Lec16.circulation - BIOLOGY 325H Circulatory Systems, Part...

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BIOLOGY 325H Circulatory Systems, Part II February 22, 2008 In today’s lecture we shift focus from the heart to the vascular system, i.e. a highly branched network of vessels through which the blood flows from the time it leaves one of the heart’s ventricles until it returns to the appropriate atrium. The anatomy of the vascular system is deceptively simple, with only three general classes of vessel and a relatively straightforward arrangement of tissues in the vessel walls. But in fact the vascular system displays a number of subtle adaptations that greatly increase the efficiency of its function. Blood is rapidly dispersed (at velocities up to 50 cm/sec) throughout the human body, yet is able to undergo maximal exchange of its dissolved gases and nutrients/wasteproducts with the body tissues it passes through. And the bloodstream moves continually forward, even though the heart itself is relaxing – and hence not producing any force - for more than one-half of each cardiac cycle. In addition to these general features of cardiovascular physiology, an animal can finely tune the functional activity of its circulatory system to meet a wide variety of physiological needs. The pattern of blood flow in your body varies greatly when you are actively exercising as opposed to quietly digesting a meal, or when you are exposed to freezing temperatures as opposed to lying in the sun on a hot summer’s day. This physiological plasticity is even more pronounced when one considers an animal such as the seal, which can regulate its circulatory physiology such that it can dive under water for up to an hour relying solely on the O 2 stored in its muscles and blood. Learning Goals 1. How do (i) pressure and (ii) velocity change as blood flows through the systemic (or pulmonary) circuit? In what part of the vascular system does the blood pressure fluctuate with the phases of the cardiac cycle? [ Where does a physician take your pulse or blood pressure, and why? ] 2. What is the physiological function of capillaries? How is the structure of a capillary bed adapted to perform this function? How is the velocity of blood flow through the circulatory system adapted to this function? 3. Learn Fick’s Law of Diffusion (Sadava, pg. 1026) and appreciate that it applies to both gases and solids that are dissolved in a liquid. Can you restate your answers to Question 2 in terms of the variables in Fick’s Law? 4. Given the diameter of a series of interconnected blood vessels, you should be able to calculate the relative velocity of blood flow through each vessel. 5. What is the relationship between blood pressure and osmotic pressure along the length of a capillary? What is capillary effusion, and how does it relate to these two distinct types of pressure? 6. What is the meaning of the terms ‘vasoconstriction’ and ‘vasodilation’? What role do precapillary
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Lec16.circulation - BIOLOGY 325H Circulatory Systems, Part...

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