Editing Tears (section)

=== Chemical composition ===
Tears are made up of three layers: lipid, aqueous, and mucous.<ref name="Moshirfar2014">{{cite journal |vauthors=Moshirfar M, Pierson K, Hanamaikai K, Santiago-Caban L, Muthappan V, Passi SF |title=Artificial tears potpourri: a literature review |journal=Clin Ophthalmol |date=July 2014 |volume=8 |pages=1419–33 |pmid=25114502 |pmc=4124072 |doi=10.2147/OPTH.S65263 |doi-access=free }}</ref> Tears are composed of [[water]], [[salt (chemistry)|salt]]s, [[antibody|antibodies]], and [[lysozyme]]s (antibacterial enzymes); though composition varies among different tear types. The composition of tears caused by an emotional reaction differs from that of tears as a reaction to irritants, such as onion fumes, dust, or allergens. Emotional tears contain higher concentrations of stress hormones such as [[adrenocorticotropic|adrenocorticotropic hormone]] and [[enkephalin|leucine enkephalin]] (a natural pain killer), which suggests that emotional tears play a biological role in balancing stress hormone levels.<ref>{{cite journal|last1=Frey|first1=William H.|last2=Desota-Johnson|first2=Denise|last3=Hoffman|first3=Carrie|last4=McCall|first4=John T.|date=October 1981|title=Effect of Stimulus on the Chemical Composition of Human Tears|journal=American Journal of Ophthalmology|volume=92|issue=4|pages=559–567|doi=10.1016/0002-9394(81)90651-6|pmid=7294117}}</ref> 
{| class="wikitable"
|-
! style="width: 10%;"|Name
! style="width: 40%;"|Contents
! style="width: 10%;"|Secretors
! style="width: 40%;"|Functions
|- style="vertical-align: top;"
|Lipid layer
|[[Lipid|Oils]]
|[[Meibomian gland]]s (or tarsal glands)
|Coats the aqueous layer, provides a [[hydrophobe|hydrophobic]] barrier that envelops tears and prevents their spilling onto the cheek. These glands are located among the [[Tarsus (eyelids)|tarsal plates]], and thus deposit the tear fluid between the eye proper and the oil barriers of the lids.<ref name="ReferenceA">"eye, human."Encyclopædia Britannica from [[Encyclopædia Britannica 2006 Ultimate Reference Suite DVD]] 2009</ref>
|- style="vertical-align: top;"
|Aqueous layer
|[[Electrolyte]]s, 60 metabolites—amino acids (1-Methylhistidine/3-Methylhistidine, arginine, Asymmetric, asymmetric dimethylarginine/symmetric dimethylarginine, citrulline, creatine, glutamine, homoarginine, hydroxyproline, phenylalanine, proline, pyroglutamic acid, serine, taurine, theonine, tryptophan, tyrosine, urocanic acid, Valme), amino alcohols (panthenol), amino ketones (allantoin, creatine), aromatic acids (cinnamic acid, o-Coumaric acid/m-Coumaric acid/p-Coumaric acid), carbohydrates (N-Acetylneuraminic acid), carnitines (acetylcarnitine, carnitine, hexanoylcarnitine, palmitoylcarnitine), cyclic amines (Niacinamide), dicarboxylic acids (fumaric acid/Maleic acid), Nucleosides (1-Methyladenosine, adenosine, cytidine, guanosine, inosine, S-Adenosyl-homocysteine, S-Adenosylmethionine, uridine, and [[xanthosine]]), nucleotides (ADP, AMO, CMP, Cytidine diphosphate choline, GMP, IMP, UDP, UMP, UDP-N-acetylgalactosamine/UDP-N-acetylglucosamine), peptides (Oxidized glutathione), phospholipids (1-Palmitoyl-lysophosphatidylcholine), purines and derivatives (Hypoxanthine, Theobromine, uric acid, xanthine), purines and derivatives (4-Pyridoxic acid), Quaternary Amines (Acetylcholine, Glycerophosphocholine, phosphocholine), and Tricarboxylic Acids (citric acid), and other substances such as proteins (e.g., [[antibody|antibodies]],<ref name="Moshirfar2014" /> [[lipocalin]], [[lactoferrin]], [[lysozyme]],<ref>{{cite web|url=http://www.medrounds.org/ocular-pathology-study-guide/2005/10/tear-proteins.html|title=Ocular Pathology Study Guide: Tear Proteins<!-- Bot generated title -->|website=medrounds.org|url-status=dead|archive-url=https://web.archive.org/web/20060627200147/http://www.medrounds.org/ocular-pathology-study-guide/2005/10/tear-proteins.html|archive-date=2006-06-27}}</ref> and [[lacritin]])
|[[Lacrimal gland]]
|Promotes spreading of the tear film, the control of infectious agents, and osmotic regulation.
|- style="vertical-align: top;"
|Mucous layer
|[[Mucin]]s
|Conjunctival [[goblet cell]]s
|Coats the [[cornea]], provides a hydrophilic layer and allows for even distribution of the tear film.
|}