Regional anatomy
The thorax is an irregularly shaped cylinder with a narrow opening (superior thoracic aperture) superiorly and a relatively large opening (inferior thoracic aperture) inferiorly.
The thorax consists of:
- a wall,
- two pleural cavities,
- the lungs, and
- the mediastinum.
The thorax:
- houses and protects the heart, lungs, and great vessels,
- acts as a conduit for structures passing between the neck and the abdomen,
- plays a principal role in breathing, and
- provides support for the upper limbs.
The thorax also provides support for the upper limb. Muscles anchored to the anterior thoracic wall provide some of this support, and together with their associated connective tissues, nerves, and vessels, and the overlying skin and superficial fascia, define the pectoral region.
PECTORAL REGION
The pectoral region is external to the anterior thoracic wall and anchors the upper limb to the trunk. It consists of:
- a superficial compartment containing skin, superficial fascia, and breasts; and
- a deep compartment containing muscles and associated structures.
Breast
The breasts consist of mammary glands, associated skin, and connective tissues. The mammary glands are modified sweat glands in the superficial fascia anterior to the pectoral muscles and the anterior thoracic wall .
The mammary glands consist of ducts and associated secretory lobules. These converge, forming 15 to 20 lactiferous ducts, which open independently onto the nipple.
The nipple is surrounded by a circular pigmented area of skin, the areola.
A well-developed, connective tissue stroma surrounds the ducts and lobules of the mammary gland. In certain regions, this stroma condenses, forming well-defined ligaments, the suspensory ligaments of breast, which are continuous with the dermis of the skin and support the breast.
In nonlactating women, the predominant component of the breasts is fat, whereas glandular tissue is more abundant in lactating women.
The breast lies on the deep fascia of the pectoralis major muscle and other surrounding muscles. A layer of loose connective tissue (the retromammary space) separates the breast from the deep fascia and provides some degree of movement over underlying structures.The base, or attached surface, of each breast extends vertically from ribs 2 to 6, and transversely from the
sternum to as far laterally as the midaxillary line.
Arterial supply
The breast is related to the thoracic wall and to structures associated with the upper limb; therefore, vascular supply and drainage can occur by multiple routes :
- laterally, vessels from the axillary artery—superior thoracic, thoracoacromial, lateral thoracic, and
subscapular arteries;
- medially, branches from the internal thoracic artery; and
- from the second to fourth intercostal arteries via branches that perforate the thoracic wall and
overlying muscle.
Venous drainage
Veins draining the breast parallel the arteries and ultimately drain into the axillary, internal thoracic, and intercostal.
Innervation
Innervation of the breast is via anterior and lateral cutaneous branches of the second to sixth intercostal nerves. The nipple is innervated by the fourth intercostal nerve.
Lymphatic drainage
Lymphatic drainage of the breast is as follows:
- Approximately 75% is via lymphatic vessels that drain laterally and superiorly into axillary nodes .
- Most of the remaining drainage is into parasternal nodes deep to the anterior thoracic wall and associated with the internal thoracic artery.
- Some drainage may occur via lymphatic vessels that follow the lateral branches of posterior intercostal arteries and connect with intercostal nodes situated near the heads and necks of ribs.
Axillary nodes drain into the subclavian trunks, parasternal nodes drain into the bronchomediastinal trunks, and intercostal nodes drain either into the thoracic duct or into the bronchomediastinal trunks.
Breast in men
The breast in men is rudimentary and consists only of small ducts, often composed of cords of cells, which normally do not extend beyond the areola. Breast cancer can occur in men.
THORACIC WALL
The thoracic wall consists of skeletal elements and muscles:
- Posteriorly, it is made up of 12 thoracic vertebrae and their intervening intervertebral discs.
- Laterally, the wall is formed by ribs (12 on each side) and three layers of flat muscles, which span the intercostal spaces between adjacent ribs, move the ribs, and provide support for the intercostal spaces.
