Instruct: Given a question, retrieve documents that answer the question.
Query: How many mammary glands do human women have?
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.
This is the most common cause of anovulation and is thought to account for about 70% of all cases. About half the women with hormonal imbalances do not produce enough follicles to ensure the development of an ovule, possibly due to poor hormonal secretions from the pituitary gland or the hypothalamus. The pituitary gland controls most other hormonal glands in the human body. Therefore, any pituitary malfunctioning affects other glands under its influence, including the ovaries. This occurs in around 10% of cases. The mammary glands are also controlled by the pituitary gland, so lactation can also be affected. The pituitary gland is controlled by the hypothalamus. In 10% of cases, alterations in the chemical signals from the hypothalamus can easily seriously affect the ovaries.
Many have questioned the evolution of overt menstruation in humans and related species, speculating on what advantage there could be to losing blood associated with dismantling the endometrium rather than absorbing it, as most mammals do.
The female will ovulate spontaneously and be receptive to the male to be bred (express estrus) at regular biologically defined intervals. The female is receptive to males only while experiencing estrus.
A recent suggestion, based upon observations that men and women have the same number of ribs, speculates that the bone was the baculum, a small structure found in the penis of many mammals, but not in humans.
In zoology, male lactation is the production of milk from a male mammal's mammary glands. Such production is known as lactation. It is well-documented in the Dayak fruit bat. The term "male lactation" is not used in human medicine. It has been used in popular literature, such as Louise Erdrich's "The Antelope Wife," to describe the phenomenon of male galactorrhea, which is a well-documented condition in humans, unrelated to childbirth or nursing. Newborn babies of both sexes can occasionally produce milk; this is called neonatal milk (also known as "Witch's milk") and not considered male lactation.
The number of children born to one woman can vary dependent on her window from menarche to menopause. The average window of fertility is from 13.53 to 49.24. Taking into consideration lactational amenorrhea and the period between conception and birth, the average woman is capable of experiencing around 20 births. However, if the duration of lactation is cut short due to use of a formula substitute or the woman has multiple births, the number of offspring could exceed 20.
The ova, which are the female sex cells, are much larger than the sperm and are normally formed within the ovaries of the fetus before its birth. They are mostly fixed in location within the ovary until their transit to the uterus, and contain nutrients for the later zygote and embryo. Over a regular interval, in response to hormonal signals, a process of oogenesis matures one ovum which is released and sent down the Fallopian tube. If not fertilized, this egg is released through menstruation in humans and other great apes, and reabsorbed in other mammals in the estrus cycle.
Females of most mammal species advertise fertility to males with visual behavioral cues, pheromones, or both. This period of advertised fertility is known as "oestrus", "estrus" or "heat". In species that experience estrus, females are generally only receptive to copulation while they are in heat (dolphins are an exception). In the estrous cycles of most placental mammals, if no fertilization takes place, the uterus reabsorbs the endometrium. This breakdown of the endometrium without vaginal discharge is sometimes called "covert menstruation". Overt menstruation (where there is blood flow from the vagina) occurs primarily in humans and close evolutionary relatives such as chimpanzees. Some species, such as domestic dogs, experience small amounts of vaginal bleeding while approaching heat; this discharge has a different physiologic cause than menstruation.
Menstruation in mammals is the shedding of the uterine lining (endometrium). It occurs on a regular basis in uninseminated sexually reproductive-age females of certain mammal species.
There is a market for human breast milk, both in the form of wet nurse service and milk product. As a product, breast milk is exchanged by human milk banks as well as directly between milk donors and customers mediated by websites on the Internet. Human milk banks generally have standardized measures for screening donors and storing the milk, while donors on websites vary in regard to these measures. A study in 2013 came to the conclusion that 74% of breast milk samples from providers found from websites were colonized with Gram-negative bacteria or had more than 10,000 colony-forming units/mL of aerobic bacteria. Growth happens during transit. According to the FDA, the bacteria in fresh milk doubles every 20 minutes. Breast milk is considered to be healthier than cow's milk and infant formula when it comes to feeding an infant in the first 6 months of life, but only under extreme situations do international health organizations support feeding an infant breast milk from a healthy wet nurse rather than that of its biological mother. One reason is because the unregulated breast milk market is fraught with risks such as drugs of abuse and prescription medications being present in donated breast milk. The transmission of these substances through breast milk can do more harm than good when it comes to the health outcomes of the infant recipient.
