Yawning is our body’s way of accessing an increased amount of oxygen when we are tired or lack of oxygen. Everyone yawns, and most people know that it is in some way related to tiredness, so why do your eyes water when yawning? What is the reason for the lacrimal glands getting involved in the process at all? This article will aim to answer these questions.
Why Do Your Eyes Water When You Yawn?
When someone yawns, there is a small increase in pressure within the skull, which is likely caused by an increase in the amount of oxygen inhaled during a long yawn, or by tensing of facial muscles. This increase in pressure causes the fluid that surrounds the brain, cerebrospinal fluid, or CSF, to be pushed or forced out of the brain’s system of ventricles faster than normal. The excess fluid enters the lacrimal system, which is the system that creates tears, and is pushed out as tears.
Pressure on the Lacrimal Bag
When asking, ‘why do your eyes water when you yawn?’ Much consideration must be placed upon the lacrimal system. As mentioned, tears are created via the lacrimal system; this system is comprised of three key components: lacrimal glands, lacrimal bag, and lacrimal ducts. Lacrimal glands are situated near the nose on the inside of the eye lids, and are responsible for excreting fluid into the lacrimal bag. From there, it is expelled via the lacrimal ducts into the eye, to help ensure optimum moisture. When one yawns, it is plausible that excess pressure is put upon the lacrimal system, particularly the lacrimal bag, which causes liquid to be expelled in the form of tears.
Lacrimal gland excretion, or tears, is controlled by the autonomic nervous system. This system controls involuntary bodily functions, such as your heartbeat and digestive system, as opposed to the somatic nervous system which controls voluntary actions, such as walking. When certain autonomic nerves are activated, the glands of the lacrimal system excrete liquid in the form of tears, which appear and fall from the eyes. Along with the excretion of fluid, the activation of the nerves also causes nasal glands to secrete, as well as cause your pupils to become smaller. It is possible that, when yawning, you are causing activation of these nerves.
On most occasions when people yawn, they tightly shut their eyes during the process. This also has an attributing factor to the production of tears in two ways. Firstly, it causes pressure to be placed upon the lacrimal duct, which in turn causes an increased amount of fluid to be forced into the eyes. Secondly, it causes the tear ducts to close, which would usually drain excess fluid from the eye’s surface. A combination of these two actions causes an excess build of tear fluid within the eye, with nowhere to go, meaning once you have finished yawning, your eyes will be watery.
Description and the Composition of Different Types of Tears
Not all tears within the eye are the same; some research even suggests that there are differences at a chemical level when comparing different types of tears. The three types of tears are basal tears, reflex tears and psychic tears. The characteristics and function of each type is detailed below:
Basal Tears
Basal tears, also known as lubricating tears, do exactly that; lubricate the eye. They are produced consistently throughout the day to ensure that the eye is kept moist, as well as offer protection. Basal tears contain a precise mixture of water, oil, mucous, antibodies, and nutrient proteins, which moisten, nourish, and protect the eye’s front surface. Within this tear fluid, the following can be found:
- Water
- Mucin
- Lysozymes
- Lipids
- Lactoferrin
- Liacritin
- Lipocalin
- Glucose
- Immunoglobulins
- Urea
- Sodium
- Potassium
Some substances within the fluid also make up part of the immune system (such as lysozyme). This substance, and others, battle against bacteria and prevent infection. This is done by dissolving the outer coating of bacteria, or peptidoglycan. On average, around 0.75-1.1g of basal tears are secreted within a twenty-four hour time period, although the rate in which tears are produced slows as a person ages.
Reflex Tears
Reflex tears do not have the same value as basal tears in terms of lubrication. Reflex tears are comprised mainly of water, and act almost as a defence mechanism for your eye. When an irritant comes into contact with the eye, like when you are cutting onion, for example, reflex tears will fill your eye to wash away any unwanted substances. These tears may also form from lack of lubrication within the eye, a condition known as dry eye syndrome. A signal is sent through the nervous system to say that the eye requires more fluid, and reflex tears are formed. Although they provide the eyes with more moisture, as mentioned, they do not have the same lubrication properties as basal tears, and do not coat the eyes effectively. When excess amounts of this tear are produced, it can fall out of the eye and run down the cheek, in what is known as crying.
Crying or Weeping (Psychic Tears)
This type of tear is produced due to reaction to an emotional occurrence. This can be a result of positive or negative emotions, many people crying with tears of sadness, or tears of joy. These types of tears can also be accompanied by blushing (reddening of the face), convulsive breathing, and sometimes cause the entire upper-body to spasm. Psychic tears are chemically different to basal and reflex tears, as psychic tears contain a larger amount of the hormones prolactin, leucine enkephalin, and adrenocorticotropic hormone. This type of tear is a result of stimulation of the limbic system, which controls emotion, and also has some control over the autonomic system. The acetylcholine neurotransmitter, via the muscarinic and nicotinic glands, activates the lacrimal glands to produce tears.