Tear Duct Anatomy Tear Duct Anatomy Tear Duct Anatomy When the eye blinks, the lid pushes the tears across the eye into the drains (puncta) at the inner corner. The drains empty into channels (canaliculi) that connect the eye with the nose. The channels drain into a tear sac (lacrimal sac) that lies beside the nose. The sac narrows into the tear duct (lacrimal duct), which drains through the nasal bone into the nostril. Credits Primary Medical ReviewerJohn Pope, MD - Pediatrics Specialist Medical ReviewerChristopher J. Rudnisky, MD, MPH, FRCSC - Ophthalmology Current as ofNovember 20, 2015 WebMD Medical Reference from Healthwise This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.© 1995-2015 Healthwise, Incorporated. Healthwise, Healthwise for every health decision, and the Healthwise logo are trademarks of Healthwise, Incorporated. Top Picks Anatomy of the Eye | Anatomy Flashcards Before discussing conditions affecting the eye, we need to review some basic eye anatomy.

Anatomy can be painful for some (personally, I hated anatomy in medical school) so I’m going to keep this simple. Let us start from the outside and work our way toward the back of the eye. Eyelids The eyelids protect and help lubricate the eyes. The eyelid skin itself is very thin, containing no subcutaneous fat, and is supported by a tarsal plate. This tarsal plate is a fibrous layer that gives the lids shape, strength, and a place for muscles to attach. Underneath and within the tarsal plate lie meibomian glands. These glands secrete oil into the tear film that keeps the tears from evaporating too quickly. Meibomian glands may become inflamed and swell into a granulomatous chalazion that needs to be excised. Don’t confuse a chalazion with a stye. A stye is a pimple-like infection of a sebaceous gland or eyelash follicle, similar to a pimple, and is superficial to the tarsal plate. Styes are painful, while chalazions are not. Eyelid Movement Two muscles are responsible for eyelid movement.

The orbicularis oculi closes the eyelids and is innervated by cranial nerve 7. Patients with a facial nerve paralyses, such as after Bell’s Palsy, can’t close their eye and the eye may need to be patched (or sutured closed) to protect the cornea. The levator palpebrae opens the eye and is innervated by CN3. Oculomotor nerve palsy is the major cause of ptosis (drooping of the eye). In fact, a common surgical treatment for ptosis involves shortening the levator tendon to open up the eye. CN 3 opens the eye like a pillar CN 7 closes like a fish-hook Conjunctiva The conjunctiva is a mucus membrane that covers the front of the eyeball. When you examine the “white part” of a patient’s eyes, you’re actually looking through the semi-transparent conjunctiva to the white sclera of the eyeball underneath. The conjunctiva starts at the edge of the cornea (this location is called the limbus). It then flows back behind the eye, loops forward, and forms the inside surface of the eyelids.

The continuity of this conjunctiva is important, as it keeps objects like eyelashes and your contact lens from sliding back behind your eyeball. The conjunctiva is also lax enough to allow your eyes to freely move. When people get conjunctivitis, or “pink eye,” this is the tissue layer affected. There is a thickened fold of conjunctiva called the semilunar fold that is located at the medial canthus – it is a homolog of the nictitating membrane seen on sharks. Tear Production and Drainage The majority of tears are produced by accessory tear glands located within the eyelid and conjunctiva. The lacrimal gland itself is really only responsible for reflexive tearing. Tears flow down the front of the eye and drain out small pores, called lacrimal punctum, which arise on the medial lids. These puncta are small, but can be seen with the naked eye. After entering the puncta, tears flow down the lacrimal tubing and eventually drain into the nose at the inferior turbinate. This explains why you get a runny nose when you cry. In 2-5% of newborns, the drainage valve within the nose isn’t patent at birth, leading to excessive tearing.

Fortunately, this often resolves on it’s own, but sometimes we need to force open the pathway with a metal probe. Lid Lacerations Most lacerations through the eyelid can be easily reaproximated and repaired. However, if a laceration occurs in the nasal quadrant of the lid you have to worry about compromising the canalicular tear-drainage pathway. Canalicular lacerations require cannulation with a silicone tube to maintain patency until the tissue has healed. Warning: Drug absorption through the nasal mucosa can be profound as this is a direct route to the circulatory system and entirely skips liver metabolism. Eyedrops meant for local effect, such as beta-blockers, can have impressive systemic side effects when absorbed through the nose. Patients can decrease nasal drainage by squeezing the medial canthus after putting in eyedrops. They should also close their eyes for a few minutes afterwards because blinking acts as a tear pumping mechanism. The Eyeball: The eyeball is an amazing structure. It is only one inch in diameter, roughly the size of a ping-pong ball, and is a direct extension of the brain. The optic nerve is the only nerve in the body that we can actually see (using our ophthalmoscope) in vivo.

