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Chapter 19

Ch. 19 cardiovascular system notes

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Boston College
ENGL 1010
Laura Sterrett

• Blood vessels- form closed delivery system that begins/ends at the heart • Arteries- carry blood away from the heart, diverge, form smaller divisions • Veins- carry blood toward heart, converge into successively larger vessels • Lumen- blood containing space of a vessel • Tunica intima- innermost tunic, contains endothelium of simple squamous cells, minimizes friction as blood moves • Tunica media- circularly arranged smooth muscle cells and sheets of elastin, bulky layer, maintain blood pressure and continuous blood circulation • Vasoconstriction- smooth muscle contraction limits lumen diameter • Vasodilation- increase in lumen diameter as smooth muscle relaxes • Tunica externa- outermost layer, composed of loosely woven collagen fibers to reinforce vessel and anchor it in surrounding structures, infiltrated with nerve fibers, lymphatic vessels, and elastin fivers, contains vasa vasorum • Vasa vasorum- system of tiny blood vessels, nourish external tissues of blood vessel wall • Elastic arteries- thick-walled, near heart, 2.5cm to 1cm, low-resistance because of large lumens, referred to as conducting arteries, contain the most elastin, blood flows through relatively continuously, walls experience high pressures • Muscular/distributing arteries- deliver blood to specific body organs, account for most arteries, 1cm to 0.3mm, thickest media, have more smooth muscle and less elastic tissue, more active in vasoconstriction • Arterioles- 0.3mm to 10um, mostly just smooth muscle cells, larger arterioles have some scattered elastic fibers • Capillaries- smallest blood vessels, thin walls consisting of thin tunica intima, 1mm with diameter 8-10um, highly concentrated in most tissues except tendons, ligaments, cartilage, and epithelia, site for exchange of gases, nutrients, hormones, and more between blood and interstitial fluid • Continuous capillaries- abundant in skin and muscles, most common, endothelial cells form uninterrupted lining, adjacent cells joined by tight junctions • Intercellular clefts0 gaps of unjoined membrane in tight junctions, allow limited passage of fluids and small solutes • Fenestrated capillaries- some endothelial cells have oval pores/fenestrations covered in membrane/diaphragm, permeable to fluids and small solutes, found where active absorption or filtrate formation occurs like in endocrine organs or small intestine • Sinusoidal capillaries- leaky capillaries, found in liver, bone marrow, lymphoid tissues, and some endocrine organs, have large, irregularly shaped lumens, fenestrated, fewer tight junctions and larger intercellular clefts, allow passage of blood cells and larger molecules between blood and surrounding tissues • Kupffer cells- remove and destroy contained bacteria in liver, large macrophages, form part of discontinuous lining of sinusoid endothelium • Capillary beds- interweaving networks of capillaries, consists of vascular shunt that is a vessel connecting arteriole and venule at ends of bed and true capillaries, which are exchange vessels • Microcirculation- flow of blood from arteriole to venule through a capillary bed • Terminal arteriole- feeds the capillary bed • Metarteriole- vessel structurally intermediate between an arteriole and a capillary, continuous with thoroughfare channel, after terminal arteriole • Thoroughfare channel- intermediate between a capillary and a venule • Postcapillary venule- joined with thoroughfare channel, drains the bed • True capillaries- 10 to 100 per bed • Precapillary sphincter- cuff of smooth muscle fibers, surrounds root of each capillary at the metarteriole, acts as a valve to regulate blood flow into capillary • Blood flows through true capillaries when precapillary sphincters are open • Blood flows through shunt when precapillary sphincters are closed • Venules- 8 to 100um in diameter, consist of endothelium, porous, may have one or two layers of smooth muscle cells and thin externa on larger venules • Veins- three distinct tunics, thinner walls and larger lumens, thick tunica externa • Capacitance vessels/blood reservoirs- veins hold 65% of body’s blood supply • Venous valves- formed from folds of tunica intima, abundant in veins of limbs, absent in ventral body cavity, help when blood flows against gravity • Varicose veins- due to leaky valves, caused by elevated venous pressure or hindered venous return • Venous sinuses- flattened veins with thin walls made of endothelium, supported by surrounding tissue as opposed to additional tunics • Vascular anastomoses- unification sites of vascular channels • Arterial anastomoses- merging sites of arteries supplying same area • Collateral channels- alternate pathways for blood to reach a given region • Arteriovenous anastomoses- metarteriole-thoroughfare channel shunts of capillary beds that connect arterioles and venules • Venous anastomoses- interconnection of veins • Blood flow- volume of blood flowing through a vessel, organ, or entire circulation in a given period (ml/min), varies with tissues being supplied • Blood pressure (BP)- mmHg, force per unit area exerted on a vessel wall by blood • Resistance0 opposition to flow, measure of amount of friction blood encounters, usually peripheral resistance (systemic), due to blood viscosity, vessel length, and vessel diameter • Blood Flow (F), difference in blood pressure (dP), peripheral resistance (R) F=dP/R • Blood pressure highest in aorta, and 0mmHg in right atrium • Blood pressure regularly rises and falls in elastic arteries which feature compliance, so they are pulsatile • Systolic pressure- 120 mmHg, highest pressure of aorta • Diastolic pressure- 70-80mmHg, lowest pressure of aorta when valves are closed • Pulse pressure- difference between systolic and diastolic pressures (pulse) • Mean arterial pressure- pressure that propels the blood to the tissues • MAP= diastolic pressure + (1/3)xpulse pressure • Blood pressure in capillaries is about 35mmHg at start, 15mmHg at end • Respiratory “pump”- important for venous return, due to pressure changes in ventral body cavity during breathing, inhale forces blood towards heart • Muscular “pump”- important for venous return, skeletal muscle activity contraction and relaxation slowly pushes blood
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