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gigu > Secretions of the gastrointestinal tract > Flashcards

Secretions of the gastrointestinal tract Flashcards

1
Q

What is the function of saliva?

A

Initial digestion of starches and lipids

dilution and lubrication of ingested food

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2
Q

Describe parotid glands

A

Serous cells

Secrete water, ions, & enzymes

25% of daily output

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3
Q

Describe submaxmillary and sublingual glands

A

Serous and mucous cells

secrete aqueous fluid & mucin glycoprotein for lubrication

75% of daily output

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4
Q

What secretes inital saliva?

A

Acinar cells

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5
Q

How do myoepithelial cells secrete saliva?

A

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

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6
Q

In what space is saliva similar in ionic composition to plasma?

A

In the intercalated duct

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7
Q

How do ductal cells modify inital saliva to produce final saliva?

A

Ductal cells alter the concentration of various electrolytes to make it hypotonic

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8
Q

Describe saliva in comparision to plasma in the intercalated duct and the striated duct

A

Intercalated duct-isotnic to plasma

Striated duct- Hypotonic

More K+ and HCO3-

Less Na+ and Cl-

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9
Q

How does HCO3- leave the cell to the lumen?

A

Via CAMP-activated CFTR Cl- channel or the Cl-/HCO3- exchanger

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10
Q

Where do parasympathetic nerves originate for salivary glands?

A

Facial and glossopharyngeal

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11
Q

Where do parasympathetic postsynaptic fibers originate?

A

In autonomic ganglia and innervate individual glands

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12
Q

Where do sympathetic preganglionic nerve originate?

A

Cervical ganglion

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13
Q

Where do sympathetic postganglionic fibers go?

A

Extend to the glands in the periarterial spaces

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14
Q

What stimulates the parasympathetic nervous system to secrete saliva?

A

Food

Nausea

Smell

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15
Q

What inhibits the parasympathetic nervous system to secrete saliva?

A

Dehydration

Fear

Sleep

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16
Q

Describe the parasympathetic pathway of salivary secretion

A

CN VII and CN IX –> Ach –> mAChR –> IP3 and increase in Ca2+ at acinar or ductal cells –> saliva

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17
Q

Describe the sympathetic pathway of salivary secretion

A

T1-T3 –> NE –> Beta-adrenergic receptor –> cAMP –> Saliva

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18
Q

How do ADH and aldosterone modify the composition of saliva?

A

Decreasing Na+ and increasing K+ concentration

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19
Q

What are the main components of gastric juice?

A

HCl (H+)

Pepsinogen

Mucus

Intrinsic Factor

H20

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20
Q

Where is the oxyntic gland and what does it do?

A

Proximal 80% of the stomach (body and fundus)

Secretes acid

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21
Q

Where is the pyloric gland and what does it do?

A

Distal 20% of the stomach (antrum)

Synthesizes and releases gastrin

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22
Q

What determines the maximal secretory rate of HCl?

A

The number of parietal cells

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23
Q

What is the function of the low gastric pH?

A

To convert pepsinogen to pepsin

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24
Q

Where is HCl formed?

A

In the body of the stomach by parietal cells

At the villus-like membranes of the canaliculi

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25
Q

Name the cells in the stomach, what they secrete and where they are located

A

Parietal cells –> IF and HCl (Body)

Chief cells –> pepsinogen (Body)

G cells –> gastrin (Antrum)

Mucus cells –> mucus, HCO3- and pepsinogen (Antrum)

26
Q

What is secreted at the luminal side and what is absorbed at the basolateral side of a gastric parietal cell?

A

H+ is secreted (Cl- follows)

HCO3- is absorbed (Cl- goes into the cell)

27
Q

Which receptors stimulate Gq (IP3/Ca2+)?

A

M3 Receptor and CCKB

28
Q

Which receptors impact cAMP?

A

H2 Receptor –> Gs (stimulatory)

Somatostatin–>Gi (Inhibitory)

29
Q

What does atropine do?

A

Blocks direct pathway of vagal stimulation but does not block vagal effects on gastrin secretion

30
Q

How is gastrin release regulated?

A

Somatostatin acts on G cells to inhibit gastrin release

Vagal activation stimulates gastrin release by GRP and inhibiting somatostatin

Gastrin itself increases somatostatin

31
Q

What do antagonists of H2 receptors do?

A

Block the direct action of histamine and block potentiated effects of ACh and gastrin

32
Q

What do antagonists of mAChRs do?

A

block the direct effects of ACh and the ACh-potentiated effects of histamine and gastrin

33
Q

What does Cimetidine do?

A

Blocks histamine from reaching H2 Receptor

Used to treat duodenal and gastric ulcers, GERD etc.

34
Q

What does Omeprazole do?

A

Inhibits H+/K+ ATPase, used in the treatment of ulcers to reduce H+ secretion

35
Q

Describe the cephalic phase

A

Vagus nerve –> parietal cell–> secretion of HCl

Vagus nerve –> GRP to G cells –> Gastrin –> Parietal cell–> HCl

36
Q

Describe gastric phase

A

distension

Vagus nerve –> parietal cell–> secretion of HCl

Vagus nerve –> GRP to G cells –> Gastrin –> Parietal cell–> HCl

37
Q

Describe Intestine phase

A

Distension of small intestine

Stimulates acid secretion

38
Q

What stimulates pepsinogen secretion by chief cells and mucus cells?

A

Vagus nerve

requires H+ secretion from parietal cells to lower pH

39
Q

What is the purpose of pepsin?

A

Degrades food proteins into peptides

Optimal pH is between 1.8-3.5

40
Q

What is the purpose of intrisic factor?

A

It is required for the absoprtion of Vitamin B12 (cobalamin) in the ileum

Failure to secrete IF is associated with achlorhydria and absence of parietal cells

41
Q

What does B12 originally bind to?

A

R-protein in the stomach

Switches to IF in the duodenum due to pancreatic proteases

42
Q

What is the cause of pernicious anemia?

A

Stomach does not produce enough IF, low vitamin B12

43
Q

What are common causes of pernicous anemia?

A

Atrophic gastritis

Autoimmune metaplastic atrophic gastritis

44
Q

What can cause disruption in the absoprtion of vitamin B12?

A

Gastrectomy: loss of parietal cells

Gastric bypass: Exclusion of stomach, duodenum, and proximal jejunum

45
Q

What are protective factors of the gastroduodenal mucosa?

A

HCO3-

Mucus

Prostaglandins

Mucosal blood flow

GF

46
Q

What are damaging factors of the gastroduodenal mucosa?

A

H+ and pepsin

H. pylori

NSAIDS

Stress, smoking, and alcohol

47
Q

What is zollinger-Ellison syndrome?

A

Large secretion of gastrin by duodenal or pancreatic tumors

increase in H+ secretion by parietal cells and increase in parietal cell mass

48
Q

What are the effects of zollinger-ellison syndrome?

A

Inactivates pancreatic digestive enzymes

Interferes with the emulsifcation of fat

Damages intestinal epitheial cells and villi

Leads to maldigestion and malabsoprtion

49
Q

How does the secretion stimulation test work?

A

Normal conditions: secretin inhibits gastrin release

Gastrinoma: secretin causes an increase in gastrin release

50
Q

What are predominant causes of peptic ulcer disease?

A

H. Pylori and NSAIDS

51
Q

What does H. Pylori do?

A

Releases cytotoxins that breadown the mucosal barrier

Cytotoxins coverts urea to ammonia (NH3) which alkalinzes the local environment

The resulting ammonium (NH4) causes mucosal damage

H. Pylori uses urease so you can test for urease to determine if H. Pylori is present

52
Q

What is the main presentation of gastric ulcers?

A

Low H+ secretion

High gastrin levels

53
Q

What is the main presentation of dudenal ulcers?

A

Increased H+ secretion

Increased gastrin levels

54
Q

What is the sympathetic and parasympathetic innervation of the pancreas?

A

Sympathetic: Postganglionic nerves from celiac and superior mesenteric plexuses

Parasympathetic: Vagus nerve

  • Preganglionic fibers synapse in the ENS
  • Postganglionic fibers synapse on the exocrine pancreas
55
Q

What do acinar cells in the pancreas secrete?

A

Amylases and lipases in active form

proteases in inactive forms which are converted into active form in the duodenum

56
Q

What is secreted by centroacinar and ductal cells in the pancreas?

A

Secrete a HCO3- liquid via the Cl-/HCO3-

57
Q

What channel has a mututation in cystic fibrosis?

A

Cystic Fibrosis Transmembrane conductance regulator (CFTR)

58
Q

What induces release of pancreatic enzymes into the duodenal lumen?

A

CCK

59
Q

What induces the secretion of HCO3- from pancreatic cells into the duodenum?

A

Secretin

60
Q
A

gigu (40 decks)

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