Lacrimal Glands and Conjunctiva Flashcards
What is the function of the Main Lacrimal Gland
Primary provider of the aqueous secretory component to the tear film
Where is the lacrimal gland located?
In the fossa
What are the two lobes of the lacrimal gland?
Orbital (larger/ above) and Palbebral (below)
Where is the lacrimal gland divided?
Divided by the lateral horn of the levator and extensions of the Müller’s muscle into an orbital lobe and palpebral lobe
What is the color of the lacrimal gland?
pinkish gray
What is the lacrimal gland surrounded by?
Connective Tissue
What is the lacrimal gland made up of?
many acini that drain into progressively larger tubules
What are acini made up of?
A basal myoepithelial cell layer with inner columnar secretory cells
Because of the acini, the lacrimal gland requires _____ movement to allow the contents to be drained
muscle
When does the lacrimal gland start developing?
Third month of fetal life but not functional until after birth
When do newborns begin to produce tears?
2 weeks - 2 months
What is the function of the accessory lacrimal glands?
Secondary provider of the aqueous secretory component to the tear film
What are the names of the accessory lacrimal glands?
Glands of Krause and Wolfring
Where is the gland of Wolfring located?
In the tarsal plate of the eyelid
Where are there few accessory glands (lower or upper eyelid)?
Lower eyelid
What type of secretion comes from the Gland of Wolfring?
Serous which forms the middle portion of trilaminar tears
Where is the Conjunctival Lacrimal Gland of Krause located?
In the conjunctival fornix
Which contributes more: Gland of Krause or Lacrimal Gland?
Lacrimal Gland
Where does the arterial supply of the lacrimal gland come from?
The lacrimal branch of the ophthalmic artery
A branch of the infraorbital artery
The recurrent meningeal artery
Which nerve carries the sensory stimuli from the lacrimal gland?
The lacrimal branch of the trigeminal nerve (CN V)
What does the tear film cover?
The ocular surface (cornea and conjunctiva)
What are the three layers of the tear film?
Outer lipid layer
Middle aqueous layer
Inner mucous layer
What is the function of the tear film?
- Primary source of oxygen to cornea
- Lubricant between lids and ocular surface
- Movement of tears removes foreign bodies,
- Contain antibacterial proteins
Is the cornea vascular or avascular?
Avascular
Which glands secrete the lipid layer?
Sebaceous glands
Meibomian gland
Sebaceous gland of Zeiss
Which glands produce the aqueous layer?
Serous glands
Lacrimal gland
Fornix accessory lacrimal gland
Palbebral accessory lacrimal gland
Which glands secrete the mucous layer?
Goblet cells
Epithelial cells
Lacrimal gland (very little)
How thick are each of the layers in tears?
Lipid - 0.1 microns
Aqueous - 7 microns
Mucous - 0.02 to 0.05 microns
Holocrine secretion
When the discharged secretion contains the entire secreting cells laden with the secretary material
What does the blink do?
The blink releases the meibomian material from the ducts onto the tears
What do the sebaceous glands do?
Secrete lipids onto the tear film (wax monoesters, sterol esters, hydrocarbons, triglycerides, diglycerides, free sterols (including cholesterol), free fatty acids, and polar lipids (including phospholipids)
Two possible steps where regulation could occur in the meibomian?
- Controlling the rate of lipid synthesis in the ER
- Regulating the rupture of alveolar cells
In terms of regulation in the meibomian gland what would androgen sex steroids or testosterone do?
May regulate synthesis and secretion
Testosterone - females
In terms of regulation in the meibomian gland what would neurotransmitters do?
Alter synthesis or rupture of cells
Neural regulation of the Meibomian Gland would be controlled by?
Vasoactive intestinal peptide (VIP) neuropeptide (NPY)
What do normal lacrimal glands do?
Keep ocular surface moist, well lubricated, free of mechanical and chemical irritants
Two levels of tear secretion?
Low order secretion during normal activities
High order secretion during reflex tearing
What does the lacrimal gland secrete?
Nutrients, growth factors, immunoglobulins in N+, K+-, and CL– rich solution
The final tear film is a mixture is?
NaCl-rich
The main lacrimal gland is a lubuloacinar exocrine that secretes?
Proteins
Electrolytes
Water
The proteins secreted by the lacrimal glands are?
Lysozyme
Lactoferrin
Lipocalin
(SIgA), epidermal growth factor, (TGFs), and interleukins
Conjunctival CL- secretion into tears accounts for what percentage of active transport of the conjunctiva
60-70%
The primary source in mucous layer is?
Goblit cell
What do mucins contain?
Glycoproteins
What are glycoproteins?
protein backbone with carbohydrate side chains
What type of glycoproteins are in the mucous layer?
Large heterogenous glycoproteins (at least 50% carbohydrate by mass)
Secretion of the mucous layer happens because of
activation of the sensory nerves
What is the secondary type of cell secreted by the mucous layer?
Stratified Squamous Cells of conjunctiva and corneal epithelia
What is the punctum?
Opening on the medial portion of each eyelid
What are the superior and inferior canaliculu lined with and surrounded by?
Lined with stratified squamous epithelium
Surrounded by the orbicularis muscle
How large are the puncta?
0.3 mm
How big are the canaliculi?
10 mm in length
0.5 to 1.00 mm in diameter
How commonly is the common canaliculus found?
Formed in 90% of individuals from superior and inferior canaliculi
How much of the tear volume is lost to evaporation?
10-25%
After evaporation, where are remaining tears drained?
