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Module 104: Nutrition, Metabolism and Excretion > Theme 1: Lecture 5 - Salivary and gastric secretion > Flashcards

Theme 1: Lecture 5 - Salivary and gastric secretion Flashcards

1
Q

What do secretions do

A

Lubricate, protect and aid digestion

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2
Q

Name 2 types of exocrine glands

A
  • Salivary glands

- Gastric glands

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3
Q

Name a type of endocrine gland

A

enteroendocrine cells in the stomach and small intestine

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4
Q

What is the role of salivary secretions

A
  • Lubrication
  • Protection-oral hygiene
  • Initiate chemical digestion
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5
Q

Name the 3 major salivary glands

A
  • Parotid
  • Submandibular
  • Sublingual
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6
Q

Name 4 dispersed (minor) salivary glands

A

-Labial
-Buccal
-Palatal
-Lingual
(mucosa of the mouth and tongue)

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7
Q

Describe the parotid salivary gland

A
  • Serous, watery secretions containing salivary amylase for starch digestion
  • Sits anterior and inferior to the ear
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8
Q

Describe the submandibular salivary gland

A
  • Mixed serous and mucus

- Sits inferior to the mandible

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9
Q

Describe the sublingual salivary gland

A
  • Mucus: thicker mucus dominant secretions for lubrication

- Sits in the floor of the oral cavity

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10
Q

Describe the composition of saliva

A
  • Water (99.5%)
  • Electrolytes
  • Enzymes
  • Secretory IgA
  • Mucin
  • Organics urea and uric acid
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11
Q

Name the electrolytes in saliva

A

K+, HCO3-, Na+, Cl-, (PO4)3-

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12
Q

Name 5 enzymes found in saliva

A
  • a-amylase (ptyalin)
  • Lysozyme
  • Lingual lipase (serous salivary glands of tongue)
  • Lactoferrin
  • Kallikrein
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13
Q

What is the function of water in saliva

A

Solvent dissolves food components to aid taste, swallowing, initiation of digestion, oral hygiene

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14
Q

What is the function of electrolytes in saliva

A

Buffer for acidic food contents

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15
Q

What is the function of a-amylase (ptyalin) in saliva

A

Hydrolysis of a-1,4 glycosidic bonds in starch to disaccharide maltose, trisaccharide maltotriose and a-dextrin, ~75%

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16
Q

What is the function of lysosome in saliva

A

Hydrolysis of peptidoglycans in wall of gram negative bacteria

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17
Q

What is the function of lingual lipase in saliva

A

Hydrolysis of lipid triglycerides to fatty acid and diglycerides (optimal in acidic pH)

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18
Q

What is the function of lactoferrin in saliva

A

Chelates iron to prevent microbial multiplication

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19
Q

What is the function of kallikrein in saliva

A

converts plasma protein a-2- globulin into bradykinin (vasoconstrictor)

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20
Q

What is the function of secretory IgA in saliva

A

prevents microbial attachment to epithelium

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21
Q

What is the function of mucin in saliva

A

lubrication

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22
Q

What is the function of organics urea and uric acid

A

Waste product removal for excretion

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23
Q

What are cells lining the acinar structure of the salivary glands

A
  • Aciner cells
  • Myoepithelial cells
  • Ductal cells
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24
Q

What is the role of the acinar of salivary glands

A
  • Functional unit of the salivary gland

- A small saclike cavity in a gland

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25
Q

Describe the properties of the salivary gland

A
  • Large volume of saliva produced compared to mass of gland
  • Low osmolarity
  • High K+ concentration
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26
Q

Describe the formation of hypotonic saliva

A

Stage 1
-Acinar cells secrete isotonic saliva similar to blood plasma in electrolyte composition
Stage 2
-Ductal cells secrete HCO3- and K+ ions with reabsorption of NaCl and limited movement of water by osmosis
-produces HCO3- and K+ rich hypotonic saliva

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27
Q

Describe the electrolyte composition of saliva in relation to plasma

A

Na+ and Cl- < plasma

HCO3- and K+ > plasma

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28
Q

Does the composition of saliva change with flow rate

A

Yes

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29
Q

Describe the composition of saliva at a low rate of secretion

A

maximum reabsorption of electrolytes produces hypotonic saliva (lower concentration of osmotically active electrolytes)

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30
Q

Describe the composition of saliva at a high rate of secretion

A

reduced reabsorption of electrolytes produces alkaline, HCO3- rich saliva with increased osmolality closer to that of primary isotonic saliva

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31
Q

What is the dominant regulator of salivary secretion

A

Parasympathetic ANS

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32
Q

What is the stimulus for salivary secretion

A

Sight, thought, smell, taste (esp. sour acidic taste), tactile stimuli, nausea

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33
Q

What does the parasympathetic ANS do in terms of salivary secretion

A
  • Increase salivary secretion
  • vasodilation
  • myoepithelial cell contraction
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34
Q

