VAN 221: Veterinary Splanchnology and Applied Anatomy (1+1)

LUNGS (OX)

Ox

• The lungs, the essential organs of respiration are right and left and each occupy the greater part of the thoracic cavity
• They are accurately adapted to the walls of the cavity and the other organs contained in it. Each lung is soft, spongy and highly elastic
• It crepitates when pressed and floats in water
• The colour varies according to the amount of blood contained in the lung. During life, it is pink in colour
• In dissected bodies, it is light grey in colour and slightly tinged with red. The average weight of lungs is 3.4 kg
• The right lung weighs about half as much as the left one
• The fetal lung presents the following characters,
  • It is much smaller
  • It is firmer and does not crepitate
  • It is pale grey in colour
  • It sinks in water
• In form, the lungs are like the casts of the cavities in which they are situated
• When well hardened in situ, their surfaces present impressions and elevations corresponding exactly to the structures with which they are in contact
• The right lung is larger than the left.
• Each lung presents for description two surfaces, two borders, a base and an apex. The costal surface is convex and lies against the lateral wall of the thorax, it presents impressions of the ribs
•  The mediastinal surface is less extensive and molded on the mediastinum and its contents
• It presents a little in front of it middle, an irregular depression -the hilus of the lung where the structure, which compose the root of lung, enter or leave the organ
• In front of the root, each lung presents a large cavity adapted to the heart -the cardiac impression. Behind the hilus and slightly above it are two grooves -a dorsal one for the aorta and a ventral for the oesophagus.
• The dorsal border is long, thick and rounded. The ventral border is thin and presents two deep fissures, which divide the lungs into a variable number of lobes
• The left lung presents a large quadrilateral cardiac notch extending from the ventral end of the third intercostal space to the fourth intercostal space and here the pericardium and heart are in contact with the chest wall. Behind this notch there is a fissure
• The fissure and notch divide the left lung into three lobes - the one in front of the cardiac notch is the apical lobe, and behind it is the cardiac lobe and behind the fissure is the diaphragmatic lobe. On the right lung, there are two fissures on the ventral border dividing it into apical, cardiac and diaphragmatic lobes
• The apical lobe is divided into two parts by a deep fissure
• The apical lobe of the right lung is much larger than that of the left lung and occupies the space in front of the pericardium, pushing the mediastinum against the left wall
• The apical lobe of the right lung receives a special bronchus from the trachea opposite the third rib or space and is adherent to the trachea from here backward
• The mediastinal face presents a small mediastinal or intermediate lobe.
• The base of the lung is oval in outline; its surface (diaphragmatic surface) is deeply concave, in adaptation to the thoracic surface of the diaphragm
• Laterally and dorsally it is limited by a thin convex basal border, which fits into the narrow recess between the diaphragm and lateral chest wall.
• The apex of the lung is prismatic, narrow and flattened transversely. It curves downward, and is related deeply to the cranial mediastinum and to the cranial part of the pericardium.
• The root of the lung is composed of the structures, which enter or leave the lung at the hilus on the mediastinal surface. These are
  • The bronchus
  • The pulmonary artery
  • The pulmonary veins
  • The bronchial artery
  • The pulmonary nerves and
  • The pulmonary lymph vessels
• The bronchus is situated dorsally with the bronchial artery on its upper surface and the pulmonary artery immediately below it
• The pulmonary veins lie chiefly below and behind the artery

Bronchi

• Each bronchus enters the hilus of the lung
• The left bronchus first gives off a branch, which supplies both the apical and cardiac lobes and is then continued as the stem bronchus to the diaphragmatic lobe
• The right bronchus gives off a branch, which supplies the cardiac lobe and is continued as the stem bronchus to the diaphragmatic lobe
• A branch is detached from the medial face of the stem bronchus to the mediastinal lobe
• The apical bronchus from the trachea supplies the apical lobe. The lobulation of lung is very evident on account of abundant interlobular tissue