Upper GI Tract Structure and Function

Question 1

What is the purpose of chewing?

Answer 1

• Prolong taste experience

- Defence against respiratory failure

Question 2

How is chewing controlled voluntarily?

Answer 2

Via somatic nerves which act on the skeletal muscles of the mouth and jaw

Question 3

How id chewing controlled as a reflex?

Answer 3

• Contraction of jaw muscles leads to pressure of food against our gums, hard palate and tongue
• Mechanoreceptors detect pressure and lead to inhibition of jaw muscles in order to reduce pressure and contraction

Question 4

What glands secrete saliva?

Answer 4

• Parotid
• Submandibular
• Sublingual

Question 5

What is saliva composed of?

Answer 5

• Water
• Mucins
• a-Amylase
• Electrolytes
• Lysozyme

Question 6

What is the purpose of water in saliva?

Answer 6

• It is 99% of the secreted fluid
• Softens, moistens and dilutes particles
• Acts as solvent

Question 7

What is the purpose of mucins in saliva?

Answer 7

• Major protein component
• Combined with water forms mucus
• Viscous solution which acts as a lubricant

Question 8

What is the function of a-Amylase in saliva?

Answer 8

-Catalyses the breakdown of polysaccharides into disaccharides

Question 9

What is the function of electrolytes in saliva?

Answer 9

Tonicity/pH

Question 10

What is the function of lysozyme in saliva?

Answer 10

• Acts as a bacteriocidal

- Cleaves polysaccharide component of bacterial cell wall

Question 11

How is salivary secretion controlled?

Answer 11

By parasympathetic and sympathetic nervous system

Question 12

How does the parasympathetic system affect salivary secretion?

Answer 12

Stimulates it

Question 13

How does the sympathetic system affect salivary secretion?

Answer 13

Stimulates it

Question 14

How does the parasympathetic system act on salivary secretion?

Answer 14

• Via facial and glossopharyngeal nerves (cranial VII and IX)
• Stimulation leads to profuse watery salivary secretion

Question 15

How does the sympathetic system act on salivary secretion?

Answer 15

• Stimulation leads to small volume of viscous salivary secretion
• a1 adrenoreceptors responsible for high mucus content
• B2 adrenoreceptors responsible for high amylase ccontent

Question 16

How is salivary secretion controlled by reflex?

Answer 16

• Presence of food in the mouth

- Chemoreceptors detect it via the walls of the mouth and tongue

Question 17

What is the oesophagus?

Answer 17

Conduit between pharynx and stomach

Question 18

What are the 4 layers of the oesophagus?

Answer 18

• Mucosa
• Submucosa
• Muscularis externa
• Adventitia

Question 19

What lines the mucosa?

Answer 19

Stratified squamous epithelium (non-keratinised)

Question 20

What is the function of the submucosal glands?

Answer 20

Acts as ducts to provide lubrication

Question 21

What is the composition of the muscularis externa?

Answer 21

• Upper 1/3 (superior) is skeletal muscle

- Lower 2/3 (inferior) is smooth muscle

Question 22

What do the upper and lower oesophageal sphincters do?

Answer 22

Regulate movement of material into and out of the oesophagus

Question 23

What happens during the voluntary oral phase of swallowing?

Answer 23

Bolus pushed to back of mouth by tongue

Question 24

What happens during the pharyngeal phase of swallowing?

Answer 24

• Presence of bolus leads to a sequence of reflex contractions of pharyngeal muscles
• Co-ordinated by swallowing centre (medulla)
• Soft palate reflected backward and upward which closes of the nasopharynx

Question 25

What happens as the bolus approaches the oesophagus?

Answer 25

The upper oesophageal sphincter relaxes and epiglottis covers the opening to larynx to prevent food entering the trachea

Question 26

What happens once food has entered the oesophagus?

Answer 26

Upper oesophageal sphincter contracts to prevent food reflux

Question 27

What happens in the oesophageal phase of swallowing?

Answer 27

- Propulsion of bolus to stomach - Peristalic wave sweeps along entire oesophagus - Propelled to stomach

Question 28

What happens as the bolus nears the stomach?

Answer 28

The lower oesophageal sphincter relaxes to allow the bolus to enter the stomach

Question 29

Describe the receptive relaxation of the stomach.

Answer 29

- Initiated following relaxation of the lower oesophageal sphincter and entry of bolus into stomach - Vagal reflexes lead to relaxation of thin, elastic smooth muscle of gastric fundus and body - Stomach volume increases from 50ml to 1500ml with no change in pressure

Question 30

What are the 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 (B12 absorption)

Question 31

What regions does food of the stomach does food travel through from the oesophagus?

Answer 31

- Oeosphasgus - Gastroesophageal (cardiac) opening - Cardiac region - Fundus - Body - Pyloric region - Pyloric opening

Question 32

What is the serosa of the stomach?

Answer 32

Connective tissue layer

Question 33

What is the muscularis externae of the stomach composed of?

Answer 33

- Longitudinal layer - Circular layer - Oblique layer

Question 34

How doe the submucosa and mucosa differ when the stomach is empty compared to full?

Answer 34

- Folded (rugae present) when empty | - Stretched as stomach fills

Question 35

Describe the lumenal surface of the stomach.

Answer 35

- Surface mucus cells - Gastric pits - Gastric glands - Mucus neck, parietal and chief cells