How are tears formed

The structure of the human eye is very complex, and one of the parts is called the lacrimal gland. The main function of this part is to secrete tears, which are mainly a kind of fluid in the eyes. When people are in a state of extreme sadness or extreme happiness, they cannot help but shed tears. However, many people don’t know how tears are formed. Today I will introduce to you the process of tear formation.

There are two types of tears: reflex tears and emotional tears; emotional tears contain more protein than reflex tears, and emotional tears have a chemical substance similar to analgesics. Lactoferrin, β-lysin and other substances in tears have defensive functions and can inhibit bacterial growth. In addition, the secretion of tears promotes normal cell metabolism and prevents the formation of tumors. Reflex tears have a higher salt content than emotional tears.

Cause

Tears do not necessarily indicate a change in emotion. When foreign objects such as dust fall into our eyes, a large amount of tears will be produced to flush the foreign objects out. In addition to a large amount of water, tears also contain lysozyme, immunoglobulin, complement system, lactoferrin, β-lysin, etc., which have the effect of inhibiting bacterial growth. Therefore, tears have another very important function - defense.

Charles Darwin, the founder of the theory of evolution, once speculated that tears are some kind of evolutionary "relic" and have nothing to do with the competition for survival in the evolutionary process. When you cry, the capillaries around your eyes become filled with blood, and small muscles contract to protect your eyes, causing the tear glands to secrete tears. Darwin believed that for the human body. Tears themselves are meaningless "by-products".

American anthropologist Ashley Montag's views are completely opposite to Darwin's. He believes that crying is beneficial to the human body and that this benefit has a certain influence in evolution. Therefore, it can be preserved from generation to generation through natural selection. The fact that humans shed tears is the result of the survival of the fittest. He gave an example: Tears contain lysozyme, which is a self-defense substance of the human body that can protect the nasopharyngeal mucosa from bacterial infection. Observations show that dry crying without tears can easily cause the nasopharyngeal mucosa to dry out and become infected.

More and more scholars agree with Montag's view and believe that crying may have certain benefits to the human body.

Tear gland

The lacrimal gland is composed of tubular glands and ducts, and it is the organ that secretes tears. The lacrimal gland is located in the lacrimal fossa above the eye socket and is divided into two parts: the upper part is the orbital part, also called the upper lacrimal gland, which is larger and shaped like an almond, approximately 12mm×20mm; the lower part is the palpebral part, also called the lower lacrimal gland, which is smaller. The lacrimal gland has 10 to 12 excretory ducts, through which tears are discharged after being produced. Under normal circumstances, the lacrimal gland secretes about 0.5 to 0.6 ml of tears during the day to moisten the conjunctiva and cornea of ​​the eyeball. When a person sleeps, the tear gland stops secreting tears.

After tears are produced, they are excreted through the lacrimal duct, which is composed of the lacrimal puncta, lacrimal canaliculi, lacrimal sac and nasolacrimal duct. There is one lacrimal punctum on the inner side of the upper and lower eyelid margins. Tears enter the sewer-like lacrimal canaliculus from the lacrimal punctum, and then enter the lacrimal sac through the lacrimal canaliculus, which is about 10 mm long. The lacrimal sac is specifically used to collect and store tears and prevent them from flowing out. The size of the lacrimal sac is about 12mm×6mm. There is a tube with a length of 12 to 24mm and a diameter of 3 to 6mm below the lacrimal sac that goes directly to the nasal cavity. This is the nasolacrimal duct. The tears in the lacrimal sac enter the nasal cavity through the nasolacrimal duct. So when we put eye drops in, we need to press the root of the nose with our fingers to prevent the eye drops from flowing into the nasal cavity through the nasolacrimal duct.