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Hair
Hair Follicles
• A follicle is a deep pit where hair grows. The shaft of a hair is formed at the base of a follicle by a root consisting of capillaries and germinative cells. Cells of a hair shaft quickly fill with keratin and die
• Hairs on the head stop growing in ~3-4 years, but new growth from the same root begins afterwards; your hair grows at an average rate of 0.3 mm per day
• Hair can have different jobs:
– Ex) hair on your head keeps it warm, eye lashes and eyebrows protect your eyes
• Your lips, palms of hands and soles of feet don’t have any hair – the rest of the body does, but it is not always easily visible
–Ex) easier to see leg hair than the hair on the back of your ears
• You have more than 100 000 hairs on your head; about 50-100 fall out each day from brushing, washing etc
• Each hair follicle has a tiny erector muscle attached to it. You get goose bumps when these muscles contract (if you don’t have hair on your arms you don’t get goose bumps!)
• Each follicle has a flask-shaped sebacous gland attached to one side. These glands produce an oily liquid called sebum which spreads over the hairs and skin making them supple and water proof and help prevent growth of bacteria; it keeps hair from becoming dry and brittle
• If the secretion of sebaceous glands accumulates inside the hair follicle, it oxidizes, forming a blackhead; if the glands become infected, they cause pimples or acne
• Hair follicles determine whether you will have straight or curly hair, and whether you will have coarse, thick hair, or thin and fine– Someone with ‘thick’ hair literally has thicker
strands of hair than someone with thin hair
• Hair is coloured by melanin (lighter hair = less melanin)
• Permanent hair loss or baldness is a tendency inherited by men in particular; hair loss progresses with age
• Hair loss may be affected by the hormone testosterone or can be caused by illness, poor circulation to the hair follicles, infections of the scalp, and some types of shampoo
• Hairs are sensory organs with nerve endings located around the roots; hairs act as tiny triggers to indicate when an object is in close contact with the body
