GIT - Saliva, oesophagus and swallowing Flashcards
What volume of saliva is excreted by which glands daily. what is it excreted in response to
500 - 1000mls
Parotid, submandibular, sublingual
thought, smells, taste and presence of food in the mouth or stomach
What is saliva made up of
98% water 2% other - electrolytes: hypotonic lower Na but higher K vs plasma. Resting pH is 7.0 --> 8.0 when HCO3 is secreted - proteins and enzymes - Bacerticidal substances - HCO3 -
Name the proteins, enzymes and bactericidal substances found in saliva
Mucin
Haptocorrin
alpha - amylase
Lingual lipase
What is the function of haptocorrin
Protection of the acid sensitive vitamin B12
What are the 4 functions of saliva
LUBRICATION –> protects pharyngeal and oesophageal mucosa from damage during swallowing.
DIGESTION
- alpha - amylase: identical to pancreatic amylase –> catalyses CHO polymers at pH of 7.0. Cleaves up to 75% of starch before becomming denatured in the stomach. Mixing into food well –> prolonged action –> center food bolus protected from acids in stomach
- lingual lipase: commences digestion of triglycerides. (NB in neonates with immature pancreatic lipase)
- Haptocorrin: binds and protect B12 from lo pH environment of stomach
NEUTRALIZATION of acid
- when stomach acid enters oesophagus (reflux)/oral cavity (vomiting).
- protects enamel against acid erosion
ANTIBACTERIAL
Little evidence for significant bactericidal action in humans despite present of bactericidal substances
In which patients is lingual lipase important and why
- lingual lipase: commences digestion of triglycerides. (NB in neonates with immature pancreatic lipase)
How is saliva produced
In salivary glands, acinar cells, surrounded by contracile myoepithelial cells produce saliva in 2 phases
- Acinar cells –> active transport of Na, Cl, HCO3- + passive movement of H2O (resemble plasma
- Ductal cells –> Secondary secretion of K+ and HCO3- and reabsorption of Na, Cl. Reabsorption > secretion. therefore saliva becomes more hypertonic as it progresses through the duct.
How does the rate of saliva production effect its composition
High rate –> Higher Na + HCO3-
Low rate –> Higher K + Cl
What effect does aldosterone have on salivary composition
Aldosterone increase Na reabsorption a K secretion similar to its affects in the kidney
What are the effects of the autonomic nervous system on the secretion of saliva
Secretory unit = acinus
Acini of parotid / submandibular and sublingual glands have:
PSNS
- vasodilation + myoepithelial contraction –> secretion of serous electrolyte rich saliva
SNS
- vasoconstriction + myoepithelial cell contraction –> brief increase in secretion of mucous saliva rich in amylase followed a period of reduced saliva production
Which glands produce mucous vs serous saliva
Serous saliva: parotids / submandibular
Mucous saliva: sublingual
What is the anatomical innervation of the salivary glands
Parotid - Glossopharyngeal = CN9. PReganglionic fibres synapse at the OTIC ganglion
Submandibular and sublingual = Facial CN7. Preganglionic fibres synapse at submandibular region
Postganglionic fibres travel in the lingual nerve
What is swallowing
Complex process involving co-ordinated voluntary and involuntary muscle movement
Food bolus from oral cavity, via pharync into oesophagus with closure of larnyx to prevent pulmonary aspiration.
Control: swallowing center in medulla oblongata
Describe the phases of swallowing?
3 PHASES
ORAL
- Voluntary
- bolus pushed into hard palate by tongue
- sensory information from hard palate to medulla
- glossopharyngeal nerve sensory
- triggers involuntary phases of swallowing
PHARYNGEAL
- Involuntary
- Closure naspharynx (soft palate)
- Protection of laryngeal inlet
–> 1. Adduction vocal cords
–> 2. Adduction aryepiglottic folds
both 1 and 2 above - recurrent laryngeal nerve supply
–> 3. Elevation of hyoid (larynx moves superiorly and anteriorly.