The outer wall of the eye is called the sclera. The sclera is white, fibrous, composed of collagen, and is actually continuous with the clear cornea anteriorly. In fact, you can think of the cornea as an extension of the sclera as they look similar under the microscope. The cornea is clear, however, because it is relatively dehydrated. At the back of the eye, the sclera forms the optic sheath encircling the optic nerve. The eyeball is divided into three chambers, not two as you might expect. The anterior chamber lies between the cornea and the iris, the posterior chamber between the iris and the lens, and the vitreous chamber extends from the lens back to the retina. The eye is also filled with two different fluids. Vitreous humor fills the back vitreous chamber. It is a gel-suspension with a consistency similar to Jell-O. With age and certain degenerative conditions, areas of the vitreous can liquefy. When this occurs, the vitreous can fall in upon itself – usually a harmless event called a PVD (posterior vitreous detachment).

However, this normally benign vitreous detachment can sometimes tug on the retina and create small retinal tears. Aqueous humor fills the anterior and posterior chambers. This is a watery solution with a high nutrient component that supports the avascular cornea and lens. Aqueous is continuously produced in the posterior chamber, flowing forward through the pupil into the anterior chamber, where it drains back into the venous circulation via the Canal of Schlemm. We’ll discuss the aqueous pathway in detail in the glaucoma chapter. The Cornea: The cornea is the clear front surface of the eye. The cornea-air interface actually provides the majority of the eye’s refractive power. The cornea is avascular and gets its nutrition from tears on the outside, aqueous fluid on the inside, and from blood vessels located at the periphery. On cross section, the cornea contains five distinct layers. The outside surface layer is composed of epithelial cells that are easily abraded. Though epithelial injuries are painful, this layer heals quickly and typically does not scar. Under this lies Bowman’s layer and then the stroma.

The corneal stroma makes up 90% of the corneal thickness, and if the stroma is damaged this can lead to scar formation. The next layer is Descemet’s membrane, which is really the basal lamina of the endothelium, the final inner layer. The inner endothelium is only one cell layer thick and works as a pump to keep the cornea dehydrated. If the endothelium becomes damaged (during surgery or by degenerative diseases) aqueous fluid can flow unhindered into the stroma and cloud up the cornea with edema. Endothelial cell count is very important as these cells don’t regenerate when destroyed – the surviving endothelial cells just get bigger and spread out. If the cell count gets too low, the endothelial pump can’t keep up and the cornea swells with water, possibly necessitating a corneal transplant to regain vision. Decemet’s membrane is “deep,” while Bowman’s layer is high up in the “belfry.” A belfry is a room, usually high up in a tower, where bells are hung.

The Anterior Chamber Angle: The angle formed by the inner cornea and the root of the iris is particularly important in ophthalmology. Here you find the trabecular meshwork with its underlying Schlemms Canal. This is where aqueous is drained, and blockage of this pathway/angle will become important as we discuss glaucoma. The Uvea: The iris, ciliary body, and the choroid plexus are all continuous with each other and are collectively called the uvea. This is an important term, as many people can present with painful “uveitis” – spontaneously or in associated with rheumatologic diseases. The iris is the colored part of the eye and its primary function is to control the amount of light hitting the retina. Sympathetic stimulation of the pupil leads to pupil dilation and parasympathetic stimulation leads to constriction. In other words, if you see a bear in the woods, your sympathetics kick in, and your eyes dilate so you can see as much as possible as you run away. I’ll be using this mnemonic/metaphore many times throughout this book to help you remember this concept. The inner iris flows back and becomes the ciliary body.

The ciliary body has two functions: it secretes aqueous fluid and it controls the shape of the lens. The ciliary body contains sphincter muscles that change the lens shape by relaxing the zonular fibers that tether to the lens capsule. The choroid is a bed of blood vessels that lie right under the retina. The choroid supplies nutrition to the outer one-third of the retina which includes the rod and cone photoreceptors. Retinal detachments can separate the retina from the nutritious choroid, which is disastrous for the photoreceptors as they quickly die without this nourishment. FUN FACT: An ostrich’s eye is larger than its brain. Lens: The lens sits behind the iris. The lens is unique in that it doesn’t have any innervation or vascularization. It gets its nourishment entirely from nutrients floating in the aqueous fluid. The lens also has the highest protein concentration of any tissue in the body (65% water, 35% protein). The lens has three layers in a configuration similar to a peanut M&M. The outer layer is called the capsule. The capsule is thin with a consistency of saran wrap and holds the rest of the lens in place.

