What is the entrace to the GI tract?
What does the mouth serve to do?
- Disrupts foodstuffs
- Mix foodstuffs with saliva to form boluses
What can happen once food boluses have been formed?
They can be swallowed
What is the function of teeth?
- Mix food with saliva
Which type of teeth cut?
Which type of teeth crush?
What generates the force behind the teeth?
The powerul muscles of mastication, the Masseter
What innervates the Masseter?
A branch of the trigeminal nerve
What is the tongue?
A collection of 8 muscles
What does the tongue do?
- Works to manipulate food for mastication and form it into a bolus
- Aids swallowing by pushing bolus to back of mouth
Label this diagram
- A - Nasopharynx
- B - Oropharynx
- C - Hypopharynx
- D - Esophagus
- E - Sinus
- F - Nasal cavity
- G - Salivary glands
- H - Oral cavity
- I - Trachea
Where does the oropharynx lie?
Behind the oral cavity
What does the oropharynx form?
The portion of the pharynx below the nasopharynx but above the laryngopharynx
Where does the oropharynx extend?
From the uvula (the end of the palate), to the level of the hyoid bone
What closes over the glottis?
A flap of tissue called the epiglottis
Why is the epiglottis needed?
To prevent aspiration, as both food and air pass through the oropharynx
What is the oesophagus?
A muscular tube
What is the function of the oesophagus?
It passes food from the pharynx to the stomach
What is the oesophagus continuous with?
The lower part of the laryngopharynx
What are the layers of the oesophagus?
- Muscularis externa
What is the mucosa of the oesophagus composed of?
- Non-keratinised stratified squamous epithelium
- Lamina propria
- Layer of smooth muscle (Muscularis Mucosa)
What does the submucosa of the oesophagus contain?
The mucous secreting glands
What kind of muscle is in the muscularis externa of the oesophagus?
- Upper third is striated, skeletal muscle, under conscious control
- Lower two-thirds are smooth muscle, under autonomic control
What is the function of the skeletal muscle in the upper third of the oesophagus?
What is the function of the smooth muscle in the lower two thirds of the oesophagus?
How much saliva is produced each day?
What are the function of saliva?
- Lubricates and wets food
- Starts digestion of carbohydrates
- Protects oral environment
How does saliva start the digestion of carbohydrates?
Through the presence of amylase
How does saliva protect the oral environment?
- Keeps mucosa moist
- Washes teeth
- Maintains alkaline environment
- High Ca2+ environment
What is the purpose of the alkaline environment maintained by saliva?
Neutralises acid produced by bacteria
What is zerostomia?
Insufficient saliva production
Can a patient with zerostomia still eat?
Yes, providing the food is moist, but teeth and mucosa degrade very quickly
What are the constituents of saliva?
Is saliva hypertonic or hypotonic?
Are the electrolytes in saliva at a higher or lower concentration than plasma?
- Na+ and Cl- usually at lower concentration than plasma
- Ca2+, K+, and I- are usually at higher concentration than plasma
What makes saliva alkali?
Is HCO3- in saliva at higher or lower concentration than in plasma?
What is salivary mucus?
A mixure of mucopolysaccharides
What enzymes are in saliva?
Can we survive without salivary amylase?
Yes, it is relatively minor
How many paired salivary glands are there?
What kind of glands are the salivary?
Describe the structure of salivary exocrine glands
- Made up of acini (blind-ended tubes), lined with acinar cells.
- The acini are connected via a system of ducts to a single outlet, lined by duct cells
What does the parotid glands secrete?
What is serous saliva?
Watery secretion, rich in enzymes, but little mucus
What % of saliva is secreted from the parotid glands?
What does sub-lingual glands secrete?
What is mucus saliva?
Viscous secretion, no enzymes but lots of mucus
What % of saliva is secreted from the sub-lingual glands?
What does the sub-maxillary glands secrete?
All components of saliva (mixed serous and mucus)
Briefly describe the structure of sub-maxillary glands
Mixture of serous and mucus acini leading to a common duct
What % of saliva is secreted from the sub-maxillary glands?
Label this diagram
- A - Parotid
- B - Sub-maxillary
- C - Sub-lingual
What is the cellular mechanism to secrete water?
How is hypotonic saliva secreted?
A more concentrated solution is secreted, and solute is then reabsorbed from it to leave the final hypotonic solution
What do acinar cells secrete?
An isotonic fluid containing enzymes
What do duct cells do?
Remove Na+ and Cl- from fluid secreted from acinar cells, and add HCO3-
How do duct cells ensure that saliva remains hypotonic?
The gaps between duct cells are tight, and so water does not follow the osmotic gradient resulting from ion movement
What happens at low flow rate of saliva?
Regarding duct cells
The duct cells have the opportunity to remove most Na+, so saliva is very hypotonic
Can duct cells modify flow rate of saliva?
Yes, but their ability to do so is limited
What happens at high flow rate of saliva?
Regarding duct cells
A smaller fraction of Na+ is removed, and the saliva becomes less hypotonic
What does the stimulus for secretion promote?
Regarding ion movement
HCO3- secretion, therefore the saliva becomes more alkaline
How are Cl- ions secreted from acinar cells?
What is the result of the active secretion of Cl- ions from acinar cells into the lumen of the duct?
Water and other ions (Na+) will follow passively
What transporter has a role in ductal modification?
The Na/K-ATPase Antiporter
Where is the Na/K-ATPase involved in ductal modification located?
In the basolateral membrane of duct cells
What is the effect of the Na/K-ATPase antiporter in the duct cell membrane?
