How does tearing work?

How does tearing work?

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I found the question about tear gas very interesting. Shigeta says there that crying helps the cells of the eye to wash themselves clear of the toxic components in the tear gas.

  1. Does non-emotional tearing always work this way? Is tearing not caused by cells in the tear duct working as receptors? If not, why we have tear duct (the first in-eye part of it)?

  2. What is the cause of tear-production associated with crying during strong emotions? Is it due to hormones or nerve activation?

The regulation of tear production (lacrimation) involves reflexes initiated by sensory neurons in the cornea. Corneal pain receptors (nociceptors) and mechanoreceptors detect damaging stimuli and induce tearing to cleanse the ocular surface (and, hence, Shigeta is right as tear gas stimulates pain receptors). Corneal neurons sensitive to drying of the ocular surface also appear to increase tearing. These neurons also respond to cooling and hyperosmotic stimuli (Kurose & Meng, 2013). The tear duct is necessary to drain the tears away from the eye into the nasal cavity (Fig. 1).

Fig. 1. Tear glands and tear ducts. Source: Mayo Foundation for Medical Education and Research.

Strong emotional responses like crying can result in an overflow of tears (epiphora). Epiphora is mediated by the limbic system (the emotional center of the brain), especially the hypothalamus. Such strong parasympathetic stimulation is accompanied by other symptoms, like reddening of the face and convulsive breathing (University of Minnesota, Duluth).

- Kurose & Meng, J Neurophysiol (2013); 109(10): 2517-22


Tears are a clear liquid secreted by the lacrimal glands (tear gland) found in the eyes of all land mammals (except for goats and rabbits). [1] [2] Their functions include lubricating the eyes (basal tears), removing irritants (reflex tears), and aiding the immune system. [3] Tears also occur as a part of the body's natural pain response. [4] Humans are the only mammals known to produce tears as part of an emotional response, such as out of joy or grief. Tears have symbolic significance among humans (see crying). [4] Emotional secretion of tears may serve a biological function by excreting stress-inducing hormones built up through times of emotional distress. [5] [6] Tears are made up of water, electrolytes, proteins, lipids, and mucins that form layers on the surface of eyes. [7] The different types of tears—basal, reflex, and emotional—vary significantly in composition. [7]

  • a) Lacrimal gland
  • b) Superior lacrimal punctum
  • c) Superior lacrimal canal
  • d) Lacrimal sac
  • e) Inferior lacrimal punctum
  • f) Inferior lacrimal canal
  • g) Nasolacrimal canal

Two-layer Structure of Tears

Maintaining tear structure is important for the tears covering our eyes to function normally. Tears have two distinct layers from the outer surface: a lipid layer and an aqueous layer.

Lipid Layer

The lipid layer is secreted by the Meibomian glands on the edges of our eyelids. It prevents the evaporation of tears by covering the outer surface. If Meibomian gland function declines due to aging or inflammation, the secretion of oily substance can decrease, or the composition can change so that the oily substance changes its property to resemble wax, and gland openings can become obstructed. If this happens, tear stability declines, resulting in dry eye syndrome. This type of abnormality is called Meibomian gland dysfunction and is often seen in older patients.

Aqueous Layer

This layer makes up the majority (95%) of tears, and contains various substances including proteins. It performs the key functions of tears, such as supplying nutrients to the cornea, preventing infection and healing damage. It is secreted by the lacrimal gland on the underside of the upper eyelid. In addition, mucus mucin (secretory mucin), which is secreted by the goblet cells on the surface of the eye, helps distribute tears across the surface of the eye uniformly. Recent research has shown that this mucin plays an important role in tear stability.

How to Dissect a Flower

This article was co-authored by Bess Ruff, MA. Bess Ruff is a Geography PhD student at Florida State University. She received her MA in Environmental Science and Management from the University of California, Santa Barbara in 2016. She has conducted survey work for marine spatial planning projects in the Caribbean and provided research support as a graduate fellow for the Sustainable Fisheries Group.

There are 8 references cited in this article, which can be found at the bottom of the page.

This article has been viewed 62,068 times.

