Lacrimal System Flashcards
What does the lacrimal gland provide?
principal aqueous secretory component to the tear film.
How is the lacrimal gland divided?
lateral horn of the levator and extensions of Müller’s muscle into an orbital lobe above and a palpebral lobe below.
What is the lacrimal gland made up of?
many acini that drain into larger tubules (the acini are myoepithelial…need muscle movement to allow contents to be drained)
Where does the lacrimal gland develop?
third month of fetal life but not functional until after birth. some newborns dont have tears until 2 weeks…or could be up to 2 months
What are the accessory lacrimal glands?
secondary provider of the aqueous secretory component to the tear film
glands of Krause and Wolfring
Where is the gland of wolfring located?
tarsal plate of eyelid (palpebral)
What does wolfring gland secrete?
Secretion is serous which forms the middle portion of trilaminar tears
Why are there less accessory glands in the lower eyelid?
there is less tarsal in lower eyelid
Where is the gland of Krause located?
conjunctival fornix
Which accessory gland contributes more?
wolfring
What is the arterial supply of the lacrimal gland?
lacrimal branch of opthalmic artery;
branch of infraorbital artery;
recurrent meningeal artery
Sensory of Lacrimal Gland?
trigeminal nerve 5; cornea also has this…it triggers secretion of lacrimal gland
What does the tear film cover and what are the 3 layers?
Covers cornea and conjunctiva; 3 layers: outer lipid, middle aqueous; inner mucous layer
What is primary source of oxygen to the cornea?
Tear film since the cornea is avasclar
What are other functions of tear film?
lubricant between lid and ocular surface
the movement of tears helps remove foreign bodies, debris, and exfoliated cells
tears contain many antibacterial proteins that protect the cornea and conjunctiva from infection
Origin of Lipid Layer
(sebaceous) meibomian gland; sebaceous gland of zeiss
Origin of aqueous layer
(serous) lacrimal gland; fornix and palpebral accessory glands
origin of mucous layer
goblet cells; epithelial glands; lacrimal gland (little)
Thickness of Tears
Aqueous- 7 microns
Lipid layer- 0.1
Mucous .02-.05
How many meibomian glands are in the lower and upper lids? What is secreted?
Lower= 20-30
Upper= 30-40
Secretion is Sebum
What are meibomian glands?
sebaceous glands that secrete lipids onto tear film
What is holocrine secretion?
when the discharged secretion contains the entire secreting cells laden with the secretory material
How is the secretion of meibomian material released?
blinking allows the material to be released from the ducts onto the tear film
Two possible reasons of meibomian regulation
- Controlling the rate of lipid synthesis in ER
2. Regulating rupture of alveolar cells
What part do androgen sex cells play in regulating meibomian secretion?
Help in regulating synthesis and secretion
Neurotransmitters role in meibomian secretion?
alter the synthesis or rupture of cells
Neural regulation of meibomian secretion is regulated by?
VIP and NPY vasoactive intestinal peptide (VIP) and neuropeptide Y (NPY) found in parasympathetic nerves.
What are the two levels of tear secretion?
Low Order: during normal activities… has nutrients. secretion is good
High order: reflex tearing crying etc(mainly water or serous (not as normal as regular tears)…secretion required immediately not good for body in log run)
What type of nutrients are secreted in lacrimal gland?
Secrete mixture of nutrients, growth factors, glycoproteins and immunoglobulins in an isotonic Na+-, K+-, and Cl- –rich solution
The main lacrimal gland is a tubuloacinar exocrine gland that secretes the major portion of protein, electrolytes, and water into the tear film.
A few of these proteins are lysozyme, lactoferrin, lipocalin, secretory immunoglobulin A (SIgA), epidermal growth factor, several types of transforming growth factors (TGFs), and interleukins.
Final tear fluid is a mixture of?
Na-Cl rich fluid
Tubuloacinar exocrine gland secretes?
electrolytes proteins, and water
Sjogren’s Syndrome
dysfunction of the lacrimal gland; causes dry eye (severely dry eyes can lose transparency)
What is the significant souce of water and electroyltes in the eye?
conjunctiva because it occupies a larger part of the ocular surface than the cornea
Conjunctival Cl- secretion into tears accounts for what percentage of active transport?
60-75 % active transport to conjunctiva
What is the primary source of secretion of the mucous layer?
Goblet cells; they secrete mucin by activation of sensory nerve
What are mucins?
Mucins are a heterogeneous collection of high-molecular weight glycoproteins that consist of a protein backbone with side chains of variable numbers of carbohydrates.
Relationship between mucins and cornea
Cornea is hydrophobic and mucins allow cornea to keep water around
Backup for cornea getting oxygen other than tear film?
limbus
Secondary source of mucin secretion?
stratified squamous cells of conjunctiva and corneal epithelia
What are 4(3) parts of the excretory system pathway?
- punctum
The opening on the medial portion of each eyelid - superior and inferior caniculi (really common caniculus but remains separate in some pts)
Lined with stratified squamous epithelium
Surrounded by the orbicularis muscle - Nasolacrimal sac (Hasner’s valve is present at opening of duct into nose)
How big is the drainage structure?
10mm in length; 0.5-1mm in diameter
How much tear volume is lost due to evaporation?
10-25% (lipid reduces evaporation)
Where do the remaining tears go?
drain through the excretory system into the nose; some absorbed in nasolacrimal system
Gravity’s role in tear drainage?
due to gravity 4x as much tears drain through inferior punctum vs superior punctum
What is needed for optimal visual function?
adequate secretion and drainage of tears
Contraction of the pretarsal obicularis during eyelid closure does what?
shortens and compresses caniculi which pumps tears towards the lacrimal
Facial paralysis leads to? and highlights?
leads to epiphora and highlights function of obicularis oculi
volume of tears drained per blink
2ml
True or False: the lacrimal excretory system functions way below capacity?
True; 1 blink transports more tears than 1 min of basic secretion
Doane vs Jones
In Doane’s model siphoning by the lacrimal sac occurs during relaxation of the blink, rather than during closure as suggested by Jones.
Gravity increases lacrimal drainage
Situations leading to insufficient tear layer
Atrophy of lacrimal gland (eg. Sjogren’s Syndrome)
Increase in age
Compromised innervation
Causes of dry eye complaints in contact lens wearers
Insufficient tears Poor tear quality (decreased/short tear break up time (TBUT) Infrequent blinking Incomplete blinking Reflex tears (have low osmolarity) Poor contact lens wetting Blepharitis
After having LASIK surgery, why will almost every patient will have an acute dry eye complaint?
the trigeminal nerve is cut
connection between cornea and lacrimal gland is cut off
Positive and Negatives of Jones Test?
Put flor in conjunctiva
Blow nose you should have green dye= functioning
No dye comes out- blockage or pump not working
Inject saline and get dye…lacrimal pump not working well
Inject saline and nothing= released block but dye never got in
