Lecture 6 Upper GI Tract Structure & Function

Question 1

What is the purpose of chewing

Answer 1

prolong taste and a defence against respiratory failure

Question 2

How does the nervous system control chewing

Answer 2

Controlled voluntarily through somatic nerves (skeletal muscles of mouth/jaw) and reflex is through contraction of jaw muscles

Question 3

What are the 3 pairs of salivary glands

Answer 3

Parotid
Sub-mandibular
Sublingual

Question 4

Saliva consists of what components

Answer 4

Water
Mucins
a-Amylase
Electrolytes
Lysozyme

Question 5

What is the purpose of water in saliva

Answer 5

99% of secreted fluid. Softens, moistens, dilutes particles. Solvent

Question 6

What is the purpose of mucins in the saliva

Answer 6

major protein component. Mucins + water = mucus. Viscous solution – lubricant function

Question 7

What is the purpose of a-amylase in the saliva

Answer 7

catalyses breakdown of polysaccharide (starch, glycogen) into disaccharide (maltose) + glucose

Question 8

What is the purpose of electrolytes in saliva

Answer 8

tonicity/pH

Question 9

What is the purpose of lysozymes in saliva

Answer 9

Bactericidal -cleaves polysaccharide component of bacterial cell wall

Question 10

Parasympathetic and Sympathetic salivary secretion is inhibitory/Stimulatory

Answer 10

Both stimulatory

Question 11

Describe the parasympathetic control of salivary secretion

Answer 11

• Cranial nerves VII (facial) & IX (glossopharyngeal)

* Stimulation  profuse watery salivary secretion

Question 12

Describe the sympathetic control of the salivary secretion

Answer 12

• Stimulation  small volume, viscous salivary secretion
• High mucus content (a1 adrenoreceptors)
• High amylase content (B2 adrenoreceptors)

Question 13

Describe the reflex control in the mouth

Answer 13

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

Question 14

How long is the oesophagus

Answer 14

25cm

Question 15

What are the four layers of the oesophagus

Answer 15

Mucosa
Submucosa
Muscle Externa
Adventitia/Serosa

Question 16

What is the mucosa in the oesophagus lined with

Answer 16

Simple stratified non-keratinising epithelium

Question 17

What is the function for the submucosal glands in the oesophagus

Answer 17

Lubrication

Question 18

What is the muscularis externa composed of

Answer 18

1/3 skeletal muscle

Lower 2/3 smooth muscle

Question 19

Oral Phase of swallowing

Answer 19

Voluntary

• Bolus pushed to back of mouth by tongue

Question 20

Pharyngeal Phase of Swallowing

Answer 20

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

Question 21

Oesophageal phase of swallowing

Answer 21

• UOS contracts (prevents food flux)
• Propulsion of bolus to stomach
• Peristaltic wave sweeps along entire oesophagus
• Propelled to stomach in 10 secs
• Lower oesophageal sphincter (LOS) relaxes  bolus enters stomach

Question 22

Describe the Receptive relaxation of stomach when food enters

Answer 22

• Initiated following relaxation of LOS and entry of bolus into stomach
• Vagal reflexes  relaxation of thin, elastic smooth muscle of gast

Question 23

Function of 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

Describe the histology of the stomach

Answer 24

• Serosa= connective tissue outer layer
• Muscularis externae = three layers: longitudinal (outer), circular (middle), oblique (inner)
• Submucosa and mucosa folded (rugae) when empty and stretch as stomach fills