In humans, the 16,569 base pairs of mitochondrial DNA encode for only 37 genes. Human mitochondrial DNA was the first significant part of the human genome to be sequenced. In most species, including humans, mtDNA is usually inherited solely from the mother. However, in exceptional cases, human babies sometimes inherit mtDNA from both their fathers and their mothers resulting in mtDNA heteroplasmy.
In the human body at birth, there are over 270 bones, but many of these fuse together during development, leaving a total of 206 separate bones in the adult, not counting numerous small sesamoid bones. The largest bone in the body is the femur or thigh-bone, and the smallest is the stapes in the middle ear.
Singer and Grismaijer argue that bra-wearing may cause breast cancer because of a purported effect on lymphatic circulation. Their interpretation is that constriction from tightly worn bras inhibits the proper functioning of the lymphatic system and leads to a buildup of fluid within the breast tissue. According to the authors, bra-induced constriction of the breast lymphatic vessels concentrates toxins within the breast tissue, which may ultimately lead to cancer.
The fat graft breast reconstructions for 33 women (47 breasts, 14 irradiated), whose clinical statuses ranged from zero days to 30 years post-mastectomy, began with the pre-expansion of the breast mound (recipient site) with an external vacuum tissue-expander for 10 hours daily, for 10–30 days before the first grafting of autologous fat. The breast mound expansion was adequate when the mastectomy scar tissues stretched to create a 200–300 ml recipient matrix (skin envelope), that received a fat-suspension volume of 150–600 ml in each grafting session.
Menopause, the natural or surgical cessation of the menstrual cycle, is due to an overall decrease in ovarian production of the hormones estradiol and progesterone. These hormonal changes are also associated with an increase in WHR independent of increases in body mass. Significantly, studies find that large premenopausal WHRs are associated with lower estradiol levels and variation in age of menopause onset. Circulating estrogen preferentially stores lipid deposits in the gluteofemoral region, including the buttocks and thighs, and evidence suggests that menopause-associated estrogen deficiency results in an accumulation of adipose deposits around the abdomen. These menopause-induced changes in body fat distribution can be counteracted with hormone replacement therapy. In contrast, aging males gradually accumulate abdominal fat, and hence increased WHR, in parallel with declining androgen levels.
The copulatory organ is absent in this species. The gonads of hagfishes are situated in the peritoneal cavity. The ovary is found in the anterior portion of the gonad, and the testis is found in the posterior part. The animal becomes female if the cranial part of the gonad develops or male if the caudal part undergoes differentiation. If none develops, then the animal becomes sterile. If both anterior and posterior parts develop, then the animal becomes a functional hermaphrodite. However, hermaphroditism being characterised as functional needs to be validated by more reproduction studies (Patzner 1998). Of 11 females (405–575 mm total length (TL)) examined by Nani and Gneri (1951), those longer than 500 mm were mature. A 507 mm female contained eggs ranging in size from 24.5 x 6.6 to 28 x 8 mm.
While most humans are "trichromatic" (having three types of color receptors), many animals, known as "[[Tetrachromacy|tetrachromats]]", have four types. These include some species of [[spider]]s, most [[marsupial]]s, [[bird]]s, [[reptile]]s, and many species of [[fish]]. Other species are sensitive to only two axes of color or do not perceive color at all; these are called "dichromats" and "monochromats" respectively. A distinction is made between "retinal tetrachromacy" (having four pigments in cone cells in the retina, compared to three in trichromats) and "functional tetrachromacy" (having the ability to make enhanced color discriminations based on that retinal difference). As many as half of all women are retinal tetrachromats. The phenomenon arises when an individual receives two slightly different copies of the gene for either the medium- or long-wavelength cones, which are carried on the [[X chromosome]]. To have two different genes, a person must have two X chromosomes, which is why the phenomenon only occurs in women. There is one scholarly report that confirms the existence of a functional tetrachromat.
Human milk contains 0.8% to 0.9% protein, 4.5% fat, 7.1% carbohydrates, and 0.2% ash (minerals). Carbohydrates are mainly lactose; several lactose-based oligosaccharides have been identified as minor components. The fat fraction contains specific triglycerides of palmitic and oleic acid (O-P-O triglycerides), and also lipids with trans bonds (see: trans fat). The lipids are vaccenic acid, and Conjugated linoleic acid (CLA) accounting for up to 6% of the human milk fat.
