blood vessels and hemodynamics ch 19 Flashcards


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1

5. Valves prevent blood from flowing backwards in veins. They are formed from folds of the tunica intima,

6. In the systemic circuit, veins contain more blood than arter-
is (see Figure 19.6).

7. Veins have more anastomoses than arteries.

8. The three
factors that determine resistance are blood viscosity, vessel length, and vessel diameter. Vessel diameter is physiologically most important.

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When you first stand up, mean arterial pressure (MAP) temporarily decreases and this is sensed by aortic and carotid baroreceptors. Medullary cardiac and vasomotor center reflexes increase sympathetic and decrease parasympathetic outflow to
the heart. Heart rate and contractility increase, increasing cardiac output and therefore MAP. Further, sympathetic constriction of arterioles increases total peripheral resistance, also increasing MAP. (In addition, increased constriction of veins increases venous return, which increases end diastolic volume, increasing stroke volume, and therefore cardiac output and MAP.)

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14. The kidneys help maintain MAP by influencing blood volume. In
renal artery obstruction, the blood pressure in the kidney is lower than in the rest of the body (because it is downstream from the obstruction). Low renal blood
pressure triggers both direct and indirect renal mechanisms to increase blood
pressure by increasing blood volume. This can cause hypertension (called "secondary hypertension" because it is secondary to a defined cause- in this casethe renal artery obstruction).

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bob is in vascular shock due to anaphylaxis, a systemic allergic reaction to his medication. His blood pressure is low because of widespread vasodilation triggered by the massive release of histamine. Bob's rapid heart rate is a result of the baroreceptor reflex triggered by his low blood
pressure. This activates the sympathetic nervous system, increasing heart rate, in an attempt to restore blood pressure.

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16. Diuretics cause a decrease in blood
volume (because more fluid is lost in urine), decreasing cardiac output, which decreases blood pressure. Beta-blockers block beta-adrenergic receptors. Their antihypertensive effects are primarily due to their action in the heart, where they
decrease contractility (and therefore stroke volume) and heart rate, resulting in lower cardiac output. Ca?+ channel blockers decrease Ca?+ entry into arteriolar smooth muscle, decreasing its contraction (causing vasodilation) and resulting in decreased total peripheral resistance. By acting on Ca?+ channels in the heart. these drugs may also decrease contractility and heart rate.

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In a bicycle race, autoregulation by intrinsic metabolic controls causes arteriolar smooth muscle in your legs to relax, dilating the vessels and supplying more O, and nutrients to the exercising muscles.

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18. Extrinsic mechanisms, primarily the sympathetic
nervous system, prevent blood pressure from plummeting by constricting arterioles elsewhere (such as
the gut and kidneys). In addition,cardiac output increases, which
also helps maintain MAP.

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