–> 4, Epiglottis moves downward
- propulsion of food bolus by superior and middle pharyngeal constrictor muscles
Cricopharyngeus (upper oesophageal sphincter) relaxes to allow food bolus to pass into the oesophagus
- Medulla co-ordinates 1 - 2 seconds of apnoea during pharyngeal phase of swallowing.
OESOPHAGEAL
- Food enters oesophagus –> closure of UOS and partial opening of LOS
- peristalsis
- -> Primary peristaltic wave: medulla. Entire oesophagus regardless of location of food
- -> Secondary peristalsis –> local initiation induced by stretching of the oesophageal wall
- by the time food reaches LOS –> completely relaxed.
- then contraction of LOS to prevent acid reflux
Differentiate the speed of food bolus movement in the oesophagus vs. pharynx during swallowing
Pharynx: 30 cm/s
Oesophagus: 3 cm/s
Name the muscles involved in the pharyngeal phase of swallowing and their functions
Closure of nasopharyncx (soft palate)
Protection of laryngeal inlet
- Adduction vocal cords
- LATERAL CRICOARYTENOID
- OBLIQUE and TRANSVERSE ARYTENOIDS - Adduction aryepiglottal folds
- ARYEPLIGLOTTIC muscles - Elevation of hyoid
- DIGASTRIC and STYLOHYOID muscles
Movement of food bolus through larynx
- SUPERIOR AND MIDDLE PHARYNGEAL CONSTRICTORS
- CRICOPHARYNGEUS = UOS
Name three categories of causes that cause aspiration pneumonia
- Decreased level of consciousness
- Disorders of oesophagus
- GORD
- Stricture
- Tracheoesophageal fistula - Problems with swallowing
- Myaesthenia Gravis
- MND
- GBS
- Critical illness polyneuropathy
- Stroke
- Multiple sclerosis
How do the muscles fibres differ in the different regions of the oesophagus
Upper 1/3 = skeletal (striated) muscle
Lower 2/3 = Smooth muscle
What type of epithelium is present lining the oesophagus and when is this not the case?
Stratified squamous epithelium
Chronic GORD –> Barrett’s oesophagus –> normal mucosa replaced with columnar epithelium similar to that found in the gastric/duodenal mucosa (metaplasia)
What factors prevent reflux of stomach content into the oesophagus
BARRIER PRESSURE = difference between the LOS pressure (20 - 30 mmHg) and intragastric pressure (5 - 10 mmHg)
- LOS: distal 2 - 4 cm of oesophagus = tonic contraction
- Diaphragmatic contraction as oesophagus transverses
- Acute angle of passage into stomach
How does the resting pressure of the UOS and LOS differ
UOS = 100 mmHg LOS = 20 - 30 mmHg
Which factors decrease barrier pressure
- Swallowing
- Pregnancy (progesterone + Gravid uterus –> RAIP)
- Hiatus hernia (Loss of alignment with diaphragm + loss of acute angle of passageway into stomach
- Drugs
- Alcohol
- Volatiles
- Propofol and thiopentone
- Opioids
- Atropine and glycopyrrolate
Which anaesthetic drugs increase/decrease/no change LOS tone
Decrease
- Alcohol
- Volatiles
- Propofol and thiopentone
- Opioids
- Atropine & glycopyrrolate
Incrase
- Succinylcholine
- Neostigmine / Edrophonium
No effect
1. Non-depolarising muscle relaxants
Define Mendelson syndrome
Pneumonitis caused by pulmonary aspiration of gastric contents associated with general anaesthesia.
Aspiration > 25 ml of gastric fluid pH < 2.5 –> sufficient to cause severe pneumonitis
How is mendelson syndrome prevented during anaesthesia
- Preoperative starvation
- Free drain NGT in SBO + aspirated before induction
- Neutralize
- PPI / H2 block / non-particulate antacid (Na citrate) - RSI with cricoid pressure
- Semi-recumbent induction
