How does the nipple function in relation to breast anatomy. What are the key components of the nipple-areola complex. How do breast ducts develop and operate. What anatomical variations can occur in nipple structure.

The Anatomy of the Nipple-Areola Complex (NAC)

The nipple-areola complex (NAC) is a crucial structure of the breast, comprising two main components: the areola and the nipple. The areola is the pigmented circular area surrounding the nipple, typically measuring 3-6 centimeters in diameter. It is usually positioned around the fourth rib. The nipple itself is a protruding structure at the center of the areola, containing the openings of the milk ducts.

Understanding the anatomy of the NAC is essential for both medical professionals and individuals alike. Why is this knowledge so important? It plays a vital role in breast health, breastfeeding, and various medical procedures such as nipple-sparing mastectomies.

Key Structures of the NAC

• Areola: The pigmented circular area surrounding the nipple
• Nipple: The protruding central structure containing milk duct openings
• Montgomery glands: Small, raised glands on the areola
• Milk ducts: Channels that transport milk from the lobules to the nipple

Historical Perspective on Breast Anatomy

Our understanding of breast anatomy has evolved significantly over time. Sir Astley Cooper made important observations about the NAC anatomy in 1840. How have these initial findings changed? While Cooper described up to 22 ducts leading to the nipple, he believed that many were non-functional, estimating that fewer than 12 were actually patent and opened at the nipple.

Current anatomical descriptions differ somewhat from Cooper’s original work. Modern understanding depicts the breast as composed of glandular and adipose tissue held together by Cooper’s ligaments, a network of connective tissue fibers.

Evolution of Breast Anatomy Knowledge

1. 1840: Sir Astley Cooper’s initial observations
2. Mid-20th century: Refinement of anatomical understanding
3. Late 20th century: Advanced imaging techniques provide new insights
4. 21st century: Molecular and cellular level studies enhance our knowledge

Embryological Development of the Breast and Nipple

The development of the breast and nipple begins early in fetal life. When does this process start? Mastogenesis, or breast development, commences around the sixth week of gestation. By the ninth month of fetal development, a clear linear elevation called the “milk line” is visible.

The mammary gland forms from a thickening in the epidermic “milk line” in the area of the future breast. Basal cells proliferate and invade the underlying mesoderm, while simultaneously, regression of the mammary segment occurs, yielding the papillary primordium.

Key Stages in Breast and Nipple Development

• 6th week: Beginning of mastogenesis
• 8th week: Formation of mammary gland from epidermic “milk line”
• 31st week: Occlusion of papillary bag, forming the NAC
• Birth: Appearance of the nipple

The areola becomes recognizable as a circular area free of hair follicles, with Montgomery glands appearing around it. These developmental processes are crucial for the eventual function of the breast in lactation and infant feeding.

Histological Structure of the Breast

Histological studies have revealed the intricate structure of the breast at a cellular level. What are the main components of breast tissue? The breast is composed of both glandular and adipose tissue. The glandular tissue is organized into lobes, which are further divided into lobules.

These lobules consist of clusters of alveoli containing mammary secretory epithelial cells. The alveoli are connected to very small ducts that join to form larger ducts draining the lobules. These larger ducts eventually merge into a unique duct for each lobe.

Breast Tissue Components

• Glandular tissue: Organized into lobes and lobules
• Adipose tissue: Located between lobes
• Connective tissue: Includes Cooper’s ligaments
• Ducts: Transport milk from alveoli to nipple

Under the areola, the single duct for each lobe widens into a lactiferous sinus before narrowing at the base of the nipple and terminating at its orifice on the nipple’s surface. This structure facilitates the efficient transport and release of milk during lactation.

Anatomical Variations and Anomalies of the Nipple

While the typical anatomy of the nipple and breast is well-established, various anatomical variations and anomalies can occur. These variations can range from minor cosmetic differences to more significant structural abnormalities. What are some common nipple variations?

