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Neural Biology 1 > lacrimal tears > Flashcards

lacrimal tears Flashcards

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1
Q

What does the lacrimal system consist of?

A

of the main and accessory lacrimal glands and the lacrimal drainage apparatus

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2
Q

What does the lacrimal drainage apparatus do?

A

(plumbing system. which removes tears from the ocular surface and ultimately drain into the nose down the nasal lacrimal duct)

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3
Q

What are the lacrimal gland a source of?

A

source of tear production)

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4
Q

What is the location of the lacrimal gland?

A

upper lateral portion of the orbit.

-sits in fossa within the frontal bone

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5
Q

What is the lacrimal gland divided by ?

A

by aponeurosis (tendon) aof LPS (levator palpable superiors) (-Partially dividing the lacrimal gland into 2 portions ) :

  • Oribital Lobe ( upper represents 2/3rds of the volume of the gland)
  • Paelpbral lobe (lower 1/3)
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6
Q

What does the LPS do ?

A

muscle which Elevates the upper eyelid

-maintiains an open palpebral aperture

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7
Q

What is the tendon aponeurosis?

A

transition from the muscular portion of muscle and its tenderness portion

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8
Q

what is the lacrimal gland made up of?

A
  • complex gland
  • Tubuloacinar gland
  • Composed of tubules (ducts- represent the stalk like structure of the grape) and secretory units of gland (acini-represents the grape like structure)
  • 10-12 ducts discharge into upper lateral fornix
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9
Q

What do the intercalated ducts do ?

A

smaller ducts- tend toget progressively large to the point where the tears discharge into the upper lateral fornix -

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10
Q

What is labelled on the diagram shown in slide 6?

A

the lacrimal gland

  • the arrows labelled are the secretary acini
  • the adipose tissue is labelled via the asterisk
  • adipose tissue resembles are white big circle (full with fat)
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11
Q

What are interstices?

A

space between the secretary acini contain numerous lymphocytes - specially B lymphocytes which transform into antibody forming cells (which are PLASMA CELLS)

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12
Q

What are secretory acinus?

A
  • Composed of secretory cells
  • Secretory cells contain large amounts or rER
  • Cells linked by tight junctions- which encircle the central secretory duct
  • Surrounded by myoepithelial cells- contractile epithelial cells
  • also contain large amount of RER , mitochondria and Golgi appartus - typical organelles of a secretory cell
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13
Q

What is in the 3D representation of the gland?

On slide 8

A
  • secretory acini as the green and transitioning into the secretory ducts which are shown in yellow
  • Shows position of myoepthelial cells- dendritic in appearance - wrap around the acini
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14
Q

What do myoepthelial cells do?

A

exert an contractile force, squeezing the acinus

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15
Q

What does the lacrimal gland contain a large volume of?

A

representing a tear resovoir containing a lot of tears- large volume- which can be expressed quickly- emotionally, or due to trauma to ocular surface (e.g. foreign body in eye)stimulation of sensory system (on ocular surface) the sensory nerves on ocular surface would trigger reflex tearing and those tears are stored in gland.

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16
Q

How can tears be expressed so quickly?

A

through the collective squeezing force on the acini and duct expressing tears on the surface of the eye.

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17
Q

What do the ductile cells do?

A

although secerroty unit is reposnidble for tear production

  • ductile cell can modify the composition of the tear film. by secreting particular electrolytes into the tear.
  • so if you took a sample of tears form acinus and ducts there is a subtle difference in the electrolyte concentration between those 2 tear sample
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18
Q

How much does the main lacrimal gland represent ?

A

95% of the total lacrimal tissue

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19
Q

What is the remainder 5% of the lacrimal gland?

A

accessory lacrimal glands

5% of total lacrimal tissue

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20
Q

What are the accessory lacrimal gland?

A

little lacrimal units

-structurally and functionally identical to the main lacrimal gland

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21
Q

Where is the accessory lacrimal gland located ?

A

Predominately in upper fornix

-directly secreting in the ocular surface

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22
Q

Who are the people that discovered the accessory lacrimal glands?

A

Eponymous Krause and Wolfring

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23
Q

What do the main and accessory gland produce?

A

aqueous/watery component of the tear film.

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24
Q

What is the contribution of the production of the aqueous component tear film?

A

meiobiam glands : they also produce the lipid component
Conjuctival goblet cells : produce the mucous component
-BUT large volume of tears is aqueous

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25
Q

What is the tear production under control of ?

A 
neural control (facial)(receives input from the parasympathetic fibres of the facial nerve) (facial (parasympathetic))
- under control of the auntonomic system
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26
Q

What is the large volume tear film?

A

aqueous

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27
Q

What is the output from the glands dependant on ?

A
  • dependent on the level of corneal stimulation (level of stimulation of ocular surface) (trigeminal)
  • level of sensory stimulation
  • reflex arc in diagram which links together the sensory system ( 5th nerve -trigeminal nerve)
  • under normal circumstances - normal tear production
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28
Q

What do the acinar cells in lacrimal gland produce ?

