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Duke Elder - Anatomy 5: Ocular appendages > Lacrimal apparatus > Flashcards

Lacrimal apparatus Flashcards

1
Q

What are the 5 key structures that comprise the lacrimal apparatus?

A
  1. lacrimal gland
  2. lacrimal puncta
  3. lacrimal canaliculi
  4. lacrimal sac
  5. nasolacrimal duct
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2
Q

What is the function of the lacrimal apparatus? 2 key things

A

Produces tears that moisten the ocular surface, thus:

  1. preventing desiccation of the delicate ocular cells and tissues
  2. facilitating non-friction-bearing movements of the lids on the globe
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3
Q

Label the following on the diagram:

  • orbital roof (cut)
  • orbial portion of lacrimal gland
  • palpebral portion of lacrimal gland
  • excretory ducts
  • levator tendon
  • canaliculi (vertical and horizontal portions)
  • lacrimal sac
  • nasolacrimal duct
  • lacrimal fold (mucous membrane)
  • inferior concha
  • maxillary sinus
A
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4
Q

How thick is the tear film?

A

7-9 μm

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5
Q

How many layers is the tear film composed of?

A

3

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6
Q

What are the 3 layers of the tear film?

A
  1. outer oily or lipid layer (from meibomian and Zeis glands)
  2. middle aqueous layer containing protein, electrolytes and water
  3. deep hydrophilic mucin layer
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7
Q

What produces the outer oily/ lipid layer of the tear film?

A

meibomian and Zeis glands

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8
Q

What 3 things is the middle aqueous layer of the tear film composed of?

A

protein, electrolytes, water

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9
Q

What structures produce the middle aqueous layer of the tear film?

A

mainly lacrimal glands, also small contributions from conjnctival epithelia and cornea

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10
Q

What structures produce the deep hydrophilic mucin layer of the tear film? 3 key structures

A

goblet cells and conjunctival epithelial cells, and some from the corneal epithelium

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11
Q

What structures is the deep hydrophilic mucin layer of the tear film associated with?

A

the microplicae-rich surface of the conjunctival epithelium

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12
Q

What is the size of the lacrimal gland?

A

20 x 12 x 5 mm, weighs 78mg

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13
Q

What structure divides the lacrimal gland into 2 separate portions?

A

the lateral horn of the aponeurosis of the levator palpebae superioris

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14
Q

What are the 2 portions of the lacrimal gland and their relative sizes?

A
  1. large orbital portion
  2. small palpebral portion
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15
Q

How are the orbital and palpebral portions of the lacrimal gland connected?

A

continuous via small isthmus around lateral border of aponeurosis

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16
Q

What is the shape of the orbital portion of the lacrimal gland? Where is it sited?

A

shaped like an almond with a convex outer surface lodged in the lacrimal fossa, and concave inferior surface moulded around tendons of levator palpebrae superioris and lateral rectus

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17
Q

Where are the convex outer and convave inferior surfaces of the orbital portion of the lacrimal gland located?

A
  • convex outer: lodged in lacrimal fossa
  • concave inferior: moulded around tendons of levator palpebrae superioris and lateral rectus
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18
Q

What proportion of the total gland is formed by the palpebral portion?

A

1/4

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19
Q

Where does the inferior surface of the lacrimal gland lie?

A

close to the eye - the gland can usually be seen when upper lid is everter

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20
Q

How do the ducts inside the lacrimal gland traverse the orbital and palpebral portions?

A
  • fine interlobular ducts unite to form three to five main excretory ducts in the orbital portion
  • the excretory ducts traverse the palpebral portion, joining a further 5-7 from this part of the gland, before entering superotemporal conjunctival fornix
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21
Q

Where do the excretory ducts of the lacrimal gland unite to supply the eye’s surface?

A

superotemporal conjunctival fornix

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22
Q

Due to the arrangement of the excretory ducts in the lacrimal gland, what will happen if the palpebral portion of the lacrimal gland is removed?

A

renders the entire gland non-functional

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23
Q

What type of tissue forms the lacrimal gland?