Through the lacrimal system into the nose
Some may be absorbed into the nasolacrimal system
There are ___ times as many tears that drain through the inferior punctum compared to the superior punctum because of gravity
4 times
What are two things necessary of tears for optimal visual function?
Adequate secretion and drainage of tears
What is the lacrimal pump theory?
contraction of the pretarsal orbicularis muscle fibers during eyelid closure compresses and shortens the canaliculi
The consistent problem of epiphora in the setting of facial paralysis is that it?
underscores the important contribution of the orbicularis muscle to lacrimal outflow.
Volume of tears drained per blink
2.0 ml
1 blink transports more tears than ____ min(s) of basic secretion
1
The lacrimal excretory system usually functions far (above or below) capacity
below
When does the siphoning by the lacrimal sac occur?
During relaxation not during closure
gravity (increases or decreases) lacrimal drainage
increases
What are some situations that lead to an insufficient tear layer?
Atrophy of lacrimal gland
Increase in age
Compromised innervation
Causes of dry eye complaints in contact lens wearers
- Insufficient tears
- poor tear quality
- infrequent blinking
- incomplete blinking
- reflex tears have low osmolarity
- poor contact lens wetting
- Blepharitis
Normal tear production varies with ____ but not ____
age
gender
Normal result of schirmer’s test
Greater then or equal to 15 mm wetting of paper have 5 minutes
Mild dry eye result of schirmer’s test?
14-9 mm wetting of paper after 5 minutes
Moderate dry result of schirmer’s test?
8-4 mm wetting of the paper after 5 minutes
Severe dry eye result of schirmer’s test?
<4 mm wetting of the paper after 5 minutes
Acinar cells secrete fluid having an _____ composition similar to that of plasma
electrolyte
What is acinar cell electrolyte secretion driven by?
Na+K--ATPase pumping Na+ out of the cell and K+ into the cell
As the flow rate of the acinar cells increases the fluid goes from _____ to _____
hypertonic
isotonic
How do ductal cells modify the fluid secreted by the acinar cells?
By secreting a fluid that is rich in KCl
The lacrimal gland is innervated by?
Parasympathetic nerves
sympathetic nerves
sensory nerves
Lacrimal gland secretion is regulated by?
The nerves that innervate the secretory cells and by the peptide and steroid hormones present in the blood that stimulate secretion
Stimulation of the sympathetic nervous system results in what kind of change in tear secretion?
No Change
parasympathetic fibers of which nerve are responsible for secretion
CN 7
What is the main contributor to tear film?
parasympathetic fibers
What can cause stimulation of lacrimal gland secretion?
Sensory nerves at optic surface
bright light hitting the optic nerve
acetylcholine and vasoactive intestinal peptide (VIP)
Norepinephrine
Conjuctiva provides passage for?
The secretion produced by the lacrimal gland and accessory lacrimal glands
What is the most immunologically active tissue of the external eye?
Conjunctiva
The normal conjunctival epithelium contain _____ neutrophils and _____ lymphocytes
6,000
14,000
Conjunctival reactions can be provoked by ____, ____, and ____
infections
allergies
inflammation
Reactions are characterized by two structural changes
papillae formation
follicle formation
Papillae are found in areas of conjunctival _____
hypertrophy
What do papillae contain?
eosinophils and neutrophils
How are papillae distinguished from follicles?
By the presence of blood vessels in their centers
Which lid are papillae most commonly found?
The upper lid
What are follicles?
clear, fluid-filled pockets containing lymphocytes and macrophages
have blood vessels passing either above or below, never within
_____ and ____ are not found in normal conjunctival epithelium (only in epithelium of what two disease?)
eosiniphils
basophils
vernal conjunctivitis
giant papillary conjunctivitis
When a contact lens has dislocated from the corna and is not visible it is most likely found where?
in the superior fornix since it has the greatest depth
What are the layers of the conjunctiva?
epithelium
stroma
Where are the palisades of vogt found?
immediately peripheral to the limbus
What is the role of the palisades of vogt?
The limbal stem cells reserve
(continually contribute cells to cornea and serve as reserve source in the event of trauma)
What are globlet cells and how wide are they?
unicellular mucin-secreting glands (holocrine) within conjuctival epithelium
11 microns wide on average
Where are the goblet cells found most frequently?
In the fornix and palpebral conjunctiva
The stroma is made up of a rich network of _____
capillaries
What is the rich supply of nutrition needed for in the stroma?
Needed for regenetation of the epithelium and formation of new goblet cells
Where are mast cells found?
in the adenoid layer of the conjunctival stroma along with other inflammatory cells
The mast cells are extremely numerous in conjunctival stroma with ______ cells per cubic mm
6,000
Mast cells are responsible for the _____ ______ reaction
immediate
hypersensitivity
What is the cytoplasm of mast cells filled by?
30 - 100 metachromatic granules
What do mast cells contain?
several preformed chemical mediators of inflammation
histamine and heparin
dramatic changes occur in mast cells membrane and cytoplasm when mast cells are bound by?
IgE
Physical properties change in mast cells so that the membrane becomes more permeable to what ions? This leads to?
Ca++
Edema and swelling of the conjunctiva
in infections of the conjunctiva ____ ____ ____ are engorded
superficial posterior vessels
What is keratitis?
inflammation of the cornea
What is iritis?
Inflammation of the iris
In keratitis and iritis what are engorged and what color are they?
Deep ciliary vessels
bright red/purple hue
Are there lymphatics within the globe?
No
The flow of the lymph is fenerally in the _____ direction toward the ______ extremes of the lid
temporal
lateral
The conjunctiva is richly supplied by what?
lymphatics
