Lacrimal System and Conjunctiva Flashcards
what is the main provider of the aqueous secretory component of the tear film
the main lacrimal gland
where is the main lacrimal gland located
in the fossa for the lacrimal gland (anterio-lateral orbit)
what divides the lacrimal gland into orbital and palpebral lobes
the lateral horn of the levator and extensions of Mullers muscle
which lobe of the lacrimal gland, orbital or palpebral, is larger
the orbital, it lies behind the orbital septum and above the levator aponeurosis
what is the normal color of the lacrimal gland
pinkish-gray
what is the lacrimal gland made up of (drains)
many acini that drain into larger tubles
what type of tissue are acini made of
basal myoepithelial cell layer with inner columnar secretory cells
why is it important that acini are myoepithelial cells
it requires muscle movement to allow the contents to be drained
when does the lacrimal gland begin to develop
near the third month of fetal life
when does the lacrimal gland begin functioning after birth
it may be as long as 2 months
when do newborn babies start to produce tears
2 weeks after birth
if the lacrimal gland doesn’t produce tears in infants, what keeps their eyes from drying out
their accessory glands are functional
what are the secondary providers of the aqueous secretory component of the tear film
glands of krause and wolfring
what was the historical perspective of the accessory glands
that they were for the main secretion (basal tearing) and the lacrimal gland was for reflex tearing
where are the glands of wolfing located
in the tarsal plate of the eyelid
which lid, upper or lower, has more accessory glands
the upper lid
what are trilaminar tears
3 layers: aqueous, mucus, and lipid
where are the glands of krause located
in the conjunctival fornix
what are the 3 arterial supply sources to the lacrimal gland
the lacrimal branch of ophthalmic artery, branch of the infraorbital artery and the recurrent meningeal artery
what is the sensory innervation to the lacrimal gland
the lacrimal branch of the trigeminal nerve (5)
what other ocular structure has innervation from the trigeminal nerve
the cornea
what is the order of the 3 layer structure of the tear film
outer lipid layer, middle aqueous layer, inner mucous layer
what is the primary source of oxygen to cornea
the tear film (the cornea is avascular)
besides supplying oxygen to the cornea, what are the other functions of the tear film
lubricant between lids and ocular surface, remove foreign bodies, debris, and has antibacterial proteins for protection
where does the lipid layer of the tear film come from
meibomian glands and gland of zeiss
where does the aqueous layer of the tear film come from
lacrimal gland, fornix accessory lacrimal gland (krause) and palpebral accessory lacrimal gland (wolfring)
where does the mucus layer of the tear film come from
goblet cells, epithelial cells, and lacrimal gland (very little)
how thick are each of the 3 layers of the tear film
lipid is 0.1 microns, aqueous is 7 microns, and mucus is 0.02-0.05 microns
what type of glands are the meibomian glands
sebaceous glands that secrete lipids onto the tear film
what is holocrine secretion (meibomian glands)
when the discharged secretion contains the entire secreting cells laden with the secretory material
what releases the meibomian material from the ducts onto the tear film
when you blink
what are the different types of lipids in the meibomian material
wax monoesters, sterol esters, hydrocarbons, triglycerides, diglycerides, free sterols (cholesterol), free fatty acids and polar lipids (phospholipids)
what are 2 possible steps where regulation could occur for meibomian gland secretion
by controlling the rate of lipid synthesis in the endoplasmic reticulum and by regulating the rupture of alveolar cells
is the regulation of meibomian secretion known
no it is not known but there are possible suggestions
can androgen sex steroids regulate synthesis and secretion of meibomian glands
yes (testosterone)
what might neurotransmitters do to regulate meibomian glands
(from the nerves surrounding the acini) alters the synthesis or rupture cells
how could meibomian secretion be neural regulated
vascoactive intestinal peptide (VIP) and neuropeptide Y (NPY) found in parasympathetic nerves
what are the proteins that are in the aqueous layer of the tear film
lysozyme, lactoferrin, lipocalin, SlgA, as well as epidermal growth factor, several types of growth factors (TGFs) and interleukins
what type of gland is the lacrimal gland
a tubuloacinar exocrine gland
why are artificial tears only a temporary fix for dry eyes
they are limited because they do not have growth factors
what is the final tear fluid a mixture of
sodium chloride rich fluid
what are the 3 things that are secreted in the aqueous layer
proteins, electrolytes, and water
what happens to the corneal transparency if eyes become severely dry
it may lose transparency
where does the final source of electrolytes and water in the aqueous layer come from
the conjunctiva
what is the mechanism for conjunctival electrolyte and water secretion
conjunctival Cl- secretion accounts for most of the conjunctival active transport (similar to the lacrimal gland)
what is a mucin
collection of glycoproteins (protein backbone and carbohydrate side chains- at least 50% carbs) secreted by goblet cells
what is the major source of the mucus layer of the tear film
the conjunctival goblet cells
what activates the secretion of the goblet cells
activation of sensory nerves
what is the secondary source of the mucus layer
stratified squamous cells of conjunctiva and corneal epithelium
what lines the superior and inferior canaliculi
stratified squamous epithelium
what muscle surrounds the superior and inferior canaliculi
the orbicularis oculi
what is the size of the opening of the punctum
0.3 mm
what is the diameter of the canaliculi
0.5-1.00 mm
about how long are the superior and inferior canaliculi
10 mm
what percentage of the population has a common canaliculi
90%
what is present at the opening of the nasolacrimal sac
Hasner’s valve (mucosal flap)
what percentage of the tear volume is lost to evaporation
10-25%
what is the lacrimal pump theory
contraction of the pretarsal orbicularis muscle fibers during eyelid closure compresses and shortens the canliculi- the shortening pumps tears towards the lacrimal sac (Jones, Jones, and Wobig)
due to gravity which punctum drains more of the tears
the inferior punctum
how would facial paralysis affect tear drainage
it would cause epiphora (orbicularis oculi muscle isn’t closing the eye)
what is the volume of tears drained per blink
about 2 ml
does the lacrimal excretory system function above or below capacity
it usually functions far below capacity
does a single blink transport more tears than produced by basic secretion in 1 min
yes
does gravity increase or decrease lacrimal drainage
increases
when does siphoning by the lacrimal sac occur
during relaxation of the blink
when do the tears come down from the lacrimal gland
with each blink, as the eye is closing a fresh supply of tears is brought down and zippered across the eye
what are 3 situations that would lead to insufficient tear layer
atrophy of lacrimal gland, increase in age, and compromised innervation
what causes dry eye complaints in contact lens wearers
insufficient tears, poor quality or decreased tear break up time, infrequent blinking, incomplete blinking, low osmolarity of tears, or blepharitis
does tear production vary with gender
no
what is the Jones test
a test used to check for how open the lacrimal drainage system is
what symptom do patients have where you would do a Jones test
epiphora
what is a positive result of the jones test
if the patient has the dye in their nose
what does a positive result of the jones test mean
the epiphora was caused by excessive tearing or primary hypersecretion
what does a negative jones test mean
there is a blockage and further investigation is needed
what is a secondary jones test
using a syringe to inject saline into the punctum and canaliculi
what did Doane emphasize for the drainage of tears
the compression of the canaliculi (lesser extend in the nasolacrimal sac during eyelid closure)
what did Doane’s model of siphoning involve
siphoning by the lacrimal sac occurs during relaxation of the blink, rather than during closure as suggested by jones