A

-they produce a complex secretion of proteins and electrolytes

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29
Q

What represents the secretory components of the pathway of tear production from the facial nerve ?

A

facial nerve - represent by the bleu axon airing from the lacrimal nucleus within the pons of brain stem and passing via a pterygopalatine ganglion and then this post ganglionic parasympathetic axon then passing to the main lactrimal gland

30
Q

What does the gland also receive?

A

a sympathetic component which comes form the superior cervical ganglion- shown in red in diagram

31
Q

What are the major proteins of the output of the lacrimal gland/ tears production?

A

secereoty IgA

32
Q

What is Secretory IgA produced by?

A
  • plasma cells (transformed b -cells ) which are located in the spaces between the secerorty units in the gland- plasma cells in the interstices of the gland.
  • has a property of being able to be secerted across cells - shows igA producing plasma cell - secreting IgA, then transported across the acinar cells into the tears- IgA transported across acini
33
Q

Where are the various components of the lacrimal drainage pathway- tear drainage ?

A
  • located on the medial side of the eye
  • just entry points to the lacrimal drainage pathway lie in the upper and lower eyelid on the medial angle of the eye - medial canthus smaller tube lead into the nasal lacrimal duct - which then ultimately drains the tears into the nose.
34
Q

What is the opening to the tear drainage system?

A
  • 2 small openings
  • Tear outflow pathway consists of the puncta (represent the opening to the outflow pathway) which initially sees the tears flowing across the, canaliculi then it comes together to form the common cancliculius which then enter the lacrimal sac (which located wihtihnt he lacrimal bone- lacrimal fossa) and it is continuous with the nasolacrimal duct (which drains tears into nose)
35
Q

What is the tear flow ?

A

an active process which is facilitated by the contraction of the orbiculares oculi in blinking
-contractile force which is helpful in pushing the tears down the outflow pathway

36
Q

What is the obicularis oculi?

A

sphincter muscle of eyelids

-process of opening, closing and blinking

37
Q

Where is the puncta located?

A
  • Upper punctum 0.5-1.0mm more medial than lower
  • located on the lid margins
  • Upper and lower punctum at the summit of an elevated papilla
  • 0.2-0.3mm aperture- openings - slit like structure
  • Angled backwards towards ‘lacrimal lake’ (collection of tears)- if angle is wrong they won’t drain efficiently - in elderly patients - changes position of the puncta- particularly the lower punctum
38
Q

What are investigative techniques in patients with presenting with watery eyes ?

A

-to identify the blockage within the drainage system and identifying the lcoation
-pushing an eye drop of a radio opaque dye into both eyes and using x-rays following the transit of this solution through he drainage system
-From puncta, the canaliculi pass vertically 2mm, widen at the ampulla
and then pass horizontally (8-10mm) before forming a common cannaliculus (>80%) which enters the lacrimal sac
.

39
Q

What is the technique called ?

A

dacryocystogram- shows outflow pathway of both right and left eye- can see the various components in the schematic diagrams - location of puncta, canacliculi, lacrimal sac then draining down into the nasal lacrimal duct.

40
Q

Where is the lacrimal sac located in?

A

a fossa formed between lacrimal and maxillary bone

41
Q

What is the lacrimal sac continued with ?

A

continuous with the nasal lacrimal duct

42
Q

What does the nasal lacrimal duct pass?

A

through a canal in the maxillary bone (nasal lacrimal canal) opening and entering in the nasal cavity beneath inferior nasal turbinate

43
Q

What is tear drainage ?

A

an active process

44
Q

What is the cycle of tear drainage ?

A
  • positon of eyelids prior to blink- system is fully open
  • when closing phase- puncta come together to meet and close
  • obicularis muscle exerts a compressive force on the lacrimal drainage system such that they cancliculi and lacrimal sac are compressed and that pushes the tears into the nasal lacrimal duct
  • as eye begins to open , and the pact separate - that negative pressure thats been built up within the tear drainage system is then released and tears flow into puncta.
45
Q

Why do people have problem with tear drainage ?

A

patients that have a. problem with blinking system - either with muscle or nerve supply- problem with tear drianeg-
-whole process is dependant on the blink and active contraction and relaxation of the obicularis.

46
Q

What is the tear film?

A

thin layer of fluid that covers the exposed part of the ocular surface (cornea and conjunctiva)

47
Q

What does the tear film perform?

A

several important functions which is essential for the integrity of the eye such as.

  • optical function-
  • Metabolic
  • Protective-
  • lubricative
48
Q

What does the optical function of the eye do ?

A

refractive surface - initial surface the light hits the eye

49
Q

What does the metabolic function of the eye do?

A

represents the interface between the oxygen that the cornea requires from the atmosphere- oxygen is in equilibrium with the tear film and exchange of oxygen takes places across the tear layer

50
Q

What does the protective function of the eye do ?