Flowers aren’t just beautiful, they’re actually complex reproductive systems! You can dissect a flower to get an inside look and some hands-on experience. You’ll get to see how the flower uses both a male and female reproductive system to create its own ovules and fertilize itself. This allows the flower to reproduce on its own. Just remove the petals and anthers, slice the anthers and stigma with a scalpel, and peel the ovary with your fingers to dissect your own flower!

When We Tear One Woman Down, We Tear All Women Down.

“Look at this one. She’s trying way too hard. She’s screaming desperate with that dress” a woman commented as another woman passed by, trying to find the end of a very long line to get into a bar over the weekend.

“It’s Saturday night, not a ball, Cinderella,” she cackled as her hand was stamped and she walked through the entryway. One of her friends added, “What was she thinking when she put on that dress? That the sequins would land her a date?” The group of friends laughed as they disappeared into the dark building.

I was shocked. The comments were harsh and unsolicited. I turned to my husband, confused and offended on her behalf, and asked if he had heard what just happened.

No (*insert my long sigh here*).

So, naturally, I started to stew on it a bit. Why were they being so harsh? Why did they care what this other woman was wearing to dance the night away? How would it feel if they directed their criticism toward me?

I got a little uncomfortable as I started thinking about what they thought of the dress I was wearing. I started pulling at it, commenting on how maybe I should have gone with something a little looser… a little more forgiving. Was I trying too hard? Who was I trying to impress? You can see where this is going.

As my mind spiralled about my own outfit, I hoped that my sequined-wearing-sister hadn’t heard those mean-spirited comments.

Sequins aside, this type of indirect aggression is what keeps us, as women, stuck. Stuck in a place of competing with other women. Stuck in taking stock of other women’s value based on how they look. Stuck in feeling insecure about our own appearance, accomplishments and goals. Stuck in perpetuating an ideal that we, as a whole, aren’t good enough.

A 2011 study found that when meeting an attractive woman, 85 percent of the female subjects gave their peer a critical once over and made harsh comments about her appearance. Another study has shown that the woman on the receiving end of such comments will feel socially excluded and can experience psychological pain that is comparable to physical pain.

Regardless of whether this indirect aggression toward other women is a result of biology or social conditioning, we all have a choice. A choice to change the overwhelming trend of tearing each other down instead of building each other up. In a society that’s striving for gender equality, it is our responsibility to be the example. To embody what a strong, supportive woman is. To push back against what is expected of us falling into a competitive, mean-girl way of interacting with one another.

In order to be a force to be reckoned with, to break the glass ceiling and to be seen for the value we offer to the world instead of the value of our appearance, we have to stop falling into these old patterns.

When we tear one woman down, we tear all women down. When we support and stand up for one another, we break the mold and give ourselves the space to lean into deeper social issues. Issues that are far more important that what we’re wearing and who we think we’re trying to impress.

Here are a few strategies to start pushing back:

1. Take stock of who you’re spending your time with and how they interact with other women. Do you see a trend that they always have something to say, or have a tendency to tear others down? Call them out when they make comments about other women. Uncomfortable, yes, but it will only continue if it isn’t brought to light.

2. Get honest with yourself. When have you fallen into this pattern? Every one of us has done it at one point or another. Don’t hide in the shame of it. Instead, take responsibility and apologize when and where you need to.

3. Do the work of figuring out what needs to be healed within yourself to stop falling into these patterns. Talk it out with a friend or set up an appointment with a therapist. Get curious about what is triggering you to be in competition with, or negative, toward other women.

4. Empower and applaud one another. The woman that got the promotion she’d been working so hard for? CELEBRATE her! The woman who wore an out-of-character sequined dress and heels that made her feel good about herself post-heartbreak? (yes, I sought her out to tell her how beautiful she looked. And, she told me her story) PRAISE her! Let her know what a beautiful badass she is to be doing something that makes her feel good.

5. Speak to your own worth whenever possible. Share your successes. Scream them from the mountain tops if you want! Focus on your accomplishments instead of comparing yourself to others. Unapologetically become the best version of yourself possible. You’ll likely inspire the women you’re surrounded with to do the same.

In the words of Madeline Albright, “there is a special place in hell for women who don’t help other women.”

Ladies, wear sequins whenever you damn well please. And, stay in your lane. Don’t get distracted by those who try to tear you, or anyone else, down.