Common Nipple Variations

• Accessory nipples: Occur in 1-5% of the population
• Inverted nipples: Nipples retracted into the breast
• Athelia: Congenital absence of the nipple-areolar complex
• Amastia: Complete absence of breast structures
• Amazia: Absence of breast tissue with preservation of the NAC

Accessory nipples, also known as supernumerary nipples, are found in 1-5% of the population with equal incidence in males and females. They are usually located in the inframammary region and are subject to the same diseases as normal nipples. When should accessory nipples be removed? Excision is typically only indicated for cosmetic purposes, discomfort during menstruation, anxiety, pain, or restriction of arm movement.

Inverted nipples are a condition where the nipple, instead of pointing outward, is retracted into the breast. In some cases, the nipple may temporarily protrude when stimulated, while in others, the inversion remains regardless of stimulus. This condition can affect both women and men and is often caused by short ducts or a wide areola muscle sphincter.

The Role of the Nipple in Breast Cancer and Mastectomy Procedures

The nipple plays a significant role in breast cancer diagnosis and treatment. How has the approach to mastectomy evolved over time? Historically, radical mastectomies involved the removal of all breast tissue, including the nipple. However, variations of mastectomy procedures have developed over time, enhancing oncological safety while allowing for immediate breast reconstruction.

Nipple-sparing mastectomy (NSM) procedures have significantly increased in frequency and have become one of the best alternatives for treating breast cancer. These techniques allow for the conservation of skin, the inframammary fold, and especially the nipple-areola complex, leading to improved overall aesthetic outcomes and better contralateral breast symmetry.

Benefits of Nipple-Sparing Mastectomy

• Improved aesthetic outcomes
• Better contralateral breast symmetry
• Preservation of the breast’s natural appearance
• Potential psychological benefits for patients

Why is preserving the nipple important for patients? The nipple-areola complex is considered the identity of the breast and plays a crucial role in patients’ self-esteem. Therefore, safe indications for sparing the NAC are continually being researched and refined to benefit more patients undergoing mastectomy procedures.

The Significance of Nipple Function in Breastfeeding

The primary biological function of the nipple is its role in breastfeeding. How does the nipple facilitate this crucial process? The nipple contains multiple openings that connect to the milk ducts, allowing milk to be expressed from the breast to the infant during feeding.

During pregnancy and postpartum, the nipple undergoes several changes to prepare for and facilitate breastfeeding. These changes include increased sensitivity, darkening of the areola, and the enlargement of Montgomery glands, which produce an oily substance to lubricate the nipple during feeding.

Nipple Changes During Pregnancy and Lactation

• Increased sensitivity
• Darkening of the areola
• Enlargement of Montgomery glands
• Potential increase in nipple size

The complex interplay between hormones, nerve endings, and the physical structure of the nipple allows for the let-down reflex, which triggers the release of milk when an infant begins to suckle. This reflex is crucial for successful breastfeeding and demonstrates the intricate functionality of the nipple beyond its anatomical structure.

Future Directions in Nipple Research and Clinical Applications

As our understanding of nipple anatomy and function continues to evolve, what are the potential future directions for research and clinical applications? Several areas of study show promise for advancing both medical treatments and our fundamental understanding of breast biology.

Emerging Areas of Nipple Research

• Advanced imaging techniques for early cancer detection
• Nipple-sparing techniques in breast reconstruction
• Molecular studies of nipple development and function
• Improved methods for diagnosing and treating nipple-related conditions

One area of particular interest is the development of more sophisticated imaging techniques that could allow for earlier and more accurate detection of breast cancer, potentially through changes in nipple structure or cellular composition. Additionally, ongoing research into nipple-sparing mastectomy techniques may lead to improved outcomes for breast cancer patients, both in terms of cancer treatment and aesthetic results.

Furthermore, molecular and genetic studies of nipple development and function could provide insights into breast diseases and potentially lead to new therapeutic targets. As our knowledge expands, we may see advancements in the diagnosis and treatment of various nipple-related conditions, from common issues like inverted nipples to more complex developmental anomalies.

In conclusion, the nipple, despite its small size, plays a crucial role in breast function, infant nutrition, and human sexuality. Its complex anatomy and development continue to be areas of active research, with potential implications for breast cancer treatment, reconstructive surgery, and our understanding of human biology. As we look to the future, ongoing studies of nipple anatomy and function promise to yield new insights and improved clinical outcomes for patients worldwide.

