Week 2 - Salivation and Swallowing, GI Embryology Flashcards
What nerve supplies the muscles of mastication?
Trigeminal nerve
How much saliva is produced each day?
1.5 litres
List some functions of saliva.
- Protects oral environment by keeping it moist and relatively alkaline
- Initiates carb digestion: salivary amylase
- Aids swallowing by helping to form a food bolus
List some effects of poor saliva production.
- Dental hygiene would suffer: dental caries and infections
- Much harder to chew and swallow food
- Harder to speak
State the components of saliva.
- Water
- Electrolytes
- HCO3-
- Bacteriostats
- Mucus
- Enzymes
Which ions are added to saliva?
K+
HCO3-
Which ions are removed from saliva?
Na+ and Cl-
State the properties of saliva that is produced in low amounts - low rate of production.
- More hypotonic
- Neutral/even slightly acidic
- Fewer enzymes compared to saliva produced in larger amounts
Saliva produced under which conditions has higher enzyme content - resting or stimulated?
Stimulated
Saliva produced under which conditions is more alkaline - resting or stimulated?
Stimulated
State three situations in which saliva production would be reduced.
- Dehydration
- Certain medications: muscarinic antagonists
- Disease: e.g. Sjogrens
At which point does the parotid duct penetrate the buccinator?
Opposite the crown of the 2nd upper molar tooth
Which cranial nerve innervates the parotid gland?
IX Cranial nerve - Glossopharyngeal nerve
Which division of the autonomic nervous system stimulates secretion of saliva rich in organic content?
Sympathetic
Which cranial nerve supplies the submandibular and sublingual glands?
Cranial nerve VII: A branch of the facial nerve called chorda tympani
John had a recent middle ear infection for which he received antibiotic treatment. Shortly afterwards, he started to feel that his mouth felt dry. What might be a possible explanation?
Loss of parasympathetic supply by chorda tympani to the submandibular and sublingual glands
Chorda tympani runs through the middle ear: infection in this area can damage this nerve
Outline the steps involved in the oral preparatory phase of swallowing.
0-7.4
- Voluntary
- Pushes bolus towards pharynx
- Once bolus touches pharyngeal wall, pharyngeal phase begins
Outline the steps involved in the pharyngeal phase of swallowing.
- 4-7.6
- Involuntary
- Soft palate seals off nasopharynx
- Pharyngeal constrictors push bolus downwards
- Larynx elevates closing epiglottis
- Vocal cords adduct, protecting airways and breathing temporarily ceases
- Opening of UOS
Outline the steps involved in the oesophageal phase of swallowing.
- 6 onwards
- Closure of the upper oesophageal sphincter
- Peristaltic wave carries bolus downwards into stomach
- Involuntary
Outline the pathway involved in the neural control of swallowing and the gag reflex.
Mechanoreceptors –> Glossopharyngeal nerve –> Medulla –> Vagus nerve –> Pharyngeal constrictors
State the anatomical narrowings present in the oesophagus.
- Junction of the pharynx and upper oesophageal sphincter
- Where it crosses the aortic arch and is crossed by the left main bronchus
- Where it penetrates the diaphragm
List three areas where presence of a tumour might make swallowing difficult.
- Oesophagus
- Oropharynx
- Cardia of the stomach
State symptoms for an upper GI malignancy (for example, oesophagus, cardiac of stomach, or oropharynx tumours).
- Dysphagia
- Weight loss
- Pain
- Malaena
- Haematemesis
Explain how a stroke (cerebrovascular accident) can make swallowing fluids more difficult than solids.
- Coordination of swallowing affected
- Fluid needs to be guided carefully into the oesophagus to avoid aspirating material into the airways
- Cerebrovascular accident can affect motor portions of the cerebral cortex/ pathways (corticobulbar tracts) that connect the cerebral cortex to the brain stem
- Damage to either - deficits in the cranial nerves that originate in the pons and medulla areas - corresponding deficit in control of the muscles of the tongue, larynx and pharynx
What is the term used for:
a. Dysphagia for solids (food sticking after swallowing)?
b. Dysphagia for liquids (initiating the swallow or choking)?
a. Oesophageal dysphagia
b. Oropharyngeal dysphagia
What technique(s) can be used to investigate oesophageal dysphagia?
- Upper GI endoscopy
2. Barium swallow
What technique(s) can be used to investigate oropharyngeal dysphagia?
- Video fluoroscopy: allows phases of swallowing to be evaluated which is particularly useful when assessing neurological disease
Define odynophagia.
Painful swallowing
State some possible causes of odynophagia.
- Oesophageal candidiasis or other causes of oesophagitis
- Peptic ulcerations
- Cancers within the oropharynx/oesophagus
What will the splanchnic mesoderm that lines the external lining of the primitive gut tube develop into?
- Smooth muscle of the viscera and blood vessels
2. Visceral peritoneum
What is the vitelline tract?
A narrow tube that joins the yolk sac and the midgut and generally obliterates during the 7th week of fertilisation
What is the result of the vitelline tract persisting throughout development?
Meckel’s diverticulum
Where does the foregut start and end?
Starts: oesophagus
Ends: 2nd part of duodenum
Where does the hindgut start and end?
Starts: 2/3rd of the way along the transverse colon
Ends: upper anal canal
What are mesenteries?
