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Fall 2019: OPT 114 Ocular Anatomy and Physiology > Tear Production > Flashcards

Tear Production Flashcards

1
Q

Old and new theories about the tear film

A

Old theory states that there are THREE layers of the tear film and 3 components: lipid, aqueous, mucin

Recent, more accurate theory states that there are are only TWO layers of the tear film, with the same 3 components: Lipid layer, mucoaqueous layer

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2
Q

Glands/cells that produce the components of the tear film

A

Lipid- Produced by the meibomian glands as meibum

Aqueous- Produced by the lacrimal gland and accessory lacrimal gland of Krause and Wolfring

Mucus- Produced by goblet cells in the conjunctival epithelium.

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3
Q

There are (more/less) meibomian glands in the tarsal plate of the upper lid and (more/less) in the tarsal plate of the lower lid

A

More in the upper lid

Less in the lower lid

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4
Q

Meibomian glands are present where

A

In the ciliary portion of the eyelid margin, on the tarsal plates

Arranged vertically so that their openings are located in a row along the eyelid margin

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5
Q

Where do meibomian gland orifices open onto?

A

The skin posterior to the gray line and anterior to the mucocutaneous junction.

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6
Q

Acini of sebaceous glands (meibomian glands)

A

Secrete meibum, by holocene method into a central duct.

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7
Q

Acinus

A

Small saclike cavity in the meibomian gland that is surrounded by secretory cells

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8
Q

What do the acini of meibomian glands secrete?

A

A mixture of lipids and proteins-

  1. Amphipatheic lipids (Phospholipids and fatty acids)
    - come in contact with mucoaqueous layer
    - Provide structural stability to the tear film

Nonpolar lipids (waxes, cholesterol, triglycerides)

  • In contact with air
  • Create a hydrophobic barrier
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9
Q

How is meibum production regulated?

A

By hormones- androgen and estrogen (lipid messengers)

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10
Q

How do androgen and estrogen stimulate hormone receptors?

A

They stimulate cells within the meibomian gland and this leads to an increase in gene transcription for enzymes associated with fatty acid and cholesterol synthetic pathways.

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11
Q

Where is meibum stored and what action allows it to be secreted?

A

It is stored in the central duct and secreted upon blinking due to mechanical (physical) pressure on the gland.

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12
Q

Chalazion

A

Sterile clogging of meibomian glands.

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13
Q

Hordeum

A

Bacterial infection of the meibomian glands.

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14
Q

Where in the conj are goblet cells located

A

Interspresed within conjunctival epithelial cells (palpebral, bulbar, and fornicil)

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15
Q

Where are goblet cells mainly concentrated at in the conj and where are they absent

A

Mainly concentrated in the nasal and inferior nasal region of the conj.
Absent at the limbus.

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16
Q

Goblet cells use which methods for secretion

A

Merocrine releasing vesicles and apocrine releasing apical portion of cell and product

17
Q

What is the most predominant mucin produced by goblet cells?

A

MUC5AC

18
Q

Mucin produced by goblet cells are rich in which three amino acids? How do these aa affect the characteristics of mucin?

A

Serine, threonine, and cysteine.

Serine and threonine serve as sights for O-glycosylation (where carbohydrates can attach), which gives a negative charge to the glycoprotein and makes mucins highly hydrophilic and able to mix with the aqueous component of the tear film.

Cysteine rich areas form disulfide bonds, which enhance adhesive properties.

19
Q

How is mucin secretion regulated?

A

Regulated by neural control. Stimulation of CN 5 in the cornea and conj contribute to the secretion of mucin.

Motor innervation is unknown. (some type of involuntary control)

20
Q

Accessory lacrimal glands are located where

A

Krause- forniceal conj stroma

Wolfring- Located in the palpebral conj stroma along posterior border of tarsal plate

21
Q

Are krause and wolfing merorcine, aprocrine, or holorcrine

A

Merocrine

22
Q

The lacrimal gland is divided into two lobes by what

A

Divided by the levator muscle. This creates the orbital lobe, which is in the lacrimal fossa of the frontal bone and the palpebral lobe is in the superior temporal eyelid. Can be seen if swollen.

23
Q

The lacrimal gland is composed of which three cells and in what amounts?

A 
Acinar (80%) 
Ductal cells (10-15%)
Myoepithelial cells (5-10%)
24
Q

Role of acinar cells in the lacrimal gland

A

Is a specialized epithelial cell that makes up glands. Secretes aqueous by merocrine method.

25
Q

Role of myoepithelial cell in the lacrimal gland

A

Specialized epithelial cell that pushes on acinar cells so that they release aqueous by merocrine method.

26
Q

What 6 components make up the aqueous portion of the tear film?

A

Water, electrolytes, soluble proteins, glucose, lactate, and urea.

27
Q

98-99% of the mucoaqueous layer is made of

A

water

28
Q

Electrolytes found in the aqueous portion of the tear film

A

Na+, Cl-, K+, Mg2+, Ca2+, bicarbonate and phosphate

29
Q

Normal osmolarity of the tear film

A

~300 mOsm/L

30
Q

Hyperosmolarity

A

Higher concentration of solutes in the tear film, resulting in less water due to abnormal tear evaporation (due to poor lipid layer, bc lipids prevent evaporation) or to low tear volume (due to low production of aqueous by the lacrimal gland or accessory lacrimal glands)

Linked to dry eye

31
Q

What electrolyte in the aqueous layer of the tear film helps maintain the pH and at what level?

A

Bicarbonate and pH 6.8-8.2

32
Q

What roles do soluble proteins play in the aqueous portion of the tear film?

A

Over 200 peptides and 1,500 proteins play a role in the immune system (lysozyme, lactoferrin, lipocalin, immunoglobulins and cytokines) and play a role in corneal wound healing (Growth factors, matrix matealloproteinases)

33
Q

The role of glucose, lactate and urea in the aqueous portion of the tear film?

A

Glucose and lactate are involved with energy metabolism and urea is a waste product due to protein metabolism

34
Q

Aqueous secretion is regulated how?

A

By neural control of CN V. CN V is stimulated every time you blink.

Brain returns response via a parasympathetic motor nerve.

35
Q

3 types of tears

A

Basal tears- occurs due to normal blinking and stimulation of CN V. Causes mucin, meibum, and aqueous to be secreted in response.

Reflex tears- Secreted in response to an irritant. Irritant stimulates CN V which causes the production and release of aqueous and mucin.

Emotional tears are secreted in response to stimulation of the limbic system and subsequent activation of the parasympathetic system

Fall 2019: OPT 114 Ocular Anatomy and Physiology (50 decks)

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