The U.S. Food and Nutrition Board and Institute of Medicine recommended daily allowance of iodine ranges from 150 micrograms per day for adult humans to 290 micrograms per day for lactating mothers. However, the thyroid gland needs no more than 70 micrograms per day to synthesize the requisite daily amounts of T4 and T3. The higher recommended daily allowance levels of iodine seem necessary for optimal function of a number of other body systems, including lactating breasts, gastric mucosa, salivary glands, oral mucosa, arterial walls, thymus, epidermis, choroid plexus and cerebrospinal fluid, among others.
The Amazonian manatee is a seasonal breeder with a gestational period of 12–14 months and a prolonged calving period. Most births take place between December and July, with about 63% between February and May, during a time of rising river levels in their native region. After the calf is born, it will begin to eat while staying with its mother for 12 – 18 months.
There were approximately 180 women in Antarctica in the 1990-1991 season. Women from several different countries were regularly members of over-wintering teams by 1992. The first all-women expedition reached the South Pole in 1993. Diana Patterson, the first female station leader on Antarctica, saw a change happening in 1995. She felt that many of the sexist views of the past had given way so that women were judged not by the fact that they were women, but "by how well you did your job."
A mammary tumor is a neoplasm originating in the mammary gland. It is a common finding in older female dogs and cats that are not spayed, but they are found in other animals as well. The mammary glands in dogs and cats are associated with their nipples and extend from the underside of the chest to the groin on both sides of the midline. There are many differences between mammary tumors in animals and breast cancer in humans, including tumor type, malignancy, and treatment options. The prevalence in dogs is about three times that of women. In dogs, mammary tumors are the second most common tumor (after skin tumors) over all and the most common tumor in female dogs with a reported incidence of 3.4%. Multiple studies have documented that spaying female dogs when young greatly decreases their risk of developing mammary neoplasia when aged. Compared with female dogs left intact, those spayed before puberty have 0.5% of the risk, those spayed after one estrous cycle have 8.0% of the risk, and dogs spayed after two estrous cycles have 26.0% of the risk of developing mammary neoplasia later in life. Overall, unspayed female dogs have a seven times greater risk of developing mammary neoplasia than do those that are spayed. While the benefit of spaying decreases with each estrous cycle, some benefit has been demonstrated in female dogs even up to 9 years of age. There is a much lower risk (about 1 percent) in male dogs and a risk in cats about half that of dogs.
The mammary glands of mammals are specialized to produce milk, the primary source of nutrition for newborns. The monotremes branched early from other mammals and do not have the nipples seen in most mammals, but they do have mammary glands. The young lick the milk from a mammary patch on the mother's belly.
Most primates have two mammary glands, but the number and positions vary between species within strepsirrhines. Lorises have two pairs, while others, like the ring-tailed lemur, have one pair on the chest (pectoral). The aye-aye also has two mammary glands, but they are located near the groin (inguinal). In females, the clitoris is sometimes enlarged and pendulous, resembling the male penis, which can make sex identification difficult for human observers. The clitoris may also have a bony structure in it, similar to the baculum (penis bone) in males. Most male primates have a baculum, but it is typically larger in strepsirrhines and usually forked at the tip.
During weaning, decreased prolactin, missing mechanical stimulation (baby suckling), and changes in osmotic balance caused by milk stasis and leaking of tight junctions cause cessation of milk production. It is the (passive) process of a child or animal ceasing to be dependent on the mother for nourishment. In some species there is complete or partial involution of alveolar structures after weaning, in humans there is only partial involution and the level of involution in humans appears to be highly individual. The glands in the breast do secrete fluid also in nonlactating women. In some other species (such as cows), all alveoli and secretory duct structures collapse by programmed cell death (apoptosis) and autophagy for lack of growth promoting factors either from the ECM or circulating hormones. At the same time, apoptosis of blood capillary endothelial cells speeds up the regression of lactation ductal beds. Shrinkage of the mammary duct tree and ECM remodeling by various proteinase is under the control of somatostatin and other growth inhibiting hormones and local factors. This major structural change leads loose fat tissue to fill the empty space afterward. But a functional lactiferous duct tree can be formed again when a female is pregnant again.