Thorax Anatomy Week 1

The Thorax

• The thorax is the part of the body between the neck and abdomen, with its circumference increasing inferiorly and reaching maximum size at the junction with the abdominal portion of the trunk.
• The thorax contains the primary organs of the cardiovascular and respiratory systems.

Thoracic Wall

• The thoracic skeleton consists of 12 pairs of ribs and their costal cartilages, 12 thoracic vertebrae and IV discs, and the sternum (manubrium, body, and xiphoid process).
• The thoracic apertures include the superior and inferior thoracic apertures.
• Joints in the thoracic wall include intervertebral, costovertebral, costochondral, interchondral, sternocostal, sternoclavicular, manubriosternal, and xiphisternal joints.

Muscles of the Thoracic Wall

• Axio-appendicular muscles include pectoralis major, pectoralis minor, subclavius, serratus anterior, serratus posterior superior, serratus posterior inferior, levatores costarum, intercostal, subcostal, and transversus thoracis.
• Pectoralis major has a clavicular head that adducts and medially rotates the humerus, and a sternocostal head that extends the humerus from the flexed position.
• Pectoralis minor stabilizes the scapula by drawing it inferiorly and anteriorly against the thoracic wall.

Intercostal Nerves

• The 12 pairs of thoracic spinal nerves include typical nerves (T3-6, T7-11) and nerve blocks.

Arteries and Veins

• The three sources of blood supply to the thorax are the thoracic aorta, subclavian artery, and axillary artery.
• The posterior intercostal arteries and subcostal arteries arise from the thoracic aorta.
• The intercostal veins accompany the intercostal arteries and nerves, and the posterior intercostal veins anastomose with anterior intercostals.

Breast

• The breast consists of glandular and supporting fibrous tissue embedded in a fatty matrix, along with blood vessels, lymphatics, and nerves.
• The mammary glands are located in the subcutaneous tissue overlying pectoralis major and minor.
• The breast extends from the lateral border of the sternum to the midaxillary line, and from the 2nd to 6th ribs.

Neurovasculature of the Breast

• The arterial supply to the breast arises from the medial mammary branches, lateral thoracic artery, and posterior intercostal artery.
• The axillary vein drains the breast, and lymphatics drain into the axillary lymph nodes.
• Nerves supplying the breast include intercostal nerves and branches of the brachial plexus.

Thoracic Wall

• Composed of bones and joints
• Muscles involved: · External intercostal · Internal intercostal · Innermost intercostal · Transversus thoracis

Muscles and Functions

• Muscles of the thoracic wall: · External intercostal · Internal intercostal · Anterior intercostal · Internal thoracic · Transversus thoracis · Musculophrenic · Pericardiacophrenic

Blood Vessels and Blood Supply

• Arteries: · Anterior intercostal · Internal thoracic

• Veins: · Superior vena cava · Superior epigastric · Musculophrenic · Pericardiacophrenic### Thoracic Wall

• The thoracic wall is composed of three layers: external intercostal, internal intercostal, and innermost intercostal muscles.

• The external intercostal muscles elevate ribs during forced inhalation.

• The internal intercostal muscles depress ribs during forced exhalation.

• The innermost intercostal muscles also depress ribs during forced exhalation.

Intercostal Nerves

• Intercostal nerves are responsible for muscular innervation and sensory innervation.
• The phrenic nerve arises from nerve roots C3, C4, C5, and travels with the pericardiacophrenic artery.
• The phrenic nerve has sensory function, innervating the fibrous pericardium, mediastinal pleura, and diaphragmatic peritoneum.
• The phrenic nerve has motor function, innervating the diaphragm.

Blood Supply

• The ascending aorta supplies the upper limbs, head, and neck.
• The pulmonary trunk supplies the lungs.
• The right atrium receives blood from the superior vena cava.
• The superior vena cava receives blood from the union of the right and left brachiocephalic veins.
• The right atrium drains blood into the right ventricle.

Circulation

• Systemic circulation involves the ascending aorta and supplies the upper limbs, head, and neck.
• Pulmonary circulation involves the pulmonary trunk and supplies the lungs.

Muscles of the Thoracic Wall

• The transversus thoracis muscle depresses ribs during forced exhalation.
• The levatores costarum muscles elevate ribs during forced inhalation.
• The serratus anterior muscles rotate the scapula and assist in forced inhalation.

Thoracic Wall Innervation

• The intercostal nerves are responsible for muscular innervation and sensory innervation.
• The phrenic nerve is responsible for innervation of the diaphragm.
• The phrenic nerve has sensory function, innervating the fibrous pericardium, mediastinal pleura, and diaphragmatic peritoneum.

Blood Flow

• Blood flows from the superior vena cava to the right atrium.

• Blood flows from the right atrium to the right ventricle.

• Blood flows from the right ventricle to the pulmonary trunk.

• Blood flows from the pulmonary trunk to the lungs.### Thoracic Wall Muscles

• External intercostal muscle

• Internal intercostal muscle

• Anterior intercostal muscle

• Internal thoracic muscle

• Innermost intercostal muscle

• Transversus thoracis muscle

• Musculophrenic muscle

• Pericardiacophrenic muscle

Veins

• Superior vena cava

Arteries

• Anterior intercostal artery
• Internal thoracic artery
• Ascending aorta
• Pulmonary trunk

Nerves

• Phrenic nerve (sensory and motor functions)

Carcinoma of the Breast

• Malignant tumors (adenocarcinomas) arising from epithelial cells of lactiferous ducts in mammary gland lobules
• Tumor enlarges and attaches to the suspensory ligament, shortening it

Lymphatic Drainage of the Breast

• 75% of lymphatic drainage occurs through parasternal lymph nodes
• 25% of lymphatic drainage occurs through anterior axillary (pectoral), posterior axillary (subscapular), and lateral axillary (humeral) lymph nodes

Mastectomy

• Removal of the breast, pectoral muscles, fat, fascia, and lymph nodes in the axilla and pectoral region
• Can result in winged scapula due to injury to the long thoracic nerve causing paralysis of serratus anterior muscle