8.6 Blood Vessels and Blood Pressure

Notes

• Arteries carry blood away from the heart; they have thick, elastic, muscular walls. Veins carry blood toward the heart; they have thinner walls and valves, and rely on skeletal muscle contraction and breathing to return blood. Capillaries are one cell thick, and exchange gases, nutrients and wastes with tissues.
• Blood vessel walls have three layers: tunica interna (endothelium), tunica media (smooth muscle) and tunica externa.
• Blood pressure (BP) is the force of blood on vessel walls; measured in mm Hg as systolic over diastolic. A normal adult is about 120/80. Hypertension is a sustained reading of 130/80 or higher (stage 1 definition used in the United States).
• BP depends on cardiac output and peripheral resistance (vessel diameter). Vasoconstriction raises BP. Baroreceptors detect BP and the medulla adjusts heart rate and vessel diameter by negative feedback. Hormones such as ADH, aldosterone and epinephrine also act.
• Pulse pressure = systolic minus diastolic. Example: 120/80 gives 40 mm Hg.
• Atherosclerosis is plaque buildup in arteries.