Tear production & Crying

Tear production and crying

the tear film that covers the suface of the eye has 3 layers:
1. lipid secreted by oil glands in the eyelids
2. aqueous-based solution from lacrimal gland (contains lysozyme and other enzymes that provide protection against infection)
3. mucous from the conjunctiva

the composition of the tear layer varies depending upon the stimulus and with age
- emotional tears contain more hormones, such as prolactin, ACTH and enkephalin
- basal tear production decreases with age

tear flow occurs via evaporation and drainage through the nasolacrimal ducts into the nasal cavity
- parasympathetic stimulation produces epiphora (overflow of tears) by:
  1. increasing tear production by the lacrimal gland
  2. decreasing outflow by facilitating closure of the lacrimal duct passage
- epiphora can be induced by:
  1. stimulation of the cornea (cranial nerve V) which produces reflex tears
  2. strong emotional responses (mediated by the limbic system, especially the hypothalamus) which produce psychic tears (crying or weeping)
    - strong parasympathetic stimulation is accompanied by other symptoms, like reddening of the face and convulsive breathing

Email: Dr. Janet Fitzakerley | ©2015 University of Minnesota Medical School Duluth | Last modified: 14-feb-15 4:15 PM