A

cornea does not have a protective layer hence needs to be constantly kept moist- also tears has antimicrobial proteins as part of protecting

51
Q

What does the lubricative function of the eye do?

A
  • facilitate the blink process and facilities movement of eyelid across the ocular surface
52
Q

What is the distribution of the tear volume ?

A

vast majority of the volume of tears (70=-80%) lies within the marginal tear strips
-collective of tears which run around the upper and lower eyelid margins-

53
Q

What can the marginal tear strips be referred to ?

A

Upper meniscus and lower meniscus

54
Q

What does the upper and Lower meniscus mean?

A

very thin strip of tears along the both lid margins

55
Q

How much of the tears are locate din the marginal tear strips ?

A

A small proportion beneath the lids or spread across the surface of the eye.
Remainder covers the cornea and exposed bulbar conjunctiva

56
Q

What are the physical properties of the pre- ocular tear film ?

A
  • The parameters
  • Osmorality
  • pH
  • Volume
  • Rate of production
  • Turnover rate
57
Q

What happens when you measure the osmorality of the tears?

A

Mean 300 mOsm/L
(range 270-315 mOsm/L)
-slightly lower osmolaritit than tear plasma which is 340mOsm/L
-Tear osmolarity - becoming a useful technique with patient with dry eye-

58
Q

What is the pH of the tears?

A

Range 6.8-8.6

59
Q

What is the volume value of tears?

A

8 ± 3µl (mircolitlres)

60
Q

What is the rate of production of the tears?

A

1-2µl/min

61
Q

What is the turnover rate of tears?

A

16± 5% per /min - replacing 5% of our tear volume per min

62
Q

What is the tear film regarded as?

A

a trilaminar structure
-with a superficial lipid layer which overlies a middle aqueous layer and deep mucin layer
-

63
Q

However what does recent evidence suggest the tear film being regarded as?

A

Recent evidence suggests a much greater mucin contribution to the tear film

64
Q

What about the consensus of the thickness of the tear film layer?

A

Recent consensus regarding the thickness of the tear film estimates a thickness of approx. 3 microns

65
Q

What is the lipid layer of the tear film”?

A
  • uppermost layer
  • complex mixture of lipids derived from the meiobian glands
  • very thin- 100nm thicj
  • Delivered onto the lid margin through ducts of meribomian glands and spread over the surface of the tear film during blinking.
  • Forms a hydrophobic barrier preventing overspill of tears and reduces tear evaporation- so if thin layer of watery surface across the eye will be quickly lost though evaporation and presence of lipid layer will reduce tear evaporation- increase the stability of the tear film
  • Hormonal and mechanical aspects to secretion- secretion of lipid layer is under neuronal control but larger affected by hormone levels - particularly levels of androgens
66
Q

What is then the process of expression of meiobian glands?

A

-as the obicularis is contracting especially the marginal bit its exerting a mechanical force on the ducts of the meiobomian gland which really helps to express the lipid onto the lid margin

67
Q

Express the action of the lipids in the eye as compared to a tap ?

A

as a tap that can switched on and off

  • coming out from the nozzle pf the tap , you can see the elastic this elastic ducts which represents the ducts of the meiobomin glands
  • the clamp represents the obicularis - acting a as a muscular pump- expressing the droplets of lipid onto the lid margin - so have collection of marginal oil and flywheel its representing the eyelid as the distrubtuion system - for spreading the tear layer across the lipid layer acorss the pre ocular tear film
68
Q

What is the aqueous layer of the tear film ?

A
  • Secretion regulated by the autonomic nervous system- component which is produced by the main dn accessory lacrimal gland
  • Contains water, electrolytes (salty), proteins
  • Electrolytes contribute to tear osmolarity
  • Proteins include IgA, lyzozyme and lactoferrin which have an antimibrobial function and lipocalin that contributes to tear stability
69
Q

What is the mucin layer of the tear film?

A

-Derives from conjunctival goblet cells (secretory musicns)- soluble muslins and the glycocalyx of the ocular surface epithelium (epithelium of cornea and conjunctiva )- cell anchored to muslins attached to the ocular surface
-Has a lubricative role and maintains a hydrophilic ocular surface- allows tears to spread easily across the surface
Contains a variety of mucin types (soluble and cell anchored)

70
Q

W

A

uppermost cells of the ocular surface with the microvilli to which anchored these mucous glyocopretinns which are formed as parts of the glycocalyx as well as the secretory muscins coming from the conjunctival goblet cells.

71
Q

What are there different types of muslins present on the ocular surface?

A

soluble mucin is referred to MUC5AC
Mucins play an important role in maintaining a healthy ocular surface and the stability of the tear film
-The gel–forming mucin MUC5AC derived from conjunctival goblet cells is the primary secretory mucin of the ocular surface
-Transmembrane proteins in the corneal and conjunctival glycocalyx include MUC1, MUC4 and MUC16

Neural Biology 1 (58 decks)

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