Anatomy of the nipple and breast ducts

Gland Surg. 2016 Feb; 5(1): 32–36.

doi: 10.3978/j.issn.2227-684X.2015.05.10

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Author information Article notes Copyright and License information Disclaimer

Over time, variations of mastectomy came up and started allowing the oncological safety and the possibility of an immediate breast reconstruction. Nipple sparing mastectomy (NSM) procedures have strongly increased in frequency and have become one of the best alternatives to treat breast cancer, also improving overall aesthetic outcomes and the achievement of contralateral breast symmetry. The nipple areola-complex (NAC) must be considered the identity of the breast concerning self-esteem of patients. This paper will remind the main anatomical topics around the nipple and breast ducts.

Keywords: Breast, breast conserving treatment, mastectomy, mammoplasty, nipple, anatomy, breast cancer

Over time, variations of mastectomy came up and led to enhance the oncological safety and the possibility of an immediate breast reconstruction. Those techniques permit the conservation of skin, inframammary fold and specially the nipple areola complex (NAC) to achieve better outcomes.

Nowadays the number of publications describing a nipple sparing mastectomy (NSM) has strongly increased. Regarding self-esteem the nipple must be considered the identity of the breast. Therefore, in order to increasing safe indications of sparing NAC this paper will revise the main anatomical topics around the nipple and breast ducts.

Several important remarks on the NAC anatomy were made by Sir Astley Cooper [1840]. Over the last 160 years some of the anatomy knowledge acquired has changed (2) since Cooper’s original work. For example, the glandular tissue is depicted as 15-20 lobes radiating out from the nipple, whereas Cooper stated that he observed up to 22 ducts leading to the nipple but considered that many of these ducts were not functional and that there were normally fewer than 12 patent ducts opening at the nipple.

Actually, the breast is described as being composed of glandular and adipose tissue held together by a loose framework of fibers called Cooper’s ligaments. Histological studies demonstrate that the lobes are composed of lobules, which consist of clusters of alveoli containing mammary secretory epithelial cells (3). The alveoli are connected to very small ducts that join to form larger ducts draining the lobules. These larger ducts finally merge to a unique duct for each lobe. Under the areola, this single duct is depicted as widening into a lactiferous sinus before narrowing at the base of the nipple and terminating at its orifice on the surface of the nipple (1,4). Adipose tissue of the breast is situated between lobes rather than within lobules.

The beginning of mastogenesis occurs around the sixth week of development. At 9 months there is a clear linear elevation, called “milk line”. By the eighth week, the mammary gland is formed from the thickening located in the epidermic “milk line” in the area of the final breast. There is a proliferation of basal cells that invade the underlying mesoderm and at the same time, it will occur a regression of mammary segment, yielding papillary primordium. After the 31^st week of intrauterine life, papillary bag suffer occlusion, forming the NAC. The nipple will appear at time of birth.

The areola is recognized by forming a circular area free of hair sketches, also appearing branched glands around (Montgomery).

These anomalies could be classified into multiple conditions.

1. Accessory nipple. One to five percent of the population, equal incidence in male and females. Usually found in the inframammary region, and are prone to the same diseases as normal nipples. Excision is only indicated for cosmetic purposes, discomfort during menstruation, anxiety, pain, or restriction of arm movement (6).

2. Athelia is characterized by the congenital absence of the nipple areolar complex with the presence of breast tissue (7). This condition can be inherited by autosomal dominant inheritance, or as a part of a syndrome (e.g., Poland’s).

3. Amastia is the complete absence of breast structures.

4. Amastia is the absence of breast tissue with preservation of the NAC.

5. Inverted nipple is a condition where the nipple, instead of pointing outward, is retracted into the breast. In some cases, the nipple will be temporarily protruded if stimulated, but in others, the inversion remains regardless of stimulus. Women and men can have inverted nipples. Most common nipple variations that women are born with are caused by short ducts or a wide areola muscle sphincter (8).

The NAC comprises two basic structures: the areola and the nipple ().

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Schematic view of nipple areola-complex (NAC).

The areola has a round shape and a varying size, on average 3 to 6 centimeters, normally situated around the forth rib level. It has sebaceous glands that make projections on its surface, forming tubercle of morgani, or areolar glands, which during pregnancy become enlarged giving rise to tubercles of Montgomery.

