Upper GI Tract Structure & Function

Question 1

What is responsible for the voluntary control of chewing?

Answer 1

Somatic nerves - skeletal muscles of mouth and jaw

Question 2

What is the reflex control of chewing?

Answer 2

*Contraction of jaw muscles -> pressure of food against gums, hard palate and tongue -> mechanoreceptors -> inhibition of jaw muscles -> reduced pressure -> contraction - etc…

Question 3

What is saliva composed of?

Answer 3

Water - 99% - moistens, solvent

Mucins - (plus water = mucus) - lubricant

Alpha amylase - enzyme

Electrolytes - pH and tonicity

Lysozyme - Bacteriocidal - cleaves polysaccharide component of bacterial cell wall

Question 4

What type of glands secrete alpha amylase?

Answer 4

Serous glands

Question 5

What is an exocrine gland?

Answer 5

Produces a secretion by a canal or duct to the surface or outside of an organ

Question 6

What is the effect of the parasympathetic nervous system on saliva production?

Answer 6

Question 7

What is the effect of the sympathtic nervous system on saliva production?

Answer 7

Question 8

What is the reflex control of salivary secretion?

Answer 8

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

Question 9

How long is the oesophagus?

Answer 9

25cm

Question 10

What is the mucosa of the oesophagus lined with?

Answer 10

Stratified squamous epithelium (non-keratinised).

Question 11

Where does the lubrication in the oesophagus come from?

Answer 11

Submucosal glands - ducts

Question 12

What is the muscularis externa composed of?

Answer 12

upper 1/3 (superior) = skeletal muscle

lower 2/3 (inferior) = smooth muscle

Question 13

What regulates the movement of material into and out of the gut?

Answer 13

oesophageal sphincters

Question 14

What is the oral phase of swallowing?

Answer 14

Bolus is pushed to back of the mouth by the tongue

Question 15

What is the pharyngeal phase of swallowing?

Answer 15

There is a reflex of pharyngeal muscles coordinated by the swallowing centre (medulla) as a result of the bolus

Soft palate reflected backward and upward (closes off nasopharynx)

Question 16

What happens when the bolus approaches the oesophagus?

Answer 16

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

Question 17

What happens once food has entered the oesophagus?

Answer 17

Upper oesophageal sphincter contracts and prevents food reflux

Question 18

How does the food reach the stomach?

Answer 18

Peristaltic wave sweeps along the entire oesophagus and propels food to the stomach in about 10 seconds

Question 19

What must happen before the bolus reaches the stomach?

Answer 19

LOS relaxes

Question 20

What is the receptive relaxation of the stomach and what controls it?

Answer 20

Initiated following the relaxation of LOS and entry of bolus into the stomach,

•Vagal reflexes - relaxation of elastic smooth muscle of fundus and body of stomach

Question 21

What is the stomach volume?

Answer 21

•50ml - 1500ml (no change in pressure)

Question 22

What are the folds in the stomach called?

Answer 22

Rugae

Question 23

What are the functions of the stomach?

Answer 23

• 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 (Vitamin B12 absorption)

Question 24

Where do the large contractions take place in the stomach?

Answer 24

The lower portions which are more muscly

Question 25

Which additional muscle layer exists around the antrum?

Answer 25

The oblique muscle layer

Question 26

What layers are folded to form rugae?

Answer 26

Submucosa and mucosa

Question 27

What is the name given to the connective tissue outer layer of the stomach?

Answer 27

Serosa

Question 28

What is the lumenal surface composed of?

Answer 28

Surface mucus cells - gastric pits - gastric glands - mucus neck, parietal and chief cells