LACRIMAL GLAND PART 1

Question 1

WHAT IS THE MAIN FUNCTION OF THE MAIN LACRIMAL GLAND AND WHERE IS IT LOCATED?

Answer 1

The main lacrimal gland provides the principal aqueous secretory component to the tear film.
The lacrimal gland is divided by the lateral horn of the levator and extensions of Müller’s muscle into an orbital lobe above and a palpebral lobe below.
The orbital lobe is the larger of the two lobes and lies behind the orbital septum and above the levator aponeurosis.

Question 2

what does the lacrimal gland appearance look like? what is it made up of?

Answer 2

The lacrimal gland appears as a pinkish gray collection of lobules surrounded by connective tissue.
The gland is made up of many acini that drain into progressively larger tubules. The acini are made up of a basal myoepithelial cell layer with inner columnar secretory cells.

Question 3

when does lacrimal glands start to develop? when do they start to function?

Answer 3

lacrimal glands start to develop in third month of fetal development.
start to function after birth.
baby cant produce tears until 2 weeks after birth or can take as long as two months.

Question 4

name the accessory lacrimal glands. what is their function?

Answer 4

Gland of Wolfring and Gland of Krause (sits up higher).
provide secondary component to aqueous layer of tear.
(Think Basal vs. Reflex tear theory)

Question 5

what is the difference between a basal tears and reflex tears?

Answer 5

Basal tears carry nutrients for eye to fight bacteria and keep it clean. Reflex tears are water only secreted by main lacrimal glands only.

Question 6

where is the Gland of Krause located?

Answer 6

conjunctival fornix

Question 7

where is gland of wolfring located?

Answer 7

In tarsal plate of eyelid. there are more accessory glands in upper lid than lower.

Question 8

where does the arterial supply of the lacrimal gland come from?

Answer 8

the lacrimal branch of the ophthalmic artery
a branch of the infraorbital artery
the recurrent meningeal artery

Question 9

where does the lacrimal gland sensory info. come from?

Answer 9

the lacrimal branch of the trigeminal nerve (CN V) carries sensory stimuli from the lacrimal gland.

Question 10

what is the tear film structure and what part of the eye does it cover?

Answer 10

it is a complex 3 layer structure.
(outer lipid layer, middle aqueous, inner mucous)
it covers the cornea and conjunctiva (the ocular surface).

Question 11

what is the tear film function?

Answer 11

primary source of oxygen to eye, has nutrients and proteins, to fights off bacteria and prevent infection in conjunctiva and cornea, keeps eye and ocular surface lubricated. cornea is avascular (has no blood vessels because has to remain clear) however does grow vessels to heal itself….no good.

Question 12

what is the origin of the lipid layer of tear?

Answer 12

Lipid layer (outermost) – Sebaceous
Meibomian gland (Tarsal glands) 
Sebaceous gland (of Zeiss)

Question 13

what is the origin of the aqueous layer of tear?

Answer 13

Aqueous (middle) – Serous
Lacrimal gland
Fornix accessory lacrimal gland (Krause)
Palpebral accessory lacrimal gland (Wolfring)

Question 14

what is the origin of the mucous layer of tear?

Answer 14

Mucous (innermost)
Goblet cells (mainly supply mucus)
Epithelial cells
Lacrimal gland (very little)

Question 15

what is the thickness of each tear layer?

Answer 15

Lipid layer approx 0.1 micons
Aqueous approximately 7 microns
Mucus layer 0.02 to 0.05 microns

Question 16

conjunctival glands are unicellular goblet cells (holocrines). True or False.

Answer 16

True

Question 17

how many miebomian glands are in the upper and lower lids?

Answer 17

upper= 30-40
lower= 20-30

Question 18

how does the meibomian gland work exactly? what is holocrine secretion?

Answer 18

sebaceous glands that secrete lipids onto the tear film.
holocrine secretion: when the discharged secretion contains the entire secreting cells laden with the secretory material.
the blink releases the meibomian material from the ducts onto the tear film.
free fatty acids, phosopholipids, etc.

Question 19

How are the meibomian glands regulated?

Answer 19

unknown how regulated.
maybe by rupture of aveolar cells or protein synthesis in ER. also androgen sex steroids, neurotransmitters.
neural regulation controlled by VIP (vasoactive intestinal peptide) and NPY (neuropeptide)

Question 20

Describe the two levels of tear secretion.

Answer 20

Two levels of tear secretion
Low order secretion during normal activities
High order secretion during reflex tearing, crying, etc

Question 21

what do the lacrimal tears secrete specifically?

Answer 21

Secrete mixture of nutrients, growth factors, glycoproteins and immunoglobulins in an isotonic Na+-, K+-, and Cl- –rich solution .
final tear fluid is rich in NaCl.

Question 22

what is the predominate cell type of lacrimal gland?

Answer 22

acinar cells.

