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Tears are a clear liquid secreted by the (tear gland) found in the of all Mammal. Tears are made up of water, electrolytes, proteins, lipids, and mucins that form layers on the surface of eyes. The different types of tears—basal, reflex, and emotional—vary significantly in composition. The functions of tears include lubricating the eyes (basal tears), removing irritants (reflex tears), and also aiding the immune system. Tears also occur as a part of the body's natural pain response. Emotional secretion of tears may serve a biological function by excreting stress-inducing hormones built up through times of emotional distress. Tears have Crying.
| Lipid layer | Lipid | (or tarsal glands) | Coats the aqueous layer, provides a hydrophobe barrier that envelops tears and prevents their spilling onto the cheek. These glands are located among the tarsal plates, and thus deposit the tear fluid between the eye proper and the oil barriers of the lids."eye, human."Encyclopædia Britannica from Encyclopædia Britannica 2006 Ultimate Reference Suite DVD 2009 |
| Aqueous layer | , 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, lipocalin, lactoferrin, lysozyme, and lacritin) | Lacrimal gland | Promotes spreading of the tear film, the control of infectious agents, and osmotic regulation. |
| Mucous layer | Conjunctival | Coats the cornea, provides a hydrophilic layer and allows for even distribution of the tear film. |
| Basal tears | In healthy eyes, the cornea is continually kept wet and nourished by basal tears. They lubricate the eye and help keep it clear of dust. Tear fluid contains water, mucin, lipids, lysozyme, lactoferrin, lipocalin, lacritin, , glucose, urea, sodium, and potassium. Some of the substances in lacrimal fluid (such as lysozyme) fight against infection as a part of the immune system. Lysozyme does this by dissolving a layer in the outer coating, called peptidoglycan, of certain bacteria. It is a typical body fluid with salt content similar to blood plasma. Usually, in a 24-hour period, 0.75 to 1.1 grams (0.03–0.04-ounce avoirdupois) of tears are secreted; this rate slows with age. |
| Reflex tears | The second type of tears results from irritation of the eye by foreign particles, or from the presence of irritant substances such as onion vapors, and other fragrances, tear gas, or pepper spray in the eye's environment, including the cornea, conjunctiva, or nasal mucosa, which trigger TRP channels in the ophthalmic nerve. It can also occur with bright light and hot or peppery stimuli to the tongue and mouth. It is also linked with vomiting, coughing, and yawning. These reflex tears attempt to wash out irritants that may have come into contact with the eye. |
| Emotional tears (psychic tears) | The third category, in general, referred to as crying or weeping, is increased tearing due to strong emotional stress, pleasure, anger, suffering, mourning, or Pain. This practice is not restricted to negative emotions; many people cry when extremely happy, such as times of intense humor and laughter. In humans, emotional tears can be accompanied by reddening of the face and sobbing—cough-like, convulsive breathing, sometimes involving spasms of the whole upper body. Tears brought about by emotions have a different chemical makeup than those for lubrication; emotional tears contain more of the protein-based hormones prolactin, adrenocorticotropic hormone, and Leu-enkephalin (a natural painkiller) than basal or reflex tears. The limbic system is involved in the production of basic emotional drives, such as anger, fear, etc. The limbic system, or, more specifically the hypothalamus, also has a degree of control over the autonomic system. The parasympathetic branch of the autonomic nervous system controls the lacrimal glands via the neurotransmitter acetylcholine through both the nicotinic and muscarinic receptors. When these receptors are activated, the lacrimal gland is stimulated to produce tears.Skorucak A. "The Science of Tears." ScienceIQ.com. Accessed September 29, 2006. |
Crying is often associated with babies and children. The infants that are unable to vocally communicate have many alternating tones in their crying, attracting the attention of the caregiver and specifically their biological mothers.Carollo A, Montefalcone P, Bornstein MH, Esposito G. A Scientometric Review of Infant Cry and Caregiver Responsiveness: Literature Trends and Research Gaps over 60 Years of Developmental Study. Children (Basel). 2023 Jun 10;10(6):1042. doi: 10.3390/children10061042. PMID: 37371273; PMCID: PMC10297674. Blood-related mothers goes through physiological changes upon exposure to the crying, with acceleration in muscles and decrease in heart rate, as well as understanding the vocalizations of the baby's crying. This is a mother-specific case, as the other caregivers, like biological father or adoptive parents, are not able to decode the sound.
Some cultures consider crying to be undignified and infantile, casting aspersions on those who cry in public settings, excluding circumstances which concerns loss of a relative or a loved one. In most Western cultures, it is more socially acceptable for women and children to cry than men, reflecting masculine sex-role stereotypes. In some Latin regions, crying among men is more acceptable. There is evidence for an interpersonal function of crying as tears express a need for help and foster willingness to help in an observer.
Some modern psychotherapy movements such as Re-evaluation Counseling encourage crying as beneficial to health and mental well-being. An insincere display of grief or dishonest remorse is sometimes called crocodile tears in reference to an Ancient Greek anecdote that crocodiles would pretend to weep while luring or devouring their prey. In addition, "crocodile tears syndrome" is a colloquialism for Bogorad's syndrome, an uncommon consequence of recovery from Bell's palsy in which faulty regeneration of the facial nerve causes people to shed tears while eating.
Treatment for dry eyes to compensate for the loss of tear film include eye-drops composed of methyl cellulose or carboxy- methyl cellulose or hemi-cellulose in strengths of either 0.5% or 1% depending upon the severity of drying up of the cornea.
Obstruction of the Lacrimal punctum, nasolacrimal canal, or nasolacrimal duct can cause even normal levels of the basal tear to overflow onto the face (Epiphora), giving the appearance of constant psychic tearing. This can have significant social consequences.
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