Anatomy and Histology

• The Pleura is  one of the two membranes around the lungs. Is a mesothelial
membrane made of  a single layer of flat cells and connective tissue
• These two membranes are called the visceral that lines the lungs and
• parietal pleurae that lines the cavity.
• In between the two membranes there is a small quantity of fluid. The pleural fluid
acts as a lubricant between the two membranes.
• ‐0.5 kPa vacuum, capillary adhesion

Pleural recesses are potential spaces within the thoracic cavity where the two pleurae
are relatively distant

• Costomediastinal: behind the sternum and costal cartilages
• Costodiaphragmatic: between the diaphragm and chest wall
• Vertebromediastinal: between the vertebral bodies and mediastinum
• Phrenicomediastinal: between the diaphragm and mediastinum

The function of these recesses is to allow the increase volume of the lungs during
inspiration.
The liquid between the pleurae  allows the lungs to move smoothly along the walls of
the cavity during breathing.

The mediastinum (from Medieval Latin mediastinus, "midway"^[1]) is the central compartment of the thoracic cavity surrounded by loose connective tissue, as an undelineated region that contains a group of structures within the thorax.

Intercostal muscles:

•  Attached between the ribs.
• Manipulate the width of the rib cage
• Three layers:

1. outer layer: external intercostal (raising of the rib cage, assisting
inhalation),
2. Middle layer: internal intercostal
3. Inner layer: innermost intercostal muscles, transversus thoracis and
subcostal muscles

Diaphragm

the diaphragm (Ancient Greek: διάφραγμα diáphragma "partition"), is a sheet of internal skeletal muscle^[2] that extends across the bottom of the thoracic cavity. The diaphragm separates the thoracic cavity, containing the heart and lungs, from the abdominal cavity and performs an important function in respiration: as the diaphragm contracts, the volume of the thoracic cavity increases and air is drawn into the lungs.

• Inspiration, i.e. increased lung volume due to contraction of the external intercostal muscles and the diaphragm
• Expiration, i.e. decreased lung volume due to contraction of internal intercostal muscles and relaxation of the diaphragm

• Three muscle layers:
• External intercostals raise ribs during inspiration (anterioinferior direction)
• Internal intercostals lower ribs during expiration (posteriosuperior direction)
• Innermost intercostals also lower ribs during expiration
• Subcostal and transverse thoracic muscles