by Talib F. Abbas
Respiratory system 4 major functions:
 1-Pulmonary ventilation
 2- Diffusion of oxygen and carbon dioxide
between the alveoli and the blood.
 3- Transport of oxygen and carbon dioxide in
the blood and body fluids to and from the
body’s tissue cells.
 Regulation of ventilation and other facts of
respiration.
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 Lung ventilation is by two ways:
 1-downward and upward movement of the diaphragm.
 2-elevation and depression of the ribs .
 Normal quiet breathing is accomplished by movement
of the diaphragm.
 when the rib cage is elevated, the ribs project almost
directly forward, so that the sternum also moves
forward, away from the spine.
 muscles that raise the rib cage are the external
intercostals.
 The most important muscles that raise the rib cage are
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the external intercostals, but others that help are the
(1) sternocleidomastoid muscles, which lift upward on
the sternum;
(2) anterior serrati, which lift many of the ribs; and
(3) scaleni, which lift the first two ribs
The muscles that pull the rib cage downward during
expiration are mainly the
(1) abdominal recti
(2) internal intercostals.
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 takes a deep breath of oxygen
 expires through a rapidly recording nitrogen meter.
 only oxygen appears, and the nitrogen concentration is
zero, at the early stage.
 the gray area represents the air that has no nitrogen.
 the pink area represents the air that has nitrogen.
 VD = Volume of Dead space.
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 relaxation pressure curve of the total
respiratory system. The pressure is zero at a lung
volume that corresponds to the volume of gas in
the lungs at the end of quiet expiration
(functional residual capacity, or FRC; also
known as relaxation volume). It is positive at
greater volumes and negative at smaller volumes.
The change in lung volume per unit change in
airway pressure (ΔV/ΔP) is the compliance
(stretchability) of the lungs and chest wall.
 law of Laplace: equals two times the tension divided by the
radius (P = 2T/r).
 The low surface tension when the alveoli are small is due to
the presence in the fluid lining the alveoli of surfactant, a
lipid surface-tension-lowering agent. Surfactant is a
mixture of dipalmitoylphosphatidylcholine (DPPC).
 . Surfactant is produced by type II alveolar epithelial cells.
Typical lamellar bodies.
 Formation of the phospholipid film is greatly facilitated by
the proteins in surfactant. This material contains four
unique proteins: surfactant protein (SP)-A, SP-B, SP-C, and
SP-D. SPA is a large glycoprotein and has a collagen-like
domain within its structure.
 Pressures in the Pulmonary Artery.(15 mmHg)
 Pulmonary capillary pressure. ( 7 mmHg)
 Left Atrial and Pulmonary Venous
Pressures.(pulmonary wedge pressure). ( 5 mmHg)
 It is important to distinguish between the anatomic
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dead space (respiratory system volume exclusive of
alveoli) and the total (physiologic) dead space
(volume of gas not equilibrating with blood; ie, wasted
ventilation). In healthy individuals, the two dead
spaces are identical and can be estimated by body
weight.
The initial gas exhaled (phase I).
mixture of dead space and alveolar gas (phase II).
alveolar gas (phase III), closing volume (CV).
phase IV, during which the N2 content of the expired
gas is increased.
 The total dead space can be calculated from the PCO2 of expired
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air, the PCO2 of arterial blood, and the tidal volume. The tidal
volume (VT) times the PCO2 of the expired gas (PECO2) equals
the arterial PCO2 (PaCO2) times the difference between the tidal
volume and the dead space (VD) plus the PCO2 of inspired air
(PICO2) times VD (Bohr’s equation):
PECO2 × VT = PaCO2 × (VT – VD) + PICO2 × VD
The term PICO2 × VD is so small that it can be ignored and
the equation solved for VD. If, for example,
PECO2 = 28 mm Hg
PaCO2 = 40 mm Hg
VT = 500 mL
then,
Vd = 150 mL
 Unlike liquids, gases expand to fill the volume
available to them, and the volume occupied by a given
number of gas molecules at a given temperature and
pressure is (ideally) the same regardless of the
composition of the gas.
 partial pressure) is equal to the total pressure times
the fraction of the total amount of gas it represents.
 The partial pressure (indicated by the symbol P) of
O2in dry air is therefore 0.21×760, or 160 mmHg at sea
level.
 The PN2 and the other inert gases is 0.79×760, or 600
mm Hg; and the PCO2is 0.0004×760, or 0.3 mm Hg.