Upper GI Tract Structure & Function

Question 1

Why do we chew?

Answer 1

1. Prolong taste experience

2. Defence against respiratory failure

Question 2

How is chewing controlled?

Answer 2

• Voluntary

- Reflex

Question 3

Voluntary:

Answer 3

Controlled by somatic nerves

Question 4

Reflex:

Answer 4

• Contraction of jaw muscle
• Pressure of food against gums increase
• Mechanoreceptors inhibit jaw muscle
• Relaxation

Question 5

What is saliva secreted by?

Answer 5

Parotid, submandibular, sublingual

3 salivary ducts

Question 6

What is in saliva?

Answer 6

• Water
• Mucins
• a-amylase
• Electrolytes
• Lysozyme

Question 7

What does the water do?

Answer 7

softens, moistens and dilutes partiles. (solvent)

Question 8

Mucins?

Answer 8

Major protein component
Adds with water to form mucus
Viscous solution - lubricant function

Question 9

a-amylase?

Answer 9

Catalyses breakdown of polysaccharide (starch glycogen) into disaccharide (maltose) + glucose

Question 10

Electrolytes

Answer 10

Tonicity/pH

Question 11

Lysozyme

Answer 11

Bacteriocidal - cleaves polysaccharide component of bacterial cell wall

Question 12

Serous alveoli secretes

Answer 12

lysozyme & amylase

Question 13

Mucous alveoli secretes

Answer 13

mucus

Question 14

Salivary secretion called by

Answer 14

Parasympathetic & sympathetic nervous system

Question 15

Parasympathetic:

Answer 15

• Cranial nerves 7 (facial) & 10 (glossopharyngeal)

- Creates watery salivary secretion

Question 16

Sympathetic:

Answer 16

• Creates small volume of viscous salivary secretion

- A1 adrenoreceptors (high mucus) and B2 adrenoreceptors (high amylase)

Question 17

Reflex control

Answer 17

Presence of food in mouth - chemoreceptors/pressure receptors (walls of mouth/tongue)

Question 18

Oesophagus connects

Answer 18

pharynx to stomach

Question 19

4 layers

Answer 19

Mucosa
Submucosa
Muscularis externa Adventitia

Question 20

Mucosa lined by

Answer 20

stratified squamous epithelium (non-keratinised)

Question 21

Muscularis externa: upper 1/3 (superior) =

Answer 21

skeletal muscle

Question 22

Muscularis externa: lower 2/3 (inferior)

Answer 22

smooth muscle

Question 23

What do Upper and lower oesophageal sphincters do?

Answer 23

regulate movement of material into and out of oesophagus

Question 24

Swallowing phases

Answer 24

Oral phase (voluntary)
Pharyngeal phase

Question 25

What happens in oral phase?

Answer 25

Bolus pushed to back of mouth by tongue

Question 26

What happens in pharyngeal phase?

Answer 26

• Soft palate goes upwards and back to prevent food going to nose
• As bolus approaches oesophagus, Upper oesophageal sphincter relaxes and opens while epiglottis covers larynx (prevent food entering trachea)
• Once food has entered oesophagus, Upper oesophageal sphincter then contracts to prevent food reflux, once food enters

Question 27

Where is the swallowing centre?

Answer 27

medulla

Question 28

Swallowing - Oesophageal phase

Answer 28

• Propulsion of bolus to stomach
• Peristaltic wave (wave of muscle contraction) sweeps along entire oesophagus
• Propelled to stomach in ~10 secs
• Lower oesophageal sphincter opens and allows food into stomach
• Stomach then relaxes and stretches (vagal reflex) and increase stomach volume (no increase in pressure)

Question 29

Functions of Stomach (5)

Answer 29

1. Temporary storage of food
2. Dissolve some food
3. Control entry into small intestine
4. Sterilise food (HCL)
5. Produce intrinsic factor (vitamin B12 absorption)

Question 30

Serosa =

Answer 30

connective tissue outer layer

Question 31

3 layers of muscularis externa:

Answer 31

longitudinal (outer), circular (middle), oblique (inner)

Question 32

Lumen surface has 3 cells in gastric pits:

Answer 32

mucus neck (mucus), parietal (HCL and intrinsic factors), chief cells (pepsinogen)