Upper GI Tract - Structure and Function

Question 1

Why does chewing occur?

Answer 1

Prolong taste experience

Defence against respiratory failure

Question 2

How does voluntary controlled chewing work?

Answer 2

Somatic nerves induce movement of skeletal muscles of mouth/jaw

Question 3

How does reflex controlled chewing work?

Answer 3

Contraction of jaw muscles triggered by pressure of food against gums, hard palate and tongue

Question 4

How is saliva secreted?

Answer 4

By 3 pairs of glands:
Parotid
Submandibular
Sublingual

Question 5

What is saliva made up of?

Answer 5

Water
Mucins
a-amylase
Electrolytes 
Lysozyme

Question 6

What is the role of water in saliva?

Answer 6

Softens, moistens and dilutes particles

Question 7

What is the role of mucins in saliva?

Answer 7

Major protein component
Mucins + water = mucus
Viscous solution which has a lubricant function

Question 8

What is the role of a-amylase in saliva?

Answer 8

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

Question 9

What is the role of electrolytes in saliva?

Answer 9

Regulates tonicity/pH

Question 10

What is the role of lysozymes in saliva?

Answer 10

Bacteriocidal - cleaves polysaccharide component of bacterial cell wall

Question 11

How is salivary secretion controlled?

Answer 11

By parasympathetic and sympathetic nervous systems which are both stimulatory

Question 12

What are the nerves involved in parasympathetic control of salivary secretion? + result of stimulation

Answer 12

Cranial nerves VII (facial) and IX (glossopharyngeal)

Stimulation causes profuse watery salivery secretion

Question 13

What is the result of stimulation of the sympathetic nerves in salivary secretion?

Answer 13

Stimulation causes small volume, viscous salivary secretion
High mucus content (a1 adrenoceptors)
High amylase content (b2 adrenoceptors)

Question 14

What is the reflex control of salivary secretion?

Answer 14

Presence of food in mount sensed by chemoreceptors/pressure receptors in the walls of mouth/tongue which causes salivary secretion

Question 15

What is the oesophagus?

Answer 15

Conduit between pharynx and stomach

Around 25cm

Question 16

What are the 4 layers of the oesophagus?

Answer 16

Mucosa
Submucosa
Muscularis externa
Adventitia

Question 17

What type of epithelium lines the mucosa of the oesophagus?

Answer 17

Stratified squamous (non-keratinised)

Question 18

What are the submucosal mucous glands?

Answer 18

Ducts that secrete mucous to provide lubrication

Question 19

What type of muscle makes up the upper 1/3 of the muscularis externa in the oesophagus?

Answer 19

Skeletal muscle

Question 20

What type of muscle makes up the lower 2/3 of the oesophagus?

Answer 20

Smooth muscle

Question 21

What do the upper and lower oesophageal sphincters do?

Answer 21

Regulate movement of material into and out of oesophagus

Question 22

What is the oral phase of swallowing?

Answer 22

Voluntary

Bolus pushed to back of mouth by tongue

Question 23

What is the pharyngeal phase of swallowing?

Answer 23

Presence of bolus causes a sequence of reflex contractions of pharyngeal muscles
Coordinated by swallowing centre (medulla)
Soft palate reflected backward and upward (closes off nasopharynx)

Question 24

What happens as the bolus approaches the oesophagus?

Answer 24

Upper oesophageal sphincter relaxes and the epiglottis covers the opening to the larynx
Prevents food from entering trachea

Question 25

What happens once food has entered the oesophagus?

Answer 25

Upper oesophageal sphincter contracts | Prevents food reflux

Question 26

What is the oesophageal phase of swallowing?

Answer 26

Propulsion of bolus to stomach A peristaltic wave sweeps along entire oesophagus Takes ~10 seconds

Question 27

What happens as the bolus nears the stomach?

Answer 27

Lower oesophageal sphincter relaxes and bolus enters the stomach

Question 28

What happens in receptive relaxation of stomach?

Answer 28

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

Question 29

What is the range of stomach volume?

Answer 29

50ml --> 1500ml | No change in pressure

Question 30

What are 5 functions of the stomach?

Answer 30

Temporary store of ingested material Dissolve food particles and initiate digestive process Control delivery of contents to small intestine Sterilise ingested material Produce intrinsic factor

Question 31

What are rugae?

Answer 31

Pleats that can open out to increase volume of the stomach

Question 32

Where does emulsification occur in the stomach?

Answer 32

Antrum

Question 33

What is the serosa of the stomach made of?

Answer 33

Connective tissue outer layer

Question 34

What are the 3 layers of the muscularis externae?

Answer 34

Longitudinal (outer) Circular (middle) Oblique (inner)

Question 35

What makes up the rugae in the stomach?

Answer 35

Submucosa and mucosa layers folded to make rugae that stretch as stomach fills

Question 36

What makes up the lumenal surface?

Answer 36

Surface mucus cells Gastric pits leading into gastric glands Mucus neck, parietal and chief cells