Upper GI tract structure and function

Question 1

What nerves control chewing?

Answer 1

Somatic nerves of skeletal muscles in the mouth/jaw

Question 2

Describe the chewing reflex

Answer 2

Contraction of jaw muscles - pressure of food against mechanoreceptors in gums, hard palate and tongue - inhibition of jaw muscles - reduced pressure - starts again```

Question 3

3 salivary glands are?

Answer 3

Parotid
Sublingual
Submandibular

Question 4

Constituents of saliva? Their functions?

Answer 4

Water - 99%, softens, moistens and dilutes
Mucins - proteins that act as lubricant
alpha amylase - breakdown of polysaccharides to disaccharides
Electrolytes - tonicity (isotonic) and pH (controlled by bicarbonate release)
Lysozyme - bacteriocidal, cleaves polysaccharides of bacterial cell wall

Question 5

What type of gland are salivary glands?

Answer 5

Exocrine - because they secrete into the mouth/gut lumen (outside the body)

Question 6

Two types of alveolus in salivary glands and what they secrete

Answer 6

Mucous alveolus - secrete mucous

Serous alveolus - secrete serous fluid (contains alpha amylase)

Question 7

Are salivary glands controlled by the sympathetic or parasympathetic NS?

Answer 7

Both

Both have stimulatory effects

Question 8

Effect of sympathetic and parasympathetic NS on salivary glands?

Answer 8

Parasympathetic - stimulatory, creates a profuse, watery salivary secretion
Sympathetic - stimulatory, smaller volume, viscous salivary secretion (high mucus and amylase content)

Question 9

Effect of presence of food in mouth?

Answer 9

Stimulates chemoreceptors and pressure receptors to begin release of saliva

Question 10

Are there ducts in the oesophagus?

Answer 10

There are ducts in the submucosal layer, secrete mucous for lubrication

Question 11

Type of muscle in the muscularis externa of the oesophagus

Answer 11

Upper 1/3 - skeletal muscle, voluntary swallowing reflex

Lower 1/3 - smooth muscle, involuntary

Question 12

What regulates movement of food into and out of the oesophagus?

Answer 12

Upper and lower oesophageal sphincters

Question 13

Describe the pharyngeal phase of swallowing

Answer 13

Pharyngeal muscle contractions coordinated by the medulla occurs
Soft palate reflected backwards to close off pharynx
UOS relaxes

Question 14

Describe the action of the upper oesophageal sphincter

Answer 14

Usually tonically contracted
Relaxes during swallowing, allows food into oesophagus
Once food is in contracts again to prevent reflux

Question 15

Describe oesophageal phase of swallowing

Answer 15

Propulsion of bolus to stomach via peristalsis

LOS relaxes and allows food bolus into stomach

Question 16

What happens to the stomach when food enters?

Answer 16

Presence of food and relaxation of LOS causes a vagal reflex resulting in relaxation of smooth m. of gastric fundus and body
Increases volume of stomach without change in pressure

Question 17

Functions of the stomach

Answer 17

Temporary storage/controlled delivery to SI
Dissolve food particles and digest proteins
Sterilize ingested material
Produce intrinsic factor (B12)

Question 18

How is mixing force generated in the stomach?

Answer 18

3 layers of smooth m. in the muscularis of the stomach, obliquely oriented layer contracts to provide grinding movement to mix stomach contents

Question 19

Where is muscle in the stomach the thickest?

Answer 19

Thickest at the bottom, generates most mixing force

Question 20

What stops food from the stomach leaking into the small intestine?

Answer 20

Pyloric sphincter

Question 21

What are gastric rugae? Their function?

Answer 21

They’re ridges in the stomach formed by the folding of the submucosa and mucosa of the stomach wall
Stretch as stomach fills to increase volume