F1iii: Outline the anatomy of the chest wall + Describe its function in respiration

  • Thorax = superior part of trunk between neck & abdomen

Fascia

  • Skin
  • Subcutaneous tissue: fat, sweat glands, blood, lymphatics, cutaneous nerves, breasts & mammary glands (mature females)
  • Deep fascia: thin fibrous membrane → inverts underlying muscle & tendons →  barrier to infection

Skeleton

Sternum

  • Flat, elongated bone at midline of thoracic cage
  • 3 parts: manubrium, body, xiphoid process
  • 3 indentations: jugular notch, clavicular notches, costal notches

Thoracic Vertebrae

  • 12 → long spinous processes
  • Costal facets on body → articulation with rib tubercles
  • Costal facets on T process → articulation with rib tubercles

Rib

  • True ribs: 1 – 7 → Attached directly on sternum with own costal cartilages
  • False ribs: 8 – 10 → Their cc attach to rib above them ∴their attachment to sternum is indirect
  • Floating rib: 11 – 12 → Attached to vertebrae but not sternum ∴ ‘floating’

Typical Rib

  • Posterior portion → costal angle →  body
  • Posterior portion → 2 facets to articulate with vertebrae

   →  Neck

   →  Tubercle to articulate with T process of T vertebral body

  • Body → long curved shaft of bone

             →  anteriorly attaches to cc →  sternum

  • Costal angle → rib is twisted on its axis to create an angle

                       →  here where it ∆ direction is its weakest link

Atypical Ribs

  • Ribs 1 – 2
    • Shorter & flatter
    • Rib 1 forms thoracic inlet & manubrium transmitting GREAT VESSELS, OESOPHAGUS, TRACHEA, NERVES + LYMPHATICS
  • Ribs 11 – 12
    • Short & floating
    • No sternal attachment
    • ∴ no neck/tubercle

Rib Movement

  • Ribs 1 – 7 attach sternum + spine → ∴ limited mobility
  • Ribs 8 – 10 have longer CC ∴ ↑mobility
  • Ribs 11 – 12 float ∴ greatest mobility

∴ all ribs have different ROM

  • Thoracic wall moves like a bucket handle
  • It moves laterally + up
  • When upper ribs are elevated the A-P diam of thorax increases → movement resembling a pump handle

Muscles of Chest Wall

  • Serratus posterior superior → elevate ribs
  • Serratus posterior inferior → depresses ribs
  • Levator costanum → elevates ribs
  • External IC → elevates ribs
  • Internal IC → depresses ribs
  • Innermost IC → elevate ribs
  • Subcostal → elevate ribs
  • Transversus thoracic → depresses ribs

Arteries & Veins (intercostal spaces)

Nerves

  • 12 pairs of spinal nerves
  • Divide into ventral & dorsal rami to supply IC space, bones, joints & muscles of thoracic wall

Chest Wall Muscles & Respiration

  • Respiration movements of chest:

Inspiration

  • Requires thorax expansion
  • ↑AP chest diameter
  • ↑lateral chest diameter
  • ↑vertical chest diameter

Passive inspiration: diaphragm + external ICs

Forceful inspiration: Scaleni, SCM, serratus anterior, serratus post superior, pec major + minor, levatores costorum

  • Pump bundle of sternum elevates = ↑AP diameter
  • Bucket handle ribs elevate = ↑lateral diameter
  • Lowering of diaphragm = ↑vertical movement of thorax
  • ∴ ↓ intrathoracic P & atmospheric air enters lungs

Expiration

  • Passive process, the opposite of inspiration

Quiet expiration: internal ICs

Forceful expiration: Traversus thoracic, rectus abdominis, internal + external obliques, serratus post inf.

  • Pump handle of sternum lowers = ↓AP diameter
  • Bucket handle elevation of ribs lowers = ↓lateral diameter
  • Diaphragm elevates → ↓vertical length thorax

∴ ↑intrathoracic P →  air pushed back to atmosphere