Quiz 3 Lacrimal Gland

What does the lacrimal gland secrete?

water, electrolytes, proteins

Lacrimal gland function

maintains tear homeostasis, meets tear fluid demand

How do the lacrimal glands maintain fluid demand

neural and hormonal feedback loops

Endocrine gland definition

systemic (circulation) passage hormone to target

Exocrine gland definition

release contents via duct to target

Types of Exocrine glands

Apocrine

Holocrine

Aqueous secretion

basal and reflex secretion

Basal secretion

accessory lacrimal glands

Primary secretion

Accessory lacrimal glands

Normal secretion of basal glands

1.2 ul/min

Characteristics of basal aqueous production

decreases with age (50% by age 65)

no daytime variation

negligible during sleep

How fast do newborns secrete basal aqueous secretions

24 hrs

Accessory glands

Responsible for <10% of total aqueous secretions

identical structure to lacrimal

provide basal tear secretions

Types of accessory lacrimal glands

Krauss and Wolfring

Location of Krauss gland

Lateral fornix

Location of Wolfring

upper margin of tarsal plate

Electrolyte compostiton

Na+

Cl-

K+

HCO_3

Ca++

Mg++

Other molecular composition

H2O

Protein

Glucose

Urea

Electrolytes

Total molecular composition of water

98.2%

Stimulus to secretion is a:

reflex

(reflex) AFFERENT Lacrimal Reflex Arc CN?

CN V (trigeminal)

Afferent Lacrimal Reflex Arc stimulates

Cornea

Conjunctiva

CN for Dazzle (eye floaters)

CN II (Optic)

CN for Taste

CN VII (facial)

Cough-sneeze-laugh

CN IX (glossopharyngeal), CN X (vagus)

EFFERENT Lacrimal Reflex Arc CN?

CN VII

EFFERENT Lacrimal Reflex Arc is from

superior salivatory (pons)

Drugs that INCREASE tear production

Pilocarpine, marijuana, epinephrine, ephedrine, hydralazine, ketamine, methacholine

Drugs that DECREASE tear production

diazepam, antihistamine, atropine, phenothiazine (chlorpromazine, amitriptyline, nitrous oxide, some beta-blockers)

Normal plasma osmolartiy

290 mOsm

Isomolar solution

290 mOsm

Hyperosmolar Solutions osmolarity

> 290 mOsm

Hypo-osmolar solutions osmolarity

<290 mOsm

What is Tonicity

the ability of a solution to cause a cell to shrink or swell

ISOtonic

a solution with the same solute concentration of the cytosol

ECF=ICF

HYPERtonic

a solution with GREATER solute concentration than the cytosol

ECF>ICF

HYPOtonic

solution with LESSER solute concentration than the cytosol

ECF

When the cell is hypertonic, it will

shrink

When the cell is hypotonic, it will

swell

Hypertonic tears result from

decreased stimulation

evaporation

Hypotonic tears result from

increased stimulation

Normal osmolarity levels

280-305 mOsm/L

Dry eye osmolarity levels

Above 318 mOsm/L

Dry Eye Syndrome (DES)

A condition of increased tear osmolarity

DES can be due to

evaporation and reduced aqueous production (secretion)

Evaporation in DES is due to

-anatomical and environmental factors

-decreased tear turnover

Meibomian gland dysfunction (lipid deficiency) causes

Evaporation in DES

Reduced aqueous production (secretion) is caused by

-reduced neural input

-inflammation

-hormonal, autoimmune disorder

Common canaliculus angles act as a

Valve of lacrimal drainage

Lacrimal Drainage is encircled by which muscle

Orbicularis muscle

and the eyelids contribute

How much % of secreted tear volume is lost by evaporation

10-25%

Where is the rest of secreted tear volume drained through

The nasal passage

Some is absorbed in the nasolacrimal system

Describe the direction of the tear flow in the eye

Originates from lacrimal + accessory glands in temporal side of eyelid -> across eye -> enter lacrimal punctum -> superior and inferior canalicula -> into lacrimal sac -> lacrimal duct -> and finally drains into the nasal cavity

Are reflex tears part of the tear film

NOOOOOOOOO HOOOOOOOO

Basal Layer of tears

Outer lipid layer

Middle aqueous layer

Mucous layer

Tear Film function

-physical protection

-buffer

-lubricate

-flushing action

-garage pickup

-bacteriostatic/lytic (lysozyme, betalysin, lactoferrin)

Optical tear film function

smooth surface of cornea

Tear film function in terms of healing

-white blood cells

-epidermal growth factor

Tear film function in terms of osmotic gradient

important for the cornea

(prefers Isomotic)

