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Theme 1: The Alimentary System > Salivary and gastric secretion > Flashcards

Salivary and gastric secretion Flashcards

(45 cards)

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1
Q

Three functions of saliva

A

Lubrication

Protection

Digestion

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2
Q

Lubrication

A

Moistening the mouth to aid swallowing

Facilitates movement of the mouth and tongue for speech

Helps to dissolve chemicals within food for its presentation to the taste receptors

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3
Q

Protection

A

Reduces the adverse effects of oral bacteria

Alkalinity of fresh saliva neutralises acid produced by oral bacteria

Flow of saliva across teeth helps wash away bacteria

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4
Q

Digestion

A

Begin breakdown of carbs and fats via alpha amylase and lingual lipase

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5
Q

Sjogren’s syndrome

A

Autoimmune disease

Destroys exocrine glands, mostly tear and salvia

Dry eyes and mouth

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6
Q

Xerostomia

A

Lack adequate saliva

Dental caries and haltosis due to bacterial overgrowth

Difficulty speaking or swallowing food

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7
Q

Volume of saliva produced

A

1.5L per day

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8
Q

Two types of secretions

A

Serous secretions:
- the main type of protein secreted is ptyalin

Mucous secretions:
- main protein is mucin acting as a lubricant

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9
Q

Three major salivary glands

A

Submandibular glands secrete approximately 70% of saliva

Parotid glands secrete 25%

Sublingual glands secrete 5%

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10
Q

Structure of salivary glands

A

Contain blind-ended acini connecting with ducts draining major ducts

Acinar cells histologically distinct from duct cells

Serous acini distint to mucous secreting acinus

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11
Q

Composition of saliva

A

Functional unit consists of acinar cells, secrete primary saliva into a duct system

Primary saliva secreted by acinus is isotonic solution resembling interstitial fluid

Duct reabsorbs NaCl, causing saliva to become hypotonic

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12
Q

Secretion and modification of saliva by salivary acinar

A

Cl- uptake by a basolaterally located Na+, K+, 2Cl- cotransporter and release through the calcium activated apical chloride channel

Sustained by Na+/K+/ATPase

Na+ enters acinar lumen paracellularly through leaky tight junctions

H2O follows via aquaporin 5 or paracellularly

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13
Q

Secretion and modification of saliva by ductal cells

A

Removal of Na+ from saliva via apical sodium channel and basolateral Na+/ K+ ATPase

Cl- removal from saliva via different chloride channels in the apical and basolateral membranes of ductal cells

Removal of salt not accompanied by water since ductal tight junctions are not leaky and aquaporins are not expressed in apical membranes

Secrete bicarbonate and potassium via unidentified apical bicarbonate chloride and potassium proton exchangers

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14
Q

Composition of saliva changes with flow rate

A

Electrolytes

  • Na+ and Cl- < plasma
  • HCO3- and K+ > plasma

High flow rate less time for ducts to absorb NaCl so resembles isotonic solution produced by acini

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15
Q

Central control of salivary secretions

A

Stimulated through thought, smell or taste of food by reflexes and nausea

Sleep, dehydration, fatigue and fear inhibit salivation

Integrated by salivary nuclei in the pons

Efferent nerves reach salivary glands via glossopharyngeal and facial nerves

Acinar secretion stimulated by acetylcholine via muscarinic receptors

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16
Q

Parasympathetic stimulation

A

Promotes watery secretion myoepithelial cells surrounding acini

Ducts contract and eject preformed saliva

Leads to increased blood flow

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17
Q

Superior cervical ganglion

A

The only hormonal effect on saliva secretion is from aldosterone which increases ductal Na+ absorption and K+ secretion

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18
Q

Composition of gastric juice

A

1-2L from several cell types produced per day

  • water, electrolytes
  • HCl
  • pepsins
  • mucus
  • intrinsic factor
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19
Q

Water, electrolytes

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A

Dissolve and dilute digested food

20
Q

HCl

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A

Hydrolyses fat and starch

Antiseptic

Converts pepsinogen to pepsin and provides optimum pH

21
Q

Pepsins

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A

Secreted as inactive pepsinogens away from stomach lining activated to form pepsins at low pH

