Why does hair turn gray or white in older individuals?
What will be an ideal response?
As people age, melanocyte activity in the hair follicles often decreases or stops, and lacking melanin, the other substances in the hair appear grayish. As follicular hair production further deteriorates, air bubbles can form in the medulla of the hair shafts, causing the hair to appear white.
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A small amount of ultraviolet radiation is beneficial because it
A) increases blood flow in the dermis. B) stimulates the synthesis of photoreceptor pigments in the eye. C) constricts blood vessels in the dermis. D) stimulates vitamin D3 synthesis in the epidermis. E) adjusts overall gland secretion rates in the body.
Neurons that use norepinephrine as a transmitter are called
A) cholinergic. B) adrenergic. C) nicotinic. D) muscarinic.
The anterior border of the perineum is the
A. anus. B. urethra. C. pubic symphysis. D. scrotum in the male and the labia majora in the female.
The main regulator of serum phosphate levels is a transport process in the ________.
A. small intestine B. pancreas C. liver D. large intestine E. kidneys