17A07: Exam Report
Compare and contrast the systemic circulation with the pulmonary circulation.
26% of candidates passed this question.
This question encompasses a wide area of cardiovascular physiology. As a compare and contrast question this question was well answered by candidates who used a table with relevant headings. Comprehensive answers included: anatomy, blood volume, blood flow, blood pressure, circulatory resistance, circulatory regulation, regional distribution of blood flow,
response to hypoxia, gas exchange function, metabolic and synthetic functions, role in acid base homeostasis and filter and reservoir functions.
A frequent cause for missing marks was writing about each circulation separately but comparing. For example: many candidates stated ‘hypoxic pulmonary vasoconstriction’, but did not contrast this to ‘hypoxic vasodilation’ for the systemic circulation. Frequently functions of the circulations were limited to gas transport / exchange.
F5iii / 17A07: Compare and contrast the systemic circulation with the pulmonary circulation
- Pulmonary circulation = flow from RV → PA → P capillaries → pulmonary vessels → P veins → LA
- Systemic circulation = flow from LA → LV → systemic arteries → capillaries → veins → RA → RV
RV → LA
LA → RV
Arterial vessels also have same 3 layers
Less smooth m.
Compressible & distensible
Rapid subdivision over short distance
Subject to Recruitment & Distention
Main arteries have 3 layers
Sympathetic, but less effect 2° minimal smooth m.
Abundant smooth m.
ANS inn. → SVR highly regulated by vascular tone
Filter, immune, blood reservoir, metabolic (inactivate, BK, 5HT, convert Angiotension I → Angiotensin II)
Deliver O2 to tissue
Remove CO2 for transport
Pressures & Flow
25/8 (MAP 15)
120/80 (MAP 100)
Pressure Drop; Inlet/Outlet
10mmHg (low R circuit)
100mmHg (high R circuit)
Arterioles – very muscular arterioles which direct BF to various organs according to need
800 – 1600 dynes/s/cm5
Undampened, highly pulsatile
Because of low resistance
Low PA resistance does not damp the pressure waveform produced by RV
Factors Affecting Flow & Resistance
Minimal effect on vessel tone
Principle determinant of SVR, esp in arterioles which is main site of Resistance
PVR lowest @ FRC
Higher R with ↑/↓ lung volume
Posture – Hydrostatic Force
Lung apex → base
30 – 40cm H2O
Low R circuit ∴gravity has a large effect of on circulation
Culminating in the…
West’s Zones 1 → 4
Large hydrostatic force from head → ~170cm H2O, but MAP is high (high resistance circuit, so minimal effect)