Instruct: Given a question, retrieve relevant passages that can help answer the question.
Query: Do men have mammary glands?
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.
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.
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.
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.
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.
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.
There is criticism of the claim that menopause and somewhat earlier age-related declines in female fertility could coevolve with a long term dependency on monogamous male providers who preferred fertile females. This criticism argues that the longer the time the child needed parental investment relative to the lifespans of the species, the higher the percentage of children born would still need parental care when the female was no longer fertile or dramatically reduced in her fertility. These critics argue that unless male preference for fertile females and ability to switch to a new female was annulled, any need for a male provider would have selected against menopause to use her fertility to keep the provider male attracted to her, and that the theory of monogamous fathers providing for their families therefore cannot explain why menopause evolved in humans.
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.
Radical feminists claim that, because of patriarchy, women have come to be viewed as the "other" to the male norm, and as such have been systematically oppressed and marginalized. They further assert that men as a class benefit from the oppression of women. Patriarchal theory is not generally defined as a belief that all men always benefit from the oppression of all women. Rather, it maintains that the primary element of patriarchy is a relationship of dominance, where one party is dominant and exploits the other for the benefit of the former. Radical feminists believe that men (as a class) use social systems and other methods of control to keep women (and non-dominant men) suppressed. Radical feminists seek to abolish patriarchy by challenging existing social norms and institutions, and believe that eliminating patriarchy will liberate everyone from an unjust society. Ti-Grace Atkinson maintained that the need for power fuels the male class to continue oppressing the female class, arguing that "the "need" men have for the role of oppressor is the source and foundation of all human oppression".
Black wildebeest are sexually dimorphic, with females being smaller in size and more slender than males. The head-and-body length is typically between . Males reach about at the shoulder, while females reach . Males typically weigh and females . A distinguishing feature in both sexes is the tail, which is long and similar to that of a horse. Its bright-white colour gives this animal the vernacular name of "white-tailed gnu", and also distinguishes it from the blue wildebeest, which has a black tail. The length of the tail ranges from .
Protandrous hermaphrodites are animals that are born male and at some point in their lifespan change sex to female. Protandrous animals include clownfish. Clownfish have a very structured society. In the "Amphiprion percula" species, there are zero to four individuals excluded from breeding and a breeding pair living in a sea anemone. Dominance is based on size, the female being the largest and the male being the second largest. The rest of the group is made up of progressively smaller non-breeders, which have no functioning gonads. If the female dies, the male gains weight and becomes the female for that group. The largest non-breeding fish then sexually matures and becomes the male of the group.
After breeding, the female can eat her mate because, like with most mantis species, they are cannibalistic. Nymphs up to their fourth instar are not cannibalistic. The female lay egg cases (ootheca) almost three times its size, and will usually hatch between 30 to 50 offspring. Ootheca survive in the same conditions as the mantis.
The fact that females appear to have outnumbered males two to one suggests that, as with modern animals with size-related sexual dimorphism, such as sea lions and other pinnipeds, "Pteranodon" might have been polygynous, with a few males competing for association with groups consisting of large numbers of females. Similar to modern pinnipeds, "Pteranodon" may have competed to establish territory on rocky, offshore rookeries, with the largest, and largest-crested, males gaining the most territory and having more success mating with females. The crests of male "Pteranodon" would not have been used in competition, but rather as "visual dominance-rank symbols", with display rituals taking the place of physical competition with other males. If this hypothesis is correct, it also is likely that male "Pteranodon" played little to no part in rearing the young; such a behavior is not found in the males of modern polygynous animals who father many offspring at the same time.
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.
