GI S2 (Done) Flashcards
Describe the main features of the mouth that allow for mastication
Teeth:
Incisors cut
Molars crush
Muscles:
Masseter
Innervated by trigeminal nerve
What is zerostomia?
Poor saliva production
Can still eat provided food is moist
However teeth and mucosa degrade quickly
What are the constituents of saliva?
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)
What are the three pairs of salivary glands?
What type of glands are they?
Pairs of:
Parotid
Sub-maxillary
Sub-lingual
Ducted acinar, exocrine
What two types of cell are present in salivary glands?
Duct cells
Acinar cells
Describe the secretions of each salivary gland pair
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
How is the Sub-maxillary gland different to the other slaivary glands in regards to cell types?
Made up of a mixture of serous and mucus acini
Common ducts for both
What proportion of saliva is secreted from each salivary gland pair?
**Parotid **- 25%
**Sub-lingual **- 5%
**Sub-maxillary **- 70%
If saliva is hypotonic, then what problems do its production pose?
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
Compare the Acinar secretions of a salivary gland to ECF
Isotonic with ECF
[Na+] and [K+] about the same
[I-] greater
[Cl-] less
[HCO3-] about the same
Plus enzymes
Outline modification of the acinar secretions of salivary glands
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-)
Outline the specific features of saliva produced at rest
Low volume
Very hypotonic
[Na+] 7-10mmol.L-1
[K+] ~20mmol.L-1
Nuetral or slightly acidic
Few enzymes
Outline the specific features of saliva produced when stimulated
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
What is the mechanism of acinar secretion?
Not ultrafiltration
Active secretion of ions (mainly Cl-)
Water and other ions follw passively
Label the boxes
Black:
Ductal cell
White, left then right:
Duct
ECF
What transporters/substances are transported on the luminal membrane of ductal cells?
Via diffusion gradient:
Na+ in
K+ out
Transporter mediated:
Cl- in
HCO3- out
What transporters/substances are transported on the basolateral membrane of ductal cells in salivary glands?
Na+/K+ ATPase:
Na+ out
K+ in
K+/Cl- Symporter:
K+ and Cl- out
Na+/H+ antiporter:
Na+ in
H+ out
How is salivary secretion controlled?
What ganglions and nerves are involved?
Largely nervous
Sympathetic:
Superior cervical ganglion
Parasympathetic:
Glossopharangeal (IX cranial)
Otic ganglion
Parasympathetic:
From centres in medulla
Describe in more detail parasympathetic mediated control of salivation
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
How could zerostomia be related to the nervous system?
Sympathetic stimulation reduces blood flow to salivary glands leading to reduced salivation
What are the 3 stages of swallowing
Voluntary
Pharyngeal
Oesophageal
What is the voluntary phase of swallowing?
Bolus moved into pharynx
Describe the pharyngeal phase of swallowing
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
Describe the Oesophageal phase of swallowing
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
What is the reasoning behing checking the swallowing relfex?
Important brainstem function
Must be checked after head injury/surgery as there is a high risk of aspiration if absent
Absent in brain death
Describe dysphagia and common causes
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)
