Ever wondered where tears come from when you cry or why your nose gets runny while crying; is there a connection between our eyes and nose, and if so, where is that connection exactly and how does it work, and why do we even have such a connection?
In this article, we talk about a very cool tiny system that lies inside our eyes; that is the lacrimal system.
So keep reading as we’re about to find out the answers to all of the previous questions.
Table of content:
- The components of the lacrimal system
- Where do tears come from?
- The composition of a tear film
- The main three types of tears
- Why do we need a tear film on our eyes?
- Five fun facts about your tears
The Components of The Lacrimal System
You may have already noticed a tiny opening at the margin of your upper and lower eyelids near the nose; that’s actually a part of this cool system. So let’s talk about each component of your lacrimal system in more detail.
Before getting into the components of this system, keep in mind that we have one distinguished system on each side. Each lacrimal system is composed of structures that are responsible for two main roles:
- Tear production, which is the role of the lacrimal gland with the help of some minor glands.
- Tear drainage, which is the responsibility of a duct system that drains tears from your eyes to your nose.
1. The Lacrimal Gland
This is the primary producer of tears inside our eyes. It secretes a watery fluid that makes up the major portion of the tear layer. This tear layer also contains some substances that work to protect our eyes against harmful microorganisms. The main lacrimal gland is about the size of an almond. It lies deep inside the cavity where your eyes lie (on the upper outer side of it), and that’s why you can’t feel or see it.
There are also some scattered minor glands that play a minor role in the tear-production process. They are called accessory lacrimal glands.
It’s very important to point out to very crucial tiny glands that work hand in hand with the lacrimal gland even though they are not part of it. These are the Meibomian glands, which are tiny glands located inside your upper lid and produce an oily film that gets mixed with the watery secretions produced by your lacrimal gland to make the tear film that covers the exposed surface of your eye. This oily component makes it less likely for your tears to evaporate quickly.
2. The Lacrimal Ducts
Your lacrimal gland sends tears through the lacrimal ducts attached to it. They are about 12 in number, and they discharge tears in the upper outer space under your upper eyelid on both eyes.
3. The Lacrimal Puncta
Moving on to the tear drainage system, which starts with these two tiny pits on the inner margins of your eyelids, near your nose. You could see them easily if you pull your upper or lower eyelid slightly outward. All of the coming structures of the tear drainage system lie at the inner lower part of your eye.
We have two puncta (the singular word of which is punctum) at the very end of each eyelid (one on each lid). See the picture above for better visualisation of where these puncta lie. They are responsible for pumping tears out of your eyes to the next station.
The process of tear drainage is aided by many mechanisms, such as capillary attraction and regular blinking.
4. The Superior and Inferior Lacrimal Canals
These are two canals that receive the tear collected by the upper and lower puncta, respectively. They then send it down to the next structure, which is called the lacrimal sac.
5. The Lacrimal Sac
This is a dilated sac that both superior and inferior lacrimal canals drain tears into. It can store tears till they find their way down to the next station, which is the nasolacrimal duct.
6. The Nasolacrimal Duct
There we go to the final station and to why we get runny noses while crying. This is due to the structure that connects your lacrimal sac to the nasal cavity, which is the nasolacrimal duct. This duct opens into the back of your nose.
Now we can see that tears flow from the place they are formed to the surface of the eye through tiny ducts (the lacrimal ducts), and then it moves in a very specific path: the puncta, the lacrimal canals, the lacrimal sac, and finally to your nasolacrimal duct which drains into your nose.
You may have already noticed that the tear production portion of your lacrimal system lies at the upper outer side of your eyes while the tear drainage system lies in the opposite direction (at the lower inner part of your eyes). This makes sense since this is a smart way for the dynamic movement of tears inside our eyes.
If you’re still finding it difficult to imagine this system, here’s an animation video from the American Academy of Opthalmology that shows you this system in less than one minute.
Where do Tears Come From?
You should be able to guess where tears come from after knowing the components of the lacrimal apparatus, as mentioned in the section above.
Tears are produced with the help of two main structures, you say (the lacrimal gland and the meibomian glands). You’re right.
But let’s go a step backwards and ask where tears come from before they are formed in these glands (what do these glands use to make tears?).
Like any other secretion of your body, it comes from your blood after being filtered in a specific way. Urine, sweat, tears, saliva, and other body secretion all come from your blood after making some modifications to this blood composition.
What Are The Main Components of a Tear Film?
There are three main layers that make up your tears, and that’s why it’s referred to as a trilaminar structure; these are:
- Mucous layer: this is the first layer that lies in close contact with the cornea (the surface of your eye). It’s secreted from special cells of the conjunctiva (a transparent membrane that covers the visible part of your eyeball).
- Watery (aqueous) layer: which is secreted from the main lacrimal gland and some accessory lacrimal glands. This layer makes up the main bulk of your tear film.
- Oily layer: which is secreted from the Meibomian glands of your upper eyelid. This is a very thin film of oily substance that plays a major role in preventing rapid evaporation of the watery secretion produced by the lacrimal gland.
It was believed that these layers line on top of each other without any interaction among them (inner mucous, middle aqueous, and outer oily layer). However, recent studies show that these layers aren’t completely separate from each other, and they get mixed with each other to make the final tear film that covers your eye.
The Different Types of Tears
We have three main types of tears that are produced in different circumstances. Each type has its own biochemical composition. These are:
1. The Basal Tears
This type of tear, as its name implies, is the basal film found on your eyes all the time. It’s constantly produced by the lacrimal gland and drained by the lacrimal drainage system.
2. The Reflex Tears
Those are the ones you get when chopping onions. They are produced only at specific conditions when your eye senses any irritant substance. So your eyes produce those tears as a defence mechanism to wash away those harmful substances. They are larger in amount when compared to basal tears, and you can easily notice them.
3. The Emotional Tears
Those are the tears you shed when experiencing a very sad or happy situation. You get emotional, and then you start to cry.
Why do we Need Tears in Our Eyes?
Our tears play a vital role in keeping our eyes moist and preventing their dryness. They have the following functions:
- Protect our eyes from dryness by keeping them constantly lubricated.
- They are a major defence mechanism for your eye. Tears Prevent any foreign objects from harming your eye besides containing antimicrobial proteins that protect you against eye infections.
- Tears supply your cornea (which doesn’t have a blood supply) with oxygen and nutrients.
- Shares in the process of light refraction to give you a clear, crisp image of the world around you. It does so by keeping the outer surface of your eye smooth for adequate refraction.
Five Fun Facts About Your Tears
Before finishing off, here are five fun facts about your tear system:
- There is a tear film layer on the surface of our eyes all the time, even when we’re not crying (this is what is referred to as basal tears).
- People with dry eyes use eyedrops that are, in fact, artificial tears to help with their condition.
- The volume of the tear film that covers your eye and its protein content decreases as you age.
- Your lacrimal gland shrinks as you age, which can partially explain the previous fact.
- Each time you blink, your eyelids equally distribute the tear film over the surface of your eye. That’s why prolonged use of phones or laptops may cause dryness in your eyes since you’re blinking less frequently, and thus, the tear film evaporates quickly, leaving your eyes dry.
A very tiny invisible system that lies deep inside our skull bones that we can’t even see or feel, yet a very crucial one to the health of our most precious sense, that is sight. That was our today’s dose of digging deep into our magnificent body systems to find out how they work. We hope you find it fun and useful to read about this system.
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The main references used in the preparation for this article are listed below for further reading.