Female mammals
From The Art and Popular Culture Encyclopedia
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| - | :''For the clam genus of family [[Carditidae]], see ''[[Glans (bivalve)]]. | + | A distinguishing characteristic of the [[class (biology)|class]] ''[[Mammalia]]'' is the presence of [[mammary gland]]s. The mammary glands are modified sweat glands that produce milk, which is used to feed the young for some time after birth. Only mammals [[Lactation|produce milk]]. Mammary glands are [[Breast#Other suggested functions|most obvious]] in [[humans]], as the female human body stores large amounts of fatty tissue near the nipples, resulting in prominent [[breast]]s. Mammary glands are present in all mammals, although they are seldom used by the males of the species. |
| - | The '''glans''' ({{IPAc-en|pron|g|l|æ|n|z}}, plural "glandes" {{IPAc-en|'|g|l|æ|n|d|,|i:|z}}; [[etymology|from]] the [[Latin]] word for "[[acorn]]") is a [[vascular]] structure located at the tip of the [[penis]] in [[male mammals]] or a [[homology (biology)|homologous]] genital structure of the [[clitoris]] in [[female mammals]]. | + | |
| - | ==Structure== | + | Most mammalian females have two copies of the [[X chromosome]] as opposed to males which have only one X and one smaller [[Y chromosome]]; some mammals, such as the [[platypus]], have different combinations. To compensate for the difference in size, one of the female's X chromosomes is [[X-inactivation|randomly inactivated]] in each cell of placental mammals while the paternally derived X is inactivated in marsupials. In birds and some reptiles, by contrast, it is the female which is [[heterozygous]] and carries a Z and a W chromosome whilst the male carries two Z chromosomes. [[Intersex]] conditions can also give rise to other combinations, such as XO or XXX in mammals, which are still considered as female so long as they do not contain a Y chromosome, except for specific cases of testosterone deficiency/insensitivity in XY individuals while in the womb. However, these conditions frequently result in sterility. |
| - | The exterior structure of the glans consists of [[mucous membrane]], which is usually covered by [[foreskin]] or [[clitoral hood]] in naturally developed [[genitalia]]. This covering, called the prepuce, is normally retractable in adulthood. | + | |
| - | The glans naturally joins with the inner [[labia (genitalia)|labia]], and the [[frenulum]] of the [[penis]] or [[clitoris]]. In non-technical or sexual discussions, often the word "clitoris" refers to the external glans alone, excluding the [[clitoral hood]], [[frenulum]], and internal body of the clitoris. | + | Mammalian females bear live young, with the exception of [[monotreme]] females, which lay eggs. Some non-mammalian species, such as [[guppy|guppies]], have analogous reproductive structures; and some other non-mammals, such as [[shark]]s, whose eggs hatch inside their bodies, also have the appearance of bearing live young. |
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| - | ==Gender differences== | + | |
| - | In males, the glans is known as the [[glans penis]], while in females the glans is known as the [[clitoral glans]]. | + | |
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| - | In females, the clitoris is above the urethra. The glans of the clitoris is the most highly innervated part of the external female genitalia. | + | |
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| - | ==Development== | + | |
| - | In the [[development of the urinary and reproductive organs]], the glans is derived from the [[genital tubercle]]. | + | |
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A distinguishing characteristic of the class Mammalia is the presence of mammary glands. The mammary glands are modified sweat glands that produce milk, which is used to feed the young for some time after birth. Only mammals produce milk. Mammary glands are most obvious in humans, as the female human body stores large amounts of fatty tissue near the nipples, resulting in prominent breasts. Mammary glands are present in all mammals, although they are seldom used by the males of the species.
Most mammalian females have two copies of the X chromosome as opposed to males which have only one X and one smaller Y chromosome; some mammals, such as the platypus, have different combinations. To compensate for the difference in size, one of the female's X chromosomes is randomly inactivated in each cell of placental mammals while the paternally derived X is inactivated in marsupials. In birds and some reptiles, by contrast, it is the female which is heterozygous and carries a Z and a W chromosome whilst the male carries two Z chromosomes. Intersex conditions can also give rise to other combinations, such as XO or XXX in mammals, which are still considered as female so long as they do not contain a Y chromosome, except for specific cases of testosterone deficiency/insensitivity in XY individuals while in the womb. However, these conditions frequently result in sterility.
Mammalian females bear live young, with the exception of monotreme females, which lay eggs. Some non-mammalian species, such as guppies, have analogous reproductive structures; and some other non-mammals, such as sharks, whose eggs hatch inside their bodies, also have the appearance of bearing live young.