How Bodybuilding Works – The Science of Bodybuilding

Before you get started in bodybuilding, inspired and raring to go you may be, you need to understand how the act of bodybuilding works. Even if you’ve been bodybuilding for years on the other hand you should take the time out to learn this important aspect of the activity to give you an important competitive edge and advantage. By understanding the fundamentals of the science and principles behind weight training you can then start to learn why you’re doing what you’re doing – and also how to improve it and why some things work better than others. The more full your understanding before you begin the more you’ll be able to apply it to the moves themselves, so get ready for some heavy(ish) science babble.

The first thing to understand is how muscle grows as well as the structure of the muscles. Muscle growth in technical lingo is called ‘hypertrophy’ and it’s actually a response to stress that we have evolved over time. Basically the muscles are made up of muscle fibre. These are the cells that make up muscle tissue, and they’re different from other cells in a variety of ways. Notably they are endowed with two nuclei unlike most other cells in the body which only have one. This means that unfortunately they can’t replicate themselves via mitosis (splitting in half to create two identical copies) meaning that we’re limited to only a finite number of fibres in each muscle.

These fibres are made from amino acids constructed in much the same way as a telescope with the various layers ‘pedaling’ inside the others to generate movement. Essentially on a microscopic layer the fibres are made up of myofibrils which are made from sarcomeres. Sarcomeres are essentially tubes made of myosin and actin – and it’s the actin ‘pedalling’ along the inside of the myosin that generates movement.

To confuse matters further – and this can come in handy later – there are actually three types of muscle fibre (or ‘twitch fibre’). These are Type I, Type IIa and Type IIx – but are also known as ‘slow twitch muscle fibre’ (type I) and ‘fast twitch muscle fibre’ (types II and IIx – with type IIx being essentially ‘faster’ twitch muscle fibre). Due to a slightly different composition and different use of actin and myosin, the slow twitch muscle fibres are more useful for slow endurance tasks while the fast twitch fibres are more suited to fast explosive movements such as jumping and sprinting. Some animals also have type IIb which is even faster than type IIx and allows for the rapid change of direction (sometimes you will read type x labelled as type b incorrectly which can get confusing and is a throwback to a time before the current type b was discovered).

For this reason, someone with more type I fibres is going to be more naturally suited to endurance sports such as the 800 metres, whereas someone with more type II and IIx will be better at sprinting or jumping. While there is a genetic element in which muscle twitch fibres you have more of, research is showing that it’s possible to change a muscle fibre from one type to another with intense training. Other studies are suggesting that some fibres sit somewhere between type I and II, and that there may in fact be countless variations of muscle fibres. As we get older more of our muscle fibres become ‘hybrids’ of the two unless we continue training.

For a bodybuilder, all muscle twitch fibres are important and it’s a good idea to work both during a long workout. This is best achieved using a variety of different training techniques – plyometric exercises are designed to target the fast twitch muscle fibres, such as clapping press ups, clean and presses and box jumps. For the slow twitch muscle fibres, static contraction or isometric exercises that require the bodybuilder to hold a weight in a difficult position is the main order of the day.

When these exercises are performed it can cause the muscle fibre to tear slightly in what’s called a ‘microtear’. This is actually a good thing however, as this is how they will grow. Basically in response to the muscle tearing, the body will use satellite cells that wait in stasis around the muscles in order to fix the tears building them up more thickly each time they do to prevent against future damage (and possibly because this is just the way they are rebuilt – just as scar tissue is tougher than many of the cells it replaces). This will require more amino acids which the body gets from protein, demonstrating why it’s so important that the body has enough protein in its system – if a repair is failed to be carried out then it misses the chance and simply won’t happen. Should you cause multiple microtears and not have adequate rest and protein to make the repairs then the muscle will shrink rather than growing (this is called dystrophy).

When the body makes repairs to damaged tissue using protein this is called called ‘anabolism’ and is the opposite to ‘catabolism’ where the body burns carbs and sometimes muscle for energy. Someone with a fast metabolism is someone whose body is quick and efficient in carrying out both these tasks. Generally wakefulness is a catabolic state while sleep is an anabolic state meaning that most muscle growth and repair occurs in our sleep. However there are other ways to induce an anabolic state, with some supplements (surprisingly that’s not actually primarily what an anabolic steroid does) and with exercise itself – after we workout we immediately go into a recovery mode or an ‘anabolic window’ making it the best time to take protein.

