Where do tears come from? Usually we say that from happiness, sadness, pain - that is, we consider them a manifestation of emotions. We focus on the psyche, forgetting about physiology. And yet they play a very important role in protecting the eyes. How does our body produce tears and what do they primarily serve?

Contents:

  1. Where do the tears come from - the distribution of tears
  2. Where do tears come from - drainage of tears
  3. Where do tears come from - composition of tears
  4. Where do tears come from - properties of tears

Where do tears come from?Our eyes produce about 1-2 microliters of tears per minute, but in the elderly this process is much slower, so seniors often complain of dryness eyes. In babies, the first tears appear at the end of the first month of life.

As many as 7 different glands are involved in the production of tears. They are:

  • proper tear gland
  • Krause's additional tear glands
  • Wolfring's additional tear glands
  • Manza glands
  • Henle's crypts
  • Molla ciliary glands
  • Zeiss sebaceous glands

Tears are formed in the proper lacrimal gland, which is located in the upper part of the eye socket. It is about 20 x 12 mm and is divided into the orbital and eyelid parts.

Tears also form in the accessory glands of Krause and Wolfring.

Conjunctival goblet cells, Henle's crypts, and Manz glands produce mucus.

The thyroid glands, sebaceous and ciliary glands produce fatty secretion.

Basal tears are secreted in accessory glands.

Tears are formed in the proper gland related to:

  • pain
  • irritation of the optic or olfactory nerve
  • mechanical pressure of the circular muscle on the lacrimal gland (this occurs when sneezing, yawning or coughing)

and emotional tears (of central origin).

Where do the tears come from - the distribution of tears

Tears are spread over the eye thanks to the work of the eye muscles.

When the eye's circular muscle contracts, tears flow along the tear strand at the upper eyelid, towards the nose, then downwards. From the temporal side, they move downwards by the force of gravity, forming the tear strand of the lower eyelid.

Both of these strands combine at the crescent fold and the lacrimal muscle to form the so-calledtear lake.

The movement of the eyelids causes the tears to be distributed evenly over the surface of the cornea with each blink, creating the so-called tear film, which consists of three layers - outer lipid (fat), middle water and inner mucin (mucous).

Where do tears come from - drainage of tears

The system that drains excess tears into the nasal cavity consists of tubules, lacrimal sac and nasolacrimal duct.

Under proper conditions, a large proportion of your tears will evaporate. The rate of tear evaporation depends on the width of the eyelid gap, blinking frequency, ambient temperature and air humidity. The natural evaporation of tears means that only a small amount of tears passes through the drainage system.

The tears flow along the upper and lower rim of the eyelids thanks to the phenomenon of capillary hair. This is how they enter the upper and lower tear ducts.

During blinking, the parathyroid part of the circular muscle of the eye exerts pressure on the tear bulbs, shortening and compressing the horizontally running segment of the tear ducts and aligning the medial tear points.

The lacrimal part of the eye's circular muscle contracts and compresses the pouch. The positive pressure generated in this way sucks tears from the tubules into the lacrimal sac.

When you open your eyes, the muscles relax, the ducts and the tear sac widen, and the negative pressure that results, together with the capillary forces, causes the tears to travel to the empty tear sac.

There, due to the force of gravity and elasticity of the tissues, they pass through the nasolacrimal canal to the lower nasal passage.

Where do tears come from - composition of tears

Tears( tear fluid ) is a substance that moisturizes and cleans the eyeball and protects the surface of the conjunctiva and cornea from germs that could lead to eye infections.

Tears are transparent liquid. The main ingredient of tears is water. In addition to it, the component of tears is also:

  • sodium chloride (about 0.9%) giving them a s alty taste,
  • proteins (about 0.5-0.7%) - albumin, lysozyme (dissolves the cell membrane of bacteria) and globulins
  • ascorbic acid
  • sugar
  • urea
  • electrolytes (chloride and phosphorus anions, sodium and potassium cations)

Our tears do not always have the same composition. And it depends on the function that the tears are supposed to perform at the moment.

If tears appear as a result of irritation, blurring of the eye, strong wind or frosty air, or when coughing, they contain more water and antibodies that would stop the development of possible infection.

When we cry because ofstrong emotions, tears contain more protein than basal tears. They also contain prolactin, leucine enkephalin (has an analgesic effect) and ACTH (a hormone that stimulates the secretion of adrenaline and cortisol).

Some medications can also influence the secretion of tears. These are mainly preparations that act on the nerve endings. Examples of such drugs include:

  • psychotropic drugs
  • drugs used in the treatment of serious rheumatic diseases
  • birth control pills

The drugs that reduce the secretion of tears also include atropine. More tears will appear, e.g. after pilocarpine.

There are also medical conditions (e.g. Sjögren's syndrome) that cause reduced tear production.

Where do tears come from - properties of tears

The main function of tears is to moisturize the eyes and disinfect them.

The tear film also prevents the cornea and conjunctiva from drying out.

Tears have bactericidal properties because they contain, inter alia, lysozyme, a cationic protein that breaks down the cell walls of bacteria.

The bactericidal effect of tears was discovered by Alexander Fleming (the creator of penicillin). During laboratory tests, a tear accidentally dripped on a slide with bacterial strains. After a few days, Fleming examined the slide and was surprised to find that there were no bacteria on its surface. The scientist examined the tear fluid and found lysozyme in it.

It is thanks to tears that bacteria cannot penetrate the body through the eyes and nose.

In case of eye irritation, tears are released profusely to rinse the surface of the eye and clean it of foreign matter.

Tears also have an analgesic effect, thanks to leucine enkephalin, which has an analgesic effect.

Worth knowing

Why does crying sometimes make you feel better? Because when you start crying, your brain releases opiate substances that make you:

  • lowers blood pressure
  • more oxygen reaches the brain
  • a feeling of relaxation appears

So, to feel better, sometimes it's worth crying a little.

About the authorAnna Jarosz A journalist who has been involved in popularizing he alth education for over 40 years. Winner of many competitions for journalists dealing with medicine and he alth. She received, among others The "Golden OTIS" Trust Award in the "Media and He alth" category, St. Kamil awarded on the occasion of the World Day of the Sick, twice "Crystal Pen" in a nationwide competition for journalists promoting he alth, and many awards and distinctions in competitions for the "Medical Journalist of the Year" organized by the NationalJournalists for He alth Association.

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Category:

Eye diseases and vision disorders