Question 23

what does the tubuloacinar exocrine gland secrete in the lacrimal gland system?

Answer 23

Tubuloacinar exocrine gland secretes:
proteins
electrolytes
water

Question 24

what are the proteins secreted by lacrimal glands?

Answer 24

Proteins secreted include:
lysozyme
lactoferrin
lipocalin
as well as: secretory immunoglobulin A (SIgA), epidermal growth factor, several types of transforming growth factors (TGFs), and interleukins

Question 25

what can lacrimal gland dysfunction indicate?

Answer 25

Lacrimal gland dysfunction may indicate dry eye condition often termed “Sjogren’s Syndrome”.
Severely dry eyes may lose corneal transparency.

Question 26

how do the cornea and conjunctiva contribute to tear process?

Answer 26

minor contributors to the aqueous component
DO release electrolytes and water
do NOT release proteins
conjunctival Cl- secretion accounts for most of conjunctival active transport

Question 27

Describe mucous layer.

Answer 27

Primary Source: Goblet Cells – secrete mucins
mucins – collections of glycoproteins (protein backbone with carbohydrate side chains)
Large heterogenous glycoproteins
At least 50% carbohydrate by mass
secreted by activation of sensory nerves
Secondary Source: Stratified Squamous Cells of conjunctiva and corneal epithelia

Question 28

Describe the flow of tears of through excretory system of the eye.

Answer 28

punctum—> inferior and superior canniculi (usually turns into common canniculi but not always)—->common canniculi (in 90% of people)—-> naso lacrimal sac (where Hasner’s valve is at the opening of the duct into the nose).

Question 29

how much of tears gets lost to evaporation?

Answer 29

10%-25% and some gets lost going through the nasolacrimal duct.

Question 30

which has more tears flowing through it inferior or superior punctum? why?

Answer 30

4 times as much tears in inferior punction because of pull of gravity. need to have great flow and drainage of tears for quality vision.

Question 31

describe lacrimal pump theory of jones and wobig?

Answer 31

On the basis of extensive anatomic dissections, Jones and Jones Wobig popularized the lacrimal pump theory. Jones proposed that contraction of the pretarsal orbicularis muscle fibers during eyelid closure compresses and shortens the canaliculi, pumping tears towards the lacrimal sac.

The consistent problem of epiphora in the setting of facial paralysis underscores the important contribution of the orbicularis muscle to lacrimal outflow.

Question 32

how much tears are drained per min?

Answer 32

volume drained= 2ml per blink

Question 33

Role of Blinking theory. Explain Doane Theory.

Answer 33

Doane used high-speed photography to assess the role of blinking in lacrimal drainage. Movements of the tear fluid were made visible by instilling carbon black into the tear film. Doane emphasized compression of the canaliculi and, to a lesser extent, in the nasolacrimal sac during eyelid closure. In Doane’s model siphoning by the lacrimal sac occurs during relaxation of the blink, rather than during closure as suggested by Jones.

The volume of tears drained per blink has been measured at 1.8 ml by Rosengren and approximately 2.0 ml by Cahlin and Chen. Because a single blink may transport more tears than those produced by basic secretion in 1 minute, the lacrimal excretory system usually functions far below capacity. This would theoretically allow for absorption of some of the volume en route to the nasal cavity.
Lacrimal drainage capacity has been shown to be correlated to the blink rate when the nasolacrimal duct is in a horizontal position. Sahlin and Chen showed that gravity tended to increase lacrimal drainage

We blink 15 times per minute.
You can put something in your eye and it get to your blood stream right away. Like IV. However, its very small and cant get as much of a drug in as an IV does.
Beta blockers can lower the ?

Mucus layer keeps water layer stuck to it and oil layer on top keeps the water from tear from evaporating.

Question 34

what did Doang emphasize in theory?

Answer 34

Doane used high-speed photography
Doane emphasized compression of the canaliculi and, to a lesser extent, in the nasolacrimal sac during eyelid closure.
Siphoning by the lacrimal sac occurs during relaxation of the blink, NOT during closure (Doane theory) See picture next slide

Gravity increases lacrimal drainage

Question 35

Doang theory explained in short

Answer 35

With each blink fresh tears are brought from top to bottom. As you open the eye, the tears are being pushed out.
Tears are spread across cornea and conjunctiva.

When you have a lump or bump or are concentrating a lot you experience partial blink. You get a dryness of cornea an conjunctiva.

Question 36

Explain positive and negative Jones test. What does it test for?

Answer 36

Green dye come out of nose is good positive test.

If dye doesn’t come out of nose. Means there is a blockage. Or the pump is not working.

Tears not sufficient to reach or the pump is deficient.
If muscle is not working well then pump will not work well.

Inject saline and nothing came out….pump wasn’t working. Negative result. means either the nasolacrimal pump or the lacrimal sac is not working properly.