upper GI structure and function

Question 1

why do we chew?

Answer 1

• to prolong taste experience

- as a defence mechanism to prevent choking

Question 2

how is chewing controlled?

Answer 2

voluntary control- somatic nerves innervate the mouth and jaw
Involuntary control- Reflex

Question 3

How does the involuntary-reflex control occur?

Answer 3

negative feedback system

• The jaw muscles contract- increase pressure of food against palate
• Mechanoreceptors in the Jaw respond to change in palate
• Inhibition of jaw muscles to reduce pressure.

Question 4

where is saliva secreted?

what type of glands are these?

Answer 4

the parotid gland
the submandibular gland
the sublingual gland

they are all exocrine glands

Question 5

what is saliva made up of?

Answer 5

1-It is made up mainly of water (99%)- moistens and dissolves
2-Mucins- the main protein component- makes it viscous so it can act as a lubricant
3-alpha-amylase: breaks down polysaccharides
4-electrolytes- control tonicty and oh
5-leukocytes- have bactericidal function-

Question 6

what is salivary secretion controlled by?

Answer 6

• parasympathetic system: the glassopharangeal and facial cranial nerves make saliva more watery
• sympathetic system: the alpha-1 and the beta-2 adrenoreceptors make the saliva more concentrated but more viscous
• reflex: chemoreceptors in the mouth detect presence of food.

Question 7

what do the alpha-1 and beta-2 adrenoreceptors do specifically?

Answer 7

alpha-1: increases mucus secretion

beta-2: increases secretion of alpha amylase

Question 8

how does swallowing occur?

Answer 8

• oral phase: food moved to back of mouth by tongue
• Pharangeal phase: reflex contractions of pharyngeal muscles are co-ordinated in medulla- the soft palate is pushed backwards and upwards
• upper oesophageal sphincter relaxes and bolus moves towards oesophagus
• epiglottis covers the trachea to prevent food going in- breathing and eating cannot occur at the same time
• upper oesophageal sphincter contracts and food reaches oesophagus= prevents the reflux of food
• oesophageal phase: peristaltic wave across oesophagus pushes the bolus to the stomach- occurs in 10 seconds
• lower oesophageal sphincter relaxes as bolus approaches stomach
• thin elastic muscle of fundus and body relaxes as the bolus reaches the stomach- causes the volume of the stomach to increase from 50ml to 1500ml

Question 9

what are the functions of the stomach?

Answer 9

• temporary storage
• initiates chemical digestion
• controls flow of contents into SI
• sterilises against bacteria due to low PH
• produces intrinsic factor which is needed for the absorption of vitamin B12

Question 10

Which is the only function which can exclusively be carried out by the stomach?

Answer 10

The production of intrinsic factor

B12 needed for the production of the RBCs

Question 11

structure of the stomach

Answer 11

• 3 layers of muscularis externa: longitudinal, oblique and circular
• submucosa and mucosa is folded when empty- when full it is distended
• lumenal surface contains mucus cells and gastric glands: parietal,chief and mucus
• gastric glands with pits

Question 12

structure of the oesophagus

Answer 12

-stratified squamous epithelial cells
muscularis externa:
-skeletal muscle in top1/3
-smooth muscle in bottom 2/3 
oesophageal sphincters control movement of food into oesophagus.

Question 13

Sympathetic and parasympathetic innervation of the salivary glands

Answer 13

sympathetic : superior cervical ganglion

Parasympathetic: the grossopharangeal and facial nerve