8.3 The Mouth, Oesophagus & Stomach Flashcards
1
Q
What type of muscle is the tongue made of?
A
Skeletal
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)
3
Q
Describe the composition of saliva
A
- 99.5% water
- 0.5% electrolytes and protein
4
Q
Broadly describe the function of saliva
A
Acts as a solvent for taste and washes away particles (e.g. dead epithelial cells)
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
6
Q
What is the salivary enzyme that
A
Begins fat digestion
7
Q
Why is it useful for saliva to moisten food particles?
A
Causes them to clump together for swallowing
8
Q
What is the function of mucus in saliva?
A
Lubricates the mouth and facilitates swallowing
9
Q
What is the antibacterial enzyme in saliva known as?
A
Lysozyme
10
Q
What substance in saliva is used to neutralise acids in foods? Why is this useful?
A
- Bicarbonate
- Prevents dental decay
11
Q
How much saliva is secreted every day?
A
1-2L
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
13
Q
What initiates the pharyngeal stage of swallowing?
A
Bolus hitting pharynx
14
Q
What are the three phases of swallowing?
A
- Oral
- Pharyngeal
- Oesophageal phase
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
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)
17
Q
How long does bolus take to reach the end of the oesophagus?
A
Solid: 5-9 sec
Liquid: 1 sec
18
Q
What are the names of the sphincters of the oseophagus?
A
- Pharyngo-oesophageal
- Gastro-oesophageal
19
Q
Think about why the two sphincters of the oesophagus must stay tonically contracted
A
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)
21
Q
Why does the mucosa of the oseophagus secrete mucous?
A
Lubrication and protection (including from reflux)
22
Q
Does any digestion occur during swallowing?
A
No, it’s a max of ten seconds. Not enough time.
23
Q
What are the three sections of the stomach?
A
- Fundus
- Body
- Antrum
24
Q
Where does most of the mixing of stomach occur?
A
Antrum (makes sense: gravity)
25
What type of mucosa is present in the antrum vs body of the stomach?
- Body: Oxyntic mucosa (acid producing)
- Antrum: Pyloric gland area (mucous secretion)
26
What is the sphincter at the end of the stomach?
Pyloric sphincter
27
How does the stomach stretch from 50mL to 1L?
Mucosa can unfold, enabling constant pressure (symphathetic stimulation enables unfolding)
28
What are the functions of the stomach?
- Store food
- Secrete HCl and enzymes
- Create chyme from mixing
29
Where are the stronger/weaker contractions of the stomach?
Stronger: Antrum
Weaker: Fundus
30
What factors affect the gastric motility of the stomach?
- Volume of chyme
- Fluidity
31
How does distension of the stomach lead to increase motility?
- Direct stretch effect
- Intrinsic plexus involvement
- Vagus nerve -> gastric hormone gastrin
32
What four factors decrease motility in the small intestine
- Fat (slow to digest)
- Acid (must be neutralised lest it damage mucosa)
- Hypertonicity (draws water from plasma)
- Distension (too much chyme; excess volume)
33
What nervous factors influence the rate at which chyme enters the duodenum?
- Enterogastric reflex
- Intrinsic and autonomic nerves
34
What hormonal factors influence the rate at which chyme enters the duodenum?
- Enterogastrones
- Secretin
- Cholecystokinin (CCK)
35
What external factors influence gastric motility? How?
- Emotion and pain
- Varies autonomic response
(e.g. fear decreases digestion)
36
What factors cause vomiting?
- Tactile stimulation of uvula
- Irritation/distension of stomach/duodenum
- Elevated intracranial pressure
- Vestibular/visual cues
- Chemical factors
- Psychogenic (mental/emotional)
37
Describe the process of vomiting
- 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
What are some feelings associated with vomiting
- Feeling of nausea
- Salivation
- Sweating
- Rapid heart rate (autonomic)
39
What is a potential problem with excessive vomiting?
- Alkalosis
- Fluid loss
40
Where are the secretory cells located in the stomach?
Mucosal in-folding (rugae)
41
How much gastric juice is secreted per day?
