In every blink the eyelashes close access to the eyes like curtains. And, in every blink, the eyes are irrigated with a lubricant secretion from sebaceous glands -tear glands- running along the edge of the eyelid, with their openings between the eyelashes. This lubrication ensures that the eyes don't dry out, keeping them wet and healthy.
Eyelashes on the upper eyelid are longer than those of the lower eyelid. The upper eyelashes can reach a length of an average of 8 mm., and tend to curve upwards. The upper eyelid has more eyelashes: around a seventy to one hundred fifty lashes and the lower eyelid has generally a row of sixty to eighty eyelashes, smaller and they curve downwards. This curved shape of both rows of eyelashes helps to slip sweat and foreign particles out of the eyes.
Like all the hair in the human body, eyelashes are a biological polymer, made up of about 10 per cent of water and 90 per cent of proteins, such as keratins, and melanins, the substances that give hair its color.
And, as all the human hair, they are fed by follicles, located below the skin. In eyelashes, those follicles have also three phases of growth: the "growing phase" lasts about 45 days, and is followed by a "declination phase" in which the growth stops, for about three weeks, and a last phase of two weeks, a span of rest, the "sheading phase", when the hair falls out. After this period, a new cycle begins and the hair is regenerated.
When an eyelash is pulled out or drops out, it needs about two months to be regenerated.
Eyelashes are human hairs on the upper and lower eyelids. Each eyelid has layers of eyelashes within a row, we can have three to five layers of eyelashes in the eyelid, which protect and frame the eyes. They have the similar anatomy of the human body hair. They are anchored to the eyelid by a root. There are small muscles located in the eyelids which, with a muscular contraction, -a reflexive and automatic response-, they blink and close the eyes before an external threat, like particles of dust, or any foreign agent which could cause damages to the eyes.
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