Integumentary System - Mammary Gland Development

Introduction

The mammary gland is the functional structure of the female breast and develops initially as a skin specialization. Breast growth and appearance in male and female children are virtually identical prior to puberty. At puberty females, under the influence of mainly sex hormone signaling, undergo a series of growth changes. Breast growth after puberty is defined by the "Tanner Stages".

In pregnancy, an additional series of signals leads to further changes in breast structure. Finally at menopause, changes in sex hormone secretion can once again alter breast structure.

The breast also associated with oncogenesis (breast cancer). Research in this area has been aided by the discovery in 1994 of the two breast cancer susceptibility genes (BRCA1, BRCA2). There is some developing evidence that modification of stem cells (progenitor cells) that exist in the mammary gland may also contribute to neoplasms (cancer).

Mammary Glands Pregnancy

During pregnancy raised estrogens and progesterone stimulate gland development, secretory alveolar structures form and differentiate, leading to milk production in late pregnancy and milk secretion during lactation. Breasts are hemispherical in shape due to fat deposition. After birth, neonatal lactation supports further growth/development.

Abnormalities

Abnormalities occur in approximately 1% of female population and include in both sexes:

• polymastia - extra breast
• polytheli - extra nipple
• supernumerary nipple (relatively common in males)
• gynecomastia (Greek, gyne = woman, mastos = breast) is the excessive development of the male breast, which can occur transiently in puberty or due to other (hormonal) abnormalities.

Breast Cancer

In 1994, two breast cancer susceptibility genes were identified BRCA1 on chromosome 17 and BRCA2 on chromosome 13.

When an individual carries a mutation in either BRCA1 or BRCA2, they are at an increased risk of being diagnosed with breast or ovarian cancer at some point in their lives. Normal function of these genes was to participate in repairing radiation-induced breaks in double-stranded DNA. It is though that mutations in BRCA1 or BRCA2 might disable this mechanism, leading to more errors in DNA replication and ultimately to cancerous growth. (text modified from: NCBI genes and disease)

Links: OMIM - BRCA1 | OMIM - BRCA2

Some Recent Findings

Incomplete development of the nail of the hallux in the newborn. "Between March and October 2008, the nails of 541 (252 females, 289 males) consecutively born neonates with an average age of 3.2 days were examined in the Neonatology Unit. Of these newborns with nail disorders, 36 were re-examined after a period that ranged from seven days to six months. The most frequent nail alteration was the incomplete development of the hallux nail, which was triangular - sometimes trapezoidal - shaped. This alteration, which had been previously reported in the literature as congenital hypertrophy of the lateral folds of the hallux, spontaneously regressed within one to three months in the infants re-examined. There was no associated inflammation or onychocryptosis at any time. The apparent hypertrophy of the nail folds seemed to be secondary to the lack of pressure of the nail lamina." Lyonization pattern of normal human nails. "To examine the X-inactivation patterns of normal human nails, we performed the human androgen receptor gene assay of DNA samples extracted separately from each finger and toe nail plates of nine female volunteers. The X-inactivation pattern of each nail was unique and constant for at least 2 years. ...These findings suggest that the composition of precursor cells of each nail is maintained at each site at least through several cycles of regeneration time, and that the nail plate has a longitudinal band pattern, each band consisting of cells with only one of the two X-chromosomes inactivated."

Textbooks

The Nail

• Human Embryology (2nd ed.) Larson Chapter 14 p443-455
• The Developing Human: Clinically Oriented Embryology (6th ed.) Moore and Persaud Chapter 20: P513-529
• Before We Are Born (5th ed.) Moore and Persaud Chapter 21: P481-496
• Essentials of Human Embryology Larson Chapter 14: P303-315
• Human Embryology, Fitzgerald and Fitzgerald
• Color Atlas of Clinical Embryology Moore Persaud and Shiota Chapter 15: p231-236

References

Reviews

<pubmed>19932326</pubmed> <pubmed>15468149</pubmed>

Search PubMed

Search Pubmed: Mammary Gland Development

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Cite this page: Hill, M.A. (2024, June 16) Embryology Integumentary System - Mammary Gland Development. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Integumentary_System_-_Mammary_Gland_Development

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© Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G