The middle layer is called the cortex, while the central layer is the hard nucleus. Cataracts are described by where they occur such as nuclear cataracts, cortical cataracts, and subcapsular cataracts. With cataract surgery the outer capsule is left behind and the artificial lens is placed inside this suporting bag. The capsule is held in place by suspensory ligaments called zonules that insert around the periphery and connect to the muscular ciliary body. Contraction of the ciliary muscle causes the zonule ligaments to relax (think about that for a minute), allowing the lens to become rounder and increase its refracting power for close-up reading. In children the lens is soft but with age the lens hardens and becomes less pliable. After age 40 the lens starts having difficulty “rounding out” and people have problems focusing on near objects. This process is called presbyopia. Almost everyone over 50 needs reading glasses because of this hardening of the lens. The Retina: The retina is the sensory portion of the eye and contains layers of photoreceptors, nerves, and supporting cells.

Histologically, many cell layers can be seen, but they are not worth memorizing at this point. The important ones include the photoreceptor layer, which is located further out (towards the periphery), and the ganglion nerve layer which lies most inward (toward the vitreous). For light to reach the photoreceptor it has to pass through many layers. After light reaches the photoreceptors the visual signal propagates back up to the ganglion nerves. These ganglion nerves, in turn, course along the surface of the retina toward the optic disk and form the optic nerve running to the brain. The macula is the pigmented area of the retina that is responsible for central vision. Within the central macula lies the fovea, which is a small pit that is involved with extreme central vision. The fovea is very thin and derives its nutrition entirely from the underlying choroid, making it susceptible to injury during retinal detachments. The optic disk is the entry and exit point of the eye. The central retinal artery and vein pass through here, along with the the ganglion nerves that form the optic nerve.

A physiologic divot or “cup” can be found here that will become important when we talk about glaucoma. The Orbital Walls: Seven different bones form the orbital walls: don’t be intimidated by this complexity, however, as these bones are not that confusing when you break them down. For example, the roof of the orbit is a continuation of the frontal bone, the zygomatic bone forms the strong lateral wall, while the maxillary bone creates the orbital floor. This makes sense, and you could probably guess these bones from the surrounding anatomy. The medial wall is a little more complex, however, but is mainly formed by the lacrimal bone (the lacrimal sac drains tears through this bone into the nose) and the ethmoid bone. The thinnest area in the orbit is a part of the ethmoid bone called the lamina papyracea. Sinus infections can erode through this “paper-thin wall” into the orbital cavity and create a dangerous orbital cellulites. Despite the fragility of the medial wall, it is well buttressed by surrounding bones, such that it’s the orbital floor that breaks most often during blunt trauma.

The maxillary bone fractures downward and the orbital contents can herniate down into the underlying maxillary sinus. This is called a “blowout fracture” and can present with enopthalmia (a sunken-in eyeball) and problems with eye-movements from entrapment of the inferior rectus muscle. We’ll discuss blow-out fractures in more detail in the trauma chapter. The back of the orbit is formed by the greater wing of the sphenoid bone, with the “lesser wing” surrounding the optic canal. There’s also a little palatine bone back there in the middle, but don’t worry about that one! The Apex: Entrance into the Orbit The orbital apex is the entry point for all the nerves and vessels supplying the orbit. The superior orbital fissure lies between the wings of the sphenoid bones, through which many vessels and nerves pass into the orbit. The “Annulus of Zinn,” a muscular band that serves as the insertion point for most of the ocular muscles, rests on top of the superior orbital fissure. The four rectus muscles attach to the annulus and the optic nerve passes right through the middle. Eye Muscles: Four rectus muscles control each eye.

These muscles insert at the sclera, behind the limbus, and each pull the eye in the direction of their attachment. The superior, medial, and inferior rectus muscles are all controlled by the oculomotor nerve (III). The lateral rectus, however, is controlled by the abducens (VI) nerve, which makes sense as the lateral rectus “abducts” the eye. The remaining two eye muscles are the superior and inferior oblique muscles. The superior oblique also originates in the posterior orbit, but courses nasally until it reaches the trochlea (or “pulley”) before inserting onto the eye. The inferior oblique originates from the orbital floor and inserts behind the globe near the macula. Because of these posterior insertions, the oblique muscles are primarily responsible for intorsion and extorsion (rotation of the eye sideways), though they also contribute some vertical gaze action. Confused, yet? Don’t kill yourself learning the action of the oblique muscles or nerve innervation as we’ll discuss these topics in greater detail in the neurology chapter. Summary: There is much more anatomy we could cover, but let’s hold off for now and discuss more detailed anatomy in future chapters as they become relevant.