Lowers [Na+] inside the cell. This means there is a concentration gradient, where [Na+] is high in the duct lumen, and low in the duct cells. Na+ diffuses passively back into the duct cells
Increases [K+] inside the cell. The resulting concentration gradient drives the expulsion of Cl- form the duct cells into the ECF. A concentration gradient is set up between the duct lumen and cells, with [Cl-] low inside, and [Cl-] high outside. This gradient drives the expulsion of HCO3- into the duct lumen.
Draw a diagram illustrating ion transport between the duct and the ECF
What is salivary secretion controlled by?
Mostly the autonomic nervous system
What is the effect of parasympathetic stimulation on the salivary gland?
- Increases the production of primary secretion (acinar cells)
- Increases the addition of HCO3- (duct cells)
What is the parasympathetic innervation of the parotid gland?
- Glossopharyngeal nerve (9th cranial nerve)
- Otic ganglion
What is the parasympathetic innervation of the submandibular and sublingual glands?
- Facial nerve (7th cranial nerve)
- Submandibular ganglion
What kind of receptors mediate the parasympathetic innervation of salivary glands?
What kind of drugs block the receptors responsible for parasympathetic innervation of the salivary glands?
What is the role of co-transmitters in the parasympathetic innervation of the salivary glands?
They stimulate extra blood flow
What is parasympathetic outflow to the salivary glands mediated by?
- Centres in the medulla
- Afferent information from the mouth and tongue, nose, and conditioned reflexes
What parts of the mouth and tongue mediate parasympathetic outflow to the salivary glands?
Taste receptors, especially acid
What shows the effect of conditioned reflexes on the outflow to salivary glands?
What is the effect of sympathetic stimulation on the salivary glands?
Reduces blood flow, limiting salivary flow and producing the typical dry mouth of anxiety
What provides sympathetic innervation to the salivary glands?
Superior cervical ganglion
What increases the rate of ductal recovery of Na+?
The release of aldosterone from the adrenal cortex (increase in ENaC, therefore increase in Na/K-ATPase)
What is the result of the increase in ductal recovery of Na+?
Makes saliva even more hypotonic
What must happen once food has been matiscated and mixed with saliva to form a bolus?
It must be swallowed
What are the phases of swallowing?
- Voluntary phase
- Pharyngeal phase
- Oesophageal phase
What happens during the voluntary phase of swallowing?
Tongue moves the bolus back onto the pharynx
What happens during the pharyngeal phase of swallowing?
- Afferent information from pressure receptors in the palate and anterior pharynx reaches the swallowing centre of the brain stem
- A set of movements is triggered
What movements are inhibited in the pharyngeal phase of swallowing?
- Inhibition of breathing
- Raising of the larynx
- Closure of the glottis
- Opening of the upper oesophageal 'sphincter'
What kind of muscle is found in the upper third of the oesophagus, and what kind of control is it under?
- Striated muscle
- Under voluntary, somatic control
What kind of muscle is found in the lower two thirds of the oesophagus, and what kind of control is it under?
- Smooth muscle
- Parasympathetic control
What happens in the oesophageal phase of swallowing?
A wave of peristalsis sweeps down the oesophagus, propelling the bolus to the stomach
How long does the oesophageal phase take to propel the food bolus to the stomach?
What is the oesophageal phase of swallowing coordinated by?
Extrinsic nerves from the swallowing centre of the brain
What happens once the food bolus has been propelled to the stomach by the oesophageal phase?
The lower oesophageal 'sphincter' opens
What is dysphagia?
The symptom of difficulty in swallowing
What is odynophagia?
The symptom of pain whilst swallowing
What may dysphagia be a consequence of?
- A primary oesophageal disorder
- A secondary consequence of another tissue
Give an example of a primary oesophageal disorder causing dysphagia?
What is achalasia?
Motility problems of the smooth muscle preventing peristalsis
Give an example of a secondary condition that may cause dysphagia?
Obstruction or compression of the oesophagus due to a tumour
Broadly speaking, what can dysphagia be split into?
- Dysphagia for solids
- Dysphagia for liquids
What is dysphagia for solids called?
How is oesophageal dysphagia investigated?
Barium swallow or endoscopy
What is dysphagia for liquids called?
How is oropharyngeal dysphagia investigated?
A flexible endoscopy evaluation of swallowing
What does a flexible endoscopy evaluation of swallowing allow?
For you to view the entire trachea/oesophagus
What is oropharyngeal dysphagia most commonly due to?
What does the stomach produce to aid the digestion of food?
- Strong acids (HCl)
- Enzymes (pepsin)
What protects the stomach from its potentially harmful products?
The mucosa of the stomach
How is the oesophagus protected from the potentially harmful products of the stomach?
By a one way valve mechanism at it's junction with the stomach
Does not have the mucosal protection that the stomach does
What is the one way valve protecting the oesophagus from stomach products called?
The lower oesophageal sphincter
What is the lower oesophageal sphincter coupled with?
The angle of His, which is formed at this point
What does the lower oesophageal sphincter and the angle of His work together to do?
Prevent the contents of the stomach refluxing back into the oesophagus
What does the crus of the diaphragm do?
Helps with the sphincteric action
What are the clinical consequences of free gastro-oesophageal reflux?
- Barrett's Oesophagus
- Gastro-oesophageal reflux disease (GORD)
What is Barrett's Oesophagus?
An abnormal change in epithelial cells of the oesophagus
What is the pathological process in Barrett's Oesophagus?
This is a metaplasia from non-keratinised stratified squamous epithelia to columnar epithelium and goblet cells.
This is an attempt to better resist the harmful contents of the stomach
What is Barrett's oesophagus strongly associated with?
Adenocarcinoma, a particularly lethal cancer
What happens in GORD?
The reflex of the stomach's contents into the oesophagus and pharynx causes several symptoms, including;
All symptoms result from the acidic contents of the stomach refluxing back out