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Foundations Of Medicine > 8.3 The Mouth, Oesophagus & Stomach > Flashcards

8.3 The Mouth, Oesophagus & Stomach Flashcards

1
Q

What type of muscle is the tongue made of?

A

Skeletal

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2
Q

What is the purpose of chewing?

A
  • Increase the surface area of food for salivary enzymes to act on
  • Mix food with saliva
  • Stimulate tastebuds (increasing secretion of substances throughout GI tract)
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3
Q

Describe the composition of saliva

A
  • 99.5% water
  • 0.5% electrolytes and protein
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4
Q

Broadly describe the function of saliva

A

Acts as a solvent for taste and washes away particles (e.g. dead epithelial cells)

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5
Q

What is the name of the salivary enzyme that breaks down polysaccharides? What does it break them into?

A
  • Amylase
  • Breaks down polysaccharides into maltose
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6
Q

What is the salivary enzyme that

A

Begins fat digestion

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7
Q

Why is it useful for saliva to moisten food particles?

A

Causes them to clump together for swallowing

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8
Q

What is the function of mucus in saliva?

A

Lubricates the mouth and facilitates swallowing

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9
Q

What is the antibacterial enzyme in saliva known as?

A

Lysozyme

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10
Q

What substance in saliva is used to neutralise acids in foods? Why is this useful?

A
  • Bicarbonate
  • Prevents dental decay
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11
Q

How much saliva is secreted every day?

A

1-2L

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12
Q

What two triggers prompt increased saliva secretion? Where do these signals travel?

A
  • Simple reflex: ressure and chemoreceptors in mouth (chewing)
  • Conditioned reflex: thinking, smelling, seeing food (pavlovs dog)
    Travel to medulla -> autonomic nervous system -> salivary glands
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13
Q

What initiates the pharyngeal stage of swallowing?

A

Bolus hitting pharynx

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14
Q

What are the three phases of swallowing?

A
  • Oral
  • Pharyngeal
  • Oesophageal phase
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15
Q

Describe the process of the pharyngeal stage of swallowing

A
  • Uvula and soft palate lift to close off nasopharynx
  • Larnyx elevates, pushing epiglottis such that it covers the opening of the trachea
  • Breathing stops
  • Involuntary reaction
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16
Q

Describe the oesophageal phase of swallowing

A
  • Pharyngeal muscles contract, forcing bolus into oesophagus
  • Peristalsis occurs, pushing the bolus toward the stomach
  • lower oesophageal sphincter closes as soon as food has passed, having opened during the elevation of the larynx
  • Swallowing centre causes peristalsis (circular: behind, longitudinal: shortens)
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17
Q

How long does bolus take to reach the end of the oesophagus?

A

Solid: 5-9 sec
Liquid: 1 sec

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18
Q

What are the names of the sphincters of the oseophagus?

A
  • Pharyngo-oesophageal
  • Gastro-oesophageal
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19
Q

Think about why the two sphincters of the oesophagus must stay tonically contracted

A
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20
Q

Primary vs secondary peristalsis

A

Primary: preceded by pharyngeal stage of swallowing

Secondary: Can occur without pharyngeal phase if oesophagus is distended (e.g. food is stuck)

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21
Q

Why does the mucosa of the oseophagus secrete mucous?

A

Lubrication and protection (including from reflux)

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22
Q

Does any digestion occur during swallowing?

A

No, it’s a max of ten seconds. Not enough time.

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23
Q

What are the three sections of the stomach?

A
  • Fundus
  • Body
  • Antrum
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24
Q

Where does most of the mixing of stomach occur?

A

Antrum (makes sense: gravity)

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25
Q

What type of mucosa is present in the antrum vs body of the stomach?

A
  • Body: Oxyntic mucosa (acid producing)
  • Antrum: Pyloric gland area (mucous secretion)
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26
Q

What is the sphincter at the end of the stomach?

A

Pyloric sphincter

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27
Q

How does the stomach stretch from 50mL to 1L?

A

Mucosa can unfold, enabling constant pressure (symphathetic stimulation enables unfolding)

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28
Q

What are the functions of the stomach?

A
  • Store food
  • Secrete HCl and enzymes
  • Create chyme from mixing
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29
Q

Where are the stronger/weaker contractions of the stomach?

A

Stronger: Antrum
Weaker: Fundus

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30
Q

What factors affect the gastric motility of the stomach?

A
  • Volume of chyme
  • Fluidity
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31
Q

How does distension of the stomach lead to increase motility?

A
  • Direct stretch effect
  • Intrinsic plexus involvement
  • Vagus nerve -> gastric hormone gastrin
32
Q

What four factors decrease motility in the small intestine

A
  • Fat (slow to digest)
  • Acid (must be neutralised lest it damage mucosa)
  • Hypertonicity (draws water from plasma)
  • Distension (too much chyme; excess volume)
33
Q

What nervous factors influence the rate at which chyme enters the duodenum?

A
  • Enterogastric reflex
  • Intrinsic and autonomic nerves
34
Q

What hormonal factors influence the rate at which chyme enters the duodenum?

A
  • Enterogastrones
  • Secretin
  • Cholecystokinin (CCK)
35
Q

What external factors influence gastric motility? How?

A
  • Emotion and pain
  • Varies autonomic response
    (e.g. fear decreases digestion)
36
Q

What factors cause vomiting?