A

branched tubulocacinar gland of the serous type

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24
Q

What is the arrangement of the tissues of the lacrimal gland?

A

composed of many lobules separated by interstitial fibrovascular septae that are continuous with the poorly developed capsule

each lobule contains numerous acini separated by loose intralobular connective and adipose tissue

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25
Q

Histologically, which gland do the lacrimal acini resemble?

A

parotid gland acini

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26
Q

How do the lacrimal acini appear in cross section?

A

series of rounded profiles

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27
Q

What does each acinus in the lacrimal gland lobules consist of?

A

single layer of cuboidal or columnar cells whose apices are directed towards a central lumen

layer of stellate-shaped myoepithelial cells surrounds each acinus

28
Q

How are the acini arranged to form ducts?

A

the central lumen of several acini unit to form intralobular ducts, which eventually form larger interlobular ducts that unite to form the main excretory duct system

29
Q

What is the characteristic histological and ultrastructural appearance of the glandular epithelial cells in the lacrimal glands?

A

Serous cells - basophilic cytoplasm (large numbers of round or oval secretory (zymogen) granules

30
Q

How can the lacrimal epithelial cells be subdivided into further subtypes?

A

depending on size and electron density of the oval secretory (zymogen) granules in the basophilic cytoplasm

31
Q

What is contained in the secretion of the lacrimal gland?

A

primarily proteinaceous, although some granules contain glycosaminoglycans

lumen on histological examination contains strongly eosinophilic and mucoid-like secretory material

32
Q

In addition to the main components of lacrimal gland secretions (proteinaceous, glycoasminoglycans, mucoid-like and eosinophilic material) what are 4 further materials in the secretions?

A
  1. Lysozymes
  2. Lactoferrin
  3. B-lysin
  4. Immunoglobulin A (IgA)
33
Q

What is the importance of lactoferrin, B-lysin, IgA and lysozyimes in the secretion of the lacrimal gland?

A

improtant in defence of ocular surface against microbial infection

34
Q

Where is IgA in the secretion of lacrimal glands derived from?

A

numerous plasma cells, present with other immunocompetent cells such as lymphocytes and mast cells, in the intralobular connective tissue

35
Q

What happens to the number of immunocompetent cells in the lacrimal tissue with age?

A

increases

36
Q

What are 4 changes in the lacrimal tissue with age?

A
  1. increase in number of immunocompetent cells
  2. increased fibrosis
  3. increased fatty infiltration
  4. decrease in acinar elements, in orbital lobe especially
37
Q

What is the nucleus controlling nerve supply to the lacrimal gland and where it it?

A

Lacrimatory nucleus of the facial nerve lies a the rostral end of the general visceral efferent column of cell bodies in the pontine tegmentum of the brainstem (include the superior and inferior salivatory nuclei)

38
Q

What influences cells in the lacrimatory nucleus of the facial nerve?

A

hypothalamus - via descending autonomic pathways (emotional states influence excess lacrimation via neuronal pathways)

39
Q

What can trigger reflex lacrimation?

A

irritation of the cornea, conjunctiva and nasal epithelia

40
Q

What neuronal pathways are involved in reflex lacrimation?

A

afferent pathways in ophthalmic and maxillary divisions of the trigeminal

interneurones connect the trigeminal sensory nculei with the lacrimatory nucleus

41
Q

Overall what is the sensory nervous supply to the lacrimal gland?

A

lacrimal nerve is branch of ophthalmic nerve, branch of trigeminal; travels via trigeminal ganglion

42
Q

What is the parasympathetic supply to the lacrimal apparatus?

A
  • originates from lacrimal nucleus in inferior part of pons
  • travels via facial nerve (nervus intermedius), then via greater petrosal nerve and nerve of the pterygoid canal
  • synapses in ptergyopalatine ganglion
  • goes through retro-orbital plexus before reaching the gland
43
Q

Where is the lacrimal nucleus?

A

inferior part of pons

44
Q

What is the sympathetic nervous supply to the lacrimal gland?