Non-human animal studies have shown that exposure to environmental contaminants with estrogenic activity can accelerate the onset of puberty. A potential mechanism has been described in rats exposed to DDT or beta-estradiol in which GnRH pulsatile secretion was found to be increased. Oral exposure of female rats to xenoestrogens has been shown to cause pseudo precocious puberty (early vaginal opening and early first estrus). A study of dioxin in immature female rats induced early follicular development and phthalates are known to decrease the anogenital distance in newborn rats. Although this article focuses on the effects of xenoestrogens and reproductive function in females, numerous animal studies also implicate environmental estrogens' and androgens' adverse effects on the male reproduction system. Administration of estrogens to developing male animals reduces testicular weight and decreases sperm production. The small phallus size of male alligators has been linked to contamination of their natural Florida habitat with DDT. Data from animal research is abundant demonstrating the adverse effects on reproduction of hormonally active compounds found in the environment.
They are mostly ambush predators, but a few ground-dwelling species are found actively pursuing their prey. They normally live for about a year. In cooler climates, the adults lay eggs in autumn then die. The eggs are protected by their hard capsules and hatch in the spring. Females sometimes practice sexual cannibalism, eating their mates after copulation. Occasionally, the females decapitate the males just before or during mating. Over 2,400 species of mantis in about 430 genera are recognized.
Hermaphroditism occurs when a given individual in a species possesses both male and female reproductive organs, or can alternate between possessing first one, and then the other. Hermaphroditism is common in invertebrates but rare in vertebrates. It can be contrasted with gonochorism, where each individual in a species is either male or female, and remains that way throughout their lives. Most fish are gonochorists, but hermaphroditism is known to occur in 14 families of teleost fishes.
There are variable results in between males of different species as to the effects of oxytocin on paternal care. Oxytocin is unchanged in California mice before and after becoming fathers, but the amount of paternal exposure to rats is associated with oxytocin and increased care. However, multiple studies on biparental species show an association between paternal care and oxytocin. Since the species in these studies are biparental, excluding rats, it is unclear as to why California mice do not have a change in oxytocin postpartum.
Whether "Smilodon" was sexually dimorphic has implications for its reproductive behavior. Based on their conclusions that "Smilodon fatalis" had no sexual dimorphism, Van Valkenburgh and Sacco suggested in 2002 that, if the cats were social, they would likely have lived in monogamous pairs (along with offspring) with no intense competition among males for females. Likewise, Meachen-Samuels and Binder (2010) concluded that aggression between males was less pronounced in "S. fatalis" than in the American lion. Christiansen and Harris (2012) found that, as "S. fatalis" did exhibit some sexual dimorphism, there would have been evolutionary selection for competition between males. The structure of the hyoid bones suggest that "Smilodon" communicated by roaring, like modern big cats. The ability to roar may have implications for the social life of "Smilodon".
It has been shown that oxytocin differentially affects males and females. Females who are administered oxytocin are overall faster in responding to socially relevant stimuli than males who received oxytocin. Additionally, after the administration of oxytocin, females show increased amygdala activity in response to threatening scenes; however, males do not show increased amygdala activation. This phenomenon can be explained by looking at the role of gonadal hormones, specifically estrogen, which modulate the enhanced threat processing seen in females. Estrogen has been shown to stimulate the release of oxytocin from the hypothalamus and promote receptor binding in the amygdala.
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.
All the milk-secreting tissue leading to a single lactiferous duct is called a "simple mammary gland"; in a "complex mammary gland" all the simple mammary glands serve one nipple. Humans normally have two complex mammary glands, one in each breast, and each complex mammary gland consists of 10–20 simple glands. The presence of more than two nipples is known as polythelia and the presence of more than two complex mammary glands as polymastia.
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.
The mammary glands of mammals are specialized to produce milk, a liquid used by newborns as their primary source of nutrition. 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.
A mammary gland is an exocrine gland in mammals that produces milk to feed young offspring. Mammals get their name from the Latin word "mamma", "breast". The mammary glands are arranged in organs such as the breasts in primates (for example, humans and chimpanzees), the udder in ruminants (for example, cows, goats, and deer), and the dugs of other animals (for example, dogs and cats). Lactorrhea, the occasional production of milk by the glands, can occur in any mammal, but in most mammals, lactation, the production of enough milk for nursing, occurs only in phenotypic females who have gestated in recent months or years. It is directed by hormonal guidance from sex steroids. In a few mammalian species, male lactation can occur.