The Breast
It is a modified sweat gland which is present in both the sex. In females, the breast is a part of reproductive system and capable of producing milk after delivery. The breast milk is the main/only source of nutrient to the new born. In males, the breast is rudimentary and the male breast is of similar structure as that of immature females. At puberty in females, under the influence of ovarian hormones, glands enlarge and breast becomes hemispherical shape. The contour and size of the breasts are mainly produced by subcutaneous fat, except during pregnancy when the mammary glands enlarge and new glandular tissue forms. In young women, the breast tends to protrude forward from a circular base, in older women tend to be pendulous and maximum size reached during lactation. The size and shape of the breast mainly depends on the gene, racial and dietary factors.
Situation and Extent
For practical reasons breast in mature female is explained.
The base of the breast extends vertically from 2nd to 6th ribs and transversely from lateral margin of sternum to mid-axillary line. It is present in the superficial fascia, 2/3 of the breast rests on the pectoral fascia (fascia overlying the pectoralis major muscle); 1/3 rests on the fascia covering the serratus anterior muscle. A small part of the breast extends along the inferolateral border of the pectoralis major toward the axilla, forming an axillary tail (of Spence). The axillary tail is more prominent when it may enlarge during a menstrual cycle and may be mistaken for a lump or enlarged lymph nodes.
Description
A small nipple is surrounded by circular pigmented area of skin called areola at the level of the 4th intercostal space. The tiny tubercles on areola produced by underlying sebaceous glands enlarge during pregnancy and secrete an oily substance that provides lubricant for areola and nipple.
The breast tissue consists of a system of ducts, "lacriferous ducts", embedded in connective tissue that does not extend beyond margin of areola. Each adult female breast of consists of 15-20 lobules(lobes) which radiate out of the nipple. The lactiferous duct from each lobule opens separately on summit of nipple and possesses a dilated portion, lactiferous sinus or ampulla, prior to its termination. Each lobe is a cluster of alveoli and drained by a lactiferous duct. The suspensory ligaments (of Cooper) anchor the skin and the gland to the deep fascia (pectoral fascia). The suspensory ligament is well developed in the superior part of the breast. The breast is separated from the pectoral fascia by loose connective tissue plane or potential space called retromammary space. This allows the breast some degree of movement on the pectoral fascia.
Blood Supply
Arteries
- Internal thoracic artery: medial mammary branches of perforating arteries and anterior intercostal branches
- Thoracic aorta: 2nd, 3rd, and 4th posterior intercostal arteries
- Axillary artery: lateral thoracic artery and thoracoacromial artery
Venous drainage
- correspond to arteries; venous drainage mainly to the axillary vein
Lymph Drainage
The lymphatic drainage of the breast is clinically important because of frequent development of cancer in the gland and subsequent metastasis of malignant cells along lymph vessels to the lymph nodes,opposite breast and even distant organs.
for practical purposes the breast is divided into 4 quadrants and lymph drainage is studied separately.
- Lateral upper and lower quadrant: To the axillary lymph nodes;Initially to the pectoral group nodes.
- Medial upper quadrant: Internal thoracic (anterior mediastinal ) group of nodes.
- Medial lower Quadrant: Drains to the opposite breast and inferior phrenic lymph nodes
Nerve Supply
The breast is supplied by anterior and lateral cutaneous branches of the 4th – 6th intercostal nerves. The nerves do not control the secretion of the milk. the secretion of the milk is controlled by hormone prolactin.