Some authors believe that such structures represent accessory mammary glands and it has been observed milk secretion output with manual expression of these tubers (this supposition leads some surgeons to prefer the use of the skin sparing mastectomy instead of nipple or areola sparing mastectomies because of oncological concerns).

In the center of the areola emerges a papillar cylindrical formation varying in size, averaging 10 to 12 millimeters (mm) wide by 9 to 10 mm in height. Its skin is similar to the areola, but has no sebaceous glands. It has 10 to 20 corresponding pores as the output of the milk ducts.

The NAC has no subcutaneous tissue. The skin of the nipple rests on a thin layer of smooth muscle, areolar muscle fibers which are distributed in two directions: radial and circular. The muscle of Sappey responsible for circular fibers and the muscle of Meyerholz, formed by the radial fibers.

The areolar muscle is continued in the papilla with longitudinal and circular fibers surrounding the milk ducts along with connective tissue support. Its contraction is responsible for the ejection of secretion in the milk sinuses and for the telotism of the papilla, “mimicking an erection”.

Below the areolar muscle there is a thin layer of fat which disappears as it approaches the papilla. In this pre-mammary fat tissue layer vessels are found running on radiated sense.

Blood supply

The NAC is mainly supplied by internal mammary artery, also known as internal thoracic artery, which is branch of the subclavian artery. Internal mammary artery sends perforating branches along the first, second, third and fourth intercostal spaces, crossing the pectoralis major and irrigating the inner half of the breast, including the NAC. The intercostal arteries, which are branch of the aorta, also cross the pectoralis major and irrigate the deep surface of the breast, complementing the arterial vascularization of the NAC.

Venous drainage of breast is divided into two systems: superficial and deep. The superficial veins run along the anterior surface of the fascia, following the path of areola under the NAC, called venous plexus of Haller.

Recently the use of breast MRIs have become increasingly common in breast cancer work-up. Previously obtained breast MRIs may facilitate oncoplastic surgery by delineating the blood supply to the NAC. Seitz et al. (9) retrospectively reviewed 52 breasts underwent to breast MRI over 1-year period. Blood supply to the NAC was classified into five anatomic zones (“NACsomes”): medial (type I), lateral (type II), central (type III), inferior (type IV) and superior (type V). Twenty-eight breasts had type I only blood supply, 22 breasts had multi-zone blood supply (type I + II, n=20; type I + III, n=2), one breast had type II only blood supply, and a single breast had type III only blood supply. Anatomic symmetry was observed in 96% of patients. Superomedial source vessels supplying the NAC were predominant ().

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Schematic view of blood supply of NAC by “NACsomes” (Type I yellow—medial, Type II green—lateral, Type III pink—central, Type IV purple—inferior and Type V orange—superior).

Innervation

The skin surface of the breast is innervated by the first to sixth intercostal nerves and a supraclavicular branch of the superficial cervical plexus. The nipple is innervated by the fourth intercostal nerve. Objective investigations about the real impact of breast size on NAC sensibility threshold should be better clarified. Longo et al. (10) suggested that large and heavy breasts may potentially produce a chronic nerve traction injury, causing an inverse relationship between breast volume and sensibility. Concerning mammoplasty, the fibrotic scar at the areolar edges could be responsible for the progressive sensibility worsening over time 6 to 48 months. Another interesting mentioned phenomenon is neural organization in the somatosensory system after reduction mammoplasty. Phantom sensations are reported after partial and total breast amputation for cancer, possibly due to both rearranging of peripheral nerves and remapping on different subcortical and cortical somatosensory areas.

Lymphatic drainage

The lymphatic drainage of the breast is carried through superficial and deep plexus. Superficially, there are the areolar plexus and the subareolar plexus of Sappey. The subareolar plexus receives the glandular lymph vessels and they continue towards the papilla and the areolar plexus, finally reaching the lymph nodes into the axilla.

