section_path: Biology/Morphological and physiological characteristics
section_name: Morphological and physiological characteristics
paragraph_text: Morphological and physiological characteristics
  
  In terms of biology, the female sex organs are involved in the reproductive system, whereas the secondary sex characteristics are involved in breastfeeding children and attracting a mate. Humans are placental mammals, which means the mother carries the fetus in the uterus and the placenta facilitates the exchange of nutrients and waste between the mother and fetus.
  
  The internal female genitalia consist of the ovaries, gonads that produce female gametes called ova, the fallopian tubes, tubular structures that transport the egg cells, the uterus, an organ with tissue to protect and nurture the developing fetus and its cervix to expel it, the accessory glands (Bartholin's and Skene's), two pairs of glands that help lubricate during intercourse, and the vagina, an organ used in copulating and birthing.
  
  The vulva (external female genitalia) consists of the clitoris, labia majora, labia minora and vestibule. The vestibule is where the vaginal and urethral openings are located.
  
  The mammary glands are hypothesized to have evolved from apocrine-like glands to produce milk, a nutritious secretion that is the most distinctive characteristic of mammals, along with live birth. In mature women, the breast is generally more prominent than in most other mammals; this prominence, not necessary for milk production, is thought to be at least partially the result of sexual selection.
  
  Estrogens, which are primary female sex hormones, have a significant impact on a female's body shape. They are produced in both men and women, but their levels are significantly higher in women, especially in those of reproductive age. Besides other functions, estrogens promote the development of female secondary sexual characteristics, such as breasts and hips. As a result of estrogens, during puberty, girls develop breasts and their hips widen. Working against estrogen, the presence of testosterone in a pubescent female inhibits breast development and promotes muscle and facial hair development.