GI and Liver Flashcards
How is swallowing initiated?
Initiated when pressure receptors in the walls of the pharynx are stimulated by food or drink, forced into the rear of the mouth by the tongue
What is the innervation of the nasopharynx, oropharynx, and laryngopharyx?
- Nasopharynx: Maxillary nerve (V2 (second branch of trigeminal nerve (V))
- Oropharynx: Glossopharyngeal nerve (IX)
- Laryngopharynx: Vagus nerve (X)
What is step 1 of the process of swallowing?
Voluntary:
- Food is compressed against the roof of the mouth and pushed towards the oropharynx by the action of the tongue
- The buccinator & supra hyoid muscles manipulate food during chewing. They also elevate the hyoid bone and flatten the floor of the mouth
What is step 2 of the process of swallowing?
Involuntary:
- The nasopharynx is closed off by the soft palate via the action of the muscles of
the palate which tense & elevate it - helping to form the bolus of food
- The pharynx is also shortened & widened (using longitudinal muscles) by the
elevation of the hyoid bone via the actions of the muscles of the floor of the palate
which depress (lower) the mandible if the hyoid bone is fixed or elevate (raise) the
hyoid bone & larynx if the mandibles is fixed - Impulses from the swallowing centre inhibit respiration, raise the larynx (as
mentioned above) and close the glottis (the area around the vocal cords and the space
between them) - keeping food from entering the trachea - As the tongue forces the food farther back into the pharynx the food tilts the epiglottis
backward to cover the closed glottis - this prevents aspiration of food - a
dangerous situation where food travels down the trachea and can cause choking or
regurgitated stomach contents are allowed into the lungs causing damage
What is step 3 of swallowing?
Involuntary:
- Pharyngeal constrictor muscles - 3 overlapping muscles that form the posterior & lateral sides of the pharynx - innervated by vagus (X). They contract sequentially from above down to drive the bolus into the oesophagus
- Depression of the hyoid bone and pharynx is carried out by the infra hyoid muscle of the neck - they fix the hyoid bone enabling the opening of the mouth.
What is the fourth and final step of swallowing?
The next stage of swallowing occurs in the oesophagus:
- Skeletal muscle surrounds the upper third of the oesophagus
- Smooth muscle surround the lower two-thirds of the oesophagus
- The luminal pressure in the pharynx at the opening to the oesophagus is equal to the atmospheric pressure and the pressure at the opposite end of the oesophagus in the stomach is slightly greater than atmospheric pressure. Thus these pressure differences tend to force both air from above and gastric contents from below into the oesophagus - however this does not occur due to the presence of sphincter muscles at both ends of the oesophagus.
- A ring of skeletal muscle surround the oesophagus just below the pharynx - called the upper
oesophageal sphincter
- A ring of smooth muscle surround the oesophagus in the last portion of the oesophagus - called the lower oesophageal sphincter
- Before food can enter the oesophagus the upper oesophageal sphincter relaxes - immediately after the food has passed through the sphincter closes, the glottis opens and breathing resumes
- Once in the oesophagus, the food moves towards the stomach by a progressive wave of muscle contractions that proceed along the oesophagus, compressing the lumen and forcing the food ahead - these are peristaltic waves
- One oesophageal peristaltic wave takes 9 seconds to reach the stomach
- The lower oesophageal sphincter opens and remains relaxed throughout the process of swallowing, allowing the arriving food to enter the stomach
Explain the gag reflex?
• The reflex elevation of the pharynx - often followed by vomiting cause by irritation
of the oropharynx - the back of the tongue
• Reflex arc between the glossopharyngeal (IX) and the vagus (X) nerves
What are the functions and features of saliva?
Functions:
- Lubricant for mastication
- Maintaining oral pH: needs to be maintained at about pH 7.4 (slightly alkaline) this is
achieved by the bicarbonate/carbonate buffer system for the rapid neutralisation of
acid
- Release digestive enzyme - salivary alpha amylase is released from the parotid gland for starch digestion
Features:
• Daily secretion = 800 -1500ml in adults
• pH ranges from 6.2 to 7.4
Serous secretion = alpha amylase for starch
digestion
• Mucous secretion = mucins for lubrication of
mucosal surfaces
What are the three main salivary glands and what percentage of salivary flow do they contribute?
Submandibular gland, Parotid gland, Sublingual Gland.
They contribute 80% of salivary flow
What are minor salivary glands?
Minor salivary glands contribute to 20% of salivary flow - they are found in the submucosa or the oral mucosa of the lips, cheeks, hard & soft plate and the tongue
Which glands have mucous secretions and which have serous secretions?
Parotid: Serous
Submandibular: Mucous and Serous
Sublingual: Mucous and Serous (mainly mucous)
Minor glands: Predominantly mucous (but some are serous)
What are the Factors affecting the composition & amount of saliva produced?
Flow Rate Circadian Rhythm (Sleep Cycle) Type and Size of Gland Duration and type of stimulus that causes saliva to be produced Diet Drugs Age Gender Time of Day
Defences of the oral cavity are provided by?
The Mucosa: Physical barrier
Salivary glands: Saliva washes away food particles
which bacteria or viruses may use as metabolic support
Palatine tonsils: act as the “surveillance system” for the immune system
Salivary glands are surrounded by lymphatic system(linked to thoracic duct and
blood): which contains a broad range of functional immune cells
Which glands are continously active and which require stimulation?
Submandibular: Continuously Active (Unstimulated components of the salivary system are dominated by submandibular components)
Sublingual: Continuously Active
Parotid: Requires stimulation to become main source of saliva
Minor Glands: Continuously Active
What is the structure of salivary glands?
