PHYSIOLOGY BOOK

1. PULMONARY CIRCULATION
BY DR . B. S . ABARNA REDDY

2. PULMONARY BLOOD VESSELS
• PULMONARY ARTERY CARRIES DEOXYGENATED BLOOD TO ALVEOLI OF LUNGS.
• BRONCHIAL ARTERY SUPPLY OXYGENATED BLOOD TO OTHER STRUCTURES OF
LUNGS.
• PULMONARY ARTERY
• DEOXYGENATED BLOOD FROM RIGHT VENTRICLE TO ALVEOLI OF LUNGS. AFTER
LEAVING RIGHT VENTRICLE ARTERY DIVIDES INTO RIGHT AND LEFT BRANCHES.
• PULMONARY ARTERY DIVIDES IN TO SMALL VESSELS FORMING CAPILLARY PLEXUS
INTIMATE RELATIONSHIP TO ALVEOLI.
• OXYGENATED BLOOD IS CARRIED TO LEFT ATRIUM BY PULMONARY VEIN.

3. BRONCHIAL ARTERY
• ARISES FROM DESCENDING AORTA
• SUPPLIES ARTERIAL BLOOD TO BRONCHI ,CONNECTIVE TISSUE AND OTHER
STRUCTURES OF LUNG
• VENOUS BLOOD IS DRAINED BY TWO BRONCHIAL VEINS.
• BRONCHIAL VEINS FROM RIGHT DRAINS TO AZYGOUS VEIN AND FROM LEFT
INTO HEMI AZYGOUS VEIN OR LEFT SUPERIOR INTERCOSTAL VEINS.
• BLOOD FROM DISTAL PORTION OF BRONCHIAL VEINS DRAINS IN TO PULMONARY
VEINS.( PHYSIOLOGICAL SHUNT).

4. PHYSIOLOGICAL SHUNT
• DEFINED AS DIVERSION WHERE VENOUS BLOOD MIXED WITH ARTERIAL BLOOD.
• COMPONENTS: FLOW OF DEOXYGENATED BLOOD FROM BRONCHIAL
CIRCULATION INTO PULMONARY VEINS WITHOUT BEING OXYGENATED .
• FLOW OF THEBESIAN VEINS IN TO CARDIAC CHAMBERS .
• VENOUS ADMIXTURE IS MIXING OF DEOXYGENATED BLOOD WITH OXYGENATED
BLOOD.
• VENOUS BLOOD IS NOT FULLY OXYGENATED AND THE REST IS AS WASTED
BLOOD.

5. CHARACTERISTICS OF PULMONARY BLOOD
VESSELS
• PULMONARY ARTERY HAS THIN WALL. ONE THIRD OF THICKNESS OF SYSTEMIC
AORTIC WALL.
• HIGHLY ELASTIC.
• SMOOTH MUSCLE COAT IS NOT WELL DEVELOPED.
• TRUE ARTERIOLES HAVE LESS SMOOTH MUSCLE FIBERS.
• PULMONARY CAPILLARIES ARE LARGER AND DENSE THAN SYSTEMIC CAPILLARIES.
• VASCULAR RESISTANCE IS LESS. ONLY ONE TENTH OF SYSTEMIC CIRCULATION.
• LOW PRESSURE VASCULAR SYSTEM
• PULMONARY ARTERY CARRIES DEOXYGENATED BLOOD FROM HEART TO LUNGS
• PULMONARY VEINS CARRIES OXYGENATED BLOOD FROM LUNGS TO HEART.

6. PULMONARY BLOOD FLOW AND BLOOD
PRESSURE
• ACCOMMODATE AMOUNT OF BLOOD IN LUNGS SAME AS AMOUNT OF BLOOD IN OTHER PARTS
OF BODY.
• BLOOD PRESSURE IS LESS IS PULMONARY BLOOD VESSELS . ENTIRE PULMONARY VASCULAR
SYSTEM IS LOW VASCULAR BED.
• ARTERIAL PRESSURE
• SYSTOLIC PRESSURE :25MMHG
• DIASTOLIC PRESSURE :10MMHG
• MEAN ARTERIAL PRESSURE :15MMHG
• CAPILLARY PRESSURE : 7MMHG