Pimp Questions 1. Why don’t objects like contact lens and eyelashes get stuck behind the eye? Because the conjunctiva covering the front of the eye loops forward and covers the inside of the eyelids as well. 2. How many chambers are there in the eyeball? Three, actually. The anterior chamber sits in front of the iris, the posterior chamber between the iris and the lens, and the vitreous chamber lies behind the lens filling most of the eye. 3. Name each of the numbered bones. Which bone is thinnest? Which is most likely to fracture after blunt injury? Which is most likely to erode from sinus infections? The bones are: (1)Sphenoid (2)Zygomatic (3)Maxilla (4)Lacrimal (5)Ethmoid (6)Frontal. The ethmoid is the thinnest bone and most likely to perforate from an eroding sinus infection (this happens mostly in kids). The maxillary floor is most likely to fracture from blunt injury. 3. What is the uvea? What eye structures compose it? The uvea comprises the iris, ciliary body, and the choroid.

They are all connected to each other and are histologically similar. Patients can present with a painful “uveitis,” an inflammation of the uvea, often secondary to rheumatological/inflammatory conditions like sarcoidosis. 4. Where does the retina get its nutrition supply? The inner 2/3rds of the retina (inner implies toward the center of the eyeball) gets its nutrition from the retinal vessels. The outer 1/3 (which includes the photoreceptors) is nourished by the underlying choroid plexus. A retinal detachment, which separates the retina from the choroid, is particularly dangerous for the photoreceptors. This is especially true for detachments involving the macula as the thin macula gets its blood supply primarily from the underlying choroid. 5. When the ciliary body contracts, how does the lens change shape (does it get rounder or flatter)? The ciliary body is a round, spincter-like muscle, so when it contracts the zonules actually relax, allowing the lens to relax and become rounder. With age, the lens hardens and has a hard time relaxing, no matter how hard the ciliary muscle contracts. This aging process is called presbyopia.

6. Which extraocular muscle doesn’t originate at the orbital apex? Unlike the other muscles, the inferior oblique originates from the orbital floor before inserting on the back of the globe near the macula. 7. Which full-thickness eyelid laceration is more dangerous – medial or lateral lacerations? Why? You worry about the canalicular tear-drainage system involvement with medial lacerations. You want to repair this system as soon as possible, to avoid chronic epiphora. 8. How many layers are there in the cornea? Can you name them?There are five: the superficial Epithelium, Bowman’s layer, Stroma, Decemet’s membrane, and the inner Endothelium. 9. How does the water content of the cornea differ from the rest of the eye? The cornea is relatively dehydrated, which helps with clarity. If water gets into the cornea, via a disrupted endothelium or a high pressure gradient from acute glaucoma, the cornea turns hazy and white. 10. A pseudophakic (i.e. implanted lens) patient is found to have excellent far vision, but reading is terrible. What’s going on?

As we get older, our natural lenses harden and do not change shape very well making it hard to accommodate and see near objects. This phenomenon is called presbyopia and is a normal finding in people over 40 years of age. A prosthetic lens is not able to change shape at all, so all patients (including small children) with implanted plastic lenses require reading glasses to read. Lacrimal apparatus - human anatomy organs Lacrimal apparatus Tweet LACRIMAL APPARATUS ANATOMY The lacrimal apparatus is the collective design of the lacrimal ducts which secrete tears (the lacrimal fluid,) and a few extra ducts that allow extra lacrimal fluid to drain into the nasal cavity. The almond-like lacrimal gland can be found along the superolateral segment of the orbit . The tuberolacrimal gland requires numerous ducts to excrete the tears into the conjunctival sac. Lacrimal fluid is part of the process of cleansing and wetting the eye, as the blinking of the eye washes the eyeball in the necessary tears.

LACRIMAL APPARATUS STRUCTURE The lacrimal puncta is found on either side of the lacrimal caruncle, and represents the two small drainage vessels required. This is the first point along the tract that the tears take through the lacrimal system. The second point includes the inferior and superior lacrimal canaliculi. These accept the drainage from the caruncle and pass the fluid onto the lacrimal sac, where it can then drain through the lacrimal duct. From there, the tears will drain directly into the nasal cavity via the inferior meatus of the cavity. Lacrimal fluid, which is a mucous based fluid, helps reduce the risks of infection as it contains a built in bactericidal substance, lysozyme, to help ward off bacteria. LACRIMAL APPARATUS DIAGRAM Image: Lacrimal Apparatus LACRIMAL APPARATUS FUNCTIONS Each lacrimal gland of each individual eye is known to produce about 1 milliliter of lacrimal fluid in a 24 hour period. Aggrevating substances cause greater amounts of fluids, such sand, dust, pollen, or onion, as the conjunctiva requires greater amounts to remain moist.

