Conclusion - Tissue Functioning and Remodeling in the Circulatory and Ventilatory Systems - page 798

Chapter 14
Conclusion
Volume 5 aims at providing the fundamental knowledge of the respiratory and
vascular tissues that convey and regulate air and blood flows. These serial flows
supply oxygen to the body's tissues and successively remove carbon dioxide
produced by the body's cells. The right cardiac pump drives blood into pulmonary
circulation. The pulmonary perfusion must locally match the ventilation. Lung
territories oxygenate blood that then returns to the left cardiac pump. The left
venticle expels blood into the systemic arterial bed to irrigate all the body's tissues,
including the heart wall and lung parenchyma.
To raise the surface area of gas exchange in lungs between alveolar air and
capillary blood, the design of the tracheobronchial tree relies on branchings of short
parent ducts to irrigate and drain all the gas exchange units inside the confined
volume of lung parenchyma within the thoracic cage.
Quasi-periodic ventilation is caused by the motion of the thoracic wall, i.e., by
cycles of contraction and relaxation of respiratory mucles. The ventilatory pump that
limits the external borders of lung parenchymas with their bronchial trees changes
the intrathoracic pressure, and hence the volume of deformable bronchioles and
alveoli. The end pressure within lung acini enables successively inhalation and
exhalation of air from the atmosphere. Rib cage displacements are controlled by
the central nervous system.
In blood circulation, the cardiac pump is a component of the blood circuitry.
Blood circulates in two serial compartments: pulmonary and systemic circulation.
Two closely apposed left and right pumps, each made of two chambers to tackle
pressures in the venous and arterial compartments, synchronously expel blood in
their respective circuits.
The heart generates starting-stopping-like flows. Arterial unsteady blood flow
becomes continuous during the cardiac cycle, but can become bidirectional or even
reverse during diastole according to the rheology of the arterial wall.
The vasculature is characterized by a complicated architecture with variable
geometry both in space and time. Moreover, the vessel geometry changes over short