4.1 Thorax and Thoracic Skeleton

THORAX COMPONENTS

THORACIC WALL

  • Components:

    • Breast

    • Skeleton/cage

    • Muscles

    • Vessels & Nerves

  • Functions:

    • Milk production

    • Protecting thoracic contents

    • Respiration

    • Muscle attachment

THORACIC CAVITY

  • Components:

    • Pleural cavity - space between the lungs and the chest wall

    • Mediastinum - contains pericardial cavity, heart, esophagus, trachea, blood vessels, nerves, etc.

  • Functions:

    • Gas exchange

    • Pumping blood

    • Transporting food & air

THORACIC SKELETON

  • Sternum: Consists of 3 fused bones (manubrium, body, xiphoid process) linking to ribs 1-7. Classified as synchondrosis (type of joint in which bones are connected by hyaline cartilage) same as ribs, non movable

  • Ribs:

    • True Ribs (1-7): Directly connected to sternum

    • False Ribs (8-10): Attach to costal cartilage

    • Floating Ribs (11-12): No anterior articulation, no articulation with sternum

  • Vertebrae: T1-T12 have ribs attached on either side.

Thoracic vertebrae:

  • costal facets on transverse process (for costotransverse joint)

  • 2 facets on body (for costovertebral joints)

RIB ARTICULATION

  • Key points about rib articulation:

    • Costal facets on transverse processes & bodies of thoracic vertebrae.

    • Costovertebral joints are synovial joints with gliding movement, enabling rib movement during respiration.

TYPICAL AND ATYPICAL RIBS

  • Typical Ribs (3-9):

    • Head with 2 facets, neck, tubercle located at the neck, and a flattened body.

  • Atypical Ribs (1, 2, 10-12):

    • Rib 1: Broad, short, one facet.

    • Rib 2: More typical in structure with rough upper surface.

    • Ribs 10-12: One facet, structures of 11-12 lack neck and tubercle.

    • Rib 11-12: no neck or tubercle

RESPIRATION MECHANICS

  • Inhalation: Muscles contract, causing superior and anterior movement of the thoracic cage (handle on a backet)

  • Exhalation: Passive process; muscles relax, leading to downward movement of the thoracic cage.

BREAST ANATOMY

  • Components:

    • Areola, nipple, adipose tissue, lobules (15-20), lactiferous duct.

  • Changes noted during puberty, pregnancy, and lactation.

BLOOD AND NERVE SUPPLY TO BREAST

  • Arterial Supply:

    • Axillary artery, subclavian artery, aorta.

  • Venous Drainage:

    • Mainly through axillary vein.

  • Nerve Supply:

    • Intercostal nerves.

LYMPHATIC DRAINAGE OF THE BREAST

  • >75% lymph drained via axillary nodes (lateral breast). (1)

  • Medial breast drained via sternal nodes. (2)

  • Important for understanding cancer spread.

THORACIC STRUCTURE AND FUNCTION

  • Thoracic cavity divided into:

    • Mediastinum (contains heart and great vessels).

    • Pleural cavities (houses lungs).

  • Thoracic cage protects thoracic structures and serves as a muscle attachment site.

BLOOD SUPPLY AND NERVOUS INNERVATION

  • Blood Supply:

    • Intercostal arteries from aorta and internal thoracic artery.

  • Nervous Supply:

    • Intercostal nerves serving dermatomes(1 nerve root) and myotomes (<1 nerve root).

MUSCLES OF THE THORACIC WALL

  • Intercostal Muscles:

    • External: Most superficial, aids in inhalation.

    • Internal: Intermediate layer, aids in forced exhalation.

    • Innermost: Deepest layer, lies close to the pleura (membrane).

JOINTS AND LIGAMENTS

  • Costochondral Joint:

    • Cartilaginous joint (synchondrosis) connecting ribs and cartilage.

  • Costovertebral and Costotransverse Joints:

    • Synovial joints allowing rib movement and stability.

CLINICAL IMPORTANCE

  • Knowledge of thoracic anatomy is crucial for procedures like sternotomy, pericardiocentesis, and thoracentesis.

  • Boundaries of thoracic wall serve as anatomical landmarks for various clinical interventions.