The aggrevating substances are typically washed away from the conjunctiva by the additional lacrimal fluids. How do Our Eyes Create Tears? (with pictures) How do Our Eyes Create Tears? Last Modified Date: 18 December 2016 Copyright Protected: Can you see through these real-life optical illusions? It would be more accurate to say that our bodies create tears for our eyes. The human eye itself is protected from outside irritants by a tear film, which is actually three layers thick. The outermost lipid layer is oily, which helps the liquid to remain in the eye. The middle aqueous layer is watery, but also contains chemicals that wash away germs and other irritants. The innermost layer of the film is called the mucous layer, and provides a smooth protective coating over the surface of the eye. The human body produces tears by stimulating two glands situated above each eye, behind the upper eyelids. These lacrimal glands are responsible for excreting lacrimal fluid, the medical term for tears. Lacrimal fluid is very salty, although there is some evidence that the salinity level changes depending on the cause of the fluid's release.

When the brain senses a need for tears, the glands excrete the lacrimal fluid into the upper eyelid area. Gravity or capillary action draws this fluid onto the eye's surface, where it either lubricates the eyeball, washes away the irritant, or simply pools at the base of the lower eyelid. Ideally, the excess tears collect in an area known as the lacrimal lake, where they will eventually be drawn into a small opening called the lacrimal duct. If the duct becomes overwhelmed or blocked, however, the excess may spill out of the lower eye and down the person's cheek. The lacrimal duct drains into the nasalacrimal duct, where the tears may either drain into the throat or nasal passages. The production of tears is essentially semi-automatic. The lacrimal glands routinely produce a small amount of liquid in order to keep the eyes lubricated and free of irritants. If a specific irritation, such as the gas from a raw onion or cigarette smoke, reaches the eyes, then the brain can send out a signal for the lacrimal glands to produce more. A person can also generate tears through the use of strong emotions.

Trained actors often have the ability to generate them in a dramatic scene by using sense memory to trigger a genuine emotional response. So-called " crocodile tears" can also be generated voluntarily by channeling a false emotional response for the benefit of others. Hard squinting can also force lacrimal fluid to pool up, creating the illusion of real tears. Ad candyquilt Post 10 @anon86626-- I think that excessive crying can damage the production of tears or the function of the tear duct. My great-grandmother had one blind eye. My mom always says that it was a result of excessive crying. She had witnessed the death of her sister and apparently cried for months afterward. There is a condition called chronic dry eye where the body cannot create enough tears for the lubrication of the eye. And this can lead to eyesight damage and I think that's what happened to my great-grandmother. fBoyle Post 9 @SarahGen-- One theory is that crying is a survival system. Our eyes can water up for various reasons like a physical irritant or when our eyes need more lubrication. But when we create tears in response to emotion, it's a survival mechanism for protection.

Emotional tears apparently show that there is a problem. This can be a signal to ourselves that there is an issue we need to deal with or it can be a sign to others that we are vulnerable and should be left alone or helped. If you think about it, it makes a lot of sense. SarahGen Post 8 @anon76807-- I would like to know the same. I know we cry when we're sad, upset, angry and even when we're happy. Buy how do we do it? Why don't animals cry? I'm sure they experience the same emotions we do but we don't see them crying like humans. There has to be more to this than we know. StarJo Post 7 I didn't know our eyes had three layers. With oil, water, and mucus covering them, it's no wonder they are well lubricated. I've never really noticed that tears come from the top part of the eye. Since they leak out of the bottom corner, I always assumed that this was where they originated. kylee07drg Post 6 @cloudel – Some people say to hold a burning match in your mouth while chopping the onion, but that's a terrible idea!

I know I would burn myself if I did this. I've read that if you use a sharp knife and chop quickly, you won't release as many irritants. However, there is one method that my grandmother taught me that works even better than this. You hold a piece of bread in your mouth while dicing the onion. A big portion of it needs to be hanging out, and I think that it absorbs the gases that the onion releases. I always do this while chopping onions. I haven't had any problems with tearing up since I began using bread. cloudel Post 5 My husband caught me crying tears of irritation in the kitchen the other day. I was chopping a red onion, and the fumes were so intense that my eyes were burning, and tears were streaming out of them. Is there any way to prevent tears from forming while I'm chopping an onion? I really hate to go through all that burning and crying, and I use onions in a lot of things I cook. I read once that you could do something with a matchstick that would help. I forgot what it was, though. seag47 Post 4 I wasn't aware of the nasalacrimal duct.

