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Lecture 12

Lecture 12: Vascular Transport 2 Closed Circulatory Systems

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Biology 2601A/B
Brent Sinclair

Organismal Phys Lecture 12: Vascular Transport 2 – Closed Circulatory Systems The Systemic Circuit • Blood is delievering O₂ and nutrients and is picking up the waste products to deliver them to the kidneys (or lungs if it is CO₂) • Involves the organs and muscles • When linear flow rate is reduced, is due to the cross-sectional area increasing (↑ in radius = ↓flow rate) Major Arteries • Muscular, elastic thick walls (smooth muscle and elastin) • Pressure of 10-20 kPa • Very elastic, which it needs to be so can stretch when receives blood from the heart; therefore allows storage of some elastic energy (in artery wall), and dampens the pressure differences • Ex: Aorta, carotid artery, femoral artery • (16/10kPa) Terminal Arteries • (12/8 kPa) • Relatively high pressure as enter heart, but drops as radius ↑’s • Arteries become smaller as they branch out towards the periphery of the circulatory system; walls of the arteries also become thinner (tension ↓’s too) Microcirculatory Beds • The systemic arteries ultimately deliver blood to networks of microscopically tiny blood vessels in all the systemic organs & tissues • Consists of 3 types of vessels ○ 1. Arterioles ○ 2. Capillaries ○ 3. Venules • Right ventricle then increases pressure to 1.9kPa for passage through lungs Veins 1 • Low pressure • Have a system of one-way valves (helps ensure blood flows continuously to heart) • Much thinner-walled than arteries • Blood flows from microcirculatory beds back to the heart through a series of veins of ↑ing diameter Pressure Drops Across Vascular System • Fluctuations indicated heart beats • At veins pressure will be boosted slightly to go through lungs; will then be boosted a lot to go through left ventricle to go back through body What About Birds? • Broadly similar (to us) • Heart pumps more and faster to meet greater oxygen demands (more beats/min) • Higher pressures • Jugular Anastamosis: the link between the left and right jugular; connects one side of the body to the other • Birds can rotate head 180°; will compress one side of jugular but will still be able to survive because the other one will compensate for it 2 Gravity and Pressure: Gravity also Affects Pressure ∆h = height difference across the system g= acceleration due to gravity; p = Fluid density (mercury> seawater>water > oil) The Problem of Being a Giraffe • The brain of a standing giraffe is 2m above its heart • To maintain a pressure of cystolic 13kPa in brain arteries, need an aortic pressure of cystolic 29 kPa • In order to compensate for this high pressure, giraffes have a disproporately large heart, with a fast heart rate (c. 170 bpm) • Also will have tight skin on legs, and muscular arteries • Has a high interstitial fluid pressure, efficient return of venous blood Giraffes Have a Drinking Problem • Head goes from being 2m above heart to 2m below it; this cause very high pressure blood into brain • Blood can pool in brain when head is below heart • To solve this, giraffe will have vasodilation in its lower body to reduce blood pressure ○ everything in lower body releases their arteries and veins; therefore ↑’s radius and ↓’s rate of flow • Elastic arteries near the brain will absorb some increased pressure (will dampen effects of sudden increase in blood pressure) • One-way valves in jugular vein prevent backflow of blood into head In General • The brain and heart need blood flow to be maintained ○ A heart attack will result when there is reduced O₂ going to heart • Kidneys require a regulated blood pressure to function; can ↑ and ↓ blood pressure to regulate the amount of fluid in kidneys Animals with a Closed Circulatory System are Able to Regulate... • Where blood goes • How much of it goes there • Animals needs to be able to respond to central requirements ○ Ex. flight-or-fight response • Also need to respond to local conditions ○ O₂ demand, localized damage, temperature How
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