Upper GI structure and function

Question 1

Why do we chew

Answer 1

1. prolong taste experience

2. defence against respiratory failure

Question 2

what are the two components to chewing

Answer 2

1. voluntary

2. reflex

Question 3

how does the voluntary aspect of chewing occur

Answer 3

somatic nerves innervate skeletal muscles of mouth/jaw

Question 4

how does the reflex aspect of chewing occur

Answer 4

contraction of jaw muscles causes pressure of food against gums/hard palate/tongue - mechanoreceptors inhibit jaw muscles - causes reduced pressure

Question 5

Where is saliva secreted

Answer 5

in three pairs of glands

1. parotid
2. submandibular
3. sublingual

Question 6

what is in saliva

Answer 6

1. water
2. mucins
3. a-amylase
4. electrolytes
5. lysozyme

Question 7

what does water do in saliva

Answer 7

SOLVENT - 99% of secreted fluid - softens, moistens, dilutes particles

Question 8

what do mucins do in saliva

Answer 8

LUBRICANT FUNCTION - viscous solution, major protein component
Mucins + water = mucus

Question 9

what does a-amylase do in saliva

Answer 9

CATALYSES breakdown of polysaccharides (starch, glycogen) into disaccharides (maltose) + glucose

Question 10

what do electrolytes do in saliva

Answer 10

TONICITY/pH

Question 11

what do lysozymes do in saliva

Answer 11

BACTERIOCIDAL - cleaves polysaccharide component of bacterial cell wall

Question 12

define exocrine gland

Answer 12

gland that exits to OUTSIDE of body

Question 13

what are the three broad types of alveoli

Answer 13

1. mucous - secrete mucus
2. serous - secrete proteins
3. mixed - secrete both

Question 14

how is salivary secretion controlled

Answer 14

BOTH parasympathetic and sympathetic (BOTH ARE STIMULATORY)

Question 15

how does parasympathetic control of salivation occur

Answer 15

1. cranial nerves VII (facial) and IX (glossopharyngeal)

2. stimulation = profuse, watery salivary secretion

Question 16

how does sympathetic control of salivation occur

Answer 16

1. stimulation = small volume, viscous salivary secretion
2. high mucus content (a1 adrenoreceptors)
3. high amylase content (B2 adrenoreceptors)

Question 17

if all control stimulatory why do we get a “dry mouth”

Answer 17

due to sympathetic stimulation - low water content with high mucus/amylase content gives impression of “dry mouth”

Question 18

what triggers reflex control of salivation

Answer 18

presence of food in mouth triggers chemoreceptors/pressure receptors (on walls of mouth/tongue)

Question 19

oesophagus function

Answer 19

conduit between pharynx and stomach (25cm) - contains upper and lower sphincters that regulate movement of material into and out of oesophagus

Question 20

layers of the oesophagus (in to out)

Answer 20

Mucosa, submucosa, muscularis externa and adventitia

Question 21

oesophageal mucosa lined by

Answer 21

non-keratinised stratified squamous epithelium

Question 22

oesophageal submucosa contains

Answer 22

mucous glands - ducts - lubrication

Question 23

oesophageal muscularis externa composition

Answer 23

upper 1/3 (superior) = skeletal muscle

lower 2/3 (inferior) = smooth muscle

Question 24

Phases of swallowing

Answer 24

1. oral (voluntary)
2. pharyngeal (reflex)
3. oesophageal

Question 25

what happens during the oral swallowing phase

Answer 25

voluntary phase - bolus is pushed to the back of the mouth by the tongue

Question 26

what happens during the pharyngeal swallowing phase

Answer 26

reflex phase -

1. presence of bolus causes a sequence of reflex contractions of the pharyngeal muscles
2. co-ordinated by swallowing centre (medulla)
3. soft palate reflected backward and upward (closes off nasopharynx)

Question 27

what happens when the bolus approaches the oesophagus

Answer 27

Upper oseophageal sphincter (UOS) relaxes and epiglottis covers opening to larynx (prevents food entering trachea)

Question 28

what happens once the bolus has entered the oesophagus

Answer 28

Upper oesophageal sphincter contracts (prevents food reflux)

Question 29

what happens during the oesophageal swallowing phase

Answer 29

1. propulsion of bolus to stomach
2. peristaltic wave sweeps along entire oesophagus
3. bolus propelled to stomach in ~10 seconds

Question 30

what happens as the bolus nears the stomach

Answer 30

Lower oesophageal sphincter (LOS) relaxes - bolus enters stomach

Question 31

what is receptive relaxation of the stomach

Answer 31

when the stomach volume increases form ~50ml to ~1500ml WITHOUT pressure change

Question 32

how is the receptive relaxation of the stomach initiated

Answer 32

Initiated following relaxation of lower oesophageal sphincter and entry of bolus into stomach - vagal reflexes cause relaxation of thin, elastic smooth muscle of gastric fundus and body

Question 33

list the functions of the stomach

Answer 33

1. temporary store of ingested food
2. dissolve food particles and initiate digestive process
3. control delivery of contents to small intestine
4. sterilise ingested material
5. produce intrinsic factor (Vitamin B12 absorption)

Question 34

stomach anatomy

Answer 34

1. oesophagus
2. gastroesophageal (cardiac) opening
3. lower oesophageal (cardiac) sphincter
4. cardiac region 
5. fundus 
6. body (greater and lesser curvature)
7. pyloric region
8.  pyloric opening (pyloric sphincter)

Question 35

stomach serosa histology

Answer 35

connective tissue outer layer

Question 36

stomach musclularis externae histlogy

Answer 36

three layers

1. longitudinal (outer)
2. circular (middle)
3. oblique (inner - adds “squeezing motion)

Question 37

submucosa and mucosa histology

Answer 37

folded (RUGAE) when empty - stretches out as stomach fills

Question 38

lumenal surface histology

Answer 38

1. surface mucus cells
2. gastric pits
3. gastric glands
4. mucus neck, parietal and chief cells