Obviously as the muscles are repaired and become thicker they require a greater load and more repetitions to be torn and this is how and why we are able to increase the load that we workout with and lift more.

But in order to cause microtears and to do the necessary exercise your body will need energy to power the muscle fibres in closing and opening (expanding and contracting). This energy comes from a source known as ATP or Andenosine Triphosphate which is thought of in scientific circles as the energy source of all life. This substance is a nucleotide made up of three phosphogen molecules bonded together by a powerful force. That’s what the name literally means tri – meaning three, phosphate – meaning phosophogen.

The power in this substance however doesn’t come from the phosphogen itself, but from the powerful bonds that bind it together, and it’s when these bonds break that they unleash the energy that the body can utilise.

A bodybuilder needs to be able to supply his muscles with a lot of ATP then in order to perform the necessary movements in the gym – and there are three ways in which they can do this.

The first way the body gets ATP is through the phosphagen system which uses the ATP stored in the muscles and body to generate that energy. The body can store enough ATP at any one time to allow for around 3 seconds of full powered exertion, at which point it will need to look elsewhere.

Fortunately breaking the ATP molecules results in some useful bi products – ADP (andenosine diphosphate) and AMP (andenosine monophosphate) with two and one bonded phosphagen molecules respectively. So if you imagine you have three bonded molecules and they break you will understandably be left with one and two, or three single molecules. It’s basic maths… The good news is that using a substance called creatine phosophate the body can then recombine these molecules to make them back into ATP ready to be broken once again for more energy. The body can store enough creatine for roughly 8-10 seconds of continued exertion, meaning that in total the body can use the phosphogen system for around 13 seconds maximum of continued exertion which is enough to sprint just over 100 metres. It is thought however that through the use of creatine supplements that this maximum time can be increased.

At this point if exertion continues the body needs to get its ATP from somewhere else and this is when it looks to its stores of the carbohydrate glycogen in what’s known as the glycogen lactic acid system. This is a slightly slower and less efficient system, which requires the body to split the glycogen first into glucose and then again into ATP. This unfortunately creates a rather unwanted by product of lactic acid (from which the substance takes its name), which creates the uncomfortable mildly painful ‘burning’ sensation we get in our muscles when we push ourselves in the gym. The body can sustain itself using the glycogen lactic acid system for a further one minute and thirty seconds.

Both these systems are anaerobic, meaning that for the first one minute fourty three seconds the body won’t be using oxygen or burning fat. In order to lose weight then the training must continue past this point and force the body to find its energy elsewhere. This is where the aerobic system comes in, relying on the oxidisation of foodstuffs in our mitochondria. In other words the body looks to our supplies of glycogen (and so ATP) stored in our cells as fat and then uses the oxygen in our blood to break them down and carry them to our muscles. This will start off burning fat (in no particular order other than that genetically determined by your body’s physiology) but eventually move on to burning muscle if you continue the exertion for too long as the body literally cannibalises itself. The aerobic system can last indefinitely until it begins to do more harm than good to the body.

So that’s basically it, how the body powers itself and re-grows and strengthens muscle. As you read the advice in various books and bodybuilding articles you should now be able to understand why it works the way it does, and at times we will reference the underlying processes to outline how and why each method or supplement works. If you’ve survived until the end of this article then well done – you’re now officially one step ahead of most bodybuilders who start their training without any underlying scientific understanding of the sport. Knowledge is power, and you’re now armed with a proper understanding that can help you adapt and tailor your own training and assess new programmes or supplements yourself as they come.

  • Swelling over the affected region along with bruising and erythema can be a sign of muscle tear.
  • Severe tenderness at the site of the injury or the affected muscle.
  • Resting pain.
  • Common symptoms of muscle tear is pain with activity or use of the muscle.
  • Muscle weakness.
  • Inability of the muscle to function in any way.

