Upper GI Tract Structure and Function

Question 1

How is chewing controlled ?

Answer 1

Voluntary: Somatic nerves (skeletal muscles of the mouth and jaw)
Reflexes: Contraction of jaw muscles and the mechanoreceptors in the mouth

Question 2

Saliva is composed of what ?

Answer 2

99% water
Mucins (lubricant)
Alpha amylase
Electrolytes 
Lysozymes

Question 3

What controls saliva secretion ?

Answer 3

The sympathetic and parasympathetic nervous system (both are stimulatory here)

Question 4

What happens to saliva during sympathetic innervation ?

Answer 4

Alpha 1 and beta 2 adrenoceptors produce small amounts of viscous thick saliva.

Question 5

What happens to saliva during parasympathetic innervation ?

Answer 5

Cranial nerves VII (facial) and IX (glossopharyngeal) produces profuse watery saliva secretions

Question 6

Roughly how long is the oesophagus ?

Answer 6

25cm long

Question 7

What are the 4 layers of the oesophagus ?

Answer 7

Mucosa
Submucosa
Muscularis externa
Adventitia

Question 8

How is the muscular layer of the oesophagus split up ?

Answer 8

Upper 1/3 is skeletal muscle and lower 2/3 is smooth muscle

Question 9

There are 4 phases in swallowing, what are they and what occurs in each ?

Answer 9

Oral phase: this phase is voluntary and is where the food bolus is pushed to the back of the mouth by the tongue

Pharyngeal phase: A sequence of reflex contractions of the pharyngeal muscles. The soft pallette reflects upwards to close off the nasal cavity.

Oesophageal phase: Upper oesophageal sphincter relaxes allowing bolus to pass as epiglottis covers opening to larynx preventing aspiration. Once food has entered oesophagus UOS closes. Food is propelled to the stomach in around 10 seconds

Stomach: Food enters the stomach as the LOS relaxes and bolus enters stomach. As bolus enters the stomach the stomach relaxes as the LOS closes.

Question 10

What is found in the stomach & allows absorption of vitamin B12 ?

Answer 10

Intrinsic factor