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What's the thorax?

What's the thorax?

Irregularly shaped cylinder with a narrow opening (superior thoracic aperture) and a relatively large opening (inferior thoracic aperture). Consists of:

• A wall,

• 2 pleural cavities

• Lungs

• Mediastinum

Functions of 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

Provides support for the upper limb

• Muscles, vessels, connective tissue, nerves, skin and fascia define the pectoral region.

Pectoral region

external to the anterior thoracic wall; anchors upper limb to trunk. Consists of:

• Superficial compartment containing skin, superficial fascia and breast.

• Deep compartment containing muscle and associated structures.

Breast

Consist of Mammary glands, associated skin and connective tissues.

Mammary glands

modified sweat glands in the superficial fascia anterior to the pectoral muscles and anterior to the thoracic wall. Consist of ducts and associated secretory lobules.

Lactiferous ducts

Secretory lobules that converge. Around 15 to 20, which open independently onto the nipple.

nipple and areola

The nipple is surrounded by the areola.

Suspensory ligaments of breast

Well-defined ligaments built from stroma that are continuous to the dermis of the skin and supports the breast.

Predominant component of breast

• In non-lactating women; fat

• In lactating women; granular tissue.

retromammary space

A layer of connective tissue separates the breast from the deep fascia and provides some degree of movement over underlying structures.

Position of the breast

Extends vertically from ribs II to VI and transversely from the sternum to as far laterally as the midaxillary line.

Clinical app: Axillary process of breast

The upper lateral region of the mammary gland and supporting tissues can project around the lateral margin of the pectoralis major muscle and into the axilla. This axillary process (axillary tail) may perforate deep fascia and extend as far superiorly as the apex of the axilla

Arterial supply of the breast

• Laterally, vessels from the axillary artery - superior thoracic, thoracoacromial, lateral thoracic and sub-scapular arteries.

• Medially, branches from the internal thoracic artery.

• From the 2nd to 4th intercostal arteries via branches that perforate the thoracic wall and overlying muscle.

Venous drainage of the breast

axillary vein, internal thoracic vein, intercostal vein

Innervation of the breast

via anterior and lateral cutaneous branches of 2-6 intercostal nerves (T2- T6 dermatomes).

the nipple is innervated by the 4th intercostal nerve.

Lymphatic drainage of the breast

• 75% via lymphatic vessels that drain laterally and superiorly into axillary nodes (which drain into the subclavian trunks)

• Most of the remaining drainage is into parasternal nodes (drain into the bronchomediastinal trunks) deep to the anterior thoracic wall and associated with the internal thoracic artery.

• Some may occur via lymphatic vessels that follow the lateral branches of posterior intercostal arteries and connect with intercostal nodes (drain to the thoracic duct or the bronchomediastinal trunk).

Breast in men

Rudimentary; mammary glands consist of small ducts often composed of cords of cells that normally do not extend beyond the areola.

Clinical app: Breast cancer

Breast cancer develops in the cells of the acini, lactiferous ducts, and lobules of the breast. Breast tumours spread via the lymphatics and veins or by direct invasion. Subcutaneous lymphatic obstruction and tumour growth pull on the suspensory ligaments resulting in the appearance of an orange peel texture (peau d'orange) on the surface of the breast. Further subcutaneous spread can induce a rare manifestation of breast cancer that produces a hard, woody texture to the skin (cancer en cuirasse).

Muscles of the pectoral region

pectoralis major, pectoralis minor, subclavius, serratus anterior. All originate from the anterior thoracic wall and insert into bones of the upper limb.

Clavipectoral fascia

continuous layer of deep fascia that encloses the subclavius and pectoralis minor and attaches to the clavicle above and to the floor of the axilla below.

Thoracic wall

Consists of skeletal elements and muscles:

• Posteriorly made of 12 thoracic vertebrae and intervening intervertebral discs.

• Laterally, 12 ribs on each side, 3 layers of flat muscles.

• Anteriorly, sternum (manubrium, body of sternum and xiphoid process)

Surface anatomy: Breast in women

Normally positioned between ribs II and VI and overlie the pectoralis major muscles.

Each mammary gland extends superolaterally around the lower margin of the pectoralis major muscle and enters the axilla. The axillary process. The positions of the nipple and areola vary relative to the chest wall depending on breast size.

Thoracic wall extends between:

• Superior thoracic aperture bordered by vertebra TI, rib I and manubrium of sternum.

