Anatomy of Thorax Thoracic wall in a Nutshell

Thoracic wall, Pleura, and Lungs

Thorax: the superior portion of the trunk.  Extends inferiorly to the T12 Vertebrae

• Jugular notch: Pocket formed by superior part of manubrium.  Clavicle comes in from either side.
• Sternal angle: shallow ridge, border between manubrium and body of sternum.  Very little fat, palable. Landmark for second rib where it attaches.  Also provides part of horizontal plane to divide thoracic cavity.  Straight back is T4/5 disc.
• Costal Margin: inferior most extension of thorax.  Rim of cartilage that runs along inferior border under skin.  Connects lower ribs with sternum.
• Mid clavicular line: artificial border, starts at halfway pt.
• Skeletal components:
  • Thoracic cage:

• • • Sternum (most anterior) 3 parts
      1. Manubrium most superiorly
      2. Body of sternum
      3. Xyphoid process (most inferior)
  • Ribs (12 pairs)
    1. 1. True ribs = 1-7. through associated cartilage, they connect onto sternum
       2. False ribs = 8-10. Share connection with other ribs. Cartilage runs together to connect with sternum.
       3. Floating ribs = 11,12. little cartilage cap, not connect with sternum
  • Costal cartilage
  • 12 thoracic vertebrae (all 12 ribs connected to) most posterior.

• Cartilage of first rib connects to manubrium.  Can’t palpate the first rib. Manubrium connects with sternal body.  At their juncture laterally, have 2^nd rib attach via costal cartilage.  Bottom of sternum has xiphoid process.
• Between ribs = Intercostals space.  Filled with three layers of muscle. Provides tract for nerve/ artery / vein bundles to travel posterior to anterior.
• Costal margin: Made up of combined cartilage components of false ribs as they fuse with 7^th rib’s cartilage.
• Most posteriorly: First thoracic vertebrae matches with first rib. Continues through 12^th thoracic vertebrae which is connected to 12^th rib. Forms a cylinder with 2 openings:

1. • Superior thoracic aperture: Contains esophagus, trachea, large blood vessels, nerves. Narrow opening formed by the T1 vertebrae, 1^st ribs, manubrium. Clavicle is not involved, but is in vicinity.  If anything is present that projects into this area = thoracic aperture syndrome.  Due to rib defect, clavicle projecting inward too much, etc.
   • Inferior thoracic aperture: 12^th Vertebrae, 11/12^th ribs posterior / laterally, costal margin anterior / laterally, and xyphosternal Junction anteriorly.

Functions of Thoracic Cage:

• Respiration, specifically, ventilation.  By changing the shape of the cage → drive air into lungs (inspiration) and out (expiration).
• Bony structure protects the viscera.
• Bones provide anchor points for skeletal muscles of neck / back / limbs.

Ribs:

• Head of the rib articulates with the body of the vertebrae through 2 facets.  Each rib articulates with 2 vertebrae.  The crest of the head is bound to the intervertebral disc between the two vertebrae.
• Laterally end of neck region of rib: tubercle that interacts with transverse process, forms a synovial joint.
• Body/shaft of rib: Has a turn toward the anterior.  Turns at about the inferior end of the scapula. Costal groove – notch in inferior deep surface = where neurovascular bundle travels.  Under each rib, have nerve, artery, vein bundle that is protected by the rib above it.
• Joints: between vertebrae and rib. True synovial joints.
• Costal vertebral joints: head of rib with body of vertebrae. 7^th rib articulates with 6^th and 7^th T vertebrae.  Forms synovial joint to allow slight gliding.  Between rib tubercle and transverse process of vertebrae (same # as rib) gives the axis of rib rotation.  Normally only have gliding inferior to 6^th vertebrae.
• Costal condral joint: where bone part of rib becomes cartilage. No cavity, not a true synovial joint. It marks the transition.
• Sternal costal articulation: True synovial joint between lateral bony wall of sternum and costal cartilage.