In order to diagnose a Muscle Tear, the treating physician will first take a medical history of the patient to inquire as to what activity may have caused the patient to present with the symptoms. The physician will then conduct a physical examination looking at the injury site to look for areas of tenderness and swelling. Here it is important to diagnose whether the Muscle Tear is complete or partial as treatment is different for partial tears and for complete tears and so is the recovery period. This can be done by taking an MRI of the injured site which can clearly show whether the patient is suffering from a partial or a complete tear of the muscle.


The recent tech stock tear has increased the wealth of Bezos, the richest man in the world, to $205 billion, making him the first person in history to be worth more than $200 billion.

The anti-fray design means you won’t have to deal with all the wear and tear that comes with regular use.

Laugh at “Like Crazy” and don’t be surprised if there’s a tear or two.

Then with my wife almost in tear s, he threatened her with jail if she refused to sign.

Tech shares have been on a tear this year as the Covid-19 pandemic drove more people online, lifting the fortunes of the companies’ founders and putting the industry under increased scrutiny.

Sam watches her fall apart, tear herself apart and is desperate.

And then he went on a tear in early 2013, creating one provocation after another, seemingly every day for more than two months.

As Kate was driven away, she appeared to wipe a tear from her eye.

Many of those gathering in the run-up to the grand jury decision wore hockey and tear gas masks to conceal their identity.

In other news, black and white pin-up shots are now officially less valuable than life-size Tiger Beat tear outs.

Louis turned at the exclamation, and looked on the faithful servant but no tear was in his eye, no sound on his lip.

By what word is the relation between “pendulum” and “a smile and tear ” described?

In the tear -stained story of humanity there has never been aught to surpass the thrilling record of Cawnpore.

In a short time you will be able, in the language of Dr. Johnson, “to tear out the heart of any book.”

The horizon, however, was lowering and hazy, and the sun had not force enough to tear the murky veil asunder.

Muscle Strain

A muscle strain is the stretching or tearing of muscle fibers. Most muscle strains happen for one of two reasons: either the muscle has been stretched beyond its limits or it has been forced to contract too strongly. In mild cases, only a few muscle fibers are stretched or torn, and the muscle remains intact and strong. In severe cases, however, the strained muscle may be torn and unable to function properly. To help simplify diagnosis and treatment, doctors often classify muscle strains into three grades, depending on the severity of muscle fiber damage:

  • Grade I strain. In this mild strain, only a few muscle fibers are stretched or torn. Although the injured muscle is tender and painful, it has normal strength.
  • Grade II strain. This is a moderate strain, with a greater number of injured fibers and more severe muscle pain and tenderness. There is also mild swelling, noticeable loss of strength and sometimes a bruise.
  • Grade III strain. This strain tears the muscle all the way through, sometimes causing a "pop" sensation as the muscle rips into two separate pieces or shears away from its tendon. Grade III strains are serious injuries that cause complete loss of muscle function, as well as considerable pain, swelling, tenderness and discoloration. Because Grade III strains usually cause a sharp break in the normal outline of the muscle, there may be an obvious "dent" or "gap" under the skin where the ripped pieces of muscle have come apart.

Although the risk of muscle strain is especially high during sports activities, you also can strain a muscle by lifting a heavy carton or by simply stepping off a curb.

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Tear System

The tear system of the eye normally keeps the eye wet enough to be comfortable without overflowing. But some people's eyes are too dry, while others are too wet.

Dry eye syndrome is what doctors call the condition when an eye is not being kept wet enough to be comfortable. There are several causes of dry eye syndrome, and more information is available in the "Dry Eye Syndrome" fact sheet from the Cole Eye Institute. Other times the tear system makes the eye too wet.

How can the tear system make the eye "too wet"?

There are three main parts in the tear system: (1) the glands that make the tear fluid (2) the openings that let tears flow out of the eye and (3) the ducts inside the nose that tears drain through. Each has a different function and a problem with any of them can lead to excess tears.

How do the tear glands normally work, and what problems can happen when they are not working properly?

The lacrimal glands underneath the skin of the upper eyelids make a fluid that is mostly salt and water. This salty water gets to the eye through small openings inside the upper eyelids. When the eyelid blinks, the watery liquid is spread across the eye. There are other glands on edges of the eyelids that make oils. The most important of these glands are called the meibomian glands.