• Inferior thoracic aperture bordered by vertebra TXII, rib XII, end of rib XI, costal margin and xiphoid process.

superior thoracic aperture

The superior margin of the manubrium is in the same 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.

The superior aspects of the pleural cavities, which surround the lungs, lie on either side of the entrance to the mediastinum.

pectoralis major

Original: medial half of clavicle and anterior surface of sternum, first seven costal cartilages, aponeurosis of external oblique.

Insertion: Lateral lip of intertubercular sulcus of humerus

Innervation: Medial and lateral pectoral nerves

Functions: Adduction, medial rotation, and flexion of the humerus at the shoulder joint

pectoralis minor

Origin: Anterior surfaces of the 3rd, 4th and 5th ribs, and deep fascia overlying the related intercostal spaces

Insertion: Coracoid process of scapula

Innervation: Medial pectoral nerves

Functions: Depresses tip of shoulder; protracts scapula

subclavius

Origin: Rib I at the junction between rib and costal cartilage

Insertion: Groove on inferior surface of middle third of clavicle

Innervation: Nerve to subclavius

Functions: Pulls clavicle medially to stabilize sternoclavicular joint; depresses tip of shoulder

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, and structures passing between the abdomen and thorax pierce or pass posteriorly to this structure.

Joints between the costal margin and sternum vertebrae TIX and TX.

Clinical app: Thoracic outlet syndrome

Describe symptoms resulting from abnormal compression of the brachial plexus of nerves as it passes over the first rib and through the axillary inlet into the upper limb. The anterior ramus of T1 passes out of the superior thoracic aperture and become part of the brachial plexus. A connective tissue band that can extend from the tip of a cervical rib to rib I is one cause of thoracic outlet syndrome by putting upward stresses on the lower parts of the brachial plexus as they pass over the first rib.

Thoracic vertebrae

12 thoracic vertebrae, each characterized by articulations with the ribs.

typical thoracic vertebrae

A typical thoracic vertebra has a heart-shaped vertebral body.

• The vertebral foramen is generally circular

and the laminae are broad and overlap with those of the vertebra below.

• The superior articular processes are at, with their articular surfaces facing almost directly posteriorly, whereas

• The inferior articular processes project from the laminae and their articular facets face anteriorly.

• The transverse processes are club-shaped and project posterolaterally.

typical thoracic vertebrae and articulation with ribs.

A typical thoracic vertebra has three sites for articulations with ribs on each side

■ Two demifacets (i.e., partial facets) located on the

superior and inferior aspects of the body for articulation with corresponding sites on the heads of adjacent ribs. The superior costal facet articulates with part of the head of its own rib, and the inferior costal facet articulates with part of the head of the rib below.

■ An oval facet (transverse costal facet) at the end of

the transverse process articulates with the tubercle of

its own rib.

rest of vertebrae articulation with ribs

Not all vertebrae articulate with ribs in the same fashion:

■ Vertebra T1: superior costal facets are complete and articulate with a single facet on the head of its own rib.

■ Vertebra TX (and often TIX): lacks inferior demifacets on the body. cause articulates only with its own ribs.

■ Vertebrae TXI and TXII: articulate only with the heads

of their own ribs. Lack transverse costal facets and have only a single complete facet on each side.

Ribs

12 pairs of ribs, terminating anteriorly in a costal cartilage. Only the true ribs (ribs 1 to 7) articulate with the sternum. False ribs (T8 to T12)

• Costal cartilages of ribs VIII and X articulate anteriorly with the costal cartilages from ribs above.

• Ribs XI and XII (floating ribs) have no anterior connection with ribs or sternum.

rib anatomy

The anterior end is continuous with its costal cartilage. The posterior end articulates with the vertebral column and is characterized by a head, neck, and tubercle.

■The head is somewhat expanded and typically presents two articular surfaces separated by a crest. The smaller superior surface articulates with the inferior costal facet on the body of the vertebra above, whereas the larger inferior facet articulates with the superior costal facet of its own vertebra.

■ The neck is a short at region of bone that separates

the head from the tubercle.

■ The tubercle projects posteriorly from the junction of

the neck with the shaft and consists of two regions, an

articular part and a non-articular part.

rib anatomy 2

■ The articular part is medial and has an oval facet for

articulation with a corresponding facet on the

transverse process of the associated vertebra.

■ The raised non-articular part is roughened by ligament

attachments.

■ The shaft is generally thin and at with internal and

external surfaces.

■ The superior margin is smooth and rounded, whereas

the inferior margin is sharp.

■ The angle forms after the shaft bends forward laterally to the tubercle.