What are the inhibitors for salivary secretion

A
  • Fatigue
  • Sleep
  • Fear
  • Dehydration
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35
Q

What is the parasympathetic innervation for the sublingual gland

A

-Cranial nerve VII (facial nerve)

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36
Q

What is the parasympathetic innervation for the submandibular gland

A

-Cranial nerve VII (facial nerve)

37
Q

What is the parasympathetic innervation for the parotid gland

A

-Cranial nerve IX (glossopharyngeal nerve)

38
Q

Where do parasympathetic signals go to in the CNS in terms of salivary secretion

A

superior and inferiorsalivatorynuclei in the medulla

39
Q

What else regulates saliva secretion apart from the parasympathetic ANS

A

Sympathetic neural stimulation but to a lesser extent than the parasympathetic NS

40
Q

Describe the effect that the sympathetic nervous system has on saliva production

A
  • Overall slight increase in secretion
  • Produces a mucin and enzyme rich saliva
  • Initial vasoconstriction (neurotransmitter noradrenaline stimulates b-adrenergic receptors)
  • Later vasodilation (salivary enzyme kallikrein action on blood plasma protein alpha-2 globulin to form vasodilator bradykinin)
41
Q

What is the sympathetic innervation of salivary glands

A

Via superior cervical ganglion

42
Q

Name 2 diseases caused by salivary gland dysfunction

A
  • Sjogren’s syndrome

- Xerostomia (dry mouth)

43
Q

Describe Sjogren’s syndrome

A
  • an autoimmune disease that destroys the exocrine glands
  • commonly affects tear and saliva production
  • dry eyes and dry mouth, known as sicca symptoms
44
Q

Describe xerostomia (dry mouth)

A
  • Patients lack adequate saliva
  • dental caries (tooth decay) and halitosis common due to bacterial overgrowth
  • difficulty speaking or swallowing solid food due to inadequate lubrication
45
Q

Describe how gastric glands are formed

A

Gastric pits in the stomach mucosa branch into gastric glands

46
Q

Name the exocrine cells in gastric glands

A
  • Mucus neck cells
  • Parietal cells
  • Chief cells
47
Q

Name the endocrine cells in gastric glands

A
  • G cells
  • D cells
  • Enterochromaffin-like (ECL) cells
48
Q

What do mucus neck cells secrete

A

thin mucus

49
Q

What do parietal cells secrete

A

HCl and intrinsic factor

50
Q

What do chief cells secrete

A

pepsinogen (also renin in neonates) and gastric lipase

51
Q

What do G cells secrete

A

hormone gastrin (in the antrum)

52
Q

What do D cells secrete

A

hormone somatostatin

53
Q

What do enterochromaffin-like (ECL) cells secrete

A

histamine

54
Q

What are the 2 major types of gastric gland

A
  • Gastric or oxyntic glands

- Pyloric glands

55
Q

Where are gastric or oxyntic glands located

A

In body and fundus of the stomach

56
Q

Where are the pyloric glands located

A

In the antrum of the stomach

57
Q

Describe gastric or oxyntic gland secretion

A
  • Exocrine secretion of HCl, pepsinogen, intrinsic factor and mucus
  • paracrine ECL cell secretion of histamine, paracrine D cell secretion of somatostatin
58
Q

Describe pyloric gland secretion

A
  • mucus and endocrine hormone gastrin

- paracrine/endocrine somatostatin

59
Q

Describe the contents of gastric juice

A
  • Water and electrolytes
  • Mucus (glycoprotein mucin) from mucus neck cells
  • Pepsinogen pro-enzyme, renin in neonates only and gastric lipase from chief cells
  • HCl and Intrinsic factor from parietal cells
60
Q

Function of water and electrolytes in gastric juice

A

medium for action of acid and enzymes, digestion of organic substances

61
Q

Function of mucus (glycoprotein mucin) in gastric juice

A

protects surface epithelium from acid/pepsin

62
Q

Function of pepsinogen pro-enzyme in gastric juice

A

Active pepsin form is an endopeptidase that cleaves peptide bonds (protein to smaller peptides)

63
Q

Function of renin in gastrin juice in neonates

A

Coagulation of milk through casein proteolysis

64
Q

Function of gastric lipase in gastric juice

A

triglycerides to fatty acid and diglycerides

65
Q

Function of HCl in gastric juice

A

Converts pro-enzyme pepsinogen to pepsin, denatures proteins, kills microorganisms

66
Q

Function of intrinsic factor in gastric juice

A

vitamin B12 absorption in the ileum, erythropoiesis in bone marrow, deficiency results in pernicious anaemia

67
Q

Describe parietal cells

A
  • Parietal cells have an intracellular branched canalicular structure and are packed with tubulovesicles in resting state
  • These contain enzymes carbonic anhydrase and H+/K+-ATPase for acid secretion
  • On stimulation of acid production tubulovesicles fuse with the canalicular membrane to form microvilli
  • HCl is formed at these microvilli and secreted
68
Q

