Resp 3 Flashcards
comparison of pulmonary and systemic circulation
- Since the pulmonary circulation is in
series with the systemic circulation,
overall blood flow rate is the same in
both circuits - In spite of similar blood flow rates,
vascular pressures are considerably
lower in the pulmonary circulation - Vessel walls of the pulmonary vasculature are much thinner and
contain less smooth muscle than
corresponding segments in the
systemic circulation
major functions of pulmonary circulation (brief)
- Gas exchange
- Blood filtration
- Blood reservoir
- Metabolic functions
- Defense
pulmonary circulation as a blood filter; microvessels, capillaries, emboli
- Because pulmonary microvessels are so numerous, some can effectively serve as filters to trap foreign materials present in the blood without significant harm to the lung
- Pulmonary circulation contains more capillaries than are normally required for gas exchange at rest, so some lung microvessels can be used to trap particles without seriously affecting gas exchange
- Emboli trapped by pulmonary vessels can later be removed by enzymatic processes, macrophage ingestion, or absorption into the lymphatic system
pulmonary artery structure; what do bronchiole arteries contain, smaller arteries associated with what
-Bronchial arteries contain layers of elastic tissue; referred to as elastic arteries
-Smaller arteries associated with
bronchioles & alveolar ducts have minimal elastic tissue; called muscular arteries
alvolar vessels
Alveolar Vessels:
* Thin-walled capillaries
* Perfuse alveolar septa
* Exposed directly to the pressure changes occurring in alveoli
pulmonary vessels resistance to flow
-Pulmonary Blood Vessels offer Low Resistance to Flow
-Pulmonary arterioles: 10-25 mm Hg
-Pulmonary venules: ~ 5 mm Hg
-Most resistance to pulmonary blood flow is in arterioles from which capillaries arise
pressures within the lung; variations, segments
-Variations in lung intravascular and
extravascular pressures influence pulmonary blood flow and its
distribution in the lung.
-Pressures in the different vascular
segments (arteries, capillaries, veins),
extravascular pressures (intrathoracic, intrapleural), and
transmural pressure across the
alveolar wall, can vary considerably
during both the cardiac and respiratory cycles. These pulmonary
vascular pressure (PVP) changes are
due in part to changes in pulmonary
vascular resistance (PVR).
passive influences on PVP and PVR
- Cardiac Pressure (blood pressure)
Pulmonary blood flow is pulsatile - Pulmonary Inflation
-During exhalation, extra-alveolar
arterioles and venules are compressed, but alveolar capillaries
actually become dilated because septa (walls of alveoli) are not stretched
-During inhalation, extra-alveolar
arterioles and venules are dilated
(reduced intrathoracic pressure), but
alveolar capillaries become compressed because the alveolar
septa are stretched tight, pushing
blood out. - Capillary Distension and Recruitment. An increase in perfusion
pressure (pulmonary artery pressure)
results in distension & recruitment of
pulmonary capillaries à decreasing
PVR - Hematocrit
* An increase in the hematocrit increases the viscosity of blood
* As blood viscosity increases, PVR increases - Vascular Anatomy/Position: The dorsal portion of lung is preferentially perfused in quadrupeds due to lower resistance
-Preferential dorsal distribution of pulmonary blood flow during:
* Exercise
* Dorsal recumbency
-Probably due to differences in branching of airways & blood vessels
active influences on PVP and PVR
- Neural and Hormonal factors
* Effect depends on amount of vascular smooth muscle in small pulmonary arteries/arterioles
-cattle, pigs»_space; horses > dogs, sheep
-Vasoconstriction of small pulmonary arteries by:
* Stimulation of α1-adrenergic receptors
* Inflammatory mediators (histamine, serotonin, bradykinin)
* Some prostaglandins (e.g. PGF2α )
Vasodilation of small pulmonary aa. by:
* Stimulation of β2-adrenergic receptors
* Nitric oxide (NO) -> diffuses through endothelium into vascular smooth muscle
* Most prostaglandins (e.g. PGE2, PGI2)
second aspect of active influence of PVP and PVR
- Oxygen Tension: dec PAO2 -> dec PaO2
-A decrease in oxygen concentration in a pulmonary arteriole causes vasoconstriction
-This is a mechanism by which blood flow is redirected to better ventilated areas of lung, e.g.:
* Neonates
* Pneumonia
* Atelectasis
* Altitude sickness
bronchial circulation; what does it provide, location and part of what, vascular pressures
-Bronchial circulation provides nutrients and gas exchange for the conducting airways
-Although it is located within the lower respiratory system, the
bronchial circulation is not part of the pulmonary circulation. Its vessels are part of the systemic circulation and receive about 2% of the cardiac output from the left heart
-Vascular pressures in the bronchial circulation are similar to those in other systemic vascular beds
bronchopulmonary anastomoses
-Anastomoses (junctions) exist between bronchial and pulmonary arteries
-Most are present at the capillary or venule level
These anastomoses provide a back-up blood supply:
-In the event that a bronchial vessel becomes occluded, blood is supplied from the pulmonary circuit through these anastomoses
-Similarly, when a pulmonary vessel is obstructed, bronchial circulation proliferates and maintains blood flow to the lung
pathological changes in pulmonary circulation; edema
-Fluid tends to enter pulmonary interstitial space due to hydrostatic pressure
->excess is normally drained by lymphatics
->if rate of fluid entry into interstitial space is excessively high, or if alveolar epithelium damaged, fluid may enter alveoli: PULMONARY
EDEMA
causes
* Increased pulmonary capillary pressure
* Decreased plasma oncotic pressure
* Damaged pulmonary capillary endothelium
* Lymphatic obstruction
* Alveolar epithelial damage
