Gastrointestinal Flashcards
What are the 4 functions of saliva?
- Lubricant for mastication, swallowing and speech
- Oral hygiene - wash, buffer and immunity (antiviral/bacterial/fungal)
- Maintains oral pH at about 7.2 (bicarbonate/carbonate buffer system)
- Digestive enzymes - aqueous solvent necessary for taste
What is the typical flow rate of saliva?
0.3 - 7 ml/minute
What is the typical daily secretion of saliva?
800 - 1500 ml in adults
What factors affect the composition and amount of saliva produced?
- Flow rate
- Circadian rhythm
- Type and size of gland
- Duration and type of stimulus
- Diet
- Drugs
- Age
- Gender
What are the three major glands and what do they secrete?
- Parotid - just serous
- Submandibula - both serous and mucous
- Sublingular - mainly mucous, some serous
What is secreted in serous fluid?
Alpha amylase - used for starch digestion
What is secreted in mucous fluid?
Mucins for lubrication of mucosal surfaces
What is saliva?
A secretion of proteins and glycoproteins in a buffered electrolyte solution
What glands are continuously active?
- submandibular
- sublingual
- minor glands
When does the parotid gland secrete saliva?
- no secretion when unstimulated
- main source of saliva when stimulated
What is whole saliva?
- Salivary gland secretions
- Blood
- Oral tissues
- Microorganisms
- Food remnants
What defends the oral cavity?
> Mucosa - physical barrier
Palatine tonsils - surveillance system for the immune system
Salivary glands - washes away food particles bacteria/viruses might use for metabolic support
How do the salivary glands aid immunity?
> Surrounded by lymphatic system - linked to thoracic duct and blood
Broad range of functional immune cells
Oral mucosa and glands have a high blood flow rate
What is the main component of unstimulated saliva?
submandibular gland secretion
What is the main component of stimulated saliva?
parotid gland secretion
What common illnesses can now be diagnosed using saliva testing?
cystic fibrosis
tuberculosis
What two tissues compose salivary glands?
> duct cells - collect to form large ducts entering the mouth, equipped with channel transporters (surrounded by acinar cells)
acinar cells - functional unit of gland
What do serous acini look like on a histology slide?
- dark stained
- nucleus in the basal third
- small central duct
- secrete water and alpha amylase
What do mucous acini look like on a histology slide?
- pale staining (foamy)
- nucleus at base of cell
- large central duct
- secrete mucous (water and glycoproteins)
Intralobular ducts divide into what?
intercalated
striated
What are intercalated ducts?
- short narrow duct segments with cuboidal cells that connect acini to larger striated ducts
What are striated ducts?
- striated like a thick lawn
- major site for the reabsorption of NaCl
What do striated ducts look like on a histology slide?
- appear striated at the basal end
- basal membrane highly folded into microvilli for active transport of HCO3 against concentration gradient
- microvilli filled with mitochondria for energy to facilitate active transport
How do ducts modify the electrolyte composition of saliva?
> ducts secrete K+ and HCO3-
ducts reabsorb Na+ and Cl-
epithelium doesn’t allow water movement so final saliva is hypotonic
What percentage of salivary flow do the three main glands contribute to?
80%
What percentage of salivary flow do the minor glands contribute to?
20%
Where are the minor glands found?
submucosa or oral mucosa of the lips, cheeks, hard and soft plate and the tongue
Where is the parotid gland found?
Superficial triangle between the:
- zygomatic arch
- sternocleidomastoid
- ramus of mandible
Where does the parotid duct run through?
(also called Stenson’s duct)
- crosses the masseter muscle
- pierces through buccinator muscle
- can be palpated a fingers breadth below the zygomatic arch
How is the parotid gland innervated?
> sympathetic sensory innervation (inhibits secretion) from the auriculo-temporal nerve
parasympathetic innervation (stimulates secretion) from the glossopharyngeal nerve (IX)
What structures pass through the parotid?
- External carotid artery
- Retromandibular vein
- Facial nerve (VII) - supplies muscles of facial expression
Is the parotid capsule tough or soft?
Tough (to protect its contents)
What is the shape of the lobes of the submandibular glands?
- Larger superficial lobe
- Smaller deep lobe in the floor of the mouth
What is another name for the submandibular duct?
Wharton’s duct
What is the course of the submandibular duct?
- begins in superficial lobe
- wraps around free posterior border of mylohyoid
- runs along floor of mouth
- empties into the oral cavity at sublingual papillae
How are the submandibular glands innervated?
> sympathetic innervation from chorda tympani brach of the facial nerve (VII)
parasympathetic innervation from lingual nerve (derived from facial nerve)
very similar to sublingual
Where are the sublingual glands positioned?
Between the mylohyoid muscle and oral mucosa of the floor of the mouth
Very close to the submandibular gland
How is saliva from the sublingual glands transmitted?
- via Wharton’s (submandibular) duct
- or small ducts that pierce the oral mucosa on the floor of the mouth
What are bigger the submandibular or sublingual glands?
Submandibular glands are larger but size is variable
How are the sublingual glands innervated?
> sympathetic innervation from chorda tympani branch of the facial nerve (VII)
parasympathetic innervation from the lingual nerve (derived from facial nerve)
very similar to submandibular
What regions are the minor salivary glands concentrated?
- buccal labial
- palatal
- lingual
What do the minor salivary glands secrete?
> ALL mucous
APART from serous glands of von Ebner (underlying circumvallate papillae)
How do minor glands drain?
They lack a branching network of ducts
Each salivary unit has its own simple duct
What is the medical name for dry mouth?
Xerostomia
What are the most common causes of xerostomia?
- consequence of cystic fibrosis
- consequence of Sjorgren’s syndrome (autoimmune attacking glands)
- drug side effects
- side effect of irradiation for head/neck cancers
What is a common cause of obstruction in the salivary glands?
> Saliva contains calcium and phosphate ions that can form salivary calculi (stones)
Most often in the submandibular gland (c 80%)
Often blocks the duct at the bend around the mylohyoid, or exit at sublingual papillae
What is the cause of inflammation of the salivary glands?
Infection secondary to blockage
How low does salivary output have to be to be classed as xerostomia?
less than 50% of normal flow
What are the effects of salivary gland dysfunction?
> low lubrication - oral function difficult
low (natural) oral hygiene - poor pH control, accumulation of plaque, opportunistic infections
What are the functions of the stomach?
- store and mix food
- dissolve and continue digestion
- regulate emptying into duodenum
- kill microbes
- secrete intrinsic factor and proteases
- activate proteases
- lubrication
- mucosal protection
What are the 6 key cells types?
Mucous cells - produce mucous, at entrance to gland
Parietal cells - produce HCl and intrinsic factor
Chief cells - produce pepsinogen
Enterochromaffin-like (ECL) cells - releases histamine
G cells - releases gastrin
D cells - releases somatostatin
Approximately how much gastric acid is secreted a day?
Approx. 2 Litres
What is the main component of gastric acid?
Hydrochloric acid
What is the secretion of gastric acid dependant on?
Energy dependant (goes against the concentration gradient)
Regulated by neural and humoral factors (nerves + hormones)
Turning on gastric acid secretion - Cephalic phase
Regulated by the sympathetic nervous system
- sight, smell, taste of food, chewing -> causes acetylcholine (ACh) release
- ACh acts directly on parietal cells -> triggers release of gastrin & histamine
net effect = increase acid production
Turning on gastric acid secretion - Gastric phase
- gastric distention, presence of peptides an amino acids -> causes gastrin release
- gastrin acts directly on parietal cells -> triggers the release of histamine which acts directly on parietal cells
net effect = increased acid production