This explains why my nose gets so uncontrollably runny when I cry. The fluid is so watery that it pours right out of my nose like tears pour from my eyes. If I don't have a tissue handy, I'm in trouble. I hate to cry in public, but it has happened before. I have even been forced to wipe my nose on my sleeve, because I had no tissue with me. anon248225 Why does the brain send the signal to the tear duct? Why not somewhere else? anon86625 Post 2 Why don't they stop if you cry for hours? Is it possible to cry all the water out of your body? anon76807 Kids Research Express: Tears Kids Research Express Online Encyclopedia Blog For Kid's Research In Sciences, Health, Environment and Technology KRE Urinary System Tears Tears, fluid produced in the lacrimal glands above the outside corner of each eye. The fluid lubricates the eyes and protects them from foreign matter and infection—the latter because it contains salt and lysozyme, an enzyme that kills microorganisms.

During normal flow, tears constantly wash over the exterior of the eye and collect at its inside corner, where they drain through two small lacrimal ducts into the nasal cavity. During heavy tear flow, such as that caused by irritation, the excess fluid that is not taken up by the lacrimal ducts spills over the eyelids, carrying off foreign bodies too large to be flushed through the lacrimal ducts. Lacrimal apparatus There is no image containing this anatomical part yet. Description The Lacrimal Apparatus (apparatus lacrimalis) consists of: the lacrimal gland, which secretes the tears, and its excretory ducts, which convey the fluid to the surface of the eye; the lacrimal ducts, the lacrimal sac, and the nasolacrimal duct, by which the fluid is conveyed into the cavity of the nose This definition incorporates text from a public domain edition of Gray's Anatomy (20th U.S.

edition of Gray's Anatomy of the Human Body, published in 1918 – from Anatomical hierarchy Water: It's More Than Just a Drink | Nutrition Information Water: It's More Than Just a Drink Home » Guide to Nutrition » Water: It's More Than Just a Drink Water: It's More Than Just a Drink Overview By Jill Weisenberger, MS, RD, CDE Eight glasses of water a day, right? Maybe not. For some time now, experts have told us to drink eight 8-ounce glasses of water each day. Because we’ve heard this mantra for so long, it’s difficult to imagine that it wouldn’t be the truth. There isn’t any evidence for it, however, concluded scientific reviews in 2002 [1] and 2008. [2] What’s more, in 2004 the Institute for Medicine (IOM) issued new fluid guidelines stating that average healthy Americans should let thirst be their guide and that even caffeinated beverages like cola, tea and coffee count toward our fluid requirements. On This Page: That’s not to say that water is not important. In fact, at least 50% of your body is water.

Take a look at what it does for you. Water in the Body Water has the following functions within the human body. Transports nutrients and other compounds. As a major component of the blood, water helps move glucose, water-soluble vitamins, minerals, other nutrients and some medications throughout your body. Cools you. When you become too hot, your blood vessels dilate and you start sweating. The sweat evaporating on your skin is cooling. Water also has a high heat capacity. This means that a lot of energy is needed to increase its temperature. Since the body contains more water than anything else, it takes quite a significant amount of heat to raise your body temperature. Protects and lubricates. It would be hard to swallow a peanut butter sandwich or practically any food without saliva, wouldn’t it? Fortunately, our salivary glands produce ample saliva, which is largely water. Tears lubricate and clean the eyes, and synovial fluid lubricates your joints. Cerebrospinal fluid protects your brain and spine from trauma. Similarly, amniotic fluid surrounds and shields the fetus. Fluids throughout your body protect and lubricate your organs and tissues. Participates in metabolism.

Most chemical reactions in your body use water in at least one of three ways: a solvent, a reactant or a product of the chemical reaction. Water produced in chemical reactions is called metabolic water, and your body uses it in the same ways it uses the water you drink. Even though the myth of drinking eight glasses of water a day may not be true, water is still an essential ingredient in your body’s system. Water in the Diet If you are the typical American adult, you consume about 20 to 25% of your daily water from solid foods. Fruits, vegetables, cooked grains and even meats and cheese provide water. The rest of your water intake comes from beverages of all types. Water Content of Selected Foods and Beverages (food and its percentage of water by weight): Apple: 85% Cheddar cheese: 37% Source: USDA Nutrient Data Lab [3] How much fluid do you really need? The IOM report does not specify water requirements. Rather it includes guidelines for total fluid intake. From both food and beverages, women should consume, on average, 91 ounces of total water, and men should have 125 ounces of total water daily.

