VISC 3292: Lacrimal System

Functions of the lacrimal system

Secrete water, electrolytes, and proteins; maintain tear film through a negative feedback loop mechanism with both neuronally/hormonally

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

Accessory lacrimal glands

Glands of Krauss and Wolfring; make up the basal tear secretion; are smaller but identical to the structure of the primary lacrimal gland; anterior structures

Basal tear secretion

Performed by the accessory lacrimal glands; less than 10% of total tear secretion; no daytime variation; decrease with age (contributing to dry eye syndrome)

Reflex tear secretion

Primary lacrimal gland; is NOT part of the tear film

Contents of lacrimal secretion

Water, electrolytes, urea, glucose, and proteins

Sensory organ of the lacrimal reflex arc

Cornea, conjunctiva, or nasal mucosa

Afferent arm of the lacrimal reflex arc

CN V

Efferent arm of the lacrimal reflex arc

CN VII

Effector organ of the lacrimal reflex arm

Lacrimal gland

Normal range for osmolarity of the tear film

280 - 305 mOsm

Hypertonic tear film

> 305 mOsm; too concentrated; occurs from inc. evaporation or decreased stimulation

Hypotonic tear film

< 280 mOsm; diluted/excess water; occurs from inc. stimulation

Functions of the tear film

Optical, protection, lubrication, bacteriostatic + bacteriolytic, healing, nutrition of cornea, maintains osmotic gradient

Layers of tear film (outer to innermost)

Lipids, aqueous, and mucous layers

Apocrine

The apex of the cell is released with secretion; includes sweat glands

Holocrine

The secretory cells enter the duct and then rupture; includes sebaceous glands