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Respiratory System Part 5

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Biomedical Physio & Kines
BPK 306
Mike Walsh

Respiratory System #5 V. PULMONARY CARDIOVASCULA PHYSIOLOGY A. Pulmonary Vasculature Compared With Systemic Vasculature a. Pulmonary arteries and arterioles much thinner and larger diameter than in systemic counterparts b. Pulmonary arterial tree very compliant = 7 mL/mm Hg. c. Pulmonary veins very similar to systemic veins B. Pulmonary Blood Pressure a. Often, systemic system is called “high pressure system”; pulmonary system called “low pressure system” b. Pulmonary arterial blood pressure = 25/8 mm Hg c. Mean pulmonary arterial pressure is 15 mm Hg d. Mean pulmonary capillary pressure is 7-10 mm Hg e. Lower pressure b/c don’t have to transport blood great distances, and it avoids pulmonary edema via Starling’s forces C. Pressure Around Pulmonary Blood Vessels a. Pulmonary caps virtually surrounded by alveoli too, so pressure surrounding caps is almost all alveolar pressure b. Pressure around pulmonary arteries and veins influenced by surrounding lung parenchyma. Thus, when lungs expand (inspiration), pulmonary arteries/veins are pulled open by surrounding tissue c. Due to diff betw pulmonary caps, and pulmonary art/veins, caps are called alveolar vessels, and arts/veins are extra-alveolar vessels d. Resistance to blood flow in pulmonary caps much greather than in systemic caps. B/c of alveolar compression of pulmonary caps e. Overall, pulmonary circulation resistance much lower than systemic system b/c most of resistance comes from Extra-alveolar vessels?? D. Pulmonary Blood Volume a. About 10% (450 mL) of total blood volume. i. This volume can decrease 50% or increase 2x under certain (mostly abnormal conditions) ii. At rest, cap blood volume is about 75 mL; incr during exercise to max capacity of 200mL E. Pulmonary Blood Flow 1. Local Effects: a. Blood flow through lungs essentially equal to cardiac output, so same factors affecting blood flow for both b. Goal of pulmonary system blood flow is opposite of systemic system c. SM of pulmonary arteries and arterioles is bathed in alveolar gas d. Hypoxic vasoconstriction: i. If alveolar O2 decr 30% (PaO2 < 70mm Hg), adjacent vessels constrict, increasing resistance and reducing blood flow. (Blood flow ctrl due to PO2 of alveolar gas, not of the blood e. Effect induced by O2 sensitive K+ channels. Low O2  K+channels close causing depol  contraction of SM f. ANS plays minor role in pulmonary BF distribution 2. Hydrostatic Effects a. Lungs about 30 cm long b. Top of lung ~ 15 mmHg less than pulmonary arterial pressure. Bottom of lung about 8 mm Hg above pulmonary arterial pressure c. Greater BP at
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