Anteriorly, the wall is made up of the sternum, which consists of the manubrium of sternum, body of sternum, and xiphoid process. the superior thoracic aperture bordered by vertebra TI,
rib I, and the manubrium of sternum; and n the inferior thoracic aperture bordered by vertebra
TXII, rib XII, the end of rib XI, the costal margin, and the xiphoid process of the sternum.
Superior thoracic aperture.
The superior thoracic aperture consists of:
- the body of vertebra TI posteriorly,
- the medial margin of rib I on each side, and
- the manubrium anteriorly.
The superior margin of the manubrium is in approximately the same horizontal plane as the intervertebral disc between vertebrae TII and TIII.
The first ribs slope inferiorly from their posterior articulation with vertebra TI to their anterior attachment to the manubrium. Consequently, the plane of the superior thoracic aperture is at an oblique angle, facing somewhat anteriorly .At the superior thoracic aperture, the superior aspects
of the pleural cavities, which surround the lungs, lie on either side of the entrance to the mediastinum .
Structures that pass between the upper limb and thorax pass over rib I and the superior part of the pleural cavity as they enter and leave the mediastinum . Structures that pass between the neck and head and the thorax
pass more vertically through the superior thoracic aperture.
Inferior thoracic aperture
The inferior thoracic aperture is large and expandable, and bone, cartilage, and ligaments form its margin . It is closed by the diaphragm (3.7B), and structures passing between the abdomen and thorax pierce or pass posteriorly to this structure. Skeletal elements of the inferior
thoracic aperture are:
-the body of vertebra TXII posteriorly,
- rib XII and the distal end of rib XI posterolaterally,
- the distal cartilaginous ends of ribs VII to X, which unite to form the costal margin anterolaterally, and the xiphoid process anteriorly.
Joints between the costal margin and sternum lie roughly in the same horizontal plane as the intervertebral disc between vertebrae TIX and TX. Thus, the posterior margin of the inferior thoracic aperture is inferior to the anterior margin.
Skeletal framework
The skeletal elements of the thoracic wall consist of thoracic vertebrae, intervertebral discs, ribs, and sternum. Thoracic vertebrae There are 12 thoracic vertebrae, each of which is characterized
by articulations with the ribs.
Sternum
The adult sternum consists of three major elements: the broad and superiorly positioned manubrium of sternum, the narrow and longitudinally oriented body of sternum, and the small and inferiorly positioned xiphoid process.
Manubrium of sternum
The manubrium of sternum forms part of the bony framework of the neck and the thorax.
The superior surface of the manubrium is expanded laterally and bears a distinct and palpable notch, the jugular notch (suprasternal notch), in the midline.
On either side of this notch is a large oval fossa for articulation with the clavicle. Immediately inferior to this fossa, on each lateral surface of the manubrium, is a facet for the attachment of the first costal cartilage. At the lower end of the lateral border is a demifacet for articulation with the
upper half of the anterior end of the second costal cartilage.
Body of the sternum
The body of the sternum is flat . The anterior surface of the body of the sternum is often
marked by transverse ridges that represent lines of fusion between the segmental elements called sternebrae, from which this part of the sternum arises embryologically. The lateral margins of the body of the sternum have articular facets for costal cartilages. Superiorly, each lateral margin has a demifacet for articulation with the inferior aspect of the second costal cartilage. Inferior to this demifacet are four facets for articulation with the costal cartilages of ribs III to VI.
At the inferior end of the body of the sternum is a demifacet for articulation with the upper demifacet on the seventh costal cartilage. The inferior end of the body of the sternum is attached to the xiphoid process.
Xiphoid process
The xiphoid process is the smallest part of the sternum . Its shape is variable: it may be wide, thin,
pointed, bifid, curved, or perforated. It begins as a cartilaginous structure, which becomes ossified in the adult. On each side of its upper lateral margin is a demifacet for articulation
with the inferior end of the seventh costal cartilage.
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