GI 2

Question 1

Describe the main features of the mouth that allow for mastication

Answer 1

Teeth:

Incisors cut

Molars crush

Muscles:

Masseter

Innervated by trigeminal nerve

Question 2

What is zerostomia?

Answer 2

Poor saliva production

Can still eat provided food is moist

However teeth and mucosa degrade quickly

Question 3

What are the constituents of saliva?

Answer 3

Water:

Saliva is hypotonic

Electrolytes:

Na+ and Cl- in lower conc than plasma

Ca2+ and K+ in higher conc than plasma

Alkali:

HCO3- in higher conc than in plasma

Bacteriostats:

Mucus

Enzymes (E.g. amylase)

Question 4

What are the three pairs of salivary glands?

What type of glands are they?

Answer 4

Pairs of:

Parotid

Sub-maxillary

Sub-lingual

Ducted acinar, exocrine

Question 5

What two types of cell are present in salivary glands?

Answer 5

Duct cells

Acinar cells

Question 6

Describe the secretions of each salivary gland pair

Answer 6

Parotids:

Watery, enzyme rich, little mucus

Serous saliva

Sub-lingual:

Viscuous, no enzymes, lots of mucus

Mucus saliva

Sub-maxillary:

All components

Mixed serous and mucus

Question 7

How is the Sub-maxillary gland different to the other slaivary glands in regards to cell types?

Answer 7

Made up of a mixture of serous and mucus acini

Common ducts for both

Question 8

What proportion of saliva is secreted from each salivary gland pair?

Answer 8

Parotid - 25%

Sub-lingual - 5%

Sub-maxillary - 70%

Question 9

If saliva is hypotonic, then what problems do its production pose?

Answer 9

Hypotonic saliva must be made from more highly conentrated ECF

However there exists no cellular mechanism to secrete water

Therefore more concentrated solution is secreted and solutes are removed

Question 10

Compare the Acinar secretions of a salivary gland to ECF

Answer 10

Isotonic with ECF

[Na+] and [K+] about the same

[I-] greater

[Cl-] less

[HCO3-] about the same

Plus enzymes

Question 11

Outline modification of the acinar secretions of salivary glands

Answer 11

Little change in volume

[Na+] falls

[K+] rises slightly

[HCO3-] falls when resting, rises dramatically when stimulated

Modification carried out by ductal cells

Ductal cells have a maximum rate of modification, so the more quickly saliva is produced the less modified it is (Except HCO3-)

Question 12

Outline the specific features of saliva produced at rest

Answer 12

Low volume

Very hypotonic

[Na+] 7-10mmol.L-1

[K+] ~20mmol.L-1

Nuetral or slightly acidic

Few enzymes

Question 13

Outline the specific features of saliva produced when stimulated

Answer 13

High volume

Less hypotonic than resting

[Na+] up to 80mmol.L-1

[K+] 8-10mmol.L-1

[HCO3-] 50-50mmol.L-1 (more alkaline)

Lots of enzymes

Question 14

What is the mechanism of acinar secretion?

Answer 14

Not ultrafiltration

Active secretion of ions (mainly Cl-)

Water and other ions follw passively

Question 15

Label the boxes

Answer 15

Black:

Ductal cell

White, left then right:

Duct

ECF

Question 16

What transporters/substances are transported on the luminal membrane of ductal cells?

Answer 16

Via diffusion gradient:

Na+ in

K+ out

Transporter mediated:

Cl- in

HCO3- out

Question 17

What transporters/substances are transported on the basolateral membrane of ductal cells in salivary glands?

Answer 17

Na+/K+ ATPase:

Na+ out

K+ in

K+/Cl- Symporter:

K+ and Cl- out

Na+/H+ antiporter:

Na+ in

H+ out

Question 18

How is salivary secretion controlled?

What ganglions and nerves are involved?

Answer 18

Largely nervous

Sympathetic:

Superior cervical ganglion

Parasympathetic:

Glossopharangeal (IX cranial)

Otic ganglion

Parasympathetic:

From centres in medulla

Question 19

Describe in more detail parasympathetic mediated control of salivation

Answer 19

Afferent information to the medulla leading to salivation:

Mouth and toungue (taste receptors, particularly acid)

Nose

Conditioned reflexes (Pavlov)

Outflow from medulla in response:

Sypathetic outflow leads to release of Ach which acts on muscarinic receptors

Duct cells Promote HCO3- secretion

Question 20

How could zerostomia be related to the nervous system?

Answer 20

Sympathetic stimulation reduces blood flow to salivary glands leading to reduced salivation

Question 21

What are the 3 stages of swallowing

Answer 21

Voluntary

Pharyngeal

Oesophageal

Question 22

What is the voluntary phase of swallowing?

Answer 22

Bolus moved into pharynx

Question 23

Describe the pharyngeal phase of swallowing

Answer 23

Pressure receptors in palate and anterior pharynx send afferent messages to brainstem swallowing centre which:

• inhibits respiration
• Raises larynx
• Closes the glottis
• Opens the upper oesophageal sphincter

Question 24

Describe the Oesophageal phase of swallowing

Answer 24

Upper third of oesophagus is voluntary muscle

Lower 2/3 is smooth muscle

Rapid peristaltic wave occurs

Transit time to stomach is about 9 seconds

Lower oesophageal sphincter opens

Question 25

What is the reasoning behing checking the swallowing relfex?

Answer 25

Important brainstem function

Must be checked after head injury/surgery as there is a high risk of aspiration if absent

Absent in brain death

Question 26

Describe dysphagia and common causes

Answer 26

Problem swallowing

Can be due to:

Achalasia (upper oesophageal sphincter doesnt open)

Obstruction or compression of oesophagus (E.g. tumours/forign body/food)

Nervous problems (E.g. after stroke)