Ramsay et al. used ultrasound imaging to re-investigate the anatomy of the lactating breast. They showed that the mean number of main ducts at base of nipple was 9.6 (range, 6-18) and 9.2 (range, 4-14) for the left breast and right breast, respectively, which was not significantly different. The common sac-like appearance of lactiferous sinuses under the areola was not observed during scanning. The mean number of ducts and the diameter of main ducts were not related to nipple diameter, areola radius or milk production for individual breasts (2).

Characteristics of nipple are an important factor in the success of breast feeding. Minimum nipple length of seven millimeters has shown to be specific for a highly successful rate of breastfeeding (11). Short, flat, or inverted nipples can be related to physical and psychological negative effects for the breastfeeding mother.

It is clear that when a total mastectomy is performed, the removal of the NAC increases the sensation of mutilation, and the risk of tumor involvement should be considered within the spectrum of lumpectomy, skin-sparing mastectomy, and modified-radical mastectomy. Controlled-trials have clearly demonstrated the oncologic equivalence of modified-radical and skin-sparing mastectomies, where the risk of future breast cancer occurrence is low but not zero (12,13).

Current reports on NSM are most common to single-institution series. However the number of NSM procedures has increased over the past years. Tumor involvement is reported in over 35% of the patients when tumor size is more than 2 cm, especially when the tumor is situated in the subareolar area (14). NSM can be performed for prophylactic mastectomy and the treatment of selected breast cancer with oncologic safety. The risk of skin and nipple necrosis is a frequent complication of NSM procedure, and it is usually related to the volume of breast removed (15).

Despite varying indications and surgical protocols reports of the development of cancer in the NAC following NSM are remarkably rare. Different aspects should be considered to be a selection criteria for NSM indication as well as primary tumors located outside the areola margins, no nipple retraction or bloody discharge from the nipple, no retro areolar microcalcifications, no inflammatory signs and no retro areolar tumor infiltration at the frozen section (13,16,17). In our experience the most important aspect to allow the indication for a NSM is the negative frozen subareolar biopsy area during the surgery. The rate of a positive subareolar biopsy ranges between 2.2% to 12% (13,18).

Tumoral aspects will be important to take into account when considering the indication of adjuvant therapies. Overall, NSM is associated with high patient satisfaction rates (19-22).

The NAC may host benign pathologies, especially during pregnancy and puerperium. In addition, it has an important role in breast surgery when tumors can be resected through an incision that circles the areola (periareolar or “round block technique”). This technique can be used in numerous types of breast surgery. It allows the scar to go up to the periareolar circle which is in itself generally inconspicuous. In cases of tumoral excision, the round block produces a discreet scar and a more regular breast contour (23). Scar in this region maintains good aesthetic. It is recommended that the incisions are made just outside the areola in darker-skinned patients and immediately inside the areola in lighter-skinned patients. This is because the lighter shade of scar tissue.

Development of the current practice depends on a solid knowledge. Consistent knowledge of the anatomy of the NAC allows surgeons to perform better surgical procedures decreasing the sensation of mutilation without decreasing the chance of cure. The NAC is undoubtedly the identity of the breast.

The authors appreciate the cooperation of all colleagues in the Breast Unit—Barretos Cancer Hospital.

Conflicts of Interest: The authors have no conflicts of interest to declare.

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16 interesting facts to know

Share on PinterestNipples come in many shapes, colors, and sizes, and they can change shape during pregnancy.

Here are some facts about nipples:

1. The nipples can be an erogenous zone for both sexes.

According to a 2020 article, nipple stimulation plays an important role in the sexual satisfaction of about 80% of females. The authors concluded that using a topical formulation that stimulates the nipples 30 minutes before sexual activity can improve orgasmic satisfaction, strength, and pleasure.

Although male breasts are less well-studied, a 2017 article states that nipples are an erogenous zone for males.

2. Nipples can be hairy.

According to Planned Parenthood, it is normal to have hairs around the nipples.

Hair can be present around the nipples in both males and females.

3. Why do males have nipples?

In mammals, once an embryo has formed, it has the potential to become either male or female.

The nipples form very early in gestation, which is why males also have nipples.

The genes responsible for the development of reproductive organs do not become activated until a later stage.

4. Accessory nipples exist.

Sometimes, a person may have an extra nipple or set of nipples.