7. REGULATION OF PULMONARY BLOOD FLOW
• FACTORS
• CARDIAC OUTPUT
• VASCULAR RESISTANCE
• NERVOUS FACTORS
• CHEMICAL FACTORS
• GRAVITY AND HYDROSTATIC PRESSURE
• CARDIAC OUTPUT : PULMONARY BLOOD FLOW IS DIRECTLY PROPORTIONAL TO
CARDIAC OUTPUT.
• REGULATED BY FOUR FACTORS
• VENOUS RETURN FORCE OF CONTRACTION
• RATE OF CONTRACTION PERIPHERAL RESISTANCE

8. VASCULAR RESISTANCE
• PULMONARY BLOOD FLOW IS INVERSELY PROPORTIONAL TO PULMONARY
VASCULAR RESISTANCE . IT IS LOW COMPARED TO SYSTEMIC VASCULAR
RESISTANCE .
• DURING INSPIRATION PULMONARY BLOOD VESSELS ARE DISTENDED BECAUSE OF
DECREASE INTRATHORACIC PRESSURE .CAUSES DECREASE IN VASCULAR
RESISTANCE ,RESULTS IN INCRESES PULMONARY BLOOD FLOW.
• DURING EXPIRATION , INCREASES PULMONARY RESISTANCE INCREASES RESULTS
IN DECREASED BLOOD FLOW.
• NERVOUS FACTORS STIMULATION OF SYMPATHETIC NERVES INCREASES
VASCULAR RESISTANCE BY VASOCONTRICTION
• STIMULATION OF PARASYMPATHETIC SUCH AS VAGUS NERVE DECREASES
VASCULAR RESISTANCE BY VASODILATION.

9. CHEMICAL FACTORS
• EXCESS OF CO2 OR LACK OF OXYGEN CAUSES VASOCONSTRICTION .CAUSE FOR PULMONARY
CONSTRICTION BY HYPOXIA IS NOT KNOWN.
• GRAVITY AND HYDROSTATIC PRESSURE : BLOOD PRESSURE IN LOWER EXTREMITY IS HIGH IN
STANDING POSITION AND UPPER PARTS ABOVE HEART LEVEL IS LOW.( EFFECT OF
GRAVITATIONAL FORCE).
• APICAL PORTION ZONE 1 PULMONARY CAPILLARY PRESSURE IS SAME AS ALVEOLAR PRESSURE
• SO PULMONARY ARTERIAL PRESSURE FLOW OF BLOOD IS JUST SUFFICIENT TO ALVEOLAR
CAPILLARIES
• IF ARTERIAL PRESSURE GET DECREASES OR ALVEOLAR PRESSURE INCREASES CAPILLARIES GETS
COLLAPSED. PREVENTS FLOW OF BLOOD TO ALVEOLI ( AREA OF ZERO BLOOD FLOW)
• NO GASEOUS EXCHANGE IN THIS ZONE .PART OF PHYSIOLOGICAL DEAD SPACE VENTILATED
BUT NOT PERFUSED
• VENTILATION PERFUSION RATIO INCREASES. GROWTH OF BACTERIA MAINLY TUBERCLE
BACILLUS LEAD TO TUBEFRCULOSIS.

10. PORTIONS
• MIDPORTION ZONE 2 PRESSURE IN ALVEOLI IS LESS THAN PULMONARY SYSTOLIC
PRESSURE AND MORE THAN PULMONARY DIASTOLIC PRESSURE .
• BLOOD FLOW INCREASES DURING SYSTOLE AND DECREASES DURING DIASTOLE.
(AREA OF INTERMITTENT BLOOD FLOW) VENTILATION PERFUSION RATIO IS
NORMAL.
• LOWER PORTION ZONE 3 PULMONARY ARTERIAL PRESSURE IS HIGH AND MORE
THAN ALVEOLAR PRESSURE DURING BOTH SYSTOLE AND DIASTOLE .(AREA OF
CONTINUOUS BLOOD FLOW ) VENTILATION PREFUSION RATIO DECREASES.