MAMMARY GLANDS

Development of Mammary Glands:. 
•Are a modified and highly specialized type of apocrine 

sweat glands.

•

Consist of parenchyma, which is formed from ducts, and connective 

tissue stroma.

•Parenchyma derives embryonically from surface ectoderm;

stroma arises from surrounding mesenchyme.

•

Mammary buds

begin to develop during the sixth week as solid downgrowths 

of the epidermis into the underlying mesenchyme

•These changes occur in response to an 

inductive influence from the mesenchyme.•

•Mammary buds develop as downgrowths from thickened mammary 

crests, which are thickened strips of ectoderm extending from the 

axillary to the inguinal regions 

•The mammary crests (ridges) appear during the fourth week 

but normally persist in humans only in the pectoral area, 

where the breasts develop

•

Each primary bud gives rise to several secondary mammary 

buds that develop into lactiferous ducts and their 

branches.

Development of Nipples and Areola :•During the late fetal period, the epidermis at the site of origin of the mammary gland becomes 

depressed, forming a shallow mammary pit

•

The nipples are poorly formed and depressed in newborn 

infants.

•Soon after birth, the nipples usually rise from the mammary 

pits because of proliferation of the surrounding 

connective tissue of the areola, the circular area of skin 

around the nipple.

The smooth muscle fibers of the nipple and areola 

differentiate from surrounding mesenchymal cells.

Gynecomastia

•The rudimentary lactiferous ducts in males normally 

undergo no postnatal development.

•Gynecomastia (Gr. gyne, woman + mastos, breast) refers 

to the development of the rudimentary lactiferous ducts 

in the male mammary tissue.

•

During midpuberty, approximately two thirds of boys develop 

varying degrees of hyperplasia of the breasts. This 

subareolar hyperplasia may persist for a few months to 2 

years.

•A decreased ratio of testosterone to estradiol is found

•80% of males with Klinefelter syndrome (XXY) have 

gynecomastia.

Absence of Nipples (Athelia) or Breasts (Amastia)

•Rare congenital anomalies may occur bilaterally or 

unilaterally.

•

Result from failure of development or disappearance 

of the mammary crests.

•May also result from failure of mammary buds to 

form.

•More common is hypoplasia of the breast, often 

found in association with gonadal agenesis and 

Turner syndrome

Gland Structure:

•Near the opening at the nipple, lactiferous ducts

are lined by a stratified squamous keratinized 

epithelium.

•

The lactiferous sinus and the lactiferous duct

leading to it are lined by stratified cuboidal 

epithelium,

•Smaller ducts leading to the lactiferous duct are 

lined by a simple columnar epithelium.

•Stellate myoepithelial cells located between the 

epithelium and the basal lamina wrap around the 

developing alveoli and become functional during 

pregnancy.

Mammary Gland Secretion: Milk Production:

•Prolactin is responsible for the production of milk

•Oxytocin is responsible for the milk ejection reflex.

•

Although the mammary gland is prepared to secrete milk even before 

birth, certain hormones prohibit this.

•When the placenta is detached in the adult female, prolactin from the 

anterior pituitary stimulates the production of milk, which reaches full 

capacity in a few days.

•Before that, for the first 2 or 3 days after birth, a protein-rich thick 

fluid called colostrum is secreted.

•Colostrumis a  

high-protein secretion, rich in vitamin A, sodium, and chloride, also contains 

lymphocytes and monocytes, minerals, lactalbumin, and antibodies 

(immunoglobulin A) to provide nutrition and 

passive immunity to the newborn.

•Milk, usually produced by the 4th day after parturition, is a fluid that 

contains minerals, electrolytes, carbohydrates (including lactose), 

immunoglobulins (mostly immunoglobulin A), proteins (including caseins), 

and lipids.

•Production of milk results from the stimuli of sight, touch, handling of the 

newborn, and anticipation of nursing, events that create a surge in 

prolactin release.

Summary: Mammary Glands •Modified and highly specialized type of apocrine sweat 

glands

•Consist of parenchyma, which is formed from ducts, and connective 

tissue stroma.

•Parenchyma derives embryonically from surface ectoderm; stroma 

arises from surrounding mesenchyme (inductive interactions).

•The 6-week embryo has two ventral ridge-like thickenings of 

epidermis, the mammary (milk) lines, extending from axillae to the 

inguinal area.

•The major part of each ridge disappears almost immediately, but one 

pair remains in the pectoral area and penetrates the 

mesenchyme.

•Then, 15-25 solid epithelial cords develop from each and are later 

canalized to form future lactiferous ducts.

•Mesenchyme gives rise to loose connective tissue around each duct. 

Denser connective tissue forms septa between them to divide the 

gland into lobes.

•Childhood gland structure is rudimentary and alike in both sexes.

•At puberty, glands in girls grow and undergo structural changes 

directly influenced by ovarian hormones (estrogen and 

progesterone).

•They are not fully formed and functional, however, until pregnancy 

and lactation.

•In pregnancy, terminal ends of ducts develop into hollow, sac-like 

secretory alveoli, which are lined by simple cuboidal epithelium.

•Women who give birth have highly specialized exocrine glands that 

synthesize and secrete milk. Prolactin, human placental lactogen, 

estrogen, and progesterone in the presence of prolactin from the 

anterior pituitary result in milk production; oxytocin from the 

posterior pituitary induces milk release.