Upper GI Tract Structure and Function

Question 1

What two reasons do we chew for?

Answer 1

• Prolonging taste

- Defence against respiratory failure (choking)

Question 2

How is chewing controlled?

Answer 2

Voluntary and reflex

Question 3

How is the voluntary aspect of chewing regulated?

Answer 3

Somatic nerves innervate skeletal muscles in jaw/mouth

Question 4

What reflexes play a role in chewing?

Answer 4

Contraction of jaw muscles increased pressure of food against gums, hard palate and tongue which stimulates mechanoreceptors which inhibit jaw muscles

Question 5

What is the oesophagus?

Answer 5

Conduit between pharynx and stomach

Question 6

Approx. how long is the oesophagus?

Answer 6

25cm

Question 7

What four layers does the oesophagus have?

Answer 7

Mucosa, submucosa, Muscular externa and adventitia

Question 8

Describe the histology of the mucosa of the oesophagus

Answer 8

Stratified, non-keratinised, squamous epithelium

Question 9

What structures are contained in the submucosa?

Answer 9

Mucous glands and ducts

Question 10

Describe the muscle distribution in the oesophagus

Answer 10

Upper third = skeletal muscles

Lower two thirds = smooth muscle

Question 11

What two structures in the oesophagus regulate movement of material?

Answer 11

Upper and lower sphincters

Question 12

What three phases of swallowing are there?

Answer 12

Oral phase
Pharyngeal phase
Oesophageal phase

Question 13

What occurs during the oral phase?

Answer 13

Bolus is pushed to the back of the mouth by the tongue

Question 14

What occurs during the pharyngeal phase?

Answer 14

Presence of bolus stimulates a series of reflex contractions of pharyngeal muscles

Soft palate reflected upwards to close nasopharynx

Upper oesophageal sphincter relaxes and epiglottis covers larynx

Question 15

What region of the brain coordinates swallowing?

Answer 15

Swallowing centre in the medulla

Question 16

What happens once food has entered the oesophagus?

Answer 16

Propulsion of food towards stomach (approx. 10s) by peristaltic wave.

Lower oesophageal sphincter relaxes

Receptive relaxation of stomach by vagal reflexes (relaxation of funds and body of stomach)

Question 17

What is the volume range of the stomach with no change in pressure?

Answer 17

50-1500ml

Question 18

What three glands produce saliva?

Answer 18

Parotid , submandibular and sublingual

Question 19

What are the components of saliva?

Answer 19

Water (99%)
Mucins
alpha-Amylase
Electrolytes 
Lysozyme

Question 20

What is mucus?

Answer 20

Combination of water and mucins (lubricartes, softens, moistens and good solvent)

Question 21

What is the function of alpha-amylase?

Answer 21

Catalyses breakdown of polysaccharides (starch and glycogen) into maltose

Question 22

What is the function of electrolytes in saliva?

Answer 22

Maintains pH and tonicity

Question 23

What is the function of lysozyme in saliva?

Answer 23

Bactericidal - cleaves polysaccaride component of bacteria cell wall

Question 24

What division of the nervous system regulates saliva secretion?

Answer 24

Autonomic (both parasympathetic and sympathetic)

Question 25

What parasympathetic nerves control secretion of saliva?

Answer 25

Cranial nerves VII (facial) and IX (glossopharyngeal)

Question 26

What is the effect of the parasympathetic system on saliva secretion?

Answer 26

Stimulates profuse watery saliva

Question 27

What is the effect of the sympathetic system on saliva secretion?

Answer 27

Small volume of highly viscous saliva High mucus (alpha-1 adrenoreceptors) and high amylase (beta-2 adrenoreceptors)

Question 28

What reflexes are involved in the salivary system?

Answer 28

Presence of food in the mouth stimulates chemoreceptors and mechanoreceptors which stimulate secretion

Question 29

What are the main functions of the stomach?

Answer 29

- Temporary food storage - Dissolves food and initiates digestion - Controls delivery of contents into the small intestine - Sterilises ingested material - Produces intrinsic factor

Question 30

What type of tissue is the serosa made of?

Answer 30

Connective tissue

Question 31

The stomach has THREE layers to the muscularis externa in the stomach. What are they?

Answer 31

Outer - longitudinal Middle - circular Inner - oblique

Question 32

How is the stomach folded when empty?

Answer 32

Folded into rugae Accommodates volume range from 50ml-1500ml without pressure change

Question 33

Describe the lumenal surface of the stomach

Answer 33

- Surface mucus cells - Gastric pits which house gastric glands - Mucus neck house parietal and chief cells