Describe the secretion of HCl in gastric parietal cells

A
  • H+/K+-ATPase proton pump drives active secretion of H+ into lumen of stomach
  • Carbonic anhydrase (CA) catalyses formation of HCO3- producing H+ ions
  • HCO3- exchanged for Cl- (alkaline tide - gastric venous blood becomes alkaline postprandially)
  • Cl- diffuses into lumen of stomach
69
Q

What stimulates gastric acid secretion

A
  • ACh: acetylcholine release from vagus
  • Gastrin from G cells
  • `Histamine from ECL cells
70
Q

What inhibits gastric acid secretion

A
  • Somatostatin from D cells (paracrine and endocrine): inhibits adenylate cyclase (AC)
  • Mucosal prostaglandin antagonists for H receptor (NSAIDs inhibit prostaglandin formation and increase gastric acid secretion)
71
Q

Describe the 2 biochemical pathways that cause H+ to be released from parietal cells

A
  • Gastrin and ACh activate phospholipase C which activates inositol triphosphate (IP3) which activates Ca2+ stimulating H+
  • Histamine binds to the H2 receptor which activates adenylate cyclase which activates cAMP stimulating release of H+
72
Q

Name 3 drugs that cause inhibition of gastric acid

A
  • Omeprazole
  • Cimetidine
  • Atropine
73
Q

How does omeprazole inhibit gastric acid

A

Proton pump inhibitor inactivates H+/K+ -ATPase

74
Q

How does cimetidine inhibit gastric acid

A

H2 receptor antagonist inhibits stimulus for acid secretion

75
Q

How does atropine inhibit gastric acid

A

inhibits muscarinic receptors and vagal stimulation of acid secretion

76
Q

What stimulates the secretion of the hormone gastrin

A

Vagus, distention, peptide

77
Q

What does the hormone gastrin do

A
  • parietal cell secretion of HCl
  • Chief cell secretion of pepsinogen
  • lower oesophageal sphincter contraction
  • Increased motility of stomach
  • Relaxation of pyloric sphincter
78
Q

How is the secretion of gastrin from G cells inhibited

A
  • H+ stimulates D cells to secrete somatostatin

- Somatostatin inhibits secretion of gastrin from G cells

79
Q

Describe a type of gastric parietal cell dysfunction

A
  • Autoimmune atrophic gastritis is an antibody mediated destruction of gastric parietal cells, which causes hypochlorhydria (insufficient acid secretion), and a deficiency of intrinsic factor IF
  • The loss of IF results in vitamin B12 mal-absorption and pernicious anaemia
80
Q

What are the 3 phases of gastric secretion

A
  • Cephalic
  • Gastric
  • Intestinal
81
Q

Describe the cephalic phase of gastric secretion

A

Vagus stimulates parietal, chief cell production of gastric juice and hormone gastrin secretion

82
Q

Describe the gastric phase of gastric secretion

A
  • Local nervous secretory reflexes, Vagal reflexes and gastrin-histamine stimulation
  • stimulate parietal, chief, mucus secretion, antral G cells (gastrin stimulates parietal cells directly and indirectly via ECL histamine release)
83
Q

Describe the intestinal phase of gastric secretion

A
  • Excitatory: Chyme with pH >3, peptides stimulates gastric secretions via vagus and gastrin
  • Inhibitory: Chyme with pH< 2, distention, protein breakdown products, hypo/hyper-osmotic products inhibit gastric secretions via cholecystokinin, secretin, gastric inhibitory polypeptide
84
Q

Why is the gastric mucosa not damaged

A
  • Surface mucous glands secrete viscous mucus layer of mucopolysaccharides /proteins
  • Mucus viscosity generates mucosal barrier (Mucin has basic side chains and HCO3- secreted from surface epithelial cells. Both neutralise H+ ions)
  • Tight junctions stop acid damaging underlying tissue
  • Net result - unstirred layer is ~pH7, pepsinogen not activated, prevents enzymatic and chemical damage
85
Q

Name a disease caused by dysfunction of the gastric mucosa

A

Gastritis

86
Q

What is gastritis

A

Inflammation of the gastric mucosa

87
Q

What is gastritis caused by

A
  • Most commonly caused by an infection by the bacteria Helicobacter pylori (Primary cause of peptic ulcer disease)
  • Gram negative bacteria produce urease which forms ammonia from urea, Ammonia neutralizes bactericidal acid and is toxic to mucosal barrier
  • Also caused by smoking, alcohol, nonsteroidal anti-inflammatory drugs (NSAIDs) (inhibit cyclooxygenase to reduce protective prostaglandin synthesis), chronic stress
88
Q

What happens after acute damage of the gastric mucosa

A

rapid regeneration is via a process called restitution - rapid division of stem cells located in the neck of gastric glands

Module 104: Nutrition, Metabolism and Excretion (23 decks)

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