According to the Genetic and Rare Diseases Information Center, these are known as supernumerary nipples, and they are a common congenital abnormality. They most frequently occur along the embryonic milk lines, just like in other mammals.

One 2016 article estimates that roughly 1–5% of the population has a supernumerary nipple.

Although most people have just one extra nipple, there have been at least two cases of people with seven nipples.

5. Nipples can occur anywhere on the body.

Although accessory nipples typically occur along the mammary crests, or milk line, they can appear anywhere on the body.

There has been a case of an accessory nipple occurring on the foot, for example.

6. Some people are born without nipples at all.

Known as athelia, this is a rare condition in which a person is born without any nipples.

7.

A set of nipples holds a Guinness World Record.

According to the Guinness World Records, in 2013, a person used their nipples to lift 71.87 pounds.

8. There are different types of nipples.

Nipples can be flat, protruding, or inverted.

According to the Center for Young Women’s Health, roughly 10–20% of females have an inverted nipple on at least one breast.

Although this will not affect a person’s health, it is important to keep inverted nipples clean.

9. Breastfeeding is still possible with inverted nipples.

Although inverted nipples can make it more difficult to breastfeed, they do not make it impossible.

According to the World Health Organization (WHO), an inverted nipple can sometimes be nonprotractile, meaning that it does not stretch out when a person pulls it. Instead, the tip goes inward.

In these cases, it is often more difficult for the baby to attach to the nipple. However, protractility often improves during pregnancy and in the first week or so after a baby is born. Otherwise, there are alternative ways to breastfeed successfully with inverted nipples.

10. Breastfeeding females can spontaneously leak milk if they hear babies crying.

This effect is called the let-down reflex.

The let-down reflex occurs when the nerves in a person’s breast send signals that release the milk to the milk ducts so that it can start to come out of the nipples.

This mechanism is important for breastfeeding or expressing milk, but it can also happen at other times. For instance, it can happen when a female hears their baby crying or even thinks about their baby. It can also sometimes happen when another baby cries.

11. Bumps on the areolae are normal.

The small bumps on areolae are also known as the Montgomery glands.

These glands secrete oil to cleanse the nipple opening and prevent the chapping and cracking of the nipple that often occurs due to breastfeeding.

According to an older study, there is also evidence to suggest that this secretion may attract newborns to the nipples.

Although these bumps are normal, a person should see a doctor if they become inflamed or secrete brown fluid.

12. Breast milk can come out of multiple places.

There are between 10 and 20 perforations in the skin of the nipples, called nipple pores, from which the milk exits the body.

When breast milk is pumped, it can either look like a single stream or be visibly coming from different “holes” in the nipple.

13. Nipples can change shape during pregnancy.

One study demonstrated that during pregnancy, nipple length and width, as well as areola width, could increase significantly.

However, if a person notices that their nipples have changed drastically, and they are not pregnant, it is important that they visit their doctor.

The Centers for Disease Control and Prevention (CDC) advise that changes to the nipples could be a sign of breast cancer.

14. Nipple cancer is a rare form of cancer, but it can happen.

Nipple cancer, also known as Paget’s disease, is a rare condition associated with breast cancer. It affects the nipple and the areola.

According to the National Cancer Institute, about 1–4% of breast cancer cases involve Paget’s disease.

This condition can also affect males, but it is much more common among females.

Although doctors do not entirely understand what causes Paget’s disease of the breast, they do have theories.

The most widely accepted theory is that cancer cells from a tumor inside the breast travel through the milk ducts to the nipple and areola. This theory would explain why this cancer is so rare in males.

15. People can get nipple tattoos.

During a mastectomy, the surgeon may sometimes need to remove the nipple too.

After undergoing this procedure, some people may opt for nipple reconstruction. The options include using a nipple prosthetic, a skin graft, or a tattoo.

16. Nipple stimulation can induce labor.

Stimulating the nipples may help the onset of labor.

According to a 2018 study, oxytocin can help induce labor. Nipple stimulation produces oxytocin.

In the same study, 3 days of breast stimulation caused oxytocin levels to increase.

Other research has shown that nipple stimulation can also have an effect on the duration of labor. A 2015 study found that stimulating the nipples during labor shortened the first stage of labor to an average of 3.8 hours.

