Upper GI tract structure and function

Question 1

What is the voluntary control of chewing ?

Answer 1

Somatic nerves-> skeletal muscle of mouth/jaw

Question 2

What is the chewing reflex ?

Answer 2

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

Question 3

Where is saliva secreted from ?

Answer 3

Parotid, submandibular and sublingual glands

Question 4

What are the componenets of saliva ?

Answer 4

Water
Mucins
Alpha-amylase
Electrolytes
Lysozyme

Question 5

What controls salivary secertion ?

Answer 5

Parasympathetic and sympathetic NS
both stimulatory

Question 6

How does the parasympathetic system control secertion ?

Answer 6

Facial and glossopharyngeal nerves stimulate a profuse watery secertion

Question 7

How does the sympathetic system control secertion ?

Answer 7

Stimulates small volume of viscous secertion
- high mucus content- alpha-1 adrenoreceptors
- high amylase content- beta-1 adrenoreceptors

Question 8

What are the four layers of the oesophagus ?

Answer 8

Mucosa: lined by stratified sqaumous epithelium (non-keratinised)

Submucosal mucous glands-> ducts-> lubrication

Muscularis externa: upper 2/3 (superior) + skeletal muscle, inner 2/3 (inferior) + smooth muscle

Adventitia

Question 9

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

Answer 9

Upper and lower oesophageal sphincter

Question 10

What is the pharyngeal phase of swallowing ?

Answer 10

Presence of bolus-> sequence of reflex contractions of pharyngeal muscles
Coordinated by swallowing centre- medulla
Soft palate reflected backwards and upward (close off nasopharynx)
Upper oesophageal sphincter relaxes and epiglottis covers opening to larynx- prevents food entering trachea
UOS contracts- prevents food reflux

Question 11

What is the oesophageal phase of swallowing ?

Answer 11

Propulsion of bolus to stomach
Peristatic wave sweeps along entire oesphagus
Propelled to stomach in ~10s
Lower oesophageal sphincter relaxes-> bolus enters stomach
Initiated following relaxation of LOS and
Vagal reflexes-> relaxation of thin, elastic smooth muscle of gastric fundus and body
Stomach volume: 50ml-> 1500ml (no change in pressure)

Question 12

What are the functions of the stomach ?

Answer 12

Temporary store of ingested materials
Dissolve food particles and initiate digestive process
Control delivery of contents to small intestine
Sterilise ingested material
Produce intrinsic factor (vitamin B12 absorption)