Role of thoracic cage in respiration is ventilation:

• Ventilation = Movement of air into lungs and out of lungs
• Inspiration = Requires an increase in the volume of the thoracic cavity which produces negative air pressure in lungs to draw air in.
• Quiet inspiration = Diaphragm contracts → lowers diaphragm to increase the vertical dimension of thoracic cavity.
• Active inspiration = Involves other respiratory muscles and is during this that you have movement of ribs (elevation) which increases the transverse and anterior-posterior dimensions of the thoracic cavity.
• Quiet expiration = Passive, diaphragm relaxes, elasticity at work.
• Active expiration = Abdominal muscles contract to exhale. Coughing.

Components of volume exchanges in thoracic cavity

• Diaphragm = Vertical axis dimension changes
• Upper ribs and sternum = Pump handle movement change anterior / posterior axis.
• Lower ribs = Bucket handle movement→transverse axis.  Associated with particularly the movement at the angle.

Thoracic wall:

• Skin
  • Breast: nipple + areola
• Subcutaneous tissue
  • Adipose tissue – contains 15-20 compound alveolar mammary glands connected by lactiferous ducts to nipples.  Ducts have dilations to hold milk = lactiferous sinuses, near nipple.
  • Suspensory ligaments (of cooper) = CT fibers that connect subcutaneous tissue with dermis of skin. Play a role in maintaining shape of breast.  No connection between breast and bone.
  • Retromammary space = Potential space between underlying connective tissue (pectoralis fascia covering pectoralis major)  and adipose tissue.

• Breast sits upon pectoralis major.  Can divide breast into 4 quadrants.
• Axillary tail of breast = superior lateral quadrant tapers.  Contains most of the glandular tissue.  Most cancer occurs here since it arises from glandular tissue.
• Fat lobules are also present and surround glandular tissue in the breast. In males, there is less fat in this area, they still have glandular tissue, but it remains inactive.
• Nipple is locator for 4^th intercostals space.
• Gap between subcutaneous tissue and adipose tissue = Retromammary space.  Very thin CT fibers running from breast tissue (fatty tissue) that forms weak connection to Fascia of pectoralis major. It is here that breast implants are placed.
• To keep it in place, would have to place it deep to the pectoralis major.

Breasts:

• Innervated by 4^th → 6^th intercostals nerves.
• Blood supply:

• • Internal thoracic artery branches (forms mammary arteries for inferior portions)
  • Pectoral branches of thoracromial artery.
  • Lateral thoracic artery.
  • Posterior intercostals artery.

• Lymphatic drainage: 75% of lymph from breast goes to axillary lymph nodes. Associated with armpit.  Lateral superior Q lymph goes to axillary.  If breast cancer develops → may drain into axillary lymph nodes (biopsy will check).  Other sources for drainage = clavicular nodes (superiorly), parasternal nodes, phrenic nodes (inferiorly) associated with diaphragm.

Muscles of the thoracic wall

Peripheral muscles: associated with the upper extremeties and back

Intercostal muscles:

• External intercostal muscles = Travel at an angle on anterior surface, angled from lateral to medial (V). Contracts to bring ribs together (2 attachment points).  Tapers into external intercostals membrane that ends at sternum. Membrane appears transparent.
• Internal intercostal muscles = Fibers are oriented almost at 90 degree angle to external.  Go from medial to lateral at angle. Has membrane tapering posteriorly.
• Innermost intercostal muscles= Fibers are same angle as internal. Has membrane tapers at both ends.
• Neurovascular bundle located between internal and innermost.
• Vein – Drains into azygos system and internal thoracic vein (most superior)
• Artery = Anterior and posterior intercostal arteries. Anterior are very small.
• Nerves ventral rami of T1-T11, T12 = subcostal nerve. (most inferior). Contains branches for autonomic system and skeletal muscles. Taper significantly as move toward anterior.
• Collateral vessels: Located just superior to rib.
• Transverse thoracic muscle = Deep surface of thoracic cage = associated with sternum
• Subcostal muscles = Inner surface of ribs posteriorly runs across 2 ribs.
• Endothoracic fascia = Deep to subcostal muscles
• Parietal pleura = Deepest part forms fascia lining inside of thoracic cavity.

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