Double layers of peritoneum that suspend the gut tube from the abdominal wall
What structure develops in the ventral mesentery of the foregut?
Liver
During what week of development does respiratory diverticulum develop in the ventral wall of the foregut?
4th week
What congenital problems arise from abnormal development of the septum that divides the oesophagus and trachea?
Tracheo-oesophageal fistula
What is the underlying pathology in Sjogren’s syndrome?
Autoimmune destruction of the salivary glands
Explain why people with xerostomia are prone to oral infections.
Saliva has anti-microbial properties - loss of this may lead to opportunistic infections, e.g. With Candida
State the risk factors for Barrett’s oesophagus.
- Smoking
- Overweight
- Age: 50-70
- Long-standing GORD
What week does primitive gut tube development begin in?
3rd week
Outline the adult derivative of endoderm.
- Future epithelial linings
2. Internal lining of the GI tract
Outline the adult derivatives of splanchnic mesoderm with relation to the GI tract.
- Future musculature
2. Visceral peritoneum
Outline the cranial and caudal points of the primitive gut tube.
Stomatodeum - future mouth (rostrally)
Proctodeum - future anus (caudally)
Outline the adult derivatives of the foregut.
- Oesophagus
- Stomach
- Liver, gall bladder, pancreas
- Duodenum (proximal to entrance of bile duct)
Outline the adult derivatives of the midgut.
- Duodenum: distal to entrance of bile duct
- Jejenum
- Ileum
- Cecum
- Ascending colon
- Proximal 2/3 of transverse colon
Outline the adult derivatives of the hindgut.
- Distal 1/3 of transverse colon
- Descending colon
- Sigmoid colon
- Rectum
- Upper anal canal
- Internal lining of bladder and urethra
Outline the blood supply of the duodenum.
Proximal to entry of bile duct: gastroduodenal artery and superior pancreaticoduodenal artery (CT)
Distal to entry of bile duct: inferior pancreaticoduodenal artery (SMA)
Outline the blood supply of the head of the pancreas.
Superior pancreaticoduodenal (CT) and inferior pancreaticoduodenal artery (SMA)
Define mesentery.
A double layer of peritoneum that suspends the gut tube from the abdominal wall
State the functions of mesenteries.
- Allow a conduit for blood and nerve supply
2. Provide mobility where needed
How are mesenteries formed?
- Primitive gut tube becomes suspended in the intraembryonic coelom
- Gut tube is surrounded by splanchnic mesoderm
- Mesenteries formed by a condensation of this mesoderm
At the point of the free edge, what anatomical structure is entered?
Lesser sac
Which embryological division can a ventral mesentery be found?
Foregut
State the position of the parotid gland.
Wraps around the ramus of the mandible
State the position of the sublingual gland.
Inferior surface of the tongue
Which ion is secreted in greater quantities into saliva at high flow rates?
Bicarbonate
What substances does the solution secreted by acinar cells in salivary glands contain?
- Water
- Electrolytes
- Mucus
- Alpha amylase
- Lingual lipase
- Kallikrein
What is the function of myoepithelial cells in salivary glands?
Contract and facilitate ejection of saliva into the mouth - move saliva from acinar structure into the mouth
What is the function of kallikrein?
- Enzyme which facilitates production of bradykinin
- Bradykinin allows vasodilation of blood vessels to allow blood flow to reach the salivary glands (which can require 10 times as much blood flow compared to skeletal muscle)
Which salivary gland produces per volume the most saliva?
Submandibular gland
What forms the lesser sac?
The right sac - comes to lie behind the stomach
What forms the greater sac?
The left sac
What are omenta?
Specialised regions of peritoneum
What is the greater omentum formed from?
Dorsal mesentery
What is the lesser omentum formed from?
Ventral mesentery
What does the free edge of the ventral mesentery conduct?
Portal triad
In which directions does the stomach rotate?
- Around the longitudinal axis
2. Around the antero-posterior axis
What is the result of stomach rotation?
- Greater and lesser curvature come to lie first on the right and left side
- Cardia and pylorus move horizontally, pushing the greater curvature inferiorly
Describe the consequences of rapid liver growth and rotation of the stomach.
- Structures on right hand side pushed to the posterior of the stomach
State the outcomes of rotation of the stomach.
- Vagus nerves lie anterior and posterior to stomach, instead of left and right
- Shifts cardia and pylorus from the midline: stomach lies obliquely
- Contributes to moving the lesser sac behind the stomach
- Creates the greater omentum
What is a peritoneal reflection?
Change in direction of the peritoneal membrane:
- Parietal peritoneum –> mesentery
- Mesentery to visceral peritoneum
- Visceral peritoneum to, etc..
What are retroperitoneal structures?
- Structures not suspended within the abdominal cavity: retroperitoneal
- Were never in the peritoneal cavity and never had a mesentery
What are secondarily retroperitoneal structures?
- Began development invested by peritoneum and had a mesentery
- With successive growth and development - mesentery lost through fusion at posterior abdominal wall
From and to where does the foregut extend?
Extends from the lung bud to the liver bud
Outline how part of the respiratory system develops from the foregut.
- In the fourth week, a respiratory diverticulum develops from the ventral wall of the foregut at the junction with the pharyngeal gut
- Respiratory primordium (ventrally)
- Oesophagus (dorsally)
