Upper GI Tract Structure & Function

Question 1

What is the purpose of chewing?

Answer 1

Prolonging Taste

Breaking up food so we dont choke and undergo resp. failure

Question 2

How is chewin controlled?

Answer 2

Both voluntarily and reflexively
Voluntary:
- Somatic nerves to skeletal muscle of jaw and mouth

Reflex:

• A cycle
• Contraction of jaw -> pressure of food on gum, hard palate and tongue -> Mechanoreceptor -> Inhibits jaw muscles -> Loss of pressure- > Contraction of jaw….

Question 3

NAme the salivary glands

Answer 3

3 paired glands
Parotid
Submandibular
Sublingual

Question 4

What are the constituents of saliva?

Answer 4

Water
Mucins
Alpha-amylase
Electrolytes (Na+/K+/Cl-/HCO3-)
Lysozyme

Question 5

What is the function of water in saliva?

Answer 5

Water is about 99% of saliva

IT softens, moistens and dilutes food particles, basically acting as a solvent

Question 6

What is the function of mucins in saliva?

Answer 6

They make up most of the protein in saliva and combine with water to make mucous.
This creates a viscous solution to act as a lubricant to chewing/swallowing

Question 7

What is the function of alpha-amylase in saliva?

Answer 7

It begins catalysing breakdown of polysaccharides into maltose & glucose.

Question 8

What does alpha-amylase act on and why does it only produce specific di/monosaccharide products?

Answer 8

Polysaccharides bound by alpha-1,4-glycosidic bonds only, specifically starch & glycogen as only cellulase breaks the beta-1,4-glycosidic bonds in cellulose.

Startch and glycogen are entirely glucose so can only be broken down to maltose and glucose not any other saccharide

Question 9

What are the purpose of electrolytes in saliva?

Answer 9

To balance tonicity and pH

Question 10

What is lysozyme and what does it do in saliva?

Answer 10

Its a bacteriocidal enzyme that cleaves polysaccharides in bacterial cell walls

Question 11

What alveoli are in salivary glands?

Answer 11

• Mucous alveoli which have cells that produce mucins
• Serous alveoli produce preotinaceous fluid full of enzymes
• Mixed alveoli have both cells

Question 12

How is salivation controlled?

Answer 12

Parasympathetic & Sympathetic NS stimulate salivation as does reflex control.

Question 13

How does the parasympathetic system affect salivation?

Answer 13

Cranial nerves VII & IX (facial & Glossopharyngeal)

They stimulate secretion of a profuse watery secretion

Question 14

How does the sympathetic system affect salivation?

Answer 14

It releases adrenaline which stimulates production of a small volume of viscous saliva.
Alpha1 adrenoceptors -> high mucous content
Beta2 adrenoceptors -> high amylase content

Question 15

How do reflexes stimulate salivation?

Answer 15

• Food goes in your mouth
• Activates chemoreceptors and pressure receptors in the walls of the mouth/tongue
• Triggers salivation

Question 16

Whats different about the muscularis externae in the stomach to the rest of the GI tract?

Answer 16

its has 3 layers

The normal circular and longitunidal + a 3rd internal oblique layer

Question 17

How does the muscularis externa vary throughout the oesophagus?

Answer 17

In the upper 3rd its skeletal muscle & therefore has voluntary control through the somatic NS.
In the lower 2/3rds it has smooth muscle and lacks conscious control.

Question 18

How do we control entry/exit of stuff into oesophagus

Answer 18

the upper and lower oesophageal sphicters (UOS + LOS)

Question 19

What are the phases of swallowing?

Answer 19

Oral (voluntary) Phase
Pharyngeal Phase
Oesophageal Phase

Question 20

What happens in the oral phase of swallowing?

Answer 20

The bolus is pushed to the back of the mouth by the tongue

Question 21

What happens in the pharyngeal phase of swallowing?

Answer 21

• Presence of bolus leads to a sequence of reflex contractions in the pharyngeal muscles
• Soft palate is reflected back and up closing off the nasopharynx
• UOS relaxes and the epiglottis covers the larynx opening

Question 22

What happens during the oesophageal phase of swallowing?

Answer 22

• UOS contracts to prevent regurgitation
• Peristaltic wave sweeps oesophagus
• LOS relaxes and bolus enters stomach

Question 23

What kind of reception does the stomach give a bolus?

Answer 23

When the LOS opens the stomach relaxes.

Question 24

What controls the stomach relaxing upons recieving food? and how is its structure different when empty?

Answer 24

A vagal reflex that leds to relaxation of elastic smooth muscle in the fundus and body.

When empty this muscle is arranged in pleats called rugae to shrink the stomach

Question 25

Where are the swallowing centres that control swallowing?

Answer 25

the medulla right next to your respiratory centres

Question 26

How big can the stomach go?

Answer 26

From 50ml to 1500ml

Question 27

What are the functions of the stomach?

Answer 27

- Temporary food store - Dissolves (liquidises) food & begins digestion - Controls steady delivery into small intestine - Sterilises ingested material - Produces intrinsic factor

Question 28

What are the sections of the stomach?

Answer 28

- Gastroesophageal (Cardiac) opening (around LO/cardiac sphincter) - Cardiac region (cardia) - Fundus - Body - (pyloric) antrum - Pyloric region - Pyloric sphincter