digestive enzymes, interferes with emulsification, and leads to maldigestion and malabsorption
(very high H+ secretion and gastrin levels)

30
Q

Pernicious anemia

A

Stomach does not produce enough IF, less B12 absorption
Atrophic gastritis is chronic inflammation of stomach mucosa that leads to loss of parietal cells and can cause pernicious anemia
Autoimmune metaplastic atrophic gastritis is when immune cells attack IF protein or gastric parietal cells

31
Q

Gastrectomy/Gastric bypass effect on B12

A

Gastrectomy causes loss of parietal cells

Gastric bypass excludes the stomach, duodenum and proximal jejunum which alters absorption of B12

32
Q

Secretin stimulation test

A

Used in diagnosis of gastrin secreting tumors
Under normal conditions, secretin administration inhibits gastrin release
In gastrinomas, injection of secretin causes a paradoxical increase in gastrin release

33
Q

Helicobacter pylori

A

Causes gastric and duodenal ulcers
Releases cytotoxins that break down mucosal barrier and underlying cells
Urease enzyme allows bacteria to colonize the mucosa by producing ammonia from urea and alkalizes the environment
Ammonium results and causes cytotoxicity

34
Q

Gastric ulcer

A

Form on lining of stomach and caused mostly by defective gastric mucosal barrier, as opposed to increased acid secretion
Increased gastrin levels because of decreased H+

35
Q

Duodenal ulcers

A 
Form on lining of duodenum, more common
Usually not malignant
H+ secretion rates are higher than normal in response to food
Increased gastrin levels 
Increased parietal cell mass
36
Q

Exocrine pancreas sympathetic/parasympathetic innervation

A

S- postganglionic nerves from celiac and superior mesenteric plexus innervate
P- vagus nerve preganglionic fibers synapse in ENS, postganglionic fibers synapse in exocrine pancreas
Parasympathetics activate, sympathetics inhibit

37
Q

Secretion of exocrine pancreas

A

Aqueous solution containing HCO3
Enzymatic secretion
Contains acinar cells (enzymatic secretion) centroacinar cells and ductal cells (latter two types secrete aqueous solution that is alkaline rich)

38
Q

Modification of initial pancreatic secretion by ductal cells

A

Net result is secretion of HCO3 into pancreatic ductal juice and absorption of H+

39
Q

Cystic fibrosis and the pancreas

A

Pancreas is one of first organs to fail in CF
CFTR is a regulated Cl channel in the apical surface of the duct cell
Some CFTR mutations are associated with loss of HCO3 secretion, causing some loss of ability to flush out active enzymes from the duct
May lead to acute and chronic pancreatitis

40
Q

CCK/Secretin regulation of pancreatic secretions

A

CCK induces release of pancreatic enzymes into the duodenal lumen
Secretin induces the secretion of HCO3 from pancreatic cells into the duodenum

GIGU (21 decks)

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