A
  • Tactile stimulation of uvula
  • Irritation/distension of stomach/duodenum
  • Elevated intracranial pressure
  • Vestibular/visual cues
  • Chemical factors
  • Psychogenic (mental/emotional)
37
Q

Describe the process of vomiting

A
  • Deep inspiration, glottis is closed, uvula is raised
  • Stomach, oesophagus and GOS are relaxed
  • Respiratory muscles (abdominal and diaphragm) are contracted, squeezing stomach and creating a pressure gradient
38
Q

What are some feelings associated with vomiting

A
  • Feeling of nausea
  • Salivation
  • Sweating
  • Rapid heart rate (autonomic)
39
Q

What is a potential problem with excessive vomiting?

A
  • Alkalosis
  • Fluid loss
40
Q

Where are the secretory cells located in the stomach?

A

Mucosal in-folding (rugae)

41
Q

How much gastric juice is secreted per day?

42
Q

What are the two areas of gastric muscosa?

A
  • Oxyntic (acid)
  • Pyloric gland area (mucous)
43
Q

Describe the pH of the mucus secreted by the stomach. How thick is this mucus layer?

A
  • Alkaline (neutralises acid)
  • Few mms thick
44
Q

Are epithelial cells of the gastric mucosa turned over rarely or regularly?

A

Regularly; pretty risky area

45
Q

Describe the types of cells in the pits/glands of oxyntic mucosa (from top to bottom)

A
  • Mucous cells (think alkaline mucus)
  • Parietal cells (HCl + inrinsic factor)
  • Chief cells (pepsinogen)
  • Enterochromaffin-like cells (histamine)
46
Q

Describe the types of cells in the pits/glands of pyloric gland area mucosa (from top to bottom)

A
  • Mucous cells
  • G cells (gastrin)
  • D cells (somatostatin/GHIH)
47
Q

Are enetrochromaffin-like cells and D cells paracrine or endocrine?

48
Q

Are G cells endocrine or paracrine?

49
Q

What stimulates mucous cell secretion?

A

Mechanical stimulation by digestive contents

50
Q

What stimulates chief cells to release pepsinogen?

A

Ach, gastrin

51
Q

What stimulates secretion of HCl and intrinsic factor from parietal cells?

A

Ach, gastrin, histamine

52
Q

What is the function of HCl in the stomach?

A

Activates pepsinogen, breaks down connective tissue, denatures proteins, kills microorganisms

53
Q

What is the function of intrinsic factor in the stomach?

A

Facilitates absorption of Vitamin B12

54
Q

Other than lubrication and pH neutralizing, what is the function of mucus in the stomach?

A

Pepsin is inhibited (no self-digestion)

55
Q

What is the major/chief digestive component in gastric juice?

A

Pepsinogen

56
Q

Describe the activation of pepsinogen

A

Pepsinogen -HCl-> Pepsin

57
Q

How does pepsin break down proteins?

A

Cleaves peptide bonds in polypeptide structure

58
Q

Roles of HCl in digestion

A

BAAD
- Breakdown connective trissue and muscle fibre
- Activates pepsinogen
- Antibacterial properties
- Denatures protein

59
Q

Draw a diagram of the processes that lead to the creation of HCl in the stomach

A

Check 8.3.docx

60
Q

How does intrinsic factor enable vitamin B12 uptake?

A
  • Binds with vitamin B12 to form complex
  • Complex is endocytosed at terminal ileum (receptor mediated)
  • Vitamin B12 goes into normal blood production
61
Q

What condition arises from a lack of vitamin B12?

62
Q

What stimulates Enterochromaffin-like cells to secrete histamine?

A

ACh, gastrin

63
Q

What is the function of histamine in the stomach?

A

Stimulates parietal cells

64
Q

What stimulates G cells to release gastrin?

A

Protein products, ACh

65
Q

What is the function of gastrin in the stomach?

A

Stimlates parietal, chief, and ECL cells

66
Q

What prompts D cells to release somatostatin into the stomach?

67
Q

Draw a diagram of the relationship between ECL cells, G cells, parietal cells, D cells, and chief cells

68
Q

What are the three phases of gastric secretion?

A
  • Cephalic phase
  • Gastric phase
  • Intestinal phase
69
Q

Describe the cephalic phase of gastric secretion

A
  • Sight, smell, thought of food causes cerebral cortex of stimulate parasympathetic response
  • Vagus nerve stimulates gastric secretion and motility by increasing muscle and gland activity
70
Q

Draw a diagram of the relationships within the cephalic phase of gastric secretion

71
Q

What are the short/long reflexes of the gastric phase of gastric secretion?

A

Short: Myenteric plexus
Long: Vagus nerve

72
Q

What is the stimulus for the gastric phase of gastric secretion?

A
  • Distension
  • Proteins/peptides
  • Caffeine
    (meditaed by nerves, hormones, and local chemoreceptors)
73
Q

Draw a map of the interactions that occur during the intestinal phase

73
Q

Draw a map of the interactions that occur during the intestinal phase

74
Q

In which section of the stomach can amylase still function?

A

Body (not the antrum; too acidic)

75
Q

Think: why is alcohol absorbed slower when consumed with a meal?

76
Q

What four factors help the mucosa to withstand acid and enzymes without damage?

A
  1. Epithelial cells almost impenetrable
  2. Tight junctions prevent acid diffusing between cells
  3. Mucus prevents penetration
  4. Bicarbonate secreted into mucus

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