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-{{Mergefrom|Teat|date=December 2008}}
-{{Refimprove|date=September 2008}}
-{{this|the anatomical structure|nipple (disambiguation)}}
-[[Image:Female nipple profile.jpg|thumb|right|Human female nipple, [[areola]] and [[breast]].]]
-In its most general form, a '''nipple''' is a [[structure]] from which a fluid emanates. More specifically, it is the projection on the [[breasts]] of a mammal by which [[breast milk]] is delivered to a mother's young.
-==Anatomy==
-In the [[anatomy]] of  [[mammal]]s, a '''[[nipple]]''' or ''mammary papilla'' is a small projection of [[skin]] containing the outlets for 15-20 [[lactiferous duct]]s arranged cylindrically around the tip. The skin of the nipple is rich in a supply of special [[nerve]]s that are sensitive to certain stimuli. The physiological purpose of nipples is to deliver [[milk]] to the infant, produced in the female [[mammary gland]]s 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 (moving their head so as to bring their mouth towards whatever is touching their face) for seeking the nipple, and a ''[[suction|suck]]ing'' instinct for extracting milk.
-Mammals typically have an even number of nipples arranged around bilaterally.  They develop in the [[embryo]], along the '[[milk line]]s'. Most mammals develop multiple nipples along each milk line, with the total number approximating the maximum litter size, and half the total number (i.e. the number on one side) approximating the average litter size for that species. In the primitive mammals ([[monotreme]]s such as the [[platypus]]), the mammary glands empty onto the skin without a nipple. In cetaceans such as whales, the infant cannot form a suction-seal to nurse, due to its mouth structure. Therefore the whale's nipple is unlike that of any other mammal. Rather than requiring a sucking action, the discharge of milk is powered by maternal muscles. The calf takes the extended nipple into its mouth, and the mother ejects or expels her milk into the mouth of the calf.
-Most [[human]]s have two nipples after birth, located near the center of each [[breast]] and surrounded by an area of sensitive, pigmented skin known as the [[areola]].  Human fetuses develop several more nipples along the milk lines, which extend from the [[axilla]] (armpit), along the abdominal muscles, down to the [[pubis]] (groin) on both sides.  Those nipples usually disappear before birth, but sometimes remain, resulting in [[supernumerary nipple]]s which occasionally have lactiferous glands attached, but usually do not.
-The pigments of the nipple and areola are [[eumelanin|brown eumelanin]] (a brown pigment) and to a greater extent [[pheomelanin]] (a red pigment).  Exposure to cold temperatures and [[breastfeeding]] are primary causes for the nipples to become [[erect]]; nipple erections are a product of the pilomotor reflex which causes [[goose bumps]]. [[Sexual arousal]] may also cause the nipples to become erect. The nipple and areola of males and females can be erotic receptors, sometimes intense enough to elicit [[orgasm]] in some individuals of either sex. They are not, however, [[sex organs]] because since mammals of both sexes all have nipples, nipples don't possess the defining quality of a sex organ of differentiating the sex of any animal.
-The average projection and size of human female nipples is slightly more than 3/8 inches (10mm).<ref>M. Hussain, L. Rynn, C. Riordan and P. J. Regan, Nipple-areola reconstruction: outcome assessment; European Journal of Plastic Surgery, Vol. 26, Num. 7, December, 2003</ref>. Pregnancy and nursing tend to increase nipple size, sometimes permanently. Pregnancy also increases the pigmentation. The erection of the nipple is partially due to the cylindrically arranged muscle cells found within it. In many women, there are small bulges on the areola, which are called '[[Glands of Montgomery|Montgomery bodies]]'.
-Sometimes, [[baby|babies]] (male or female) are born producing milk. This is called '[[witch's milk]]'; it is caused by maternal [[estrogen]]s acting on the baby and is quite common. Witch's milk disappears after several days.
-==Nipples on male mammals==
-From conception until [[sexual differentiation]], all mammalian [[fetus]]es within the same [[species]] look the same, regardless of sex. In humans this lasts for around 14 weeks after which, [[sex chromosome|genetically-male]] fetuses begin producing male [[hormone]]s such as [[testosterone]].{{Fact|date=September 2008}} Usually, males' nipples do not change much past this point. However, some males develop a condition known as [[gynecomastia]], in which the fatty tissue around and under the nipple develops into something similar to a female breast.  This may happen whenever the testosterone level drops.
-==See also==
-*[[Areola]]
-*[[Breast]]
-*[[Breastfeeding]]
-*[[Inverted nipple]]
-*[[Nipple piercing]]
-*[[Supernumerary nipple|Supernumerary (third) nipple]]
-== References ==
-<references/>
-{{Female reproductive system}}
-{{sex}}
-[[Category:Breast anatomy]]
-[[ar:حلمة]]
-[[br:Beg ar vronn]]
-[[ca:Mugró]]
-[[cs:Bradavka]]
-[[cy:Teth]]
-[[da:Brystvorte]]
-[[de:Brustwarze]]
-[[es:Pezón]]
-[[eo:Mampinto]]
-[[fa:نوک پستان]]
-[[fr:Mamelon]]
-[[ilo:Mungay]]
-[[is:Geirvarta]]
-[[it:Capezzolo]]
-[[la:Mamilla]]
-[[nl:Tepel]]
-[[ja:乳首]]
-[[no:Patte]]
-[[pl:Brodawka sutkowa]]
-[[pt:Mamilo]]
-[[simple:Nipple]]
-[[fi:Nänni]]
-[[sv:Bröstvårta]]
-[[tl:Utong]]
-[[zh:乳頭]]