Nipple
|
The udder of a cow with nipples showing |
In its most general form, a
nipple is an
appurtenance from which a fluid emanates, in this instance
breast milk, to nurture a mother's young.
In the
anatomy of
mammals, a
nipple or
mammary papilla is a small projection of
skin containing the outlets for 15-20
lactiferous ducts arranged cylindrically around the tip. The physiological purpose of nipples is to deliver to the infant
milk produced in the female
mammary glands during
lactation. In the
male, nipples are often not considered functional with regard to
breastfeeding, although
male lactation is possible. Mammalian infants have a
rooting instinct for seeking the nipple, and a
sucking instinct for extracting milk.
Mammals typically have an even number of nipples arranged bilaterally. Rarely, as in the
platypus, the mammary glands empty onto the skin without a nipple.
|
Typical human female nipple and areola. Nipple in erect state. |
In
human anatomy, the two nipples are located near the center of the
breasts, surrounded by an area of sensitive, pigmented skin known as the
areola. The nipple and areola of males and females can be erotic receptors, or considered
sex organs. Stimulation or
sexual arousal can cause the nipples to become erect.
Breastfeeding or exposure to cold temperatures often has this effect as well. Pregnancy and nursing tend to increase nipple size somewhat, and this increase may remain permanently thereafter.Small non-striated
myocytes (muscle cells) arranged cylindrically within the nipple are responsible for this erection of the nipples.
|
Human male torso with nipples |
Embryologically, nipples develop along the '
milk lines' which in humans extend from the
axilla (armpit) down to the
pubis (groin) on both sides. Other mammals such as cats and dogs develop more nipples along the milk lines, in number generally approximating the average litter size for that species, rounded up to an even number. Most people develop two nipples (one on each breast) but some have
supernumerary nipples. Occasionally, these have lactiferous glands attached.
Sometimes,
babies (male or female) are born producing milk. This, called '
witch's milk', is caused by maternal
estrogens acting on the baby and is quite normal. Witch's milk disappears after several days.
*
List of sexology topics:
Areola,
Breast,
Erection,
Male lactation,
Masters and Johnson,
Masturbation,
Nudity,
Sex organ,
Sexual arousal*
Biological development:
Breastfeeding,
Infant,
Inverted nipple,
Oxytocin,
Prolactin,
Supernumerary (third) nipple,
Tit,
Wet nurse,
Witch's milk*
Modification methods:
Nipple piercing,
Body nullification,
Jewellery*
Stephen Jay Gould, "Male Nipples and Clitoral Ripples", in
Adam's Navel and Other Essays, London: Penguin, 1995.