Learn more about nipple stimulation and labor here.

Nipples can be a good indication of a person’s health.

Although many factors can affect the nipples, if a person notices any discharge or changes in this part of the body, they should see a doctor.

Why do men have nipples? School ny genetics. Each human cell has 46 chromosomes – densely folded DNA molecules. The only exception to this rule are sperm and eggs, because they have half the number of chromosomes. When the sex cells merge, an embryo is formed, which receives equal DNA from mom and dad.

The first 22 pairs of chromosomes in men and women are absolutely no different. The child simply receives each gene in duplicate. This is beneficial for a person: they can be different, and if, for example, one option is broken, then the cell will use the backup. But the last pair is the sex chromosomes, X and Y. The egg always carries the X chromosome, and the sperm can add to it the second of the same (in which case the couple will have a girl) or a Y chromosome (and then the parents get a boy).

Everyone has at least one X chromosome, because it carries a huge amount of necessary genes. With a variety of genetic anomalies, fertilized eggs can appear with any set of sex chromosomes, but without the X chromosome, the embryo simply cannot develop.

But a set of X0 chromosomes (one sex chromosome), or XXX, or XXY, or XYY will lead to the birth of a full-fledged person, although not completely healthy. Survival does not depend on the Y chromosome. Its only function is to turn a man into a man.

Immediately after conception, the Y chromosome is inactive, and all embryos begin to develop in the same way. Only in the second month of embryonic development, her genes turn on. Then the primary sex glands in future men turn into testes and begin to produce androgens. Under the influence of these hormones, a lot of rearrangements occur that irreversibly change the basic model of a person: instead of the large labia, a scrotum is formed, instead of a clitoris, a penis. But the most important thing is that the centers of regulation of the endocrine system in the brain are formed according to the male type, so in adolescence a person will no longer be able to grow beautiful breasts.

Nevertheless, in the first weeks of embryonic development, the body nevertheless developed according to the basic, female type, and therefore the nipples had time to appear. Moreover, the breast retained the ability to respond to female sex hormones, so if there are many of them, the male breast can still grow a little.

Did you know that…

Males of some species of fruit bats (large bats) have fully developed mammary glands. They can feed their young with milk, like females. As a rare pathology, lactating mammary glands are also known in other male mammals, including humans.

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Why do men need nipples – Rambler/news

September 17, 2017, 11:01 AM

Many are interested in why the representatives of the stronger sex need such a seemingly unnecessary part of the body as nipples. In women, they perform a very specific role – they facilitate the process of feeding newborns. Men, due to the lack of such a function, do not seem to need this rudimentary organ. Then, quite legitimately, the question arises why nature supplies males with nipples.

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Erogenous zone

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In some men, the nipples are one of the erogenous zones, irritation of which enhances sexual arousal. But this does not apply to everyone. About 42% of gentlemen regard nipple touching as unpleasant and even annoying. There are those for whom this zone does not play any role in sexual terms. So it is impossible to call the sensitivity of the nipples and their role in sexual relations a sufficient reason for the mandatory presence of this organ in men.

Prenatal development

In fact, the nipples are a common and obligatory organ for both males and females due to the peculiarities of intrauterine development. They begin to form in the embryo before the seventh week. The first 6-7 weeks, all human embryos develop according to a common model – the female one. At this time, the main organs and parts of the body are laid: the rudiments of arms, legs, eyes, ears, nipples and everything else, except for the genitals.

Only after the seventh week, serious changes occur in the body of the unborn child, provoking the formation of genital organs. If the embryo is male, a hormone called androsterone begins to be produced in the blood. Under its influence, the genital tubercle gradually turns into a penis, and the folds in the inguinal region into the scrotum.

The nipples do not go anywhere, but simply remain with the fetus as an obligatory attribute of the genus of mammals. In addition to the actual nipples, all boys from the first seven weeks of “female” development also have a little tissue of the mammary glands. It is for this reason that at puberty, due to hormonal changes in young men, the chest swells slightly in the nipple area.

Evolutionary process

There is an opinion that over time the nipples in men can completely disappear, just as the human tail disappeared, leaving only the coccygeal bone as a “memento”.