This should cover your fluid losses in urine and feces, and the normal, but continual losses from the lungs and skin. The water loss from the skin and the respiratory tract is referred to as insensible water loss. If you are sick, you may lose additional water from nasal secretions, through vomiting or diarrhea or from sweating with a fever. Thus, you’ll need to drink additional beverages. How should you measure your fluid intake? There is usually no reason to measure your water intake or impose a water requirement on yourself. Healthy people will meet their fluid needs by paying attention to their thirst. If you have heard and believed that thirst is a poor indicator of hydration status, you have fallen prey to another myth. Though we often hear such things as, “by the time you’re thirsty, you are already dehydrated,” the truth is that experts define dehydration when the concentration of blood has increased by at least 5%, but thirst begins much sooner than that, usually before the concentration of blood rises 2%. Thirst may not indicate hydration status, however, for individuals with medical conditions requiring fluid control, individuals taking some medications, athletes or those involved in other strenuous activities, or people living in especially hot climates. What are some liquid sources of water?

Athletes and heavy sweaters may benefit from sports drinks. They are ideal for individuals who are very active for at least 60 minutes. They contain fluid and electrolytes lost in sweat, as well as carbohydrates to refuel and prevent fatigue. For casual exercisers who sweat little, sports drinks likely offer little more than water and extra calories. Added vitamins in sports drinks are unnecessary because we do not lose vitamins in sweat. Sodas, sweet tea and fancy coffee drinks also provide you with necessary water, but they give you plenty of unnecessary added sugars and calories, so have them only rarely. To keep your body hydrated, you can do more than just drink water. Many healthy foods contain water, as well as some of the other liquids you consume, such as milk. Eat and drink a variety of foods and liquids to make sure your fluid intake is where it should be. Water and Electrolytes: A Critical Balance Electrolytes are substances that, when dissolved in water, dissociate into positively and negatively charged ions. This makes them capable of carrying an electrical current. For example, when you dissolve salt (sodium chloride) in water, sodium and chloride separate. Sodium provides a positive charge and chloride brings a negative charge.

Electrolytes help maintain fluid balance because they draw water to them. Through osmosis, water will cross cell membranes to make the concentration of dissolved particles the same on both sides. The major electrolytes are sodium, potassium, chloride and phosphorus. Sodium: This is the major positively charged electrolyte in the extracellular fluid (fluid outside the cells). Functions: Assists with the transmission of nerve signals Participates in the active transport of glucose and some other nutrients Recommended intakes of sodium: Our actual daily requirement for sodium is very small, just a few hundred milligrams. It would be hard, perhaps impossible, to eat so little sodium and still maintain a diet adequate in other nutrients. For this reason, the IOM set the Adequate Intake (AI) at 1500 mg. The Tolerable Upper Intake Level (UL) is at 2300 mg. The 2010 Dietary Guidelines for Americans is more strict and recommends a daily limit of 1500 mg of sodium for anyone age 51 years or older, all African Americans, and all people with high blood pressure , diabetes or chronic kidney disease. This includes almost half of the population - including children!

The rest of the population is advised to limit sodium consumption to 2300 mg/day. Most Americans consume significantly more sodium than health experts consider safe. According to the Centers for Disease Control and Prevention (CDC), the average daily sodium intake for Americans over the age of two is more than 3400 mg. [4] Sources of sodium: Though it is not the saltiest food per serving, bread is the greatest contributor of sodium to the American diet because it is so frequently consumed. [5] Approximately 10% of our sodium intake is from sodium that occurs naturally in our food. Three-quarters of our intake comes from processed foods and restaurant foods. The rest comes from what we add in cooking or at the table. Thus, the most important steps to reducing sodium intake are to eat few highly processed foods and to prepare many of our meals from scratch. When you get too much or too little sodium: High sodium diets are linked to high blood pressure, bone loss and kidney stones . Low sodium intakes relative to sodium losses in sweat can cause overhydration, which can be deadly. Potassium: This is the major positively charged electrolyte in the intracellular fluid (fluid within the cells).