Composed of two morphologically and distinct epithelial tissues:
Acinar Cells
(functional unit of a salivary gland)
There are two types of acini:
- Serous acinus:
- Dark staining nucleus
- Nucleus in basal third
- Small central duct
- Secrete: water & alpha amylase
- Found mainly in the parotid gland - Mucous acinus:
- Pale staining “foamy”
- Nucleus at base
- Large central duct
- Secrete: mucous (water & glycoproteins)
- Found in submandibular & sublingual glands
Ducts (surrounded by acinar cells)
collect to form the large cut entering the mouth. Equipped with channels and transporters in the apical and basolateral membranes enabling transport of fluid and electrolytes
- Intralobular ducts are divided into intercalated & striated
- Intercalated:
• Short narrow
duct segments with cuboidal cells that
connect acini to larger striated ducts - Striated:
• Striated like a thick lawn
• Major site for reabsorption of NaCl
• Appear striated at basal end
• Basal membrane is highly folded into microvilli (giving the duct its striated appearance) for active transport of HCO3 against concentration gradient, the
microvilli are filed with mitochondria for energy to facilitate the active transport
The epithelium of the ducts reabsorbs water so final saliva is hypotonic (has less water in it so have a higher concentration of solutes (K+ & HCO3-)
What is the Structure and location, Structures passing through, and Innervation of the Parotid gland?
Structure and location: Superficial triangular outline between: - Zygomatic arch - Sternocleidomastoid - Ramus of mandible •Parotid duct: -Also called Stenson’s duct - crosses masseter muscle and pierces through the buccinator muscle where it enters the oral cavity near the second upper molar - Can be palpated a fingers breadth below the zygomatic arch
Structures passing through:
- External carotid artery
- Retromandibular vein
- Facial nerve (VII - exits skull through the
stylomastoid foramen) - supplies the muscles of facial expression
- Thus the parotid capsule is very tough
• The parotid glands are entirely made up of serous acini with ducts interspersed
Innervation:
- Sympathetic sensory innervation (inhibits/minimises secretion) is provided by the auriculo-temporal nerve which is a branch of the mandibular nerve (V3 - this
division of the trigeminal nerve exits the skull through the foramen ovale)
- Parasympathetic innervation is supplied by glossopharyngeal nerve (IX) - stimulates secretion
• Horizontally it has a triangular outline with the apex on the carotid sheath
What is the Structure and location and Innervation of the submandibular gland?
Structure and location:
Two lobes separated by mylohyoid muscle - larger superficial lobe and a smaller
deep lobe in the floor of the mouth
• The submandibular duct (Whartons duct) begins in the superficial lobe, wraps around the free posterior border of the mylohyoid, then runs along the floor of the mouth and empties into the oral cavity at the sublingual papillae - located more posteriorly than the sublingual gland
Innervation:
Parasympathetic innervation is supplied by the chorda tympani branch of the facial nerve (VII)
- Sympathetic innervation is supplied via the lingual nerve which is derived from the facial nerve (VII)
What is the Structure and location and Innervation of the sublingual gland?
Structure and location:
located more anteriorly than the submandibular glands
Located in the floor of the mouth between mylohyoid muscles and oral mucosa of
floor of mouth
• Very close to the submandibular gland
• Saliva is transmitted via the submandibular/
whartons duct as well or small ducts that pierce oral
mucosa floor of mouth
• Much smaller than submandibular - but size is variable
Innervation:
- Similar to submandibular gland
- Parasympathetic innervation is supplied by the chorda tympani branch of the
facial nerve (VII)
- Sympathetic innervation is supplied via the lingual nerve which is derived from the facial nerve (VII)
What is the Structure and location and Innervation of the minor salivary glands?
Structure and location:
Concentrated in the; buccal labial, palatal & lingual regions
• Also found at; superior pole of tonsils (Weber’s glands), tonsillar pillars & at the base
of the tongue (von Ebner’s glands - underlying circumvallate papillae)
• All minor salivary glands are mucous EXCEPT for the serous glands of von Ebner
• They lack a branching network of draining ducts so each salivary unit has its own simple duct
Innervation:
• PARASYMPATHETIC = stimulates salivary secretion
• SYMPATHETIC = inhibits salivary secretion (but some baseline secretion)
What is Xerostomia?
Dry Mouth, classified by If salivary output falls to
less than 50% of normal flow
What are the causes of xerostomia?
• medication and irradiation for head and neck cancers
• Obstruction:
- Saliva contains calcium & phosphate ions that can from salivary calculi (stones)
- Most common in submandibular gland (80% incidence) - they block the duct at the
bend around the round mylohyoid or at exit at the sublingual papillae
• Inflammation:
- Caused by infection secondary to obstruction
- Infections caused by; mumps (viral infection) - results in fever, malaise, swelling of the glands
• Degeneration:
- Complication of radiotherapy to head and neck for cancer treatment
- May be a consequence of cystic fibrosis or Sjorgren’s syndrome (autoimmune
condition where immune cells attack glands resulting in little or no saliva produced -
affects mainly women)
What are the consequences of xerostomia?
• Low lubrication - oral function becomes difficult
• Low natural oral hygiene -poor pH control =accumulation of plaque =dental caries or increases
incidence of opportunistic infections especially fungal
e.g candida - thrush
What is the name for an oral cancer?
Squamous cancer, Squamous tumours respond well to radiotherapy and chemotherapy
What epithelium is present in salivary glands?
Secretory Glandular epithelium