Lacrimal Flashcards
What are the three components of the lacrimal system?
secretory, distribution, elimination
what does decretory system of lacrimal system do?
produce majority of tear fluid - aqueous
divided into 2 portions/lobes by levator aponeurosis - orbital lobe and palpebral
lobes connected by ducts to open into conjunctival fornix.
What is a tubulo-acinar gland? What is the relationship to intralobular ducts?
Tubulo-acinar gland contain many acini (clusters of secretory cells) which join to form intralobular ducts.
Intralobular ducts then drain the lacrimal gland into the surface of the eye.
What is the purpose of the accessory lacrimal glands and where are they located?
The accessory lacrimal glands produce 10% of the aqueous production
Krausse - fornix
Wolfring – along orbital margin of tarsal plate
How is the lacrimal gland innervated?
Autonomic input
Parasympathetic
Sympathetic
Sensory input
Via lacrimal nerve (branch of trigeminal nerve)
What are anatomical structures surrounding the lacrimal sac?
Horner’s muscle and medial palpebral ligament surround the lacrimal sac. When horner’s muscle contracts, pushes tears out of lacrimal sac past the Hassner’s valve
What is the importance of the hydrophilic nature of mucins?
Helps to wet the ocular surface
What are the functional roles of the tear film?
Osmotic boundary – maintaining corneal hydration
Gas, nutrient, and waste solvent for exchange with avascular cornea
Optical Boundary
Lubricant
Protection - antimicrobial
How do you maintain tear film stability?
temperature, humidity, gland outputs and blink rates
What is a result from lack of tear film stability?
Short tear film break up time
Keratoconjunctivitis Sicca (dry eye)
What are the reasons for tear secretion?
Basic secretion
No obvious external stimuli
Reflex secretion
Tear production when external stimuli lead to c
increased tear production (irritation)
Emotional/psychogenic secretion
Discuss the three components of the tear film and secretions?
Mucin
Goblet cells in conjunctival epithelium – stored in
secretory granules within goblet cells (crypts of
Henle – pockets of mucin secreting cells present)
Maintain hydration and lubrication of cornea and
conjunctiva, protect ocular surface by coating
foreign bodies and helps wet ocular surface
(hydrophilic)
Aqueous
Secreted by lacrimal gland (accessory glands of
krausse and wolfring)
Makes bulk of tear film, maintains pH and
osmolaritiy of tears, provides oxygen and
nutrients and waste removal for cornea and
antibacterial components
Lipid
Secreted by meibomian glands (zeis and moll)
Reduces evaporation stabilising tear film, prevents
overflow of ears, smooth optical surface, prevents
contamination of tear film by skin lipids
What is the difference between basic and reflex secretions?
Reflex Secretions
Due to external stimulus (initiates neural signals)
Increases tear production
Can produce up to 100x tear volume
Main secretors of lacrimal gland – main lobe and
accessory lobe
Basic Secretions
Natural secretory
No obvious external stimuli
What are the microscopic components of the lipid layer of the tear film?
Hydrophobic outer layer protects water from escaping as non-polar
Hydrophilic inner layer bonds to the aqueous component (polar)
What are the microscopic components of the aqueous layer of the tear film?
Water
Electrolytes
Proteins
What are the microscopic components of the mucin layer of the tear film?
No distant division between aqueous and mucin
Two phase – one with more mucin the other with less mucin
Glycocalyx is the glycoprotein layer attached to the surface epithelium cells (stratified squamous cells of cornea and conjunctiva)
More about the glycocalyx
Glycoprotein present in membrane bound vesicles within the epithelium cells that fuse to the cell membrane to release the glycocalyx
Contributes to the wetability of the epithelium surface cells and bonds the mucin layer to the epithelium
Surface area for bonding increased by epithelium microvilli
What is the thickness of the tear film?
2-5um
Decreases rapidly after blinking