Functions: Assists with managing blood pressure by blunting the effects of excess sodium Aids in muscle contraction Assists in nerve transmission Recommended intakes of potassium: The AI for potassium for adults is 4700 mg per day. For children, the AI ranges between 3000 and 4700 mg, depending on age and gender. Unfortunately, less than 3% of Americans meet the AI for potassium. [6] Sources of potassium: The most notable sources of potassium are fruits, vegetables and dairy, though potassium is present in all food groups. High-potassium foods include white and sweet potatoes, beans, leafy greens, tomatoes, oranges, halibut and clams. When you get too much or too little potassium: A severe dietary imbalance of potassium is rare in healthy people. Individuals with healthy kidneys excrete excess potassium readily. If people take large doses in the form of supplements or if they have impaired kidney function, potassium can build up in the blood and alter the electrical rhythm of the heart causing heart attack and death. Because potassium helps to balance sodium, low potassium intakes are linked to high blood pressure, especially when sodium intake is excessive.

Chloride: This is the major negatively charged electrolyte in the body. Functions: Used to form hydrochloric acid (HCl) secreted into the stomach Aids in the immune function Assists in nerve transmission Recommended intakes of chloride: For men and women aged 19–50 years, the AI for chloride is 2300 mg. Sources of chloride: Chloride is usually found as sodium chloride, common table salt. When you get too much or too little chloride: Since chloride is usually consumed as table salt, there are no known toxicity symptoms for chloride alone. Deficiencies of chloride do not occur from lack of intake, but rather from severe vomiting or dehydration. Phosphorus: This is the major negatively charged electrolyte in the intracellular fluid, usually combined with oxygen in the body to form phosphate. Functions: Part of DNA, RNA, cell membranes and the mineral complex in the bone Assists in providing the body with energy, as a component of ATP (adenosine triphosphate) Helps regulate biochemical reactions by activating or deactivating various enzymes Recommended intakes of phosphorus: The Recommended Dietary Allowance (RDA) for adults is 700 mg/day.

For adolescents and teens, the RDA is 1250 mg/day. Sources of phosphorus: Where there is protein, there is usually phosphorus. Some of the best sources of this mineral are meats, eggs and dairy. Highly processed foods, especially sodas and processed meats, also provide ample phosphorous to the diet. When you get too much or too little phosphorus: Phosphorus is ubiquitous in the diet, so dietary deficiencies are extremely rare. Low blood phosphorous levels may come from parathyroid disorders, vitamin D deficiency or overuse of phosphate binding antacids. In the short-term, low phosphorous levels can cause muscle weakness. Weakening of the bones occurs when low phosphorous levels occur long term. High phosphorous levels in the blood can occur when individuals take excessive vitamin D supplements or phosphorous-containing laxatives. Individuals with kidney disease may also experience high phosphorous levels. Very high blood levels of phosphorous can cause muscle spasms and convulsions. Electrolytes are no less important than fluid for maintaining proper hydration status. And as you can see, each of the above minerals plays multiple roles in the body - from bone density to immune function, muscle contraction and nerve transmission.

Eating a balanced diet with an abundance of fresh fruits and vegetables will help assure the proper intake of these minerals. Maintain Safe Hydration Levels You can see how intricately tied water and electrolytes are in the body. A problem with one easily leads to a problem with the other. It might be hard to imagine that water, something so pure, so critical for life can be toxic. Overhydration: Overhydration or water intoxication can occur when athletes replace excessive sweat losses with plain water. Remember that sweating causes loss of water and electrolytes. When water only is replaced, the concentration of sodium in the blood becomes too low, a condition called hyponatremia. Severe hyponatremia is lethal. It can also occur when large quantities of water are consumed so rapidly that the kidneys cannot excrete the excess. Dehydration: Dehydration occurs when too much fluid is lost from the body through sweating, vomiting or diarrhea. The treatment for mild dehydration is water or water and salts. Severe dehydration requires medical attention with intravenous fluids and careful monitoring of electrolytes. Water is an essential part of the human body. Make sure you drink enough fluids and eat foods that contain water.

You may not be able to measure the exact amount of ounces you consume during a day, but if you eat healthy foods, and drink fluids that contain more water than sugars or additional calories, you should maintain safe hydration levels. Next Nutrition Guide: WHAT DETERMINES WHAT WE EAT Sources Valtin Heinz. “Drink at least eight glasses of water a day.” Really? Is there scientific evidence for “8 x 8”? Am J Physiol Regul Integr Comp Physiol 283: R993–R1004, 2002. Kolso J, Jeckel K, Wildman EC. Water, Hydration and Health: What Dietetics Practitioners Need to Know. SCAN’s Pulse Winter 2012 Vol.31, No. 1. USDA Nutrient Data Lab Accessed March 9, 2012.

Question: Lacrimal fluid lubricates which part of the human body?
Answer: Eyes