Anatomy III: Blood and Glands

Anatomy III: Blood and the Cardiovascular and Respiratory Systems

• This is a course on the anatomy of the blood and cardiovascular and respiratory systems.

Lesson 5: Mammary Glands

• Mammary glands are present in both males and females, but fully develop in women.
• In men, mammary glands consist of small ducts and epithelial cords. The glandular system does not fully develop.
• Male breast tissue is similar to subcutaneous tissue.
• Breasts mostly follow the contour of the pectoralis major muscles.
• The nipple is located in the 4th intercostal space, lateral to the midclavicular line.
• In athletic men, the pectoralis major muscles are more apparent, revealing intermammary clefts overlying the sternum and lateral borders forming the anterior axillary fold.

Breasts in Women

• Functionally, breasts are accessory to reproduction.
• The superior boundary of the breast is a flattened surface, not sharply demarcated from the thoracic wall.
• Lateral and inferior boundaries are the submammary sulcus.
• Breast tissue is comprised of glandular and supporting fibrous tissue, embedded in a fatty matrix, containing vessels, lymphatics and nerves.

Breasts in Men

• In athletic men, the contour of the pectoralis major muscles is noticeable.
• Topographic lines can be seen, such as the intermammary cleft above the sternum and the lateral border marking the axillary fold.

Bed of the Breast

• The breast bed is formed by pectoralis major and serratus anterior fasciae.
• The lateral limits run from the lateral border of the sternum to the midaxillary line, and the vertical limits from the 2nd to 6th rib.

Retromammary Space

• The retromammary space is a potential space between the breast and the pectoral fascia, filled with loose subcutaneous tissue.
• This allows breast movement over the pectoral fascia.

Suspensory Ligaments of Cooper

• These skin ligaments attach to the dermis of the overlying skin, particularly well-developed in the superior part of the gland.
• They support the lobes and lobules of the mammary gland.
• They extend from the infero-lateral edge of the pectoralis major muscle toward the axillary fossa.

Change of Breast Size

• Breast size and shape vary based on genetics, ethnicity, and diet. It changes throughout life.
• Puberty (8-15 years) causes enlargement due to glandular development and fat deposition. The areola and nipples also enlarge.
• The menstrual cycle leads to slight glandular enlargement due to hormonal changes from LH and FSH.
• Pregnancy causes mammary gland and new glandular tissue enlargement.

Mammary Glands (Structure)

• Mammary glands are modified sweat glands.
• They lack a capsule or sheath.
• Milk-secreting alveoli are clustered.
• Mammary glands enlarge when FSH and LH hormones are released, such as during monthly menstrual cycles.

Structure of the Breast

• Lobules form the breast parenchyma, each drained by a lactiferous duct.
• Lactiferous ducts converge to open into the areola.
• The final portion of the ducts forms the lactiferous sinus, where milk accumulates.
• Neonatal sucking stimulates compression of the areola and lactiferous sinus releasing accumulated milk.
• Neonatal sucking stimulates hormonal let-down reflex encouraging continued nursing.

Areolae

• Contain numerous sebaceous glands.
• Enlarge during pregnancy, providing a protective oily lubricant for the areola and nipple.
• Areola usually darkens during pregnancy and maintains this pigmentation.
• Areola is dotted with openings from areolar glands (sebaceous glands).

Nipples

• Nipples lack fat, hair, and sweat glands.
• Mostly composed of circular smooth muscle fibers.
• Functions: compress lactiferous ducts during lactation, erect in response to stimulation (like during sucking).
• In young women (nulliparous), the nipple is typically located at the 4th intercostal space, 10cm from the axillary midline. This is not a reliable location in all adults.
• Nipple inversion/retraction can be a minor congenital anomaly making breastfeeding difficult.

Arterial Supply

• Blood supply comes from various arteries: subclavian, internal thoracic artery (with anterior intercostal and medial mammary branches), axillary artery (lateral thoracic and thoraco-acromial arteries), and thoracic aorta (posterior intercostal arteries).

Venous Drainage

• Breast veins drain into: internal thoracic vein, axillary vein.
• The venous pattern over breasts may be visible through skin, particularly during pregnancy.

Lymphatics of the Breast

• Lymph from the nipple, areola, and lobules drains to the subareolar lymphatic plexus.
• ~75% of plexus lymph drains to axillary lymph nodes.
• ~25% drains to parasternal lymph nodes or to opposite breast.
• Axillary nodes drain into clavicular nodes and eventually into the subclavian lymphatic trunk.
• Parasternal nodes drain into the bronchomediastinal lymphatic trunks and then to the thoracic duct.

Nerves of the Breast

• Nerves coming from the 4th, 5th and 6th intercostal nerves (anterior and lateral) penetrate the pectoral fascia to reach the subcutaneous tissue.
• Nerves provide sensory innervation to breast skin and sympathetic innervation to blood vessels and smooth muscle of skin/nipple.

Bibliography

• Various anatomical texts are referenced including publications from Moore, Drake, Rohen, and Yokochi.