A
  • travels from intermedio-lateral grey horn in spinal cord (T1 level)
  • via superior cervical ganglion
  • via deep petrosal nerve
  • then nerve of pterygoid canal
  • then via retro-orbital nucleus and finally to the gland
45
Q

Note the sensory, secretomotor and sympathetic innervation of the lacrimal gland in the diagram

A
46
Q

What is the blood supply to the lacrimal gland?

A
  • principally lacrimal artery - early branch of ophthalmic artery
  • variable branch from infraorbital artery (indirectly from external carotid) may aid in suply
47
Q

What is the venous drainage from the lacrimal gland?

A

drains posteriorly - usually to superior ophthalmic vein in orbit

48
Q

Where does lymph drain from the lacrimal gland?

A

preauricular node

49
Q

What is the function of the collecting system of the lacrimal apparatus?

A

serves to drain normal tears that have not evaporated (normally only very small quantity) & those produced in excess lacrimation

50
Q

How are excess tears drained via the lacrimal apparatus?

A
  • drain from medial aspect of conjunctival sac
  • via canaliculi into the lacrimal sac and nasal duct
  • to empty into inferior meatus of the nasal cavity
51
Q

What are the puncta?

A

small openings visible to naked eye on medial margin of each lid at the summit fo small swellings, the papillae lacrimalis

52
Q

What is the course of excess tears after passing via the puncta?

A
  • enter the puncta from the lacus lacrimalis during blinking
  • pass into lacrimal canaliculi in upper and lower lid behind medial palpebral ligament
  • each canaliculus has vertical and horizontal components, unite to form common canaliculus before entering lacrimal sac
  • epithelium of lacrimal sac continuous with that lining nasolacrimal duct inferiorly
  • nasolacrimal duct empties into anterior part of inferior meatus of nasal cavity
53
Q

Wha tis the length and diameter of each canaliculus in the upper and lower lid behind the medial palpebral ligament?

A

10 mm long (0.5mm in diameter)

54
Q

What type of cells line the lacrimal canaliculi of the lacrimal drainage system?

A

stratified squamous non-keratinising cells

55
Q

How do draining lacrimal canaliculi enter the lacrimal sac?

A

by piercing the fascial covering

56
Q

How long is the lacrimal sac and how are its walls arranged in the upper portion?

A

12mm

walls usually in apposition in the upper portion

57
Q

Where is the lacrimal sac located?

A

lies in the lacrimal fossa, protected by the medial palpebral ligament anteriorly and lacrimal fibres of orbicularis oculi posteriorly

related medially to ethmoidal air cells and middle meatus of nasal cavity

58
Q

What do the walls of the lacrimal sac consist of? What is it lined by?

A
  • fibroelastic tissue
  • lined by mucous membrane consisting of stratified cuboidal/columnar epithelium containing goblet cells
59
Q

What is the epithelium of the lacrimal sac continuous with?

A

that lining canaliculi

nasolacrimal duct inferiorly

60
Q

Where does the nasolacrimal duct empty into?

A

anterior part of inferior meatus of nasal cavity

61
Q

What structure protects the opening of the nasolacrimal duct into the inferior nasal meatus? What is its function?

A

flap of mucous membrane - prevents air and debris passing up the duct during nose blowing

62
Q

Where is the nasolacrimal duct located?

A

lies in bony nasolacrimal canal formed by maxilla, lacrimal bone and inferior nasal concha

63
Q

What type of epithelium lines the nasolacrimal duct?

A

stratified columnar ciliated epithelium

64
Q

What does the epithelium of the nasolacrimal canal rest on?

A

vascular substantia propria

65
Q

Why is knowledge of the position of a variety of constrictions and mucous membrane folds or valves along the nasolacrimal canal important?

A

during reconstruction of congenitally malformed lacrimal drainage systems

66
Q

Which bones form the nasolacrimal canal?

A

lacrimal, maxilla, inferior nasal conchae

Duke Elder - Anatomy 5: Ocular appendages (4 decks)

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