1.5-2L
42
What are the two areas of gastric muscosa?
- Oxyntic (acid)
- Pyloric gland area (mucous)
43
Describe the pH of the mucus secreted by the stomach. How thick is this mucus layer?
- Alkaline (neutralises acid)
- Few mms thick
44
Are epithelial cells of the gastric mucosa turned over rarely or regularly?
Regularly; pretty risky area
45
Describe the types of cells in the pits/glands of oxyntic mucosa (from top to bottom)
- Mucous cells (think alkaline mucus)
- Parietal cells (HCl + inrinsic factor)
- Chief cells (pepsinogen)
- Enterochromaffin-like cells (histamine)
46
Describe the types of cells in the pits/glands of pyloric gland area mucosa (from top to bottom)
- Mucous cells
- G cells (gastrin)
- D cells (somatostatin/GHIH)
47
Are enetrochromaffin-like cells and D cells paracrine or endocrine?
Paracrine
48
Are G cells endocrine or paracrine?
Endocrine
49
What stimulates mucous cell secretion?
Mechanical stimulation by digestive contents
50
What stimulates chief cells to release pepsinogen?
Ach, gastrin
51
What stimulates secretion of HCl and intrinsic factor from parietal cells?
Ach, gastrin, histamine
52
What is the function of HCl in the stomach?
Activates pepsinogen, breaks down connective tissue, denatures proteins, kills microorganisms
53
What is the function of intrinsic factor in the stomach?
Facilitates absorption of Vitamin B12
54
Other than lubrication and pH neutralizing, what is the function of mucus in the stomach?
Pepsin is inhibited (no self-digestion)
55
What is the major/chief digestive component in gastric juice?
Pepsinogen
56
Describe the activation of pepsinogen
Pepsinogen -HCl-> Pepsin
57
How does pepsin break down proteins?
Cleaves peptide bonds in polypeptide structure
58
Roles of HCl in digestion
BAAD
- Breakdown connective trissue and muscle fibre
- Activates pepsinogen
- Antibacterial properties
- Denatures protein
59
Draw a diagram of the processes that lead to the creation of HCl in the stomach
Check 8.3.docx
60
How does intrinsic factor enable vitamin B12 uptake?
- Binds with vitamin B12 to form complex
- Complex is endocytosed at terminal ileum (receptor mediated)
- Vitamin B12 goes into normal blood production
61
What condition arises from a lack of vitamin B12?
Anaemia
62
What stimulates Enterochromaffin-like cells to secrete histamine?
ACh, gastrin
63
What is the function of histamine in the stomach?
Stimulates parietal cells
64
What stimulates G cells to release gastrin?
Protein products, ACh
65
What is the function of gastrin in the stomach?
Stimlates parietal, chief, and ECL cells
66
What prompts D cells to release somatostatin into the stomach?
Acid
67
Draw a diagram of the relationship between ECL cells, G cells, parietal cells, D cells, and chief cells
8.3.docx
68
What are the three phases of gastric secretion?
- Cephalic phase
- Gastric phase
- Intestinal phase
69
Describe the cephalic phase of gastric secretion
- 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
Draw a diagram of the relationships within the cephalic phase of gastric secretion
8.3.docx
71
What are the short/long reflexes of the gastric phase of gastric secretion?
Short: Myenteric plexus
Long: Vagus nerve
72
What is the stimulus for the gastric phase of gastric secretion?
- Distension
- Proteins/peptides
- Caffeine
(meditaed by nerves, hormones, and local chemoreceptors)
73
Draw a map of the interactions that occur during the intestinal phase
8.3.docx
73
Draw a map of the interactions that occur during the intestinal phase
8.3.docx
74
In which section of the stomach can amylase still function?
Body (not the antrum; too acidic)
75
Think: why is alcohol absorbed slower when consumed with a meal?
76
What four factors help the mucosa to withstand acid and enzymes without damage?
1. Epithelial cells almost impenetrable
2. Tight junctions prevent acid diffusing between cells
3. Mucus prevents penetration
4. Bicarbonate secreted into mucus