The oils from these glands actually float on top of the watery fluid in the tears. This keeps the water from evaporating too quickly. Some of the oils stay along the edge of the eyelid, and they help keep the tears from "leaking" over the eyelashes. If there is not enough of these oils, tears will keep overflowing from the eyes. Oddly enough, a problem with the meibomian glands can lead to overflowing tears and dry eye syndrome at the same time!

This happens when the lacrimal glands make enough salt-watery fluid to cover the eye, but the meibomian glands do not make enough oils. The surface of the eye actually dries out between blinks. This makes the eye irritated, and the lacrimal glands make even more fluid. But this fluid just overflows from the eye instead of keeping it wet.

This is one form of epiphora, which is the medical term for the condition of overflowing tears. There are several other possible causes of epiphora. The lacrimal glands might be making too much fluid because the eye is irritated by wind, bright light, dust or allergies. The other causes of epiphora are related to problems with the drainage system of the eye.

How does the tear drainage system normally work, and what can go wrong with it?

There are small openings inside the edges of the eyelids near the nose. Each upper and lower eyelid has one of these openings, called a punctum. These four openings, or puncta, act like little valves to take tears out of the eye. Each time we blink, some tear fluid is pumped out of the eye through the puncta.

If some or all of the puncta are blocked, tears will overflow. The puncta are tiny, so they can be blocked by small particles of dirt or even loose cells from the skin around the eye. Sometimes an infection near the puncta will make the area swollen, and the puncta will not work properly. Any of these things can cause epiphora.

How do the tear drainage ducts normally work? What can go wrong with them?

After the tears leave the eye through the puncta, they drain down through a little "tube" called the nasolacrimal duct. This duct goes underneath the skin and through the bones of the face into the nose. Normally, there is so little tear fluid that the nose does not get very wet. The connection between the eye and the nose is obvious, however, when someone is crying.

Even when the puncta are open and working well, the nasolacrimal duct can be blocked. Not only will this cause problems with tear drainage, it usually has other symptoms too, including:

  • Swelling and redness in the area between the eye and the nose.
  • Pain in the area around the eye and nose.

If the nasolacrimal duct is blocked, it can become infected. This is called dacryocystitis, and it can become very uncomfortable.

How can excessive tearing be treated?

Only a doctor can recommend the right treatment for someone with tearing problems.
It is not unusual for newborn babies to have excessive tearing due to insufficient drainage of the tears. More information about this problem is available in the fact sheet on "Tear Duct Obstruction in Children" from the Cole Eye Institute.

In older patients with overflowing tears, the doctor will examine the eye carefully. If the tearing problem seems to be related to dry eye syndrome, there are several treatment options (see the "Dry Eye" fact sheet). If the problem is related to allergy or other irritation of the eye, then treating the irritation will reduce excessive tearing.

In other cases, it will be necessary to perform a special test to make sure fluid can pass through the puncta and nasolacrimal duct.

What if part of the tear drainage system is blocked?

If the test shows that tears cannot get through a punctum, the doctor might recommend placing a warm, wet, clean washcloth on the eye a few times a day. This could help open up the blocked punctum and let any fluid inside drain out. Your doctor will explain exactly how to do this and how many times a day it should be done. This can open the punctum in just a few days, or it might take longer.

Your doctor might recommend a procedure to open a blocked punctum. He or she can do this right in the office by numbing the eye with anesthetic, then passing a special instrument through the punctum. This might be necessary if the nasolacrimal duct seems to be infected. The doctor will probably prescribe antibiotics if there seems to be an infection.

Sometimes an infection will have the side effect of blocking the nasolacrimal duct permanently. This is a problem for two reasons. Not only will the eye keep overflowing with tears, the blocked nasolacrimal duct will keep on getting infected. Fortunately, there is a procedure to fix this problem.

Dacryocystorhinostomy is the complicated medical name for an operation to make a new tear drainage system for the eye.

This operation may be done under general anesthesia (with the patient "asleep") or with local anesthesia (the patient is awake but does not feel the pain). The surgeon will make an incision near the nose. A small plastic tube is connected to the tear duct near the eye, and the other end opens into the nose. The plastic device keeps the new drainage system open while the eye heals. After a few months, the tube is removed. This technique is very effective at solving the problem of overflowing tears due to nasolacrimal duct blockage.