Tear film function in terms of nutrition

primary O2 for cornea

AVASCUlAR

Types of Glands

Endocrine

Exocrine

Apocrine gland definition (exocrine)

like goblet and moll (sweat), apex of secretory cell released with secretion

Holocrine gland definition (exocrine)

like Zeiss and Meibomian (sebaceous), secretory cell enters duct with secretion then ruptures

Layers of the tear film from posterior to anteiror

Mucin

Aqueous

Lipid

Total thickness of Tear Film

7-10 microns

Cornea:Glycocalyx-

-glycosylation of membrane bound proteins on surface of corneal epithelial cells

-Microvilli increase surface area

-Interacts with mucin layer of tea film

Glycocalyx function

-Plays a role in stabilization of tear film

-Protects against bacterial pathogens

Disruption of stabilization in tear film causes

instability of teas and dry eyes

can be caused by contact lenses

Mucin is

(first layer of contact with cornea)

Heterogenous collection of glycoproteins

Mucin is formed by

Sugar side chain interactions with sugar chains of glycocalyx on apical surface of epithelium

Cross linking of side chains provides tear film stability

Gradu/Eye crud

during sleep mucin is entrapped by caruncle cilia

Mucin function

-provides hydrophilic surface

-lubrication

-healing

-pathogen protection

-antioxidant

Mucin Sources

Goblet cells in conjunctiva- unicellular apocrine gland

Non-goblet epithelial cells- crypts of henle (tarsal conjuctiva), glands of manz (limbus)

Glands associated with the lid

Lacrimal gland (main)

Glands of Krauss & Wolfring (accessory lacrimal gland)

Goblet cells

Glands of Moll (sweat)

Glands of Zeis (sebaceous)

Meibomian gland (sebaceous)

Parasympathetic control of Mucin production

Acetylcholine (ACh)

Sympathetic control of Mucin production

Norepinephrine and neuropeptide Y (NPY)

Aqueous Sources

90% of tears

Lacrimal gland (90-95%)

Accessory glands (Krauss, Wolfring)~basal

Tertiary- some from bulk flow from anterior chamber (aqueous humor)

Tear Meniscus

Reservoir or lacrimal lake at the lower lid margin

Alteration indicate degree of aqueous deficiency

Lipid Secretion

Meibomian (tarsal) glands

Glands of Zeiss and Moll

Lipid Function

-delay evaporation of aqueous by 90%

-lubricate lid

-spreads with blink and carries aqueous

-decreases surface tension of tear film

-prevent overflow of tears at margin

Disruption of lipid layer leads to

clinical dry eye

Secretion and Regulation of Lipids (2)

Neural

Hormonal

Neural secrretion and regulation of lipids

Parasympathetic: Acetylcholine-ACh, Vasoactive intestinal peptide (VIP)

Sympathetic: Neuropeptide Y-NPY

Hormonal secretion and regulation of lipids

Androgens- testosterone

Blepharitis

Causes tear film disruption

Inflammation of eye lids disrupts lipid layer of tear film due to phospholipase (PLA2) secreted by inflammatory cells

Tear break up time (TBUT)

interval from last complete blink to first random "dry" spot

Normal 15-45 sec

Clinically important TBUT

<10 sec

Schirmers Test

wetting thin paper strip, one end placed in cul-de-sac of LL

-normal >10mm in 5 min

-with (BASAL) without (REFLEX) anesthetic

-sensitivity 25% (miss many dry eyes)

-specificity 90% (most caught are "true" dry)

Tear protein testing

protein antibody reaction determines presence of proteins on tear soaked filter paper

-lysozyme (quantiplate assay)

-lactoferrin (lactoplate assay): more used clinically, reasonable sensitivity and specifies for Keratoconjunctivitis (KCS)

Types of Goblet/Mucin Test (3)

-Impression cytology

-Periodic acid schiff (PAS)

-Ferning

Impression Cytology

goblet/mucin test

determines # and quality of goblet cells\

cellulose acetate paper is pressed against bulbar conjunctiva

observed microbially

Periodic acid schiff (PAS)

goblet and mucin test

stains mucin containing goblets

Ferning

goblet and mucin test

-drying patterns on slide seen in microscope

-reflect tear composition

Meibometry

asses Meibomian gland production or dysfuntion

Noninvasive test (3)

Slit lamp evaluation

Reflect grid pattern

Tear scope

Slit lamp evaluation

noninvasive test

-tear film using specular reflection

-tear meniscus

Reflect grid pattern (placido disc) from cornea

noninvasive test

-waviness shows disruption

- decreased TBUT