L4 Pulmonary & Bronchial Circulation

Question 1

What are the blood supply to the lung as an organ ?

Answer 1

• pulmonary circulation ( 100% of cardiac output as it is going to the alveoli for gas exchange, however other parts can’t benefit from this circulation )
• bronchial circulation ( 1% of cardiac output ) / ( most hemoptysis occurs by this artery )

Question 2

Where does the blood of bronchial circulation drain into :

Answer 2

1. Normally as any other vein - 1/3 to 1/2 it will drain into ( systemic vein ) that will end up in the right atrium
2. Physiological anatomical shunt - the reminder of deoxygenated blood will drain into ( pulmonary veins ) that caries the oxygenated blood to the left atrium to be pumped … this will cause a diffrence between alveolar and arterial blood ( normally it is less than 5% )

Question 3

Compare between pulmonary and systemic circulation in terms of compliance and resistance

Answer 3

Pulmonary :

1. High compliance
2. Low resistance (10X less than systemic )
   - it is pumped under low pressure (dP)

Systemic :

1. Low compliance
2. High resistance
   - it is important to oppose the gravity and prevent pooling of blood especially to prevent hypo perfusion to the brain

Question 4

Why the right ventricle have much less muscles than the left ?

Answer 4

As the pulmonary circulation is compliant and has much lower pressure and the blood being pumped against low resistance

Question 5

How the lung volumes can affect the pulmonary resistance ?

Answer 5

1. At rest lung volumes … lowest resistance
2. At low volumes … high resistance due to compression of extra-alveolar vessels
3. At large volumes … high resistance due to compression of alveolar vessels

Question 6

What are the zones and what does the mean ?

Answer 6

Zone 1 :

• only pathological in people who are on ventilation
• the alveoli are fully distended so alveolar vessels are permanently compressed

Zone 2 :

• upper 1/3
• as most blood is in the basal part so the HP in the apical part is low
• by inspiration and distention of alveoli it will compress the alveolar vessels only for seconds then will open

Zone 3 :

• lower 2/3
• high HP which will open the alveolar vessels whatever the status of alveoli

Question 7

Why very little fluid (if any) is drained from the interstitial space by the lymphatic system in pulmonary capillaries ?

Answer 7

As the net forces of pulmonary capillaries is inward ( plasma oncotic pressure )

Question 8

What are the vasodilators and vasoconstrictors to match the ventilation to perfusion ?

Answer 8

VASOCONSTRICTORS :

• low oxygen
• high CO2
• alpha catecholamine
• histamine

VASODILATORS :

• NO
• high oxygen
• acetylcholine
• beta 2 catecholamine

Question 9

How hypoxic vasoconstriction occurs ?

Answer 9

1. Hypoxia
2. Mitochondria work less , more AMP
3. Activation of AMPK
4. phosphorylation of K+ channels ( deactivated )
5. Depolarization
6. Opening of calcium channels and CICR
7. Contraction and vasodilation

This occurs in order to match the perfusion to ventilation which is low

Question 10

What is the effects of sympathetic and parasympathetic mediators ?

Answer 10

Alpha 1 > vasoconstriction
Alpha 2 > vasodilation
Beta 2 > vasodilation

Acetylcholine > vasodilation
Ach binds to endothelium producing NO that binds to the muscle activating guanyly cyclase and producing cGMP that activate protein kinase and dephosphorylate MLC

Question 11

What are the main causes of vasoconstriction and hyper-proliferation ?

Answer 11

1. Endothelin works
2. NO not working
3. Prostacyclins not working

Question 12

What is happening in any condition that cause prolonged hypoxia ?

Answer 12

1. Vasoconstriction
2. Increased pressure
3. Vascular hypertrophy