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Tears are a clear liquid secreted by the lacrimal glands (tear gland) found in the eyes of all land mammals. 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 symbolic significance among humans. Tears are made up of three layers: lipid, aqueous, and mucous. Tears are composed of water, salts, antibodies, and lysozymes (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 hormone and leucine enkephalin (a natural pain killer), which suggests that emotional tears play a biological role in balancing stress hormone levels. The lacrimal glands secrete lacrimal fluid, which flows through the main excretory ducts into the space between the eyeball and the lids. When the eyes blink, the lacrimal fluid is spread across the surface of the eye. Lacrimal fluid gathers in the lacrimal lake which is found in the medial part of the eye. The lacrimal papilla is an elevation in the inner side of the eyelid, at the edge of the lacrimal lake. The lacrimal canaliculi open into the papilla. The opening of each canaliculus is the lacrimal punctum. From the punctum, tears will enter the lacrimal sac, then on to the nasolacrimal duct, and finally into the nasal cavity. An excess of tears, as caused by strong emotion, can cause the nose to run.

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Related publications (1)

Related concepts (10)

Fiber distribution in a 3D FEM Model of the Supraspinatus Tendon

Romy Alexandra Hasler

The supraspinatus tendon is often involved in rotator cu↵ tears. The pathogenesis of such tears is not well known and can be multicausal (mechanical, inflammatory, ...). The idea of this project was to analyse the mechanical contribution to rotator cuff tears with a numerical deformation analysis of the supraspinatus tendon. The tendon was simulated under tension in two conditions: an isotropic case and an anisotropic case. In the isotropic case, the tendon was simulated with the same material properties in every direction. In the anisotropic case, the tendon’s fiber were computed and the material was defined in the fiber direction and in the transverse direction. In the isotropic case, the strain was found to be higher in the two studied position (90 ̊abduction and rest position) than in the anisotropic case. In both cases (isotropic and anisotropic) the maximal strain is situated at the distal side of the tendon insertion on the humeral head. The di↵erence in the strain value is due to the fact that the isotropic material definition is averaged in all direction and therefore is softer in the fiber direction and stronger in the transverse direction. The isotropic model is herefore not very consistant with a real tendon structure. Both models are consistent with clinical observations as supraspinatus tears occur usually at the distal side of the insertion. However, for qualitative deformation analysis an anisotropic material choice is recommended.

2014

Tears

Crying

Crying is the dropping of tears (or welling of tears in the eyes) in response to an emotional state or pain. Emotions that can lead to crying include sadness, anger, excitement, and even happiness. The act of crying has been defined as "a complex secretomotor phenomenon characterized by the shedding of tears from the lacrimal apparatus, without any irritation of the ocular structures", instead, giving a relief which protects from conjunctivitis. A related medical term is lacrimation, which also refers to non-emotional shedding of tears.

Cornea

The cornea (: corneas or corneae) is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. Along with the anterior chamber and lens, the cornea refracts light, accounting for approximately two-thirds of the eye's total optical power. In humans, the refractive power of the cornea is approximately 43 dioptres. The cornea can be reshaped by surgical procedures such as LASIK. While the cornea contributes most of the eye's focusing power, its focus is fixed.