Lec 9

• Thorax


  The region of the body between the neck and the abdomen
• Thoracic cage


  • Formed by the vertebral column behind, the ribs and intercostal spaces on either side, and the sternum and costal cartilages in front
• Mediastinum


  The median partition of the thoracic cavity
• Pleurae


  The laterally placed membranes lining the thoracic cavity
• Parietal pleura


  The lining of the thoracic wall
• Thoracic wall


  • Covered on the outside by skin and muscles, lined with parietal pleura
  • Formed posteriorly by the thoracic vertebrae, anteriorly by the sternum and costal cartilages, laterally by the ribs and intercostal spaces, superiorly by the suprapleural membrane, and inferiorly by the diaphragm
• Sternum


  A flat bone in the midline of the anterior chest wall, divided into manubrium, body, and xiphoid process
• Manubrium


  • The upper part of the sternum, articulates with the clavicles and upper costal cartilages
• Body of the sternum

  • Articulates with the manubrium and xiphoid process, and the 2nd to 7th costal cartilages
• Xiphoid process


  • A thin cartilage plate at the lower end of the sternum, becomes ossified in adulthood
• Sternal angle


  The angle formed by the articulation of the manubrium and body of the sternum
• Categories of ribs


  • True ribs (1st-7th)
  • False ribs (8th-10th)
  • Floating ribs (11th-12th)
• Typical rib


  • Long, twisted, flat bone with rounded superior border and sharp inferior border
  • Has a head, neck, tubercle, shaft, and angle
• Head of rib


  • Has two facets for articulation with the corresponding vertebral body and the vertebra above
• Neck of rib


  • Constricted portion between the head and tubercle
• Tubercle of rib


  • Prominence on the outer surface, has a facet for articulation with the transverse process of the corresponding vertebra
• Shaft (body) of rib

  • Thin, flat, and curved, with a costal groove on the inferior border
• Angle of rib


  • Where the shaft bends sharply forward
• Costal cartilages


  Bars of cartilage connecting the ribs to the sternum and each other
• Atypical ribs


  • The 1st, 2nd, and 10th-12th ribs, dissimilar in structure from the typical ribs
• 1st rib


  • Broadest, shortest, and most sharply curved of the true ribs, has a single facet on the head and two transverse grooves on the superior surface
• 2nd rib


  • Thinner and less curved than the 1st rib, has two facets on the head and a rough tuberosity for the serratus anterior muscle
• 10th-12th ribs


  • Have only a single facet on the head, are short and lack a neck and tubercle
• Manubriosternal joint


  Cartilaginous joint between the manubrium and body of the sternum
• Xiphisternal joint


  Cartilaginous joint between the xiphoid process and body of the sternum
• Joints of the rib heads

  • 1st, 11th, and 12th ribs have a single synovial joint with their corresponding vertebral body; 2nd-9th ribs have a synovial joint with their corresponding vertebral body and the one above
• Joints of the rib tubercles

  • Synovial joint between the rib tubercle and the corresponding vertebral transverse process (absent in 11th and 12th ribs)
• Joints of the ribs and costal cartilages

  Cartilaginous joints, no movement possible
• Joints of the costal cartilages with the sternum

  • 1st cartilage articulates with the manubrium, 2nd-7th cartilages articulate with the lateral border of the sternum by synovial joints, 6th-10th cartilages also articulate with each other
• Suprapleural membrane


  Membrane that forms the superior boundary of the thoracic outlet
• Tubercle of a rib


  Articulates by means of a synovial joint with the transverse process of the corresponding vertebra
• This joint is absent on the 11th and 12th ribs
• Joints of the Ribs and Costal Cartilages

  Cartilaginous joints, no movement is possible
• Joints of the Costal Cartilages with the Sternum

  • 1st costal cartilages articulate with the manubrium by cartilaginous joints that permit no movement
  • 2nd to 7th costal cartilages articulate with the lateral border of the sternum by synovial joints
  • 6th, 7th, 8th, 9th, and 10th costal cartilages articulate with one another along their borders by small synovial joints
  • Cartilages of the 11th and 12th ribs are embedded in the abdominal musculature
• Suprapleural Membrane


  Dense fascial layer that closes the thoracic outlet on either side of the structures passing between the thorax and the neck
• Diaphragm


  • Thin muscular and tendinous septum that separates the chest cavity above from the abdominal cavity below
  • Pierced by structures passing between the chest and abdomen
  • Most important muscle of respiration
  • Dome shaped with a peripheral muscular part and a central tendon
  • Origin divided into sternal, costal, and vertebral parts
• Shape of the Diaphragm

  • Curves up into right and left domes, right dome higher due to large right lobe of liver
  • Central tendon at level of xiphisternal joint
  • Domes support right and left lungs, central tendon supports heart
• Action of the Diaphragm

  On contraction, pulls down central tendon and increases vertical diameter of thorax
• Openings in the Diaphragm

  • Aortic opening
  • Esophageal opening
  • Caval opening
• Mediastinum


  • Movable partition extending from thoracic outlet to diaphragm, between sternum and vertebral column
  • Contains various structures including heart, blood vessels, trachea, esophagus, nerves