22
Q

Mucus

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A

Bicarbonate barrier

Protect surface epithelial cells from acid/ pepsin erosion

23
Q

Intrinsic factor

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A

Glycoprotein binds vitamin B12 needed for absorption in the ileum

The indispensable substance in gastric juice

24
Q

Origins of secretion

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A

Stomach has two major regions:

  • an exocrine or glandular portion consists of the fundus and body or acid secreting area
  • an endocrine or hormone secreting area that is located in the antrum or gastrin secreting area
25
Structure of gastric gland
Mucous cell Endocrine cells- D cells Chief cells Parietal cells Histamine cells Endocrine cells- G cells
26
Mucous cells
Secrete protective barrier
27
Endocrine cells- D cells
Secrete somatostatin | - regulateor of gastrin release and gastric acid secretion
28
Chief cells
Secrete pepsinogen Converted by gastric acid to active form of pepsin
29
Pariteal cells
Acid secreting, IF
30
Endocrine cells- G cells
Produce gastrin
31
Protection against self digestion and mechanical damage
Lumen
32
Gartitis
Many causes Most commonly caused by an infection by the bacteria helicobacter pylori Other common causes include smoking, use of alcohol and nonsteroidal anti- inflammatory drugs and chronic stress Surface of epithelium acutely damages
33
Acid secretion- oxyntic cell
Tubolovesicular membrane contains H+-K+ pumps responsible for acid secretion Upon stimulation tubulovesicular membrane fuses into canalicular membrane Fusion accompanied by insertion of H+/K+ ATPase and K+ and Cl- ion channels into canalicular membrane Dense mitochondria to support high metabolic activity of cell
34
Acid secretion at the luminal membrane of a stimulated parietal cell
Major component if H+/K+ ATPase which actively exchanges H+ for K+ Enormous active secretory capacity, capable of secreting protons against large electrochemical gradients Luminal pH can approach 1-2 No other part of the body can approach this level of acidification
35
Mechanism of gastric acid secretion by oxyntic cells
H+ and HCO3- made inside the cell by carbonic anhydrase H+ pumped out of the luminal membrane by H+/K+ ATPase Cl- leaves by diffusion Cl-HCO3- exchanger in basolateral membrane provides Cl- for HCl and HCO3- exits in large quantities so gastric venous blood becomes alkaline
36
Omeprazole
Proton pump inhibitor Binds irreversibly to the H+/K+ ATPase inhibiting H+ secretion until new H+/K+ ATPase protein is synthesised
37
Three major stimulators of acid secretion
1. Gastrin- predominantly secreted by antral G cells 2. Histamine- in humans probably arising from mast cells 3. Acetylcholine- secreted by postsynaptic vagal fibres innervating the gastric mucosa
38
Two major paracrine inhibitors of gastric acid secretion
1. Somatostatin- secreted from antral and oxyntic gland D cells as well as pancreatic islet cells 2. Prostaglandins- from mucosal cells
39
Atrophic gastritis
Autoimmune Antibody mediated destruction of gastric parietal cells Causes hypochlorydria and a deficiency of IF Loss off IF results in vitamin B12 malabsorption and pernicious anaemia
40
Three phases of gastric acid secretion
Cephalic: sight, cell, taste, though Gastric: antral distension, protein content, increase pH Intestinal: intestinal gastrin, absorption amino acids
41
Gatrin
G cells of pylorus and duodenum Endocrine effect Release triggered by aa and peptides in stomach Low pH inhibits release
42
Histamine
ECL cells close to parietal cells Paracrine effect by local diffusion ECL cells stimulated by gastrin and acetylcholine ACh/ gastrin has direct and indirect route of stimulation which amplify signal Leads to vasodilation of arterioles
43
Acetylcholine
Acts on parietal and ECL cells to promote acid and histamine secretion Acts on D cells to inhibit somostatin release
44
Vagal stimulation- corpus
Via ACh Increases acid secretion directly via parietal cells and indirectly via ECL and D cells
45
Vagal stimulation- antrum
Via GRP Stimulates both G and D cells Gastrin from antrum promotes acid secretion by two endocrine mechanisms - directly via parietal cells - indirectly via ECL cells

Theme 1: The Alimentary System